Chapter 1 — Electrical and Electronic Engineering Services for Buildings
Gazette pages 4515–4628 · Official gazette pages (PDF, 911 KB) — use for exact tables and figures.
Sections in this chapter
1.1 Introduction
1.1.1 Scope
The provisions of the Code presented in this Chapter, cover the Electrical and Electronic Engineering Services for Buildings to ensure that the related installation work becomes perfect and safe for the persons residing in and around the building. The term safe means safe for the persons and safe for the properties.
Provisions of the Specifications are to set minimum standards for Electrical and Electronic Engineering Installations in various Occupancy categories of buildings, as described in Part 3 of this Code, including annexes and premises. All the systems and equipment intended for the supply of normal power and standby power to all these places are covered by the provisions of this Code.
The provisions of the Code for various Electrical and Electronic Engineering systems and/or installations for the buildings include, but not limited to:
(a) Lighting and illumination.
(b) Fans, cooling and heating.
(c) Normal and standby power supply.
(d) Supply system and feeder for lifts/escalator/moving walk, including protection.
(e) Cable television distribution.
(f) Electronic access control.
(g) Burglar alarm/CCTV monitoring/security.
(h) Electrical cables/conductors and equipment.
(i) Switches, sockets, other accessories.
(j) Cables and conductors in a building that connect to the supply of electricity.
(k) Electrical protection system.
(l) Earthing system of an electrical installation.
(m) Lightning protection of a building and its electrical installation.
(n) Fire alarm.
(o) Multi-media communications, data communications and telecommunications.
Electrical wiring/cabling form a major part in the above mentioned installation works. Electrical wiring/cabling must be reasonably safe to persons and property. Installations, alteration, or extension of Electrical wiring/cabling systems conforming to the provisions of this Code shall be deemed to be reasonably safe to persons and property.
The provisions of the Code in this Chapter do not cover Installations in ship, water craft, railway rolling stock, aircraft, or automotive vehicles and recreational vehicles,
1.1.2 Designing an Electrical and Electronic Engineering Installations in
Buildings and Related Structures
The provisions of the Code presented in this Section are not meant to provide adequate information to design Electrical and Electronic Engineering Installations and Systems in Buildings and related structures. These should not be taken to be adequate or complete for the efficient design work of installations.
Such design work, the required features, detailed technical specifications, schedule of items etc., should be obtained through the services of an engineer adequately qualified in this area. Applications of energy efficient appliances should be kept in mind while preparing electrical design of a building or related installations.
1.1.3 Terminology and Definitions
This Section provides an alphabetical list of the terms used in and applicable to this Chapter of the Code. In case of any conflict or contradiction between a definition given in this Section and that in Part 1, the meaning provided in this Section shall govern for interpretation of the provisions of this Chapter.
ACCESSORY A device associated with current using equipment or with the wiring of an installation; for example, a switch, a plug, a socket outlet, a lamp holder, or a ceiling rose.
ALIVE See LIVE.
APPARATUS Apparatus means Energy Efficient Apparatus. Electrical apparatus including all machines, appliances and fittings in which conductors are used or of which they form a part.
APPLIANCE Appliance means Energy Efficient Appliance. An item of electric current using equipment other than a luminaries or an independent motor.
BDB Branch-Distribution Board located in the same floor of a building and connected to one of the SDBs in the same floor.
BRANCH A branch circuit supplying energy to one or more outlets to
CIRCUIT, which appliances are to be connected; such branch circuits do not
APPLIANCE have any permanently connected lighting fixtures except those
that are integral parts of the appliances themselves.
BRANCH A branch circuit that supplies a number of outlets for lighting CIRCUIT, and/or appliance. GENERAL PURPOSE
BRANCH A branch circuit that supplies only one utilization equipment. CIRCUIT, INDIVIDUAL
BUNCHED Cables are said to be bunched when two or more are either contained within a single conduit, duct, ducting, or trunking or, if not enclosed, are not separated from each other.
CABLE PVC insulated copper cables having copper cross section of 1 mm2 and above. A length of single insulated conductor (solid or stranded), or two or more such conductors, each provided with its own insulation. The insulated conductor or conductors may or may not be provided with an overall mechanical protective covering.
CELING ROSE A ceiling rose is used for terminating the point wiring for a Light or a Fan in the ceiling. It has brass terminals in which incoming cables are terminated using brass screws on the terminals and the outgoing flexible cables get connection through the screw connections.
CIRCUIT An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device.
SUB CIRCUIT, An outgoing circuit connected to one way of a distribution board FINAL CIRCUIT or a fuse board and intended to supply electrical energy, to one or more points, to current using appliances without the intervention of a further distribution fuse board other than a one-way board. It includes all branches and extensions derived from that particular way in the distribution board or fuse board.
CIRCUIT A device designed to open and close a circuit by non-automatic
BREAKER means and to open the circuit automatically on a predetermined
overcurrent, without injury to itself when properly applied within
its rating.
CIRCUIT A device used to break a circuit during over current or short
BREAKER circuit condition. An LV Circuit Breaker is used in a low voltage
distribution system and an HV Circuit Breaker is used in a high
voltage distribution system.
CORD, A flexible cable having large number of strands of conductors of FLEXIBLE small cross-sectional area with a soft PVC insulation. Two CABLE flexible cords twisted together may be termed as twin flexible cord. However, some flexible cords are made following the style of a twin core PVC insulated copper cables but much soft and flexible. CUTOUT Any appliance for automatically interrupting the transmission of energy through a conductor when the current rises above some predetermined value. A cutout contains a part for holding either fuse wire (rectangular cross section type) or a part for holding tubular fuse (cylindrical body rectangular cross section type). (see FUSE)
DB Distribution Board. This may be the box where the main incoming cable enters and terminates from the main service feed connection. The SDBs get feed from a DB.
DEMAND The ratio of the maximum demand of a system, or part of a
FACTOR system, to the total connected load of the system or the part of
the system under consideration.
DUCT A closed passageway formed underground or in a structure and intended to receive one or more cables which may be drawn in.
EARTH The conductive mass of the earth, whose electric potential at any point is conventionally taken as zero.
EARTH A metal plate, pipe or other conductor electrically connected to ELECTRODE the general mass of the earth.
EARTH LEAD The final conductor by which the connection to the earth WIRE electrode is made.
EARTH The conductor, including any clamp, connecting to the earthing CONTINUITY lead or to each other, those parts of an installation which are CONDUCTOR required to be earthed. It may be in whole or in part the metal (ECC) conduit or the metal sheath or armour of the cables, or the special continuity conductor of a cable or flexible cord incorporating such a conductor. ECCs of appropriate size must run from an MDB to its DBs, from a DB to its corresponding SDBs, from an SDB to the Switch Boards under this SDB, from an SDB to the BDBs if there are any, from a BDB to the Switch Boards under this BDB, from an SDB or a BDB to the Sockets under this SDB or BDB. EDB Emergency Distribution Board. This may be the box where the main incoming cable from the Emergency or Standby Generator Panel enters and. The ESDBs get feed from a EDB. EFDB Emergency Floor Distribution Board located in each of the floors of a multistoried building. The EDBs get feed from EFDB.
ENGINEER-IN- An engineer responsible for implementation/execution of the CHARGE work of a building or a project. Such an engineer is expected to have significant knowledge in Electrical Engineering, Electrical Construction, Measurement, Codes and Practices of such work and availability of different materials needed for the construction.
FDB Floor Distribution Board located in each of the floors of a multistoried building. The DBs get feed from FDB.
FUSE A device that, by the fusion of one or more of its specially designed and proportioned components, opens the circuit in which it is inserted when the current through it exceeds a given value for a sufficient time. Fuse is generally made of fusible wires of appropriate ratings which is either mounted inside glass tubes or porcelain tubes or on a two terminal cutout. FUSE SWITCH A composite unit, comprising a switch with the fuse contained in, or mounted on, the moving member of the switch. LIGHTING A device for supporting or containing a lamp or lamps (for FITTING example, fluorescent or incandescent) together with any holder, shade, or reflector; for example, a bracket, a pendant with ceiling rose, or a portable unit.
INSULATION Suitable non-conducting material, enclosing, surrounding or supporting a conductor. Usually PVC, polymer, specially treated rubber.
LIVE Electrically charged so as to have a potential different from that of earth. Also known as ALIVE.
LUMINAIRE A complete light fitting consisting of lamp, holder, starting gears, reflectors, housing and mounting accessories.
LT / LV and HT/ LT or LV in this document indicates 230 Volt single phase and
HV 400 volt 3 phase. HT or HV in this document indicates 11 kV
Line to line 3 phase system.
MDB Main Distribution Board. This is the distribution box where the main incoming cable enters and terminates from the main service feed connection of a large building. The FDBs get feed from MDB. OVER-CURRENT A current exceeding the rated current. For conductors, the rated value is the nominal current carrying capacity.
PANEL BOARD A single panel or a group of panel units designed for assembly in the form of a single panel including buses, automatic overcurrent devices, and with or without switches for the control of light, heat, or power circuits, designed to be placed in a cabinet or cutout box placed in or against a wall or partition and accessible only from the front.
PLUG A device carrying metallic contacts in the form of pins intended for engagement with corresponding socket contacts and arranged for attachment to a flexible cord or cable. A plug may contain tubular fuse inside it although some plugs do not contain fuse.
POINT (in wiring) A termination of the fixed wiring intended for the connection of current using equipment e.g., a Light, a fan, an exhaust fan.
SDB Sub- Distribution Board located in the same floor of a building and connected to the DB. The BDBs get feed from SDB.
SERVICE The conductors and equipment required for delivering energy from the electric supply system to the wiring system of the premises served.
SWITCH A manually operated device for closing and opening or for changing the connection of a circuit. A 5A SPST switch is used for the control of a Light or Fan point. A 5A SPDT switch is also used for the control of a Light or Fan point.
SWITCHBOARD An assemblage of switchgear with or without instruments; the term, however, does not apply to a group of local switches on a final sub-circuit where each switch has its own insulating base.
SWITCHGEAR Main switches cutouts or fuses, conductors and other apparatus in connection therewith, used for the purpose of controlling or protecting electrical circuits or machines or other current using appliances.
1.1.4 Voltage Ratings
The provisions of the Code specified in this Chapter covers installations utilizing nominal voltage not exceeding 415 V AC between conductors or 240 V AC to earth. The nominal voltage in Bangladesh is 230 volts AC single phase and 400 volts AC 3 phase.
1.2 Lighting and Illumination
1.2.1 Determination of Illumination Levels for Different Application (Principle of Lighting ) The essential features of an efficient lighting system are:
(a) Visual comfort through adequate illumination of the working surface,
(b) Prevention of glare,
(c) Avoidance of shadows, and
(d) Ease of maintenance. The design of a lighting system shall involve:
(a) careful planning of the brightness and colour pattern within both the working areas and the surroundings so that attention is drawn naturally to the important areas, so that details can be seen quickly and accurately, and so that the appearance inside the room is free from any sense monotony,
(b) use of directional lighting to assist perception of task detail,
(c) controlling direct and reflected glare from light sources to eliminate visual discomfort,
(d) minimizing flicker from certain types of lamps and paying attention to the colour rendering properties of the light,
(e) the correlation of lighting throughout the building to prevent excessive differences between adjacent areas, so as to reduce the risk of accidents, and
(f) the installation of emergency lighting systems, wherever necessary. The general impressions associated with different illuminance and colour appearances of light are shown in Table 8.1.1. The various colour rendering groups with examples of use are presented in Table 8.1.2.
Table 8.1.1: General Impressions Associated with Different Illuminance and Colour Appearances
Illuminance (lux) Associated Impression (Colour Appearance)
Warm Intermediate Cool
≤ 500 Pleasant Neutral Cool
500 – 1000 Pleasant to Neutral to Pleasant Cool to Neutral
Stimulating
1000 – 2000 Stimulating Pleasant Neutral
2000 – 3000 Stimulating to Pleasant to Neutral to Pleasant
Unnatural Stimulating
≥ 3000 Unnatural Stimulating Pleasant
Table 8.1.2: Lamp Colour Rendering Groups
Colour Range of Colour Examples of Use
rendering Index Ra Appearance
Group
Cool Textile industries, paint and printing
industries
1 Ra ≥ 85 Intermediate Shops, hospitals
Warm Homes, hotels, restaurants
70 ≤ Ra < Intermediate Offices, schools, department store, fine
2
85 industrial work
40 ≤ Ra < Interiors where colour rendering is of
3
70 comparatively minor importance
Note: Certain applications, e.g. colour matching, may be extremely critical with regard
to the colour rendering properties of the lamps used. Here, the minimum colour
rendering index used shall be 90.
1.2.2 Planning the Brightness Pattern
The brightness pattern seen within an interior is composed of three parts.
(a) Brightness of the task itself.
(b) Brightness of the immediate background of the task and
(c) Brightness of the general surroundings of walls, ceiling, floor, equipment, furnishing etc.
1.2.2.1 The illumination of all work areas within a building shall be a minimum of 150 lux.
1.2.2.2 Where work takes place over the whole utilizable area of a room, the general illumination over that area shall be reasonably uniform and the diversity ratio of minimum to maximum illumination shall not be less than 0.7. This diversity ratio does not however take into account of the effects of any local lighting provided for specific tasks.
1.2.2.3 When the brightness appropriate to an occupation has been determined, the brightness of the other parts of the room shall be planned to give proper emphasis to visual comfort and interest. The recommended brightness ratios are shown in Table 8.1.3.
Table 8.1.3: Brightness Ratios between Task, Adjacent Sources and Surroundings
For high task brightness (above 100
cd/m2)
Maximum ratio between task brightness and 3 to 1
the adjacent sources like table tops
Maximum ratio between task brightness and
illumination of the remote areas of the room 10 to 1
not being used as work areas
For low and medium task brightness The task must be brighter than both the
(below 100 cd/m2) background and the surroundings; the
lower the task brightness, the less
critical is the relationship.
1.2.3 Lighting Calculations
1.2.3.1 In order to determine the necessary number of lamps and luminaires for a specified illumination level or the average illuminance obtained from a particular lighting design, the Lumen Method of calculation shall be employed.
1.2.3.2 Unless the reflection factors are known to the lighting designer, the triplet 0.7/0.5/0.3 for the reflectance of ceiling, walls and working plane respectively shall be used for offices and the triplet 0.7/0.5/0.1 for other premises. Typical reflection factors of smooth coloured surfaces are given in Table 8.1.4.
Table 8.1.4: Reflection Factors of Smooth Coloured Surfaces
Colour Reflection Factor Colour Reflection Factor
Flat white 0.75 – 0.85 Light green 0.40 – 0.50
Ivory 0.70 – 0.75 Grey 0.30 – 0.50
Buff 0.60 – 0.70 Blue 0.25 – 0.35
Yellow 0.55 – 0.65 Red 0.15 – 0.20
Light tan 0.45 – 0.55 Dark brown 0.10 – 0.15
1.2.4 Recommended Illumination Values
The recommended values of illumination required for buildings of different occupancies, based on activity, are given in Tables 8.1.5 to 8.1.14. The initial illuminance should be higher than the recommended value as the illuminance drops below this value by the end of the cleaning and replacing period. A gradual transition (rather than a sudden change) of brightness from one portion to another within the field of vision is recommended to avoid or minimize glare discomfort.
1.2.5 Artificial Lighting to Supplement Daylight
Supplementary lighting shall be used when illumination from daylight falls below 150 lux on the working plane. For supplementary artificial lighting when daylight availability becomes insufficient, cool daylight fluorescent tubes with semi-direct luminaires are recommended. To ensure a good distribution of illumination, the mounting height should be between 1.5 and 2.0 m above the work plane with a separation of 2.0 to 3.0 m between the luminaires.
1.2.6 Selection of Appropriate Light Fittings
1.2.6.1 Light fitting
An electric lamp and its fitting accessories, reflector, diffuser, mounting brackets, suspenders etc., shall be regarded as one unit. During design, an appropriate type of light fitting shall be selected to match the requirement of desired distribution of light. While selecting light fittings having focus or aiming arrangements which enable the light distribution to be varied by adjustment of the lamp position, care should be taken to select the appropriate type of fitting with appropriate beam to serve the aimed lighting applications.
1.2.6.2 Classification of light fittings
Light fittings may be classified into five categories according to the proportion of the total light output in the lower hemisphere. These are:
• Direct fittings, giving 90-100 percent light downwards
• Semi-direct fittings, giving 60-90 percent downwards
• General diffusing fittings, giving 40-60 percent light downwards
• Semi-indirect fittings, giving 10-40 percent light downwards
• Indirect fittings, giving 0-10 percent light downwards
(a) Direct fittings: Direct fittings shall be used in situations where efficiency of illumination is the major criterion, while contract of the light source with the surroundings, shadows, and direct/reflected glare may be considered to be of relatively minor importance.
(b) Semi-direct fittings: Semi-direct fittings shall be used in areas where it felt that the reduction of contrast resulting from the small indirect component of light directed towards the ceiling shall be sufficient for the purpose.
(c) General diffusing fittings: General diffusing fittings shall be used where, in addition to a substantial indirect component of light aiding materially to the diffused character of the general illumination, an upward component providing a brighter background against which to view the luminance, especially for interiors with light-colored ceiling and walls, is desirable.
Table 8.1.5: Recommended Values of Illumination for Residential Buildings Illuminance Illuminanc Area or Activity Area or Activity
(lux) e (lux)
Dwelling Houses Hotels
Bedrooms Entrance halls 150
General 70 Reception and accounts 300
Bed-head, Dressing table 250 Dining rooms (tables) 150
Kitchens 200 Lounges 150
Dining rooms (tables) 150 Bedrooms
Bathrooms General 100
General 100 Dressing tables, bed heads, etc. 250
Shaving, make-up 300 Writing rooms (tables) 300
Stairs 100 Corridors 70
Lounges 100 Stairs 100
Garages & Porches 100 Laundries 200
Illuminance Illuminanc
Area or Activity Area or Activity
(lux) e (lux)
Basement Car Park 100 Kitchens
Porches, Entrances 70 Food stores 100
Sewing and darning 600 Working areas 250
Reading (casual ) 150 Goods and passenger lifts 70
Home work and sustained reading 300 Cloak-rooms and toilets 100
Bathrooms 100
Above mirror in bathrooms 300
Table 8.1.6: Recommended Values of Illumination for Educational Buildings Area or Activity Illuminance (lux) Area or Activity Illuminance (lux)
School and College Assembly halls Offices 300
General 150 Staff rooms and common rooms 150
When used for 300 Corridors 100
examinations
Stairs 100
Platforms 300
Gymnasium 100
Class and Lecture Rooms
General 150
Desks 300
Matches 300
Black boards 300
Library see Table 8.1.8
Embroidery and sewing rooms 500
Living quarters see Table 8.1.5
Laboratories 350
Art rooms 400
Table 8.1.7: Recommended Values of Illumination for Health Care Buildings Area or Activity Illuminance (lux) Area or Activity Illuminance (lux)
Hospitals and Clinics Hospitals and Clinics (contd.)
Reception and waiting rooms 150
Outpatient department 150 Doctor's examination rooms 150
Wards Radiology departments 100
General 150 Casualty 150
Beds 150 Stairs and corridors 100
Operating theatres Dispensaries 250
General 300
Tables (with adjustable
operation lamp lighting)
Minor 2000
Major 5000
Table 8.1.8: Recommended Values of Illumination for Assembly Buildings Area or Activity Illuminance (lux) Area or Activity Illuminance (lux)
Cinemas Theatres
Foyers 150 Foyers 150
Auditorium 100 Auditorium 70
Corridors 100 Corridors 90
Stairs 150 Stairs 150
Libraries Indoor Sports Centre
Shelves (stacks) 150 Halls 200
Reading rooms (newspapers and Swimming pools 250
magazines) 200
Lawn or table tennis,
Reading tables 300 badminton, volley ball
Book repair and binding 300 Tournament 300
Cataloguing, sorting and stock rooms 150 Club 200
Museums and Art Galleries Recreational 150
Museums Shooting ranges
General 200
On target 300
Displays special lighting
Firing point 200
Art galleries
Range 100
General 250
Football 500
Paintings 250
Restaurant
Dining rooms 150
Cash desks 300
Self-carrying counters 300
Kitchens 200
Cloak-rooms and toilets 100
Table 8.1.9: Recommended Values of Illumination for Business and Commercial Buildings
Illuminance
Area or Activity Area or Activity Illuminance (lux)
(lux)
Airport Building Doctor's Surgeries
Reception areas (desks) 300 Waiting rooms and consulting 150
rooms
Baggage, customs and immigration 300
halls Corridors 70
Circulation areas, lounges 200 Stairs 100
Banks Eyesight testing (acuity) wall
charts and near vision types 450
Counter, typing and accounting 300
book areas
Public areas, lobby 150 Jewellery and Watch-Making
Offices 200 Fine processes
700
Book Binding Minute processes
3000
Pasting, punching and stitching 200 Gem cutting, polishing and
setting 1500
Binding and folding and
miscellaneous machines 300
Finishing, blocking and inlaying Laundries and Dry-Cleaning
Works
Dental Surgeries
Receiving, sorting, washing,
Waiting rooms 300 drying, ironing (calendaring) 200
Surgeries 150 and dispatch
General 300 Dry-cleaning and bulk machine
work 200
Chairs special lighting
Fine hand ironing, pressing,
Laboratories 300 inspection, mending and 300
spotting
Offices Offices (contd.)
Entrance lobby and reception areas 150 Stairs 100
Conference rooms and executive 300 Lift landings 150
offices
Telephone exchanges
General offices 300
Manual exchange rooms (on 200
Business machine operation 450 desk)
Drawing office Main distribution frame room 150
General 300 Shops and Stores
Boards and tracing 450 General areas 150 to 300
Corridors and lift cars 70 Stock rooms 200
Display windows 500
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and
Processes
Area or Activity Illuminance
(lux)
Aircraft Factories and Maintenance Hangars
Stock parts productions 450
Drilling, riveting, screw fastening, sheet aluminium layout 300
and template work, wing sections, cowing, welding, sub-
assembly, final assembly and inspection
Maintenance and repair (hangars) 300
Assembly Shops
Rough work, for example frame assembly and assembly of 150
heavy machinery
Medium work, for example machined parts, engine assembly 300
Fine work, for example radio and telephone equipment, 700
typewriter and office machinery assembly
Very fine work, for example assembly of very small 1500
precision mechanisms and instruments
Automobile Manufacturing
Frame assembly 200
Chassis assembly line 300
Final assembly and inspection line 600
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Body Manufacturing
Parts 200
Assembly 300
Finishing and inspection 700
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Automobile Service Garages
Repairs 250
Active traffic areas 100
Storage 25
Bakeries
General working area 150
Decorating and icing 250
Breweries and Distilleries
General working areas 150
Brew house, bottling and canning plants 200
Bottle inspection special lighting
Carpet Factories
Winding and beaming 200
Designing, Jacquard card cutting, setting pattern, tufting,
topping, cutting, hemming and fringing 300
Weaving, mending and inspection 450
Chemical Works
Hand furnaces, boiling tanks, stationary driers, stationary and 150
gravity crystallizers
Mechanical furnaces, evaporators, filtration, mechanical 200
crystallizers, bleaching
Tanks for cooking, extractors, percolators 200
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Chocolate and Confectionery Factories
Mixing, blending and boiling 150
Chocolate husking, winnowing, fat extraction, crushing and 200
refining, feeding, bean cleaning, sorting, milling and cream
making
Hand decorating, inspection, wrapping and packing 300
Clay Products and Cements
Grinding, filter presses, kiln rooms moulding, pressing, 150
cleaning and trimming
150
Enameling
Colour and glazing - rough work 400
Colour and glazing - fine work 750
Clothing Factories
Matching-up 450
Cutting, sewing
Light 300
Medium 450
Dark 700
Inspection
Light 450
Medium 1000
Dark 1500
Hand Tailoring
Light 450
Medium 1000
Dark 1500
Pressing 300
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Dairies
General working areas 200
Filling and bottle inspection 450
Cooling equipment 150
Laboratories 450
Pasteurizers 150
Separators 150
Electrical Industries
Impregnating 250
Winding and insulating 500
Assembly works
Fine 500
Very fine 750
Testing 500
Electricity Generating Stations (Indoor Locations)
Turbine halls 150
Auxiliary equipment, battery rooms, blowers, auxiliary
generators, switchgear and transformer chambers 150
Boiler house (including operating floors) platforms, coal
conveyors, pulverizers, feeders, precipitators, soot and 100 to 150
slag
Boiler house and turbine house 150
Basements 100
Conveyor house, conveyor gantries and junction towers 80 to 100
Emergency lighting - all areas 30
Control rooms
Vertical control panels 200 to 300
Control desks 300
Rear of control panels 150
Switch houses 150
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Electricity Generating Stations (Outdoor Locations)
Switchyard 70
Conveyors 70
Fuel oil delivery headers 70
Oil storage tanks 70
Cat-walks 70
Platforms, boiler and turbine decks 70
Transformer and outdoor switchgear 100
Emergency lighting - all areas 50
Flour Mills
Rolling 150
Sifting 150
Packing 150
Purifying 150
Product control 300
Cleaning screens, man lifts, aisleways and walkways, bin 100
checking
Forge Shops and Foundries
Forge shop 150
Annealing (furnaces) 150
Cleaning 100
Core making (fine) 300
Core making (medium) 150
Grinding and chipping 200
Inspection (fine) 1000
Inspection (medium) 300
Moulding (medium) 300
Moulding (large) 150
Pouring 150
Sorting 200
Cupola 100
Shake out 150
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Garages
Parking areas (interior) 70
Washing and polishing, greasing, general servicing and pits 200
Gas Works
Retort houses, oil gas plants, purifiers, coke screening and
coke handling plants (indoor) 70
Governor, meter, compressor, booster and exhauster houses 100
Open type plants
Cat-walks 20
Platforms 50
Glass Works
Furnace rooms, bending, annealing lehrs 100
Mixing rooms, forming (blowing, drawing, pressing and rolling) 150
Cutting to size, grinding, polishing and toughening 200
Finishing (bevelling, decorating, etching and silvering) 300
Brilliant cutting
General 200
Fine 500
Inspection, etching and decorating 500
Glove Making
Pressing, knitting, sorting and cutting 300
Sewing
Light 300
Medium 450
Dark 700
Inspection
Light 450
Medium 1000
Dark 1500
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Hosiery and Knitwear
Circular and flat knitting machines, universal winders, cutting 300
out, folding and pressing
Lock-stitch and overlocking machines
Light 300
Medium 450
Dark 700
Mending 1500
Examining and hand finishing, light, medium and dark 700
Linking or running on 450
Iron and Steel Works
Manufacturing by open hearth
Stock yard 20
Charging floor 100
Slag pits 100
Control platforms 100
Mould yard 25
Hot top 100
Hot top storage 100
Stripping yard 100
Scrap stockyard 20
Mixer building 100
Calcining building 50
Rolling mills
Blooming, slabbing, hot strip, hot sheet 100
Cold strip, plate 150
Pipe, rod, tube, wire drawing 200
Merchant and sheared plate 100
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Tin plate mills
Tinning and galvanizing 200
Cold strip rolling 200
Motor room, machine room 150
Sheet metal works
Miscellaneous machines, ordinary bench work 200
Pressing, folding, stamping, shearing, punching and 200
medium bench work
Tin plate and galvanized sheet inspection 500
Structural Steel Fabrication
Fabrication and general work 150
Marking and cutting 300
Plating shops
Vat, baths, buffing and polishing 200
Final buffing and polishing 500
Leather Manufacturing
Cleaning, tanning and stretching, vats 150
Cutting, fleshing and stuffing 200
Finishing and scarfing 200
Machine Shops
Rough bench and machine work 150
Medium bench and machine work, ordinary automatic
machines, rough grinding medium buffing and polishing 300
Fine bench and machine work , fine automatic machines,
medium grinding, fine buffing and polishing 700
Extra fine bench and machine work, grinding fine work 1000
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Paint Works
General, automatic processes 200
Special batch mixing 450
Colour matching 700
Paper Manufacturing
Beaters, grinding, calendaring 150
Finishing, cutting, trimming, paper making machines 200
Hand counting, wet end of paper machine 350
Paper machine reel, paper inspection and laboratories 500
Rewinder 500
Paper box manufacturing 200
Pharmaceuticals and Fine Chemical Works
Raw material storage 200
Grinding, granulating, mixing and drying, tableting, 300
sterilizing, preparation of solutions, filling, labelling,
capping, wrapping and cartoning
Control laboratories and testing 300
Fine chemical processing 200
Fine chemical finishing 300
Printing Industries
Photo-engraving
Block-making, etching and staging 200
Finishing, routing and proofing 300
Masking and tint laying 300
Colour Printing
Inspection area 700
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Type foundries
Matrix making, dressing type 250
Front assembly and sorting 200
Hand casting 300
Machine casting 200
Printing plants
Machine composition and imposing stones 200
Presses 300
Composition room 450
Proof reading 300
Colour inspection and appraisal 1000
Electrotyping
Block-making, electroplating, washing and baking 200
Moulding, finishing and routing 300
Rubber Tyre and Tube Manufacturing
Stock preparation
Plasticating, milling 100
Calendering 150
Fabric preparation
Stock cutting, bead building 250
Tube tubing machines 250
Tread tubing machines 250
Tyre building
Solid tyre 150
Pneumatic tyre 250
Curing department
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Tubing curing, casing curing 350
Final Inspection
Tube, casing 1000
Wrapping 200
Shoe Manufacturing (Leather)
Cutting and stitching
Cutting tables 450
Marking, buttonholing skiving, sorting and counting 450
Stitching
Light materials 300
Dark materials 1000
Making and finishing
Nailers, sole layers, welt beaters and scarfers,
trimmers, welters, lasters, edge setters,
600
sluggers, randers, wheelers, treers, cleaning,
spraying, buffing, polishing, embossing
Shoe Manufacturing (Rubber)
Washing, coating, mill run compounding 100
Varnishing, vulcanizing, calendering, upper and sole cutting 300
Sole rolling, lining, making and finishing process 500
Soap Factories
Kettle houses and ancillaries, glycerine evaporation and distillation
and continuous indoor soap making
General areas 150
Control panels 200 to 300
Batch or continuous soap cooling, cutting and drying, soap milling and plodding
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
General areas 150
Control panels and key equipment 200 to 300
Soap stamping, wrapping and packing, granules making, granules storage and handling, filling and packing granules
General areas 150
Control panels and machines 200 to 300
Edible products processing and packing 200
Textile Mills (Cotton) Bale breaking and picking 150
Carding and drawing 200
Slubbing, roving, spinning, spooling 200 Beaming and slashing on comb
Grey goods 200
Denims 300 Weaving
Patterned cloth and fine counts, light 300
Patterned cloth and fine counts, dark 500
Plain grey cloth 200
Cloth inspection 700
Textile Mills (Silk and Synthetics) Manufacturing Soaking, fugitive tinting, conditioning, setting or twist 200
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Textile Mills (Silk and Synthetics) (contd.)
Winding, twisting, rewinding and coining, quilting and
slashing
Light thread 200
Dark thread 300
Warping (silk or cotton system) on creel, on running ends, on reel, 300
on beam, on warp at beaming
Healding (drawing-in) 700
Weaving 300 - 500
Inspection 1000
Textile Mills (Woollen and Worsted)
Scouring, carbonizing, testing, preparing, raising, brushing, 150
pressing, back-washing, gilling, crabbing and blowing
Blending, carding, combing(white), tentering, drying and
200
cropping
Spinning, roving, winding, warping, combing (coloured) and 450
twisting
Healding (drawing-in) 700
Weaving
Fine worsteds 700
Medium worsteds and fine woollens 450
Heavy woollens 300
Burling and mending 700
Perching
Grey 700
Final 2000
Table 8.1.10: Recommended Values of Illumination for Industrial Buildings and Processes (contd.)
Area or Activity Illuminance
(lux)
Wood Working
Rough sawing and bench work 150
Sizing, planing, rough sanding, medium machine and bench 200
work glueing, veneering
Fine bench and machine work, fine sanding and finishing 300
Table 8.1.11: Recommended Values Table 8.1.12: Recommended Values
of Illumination for of Illumination for
Storage Buildings Outdoor Stadiums
Colour TV
broadcasting
Area or Activity Illuminan Area or Activity Illuminanc
ce (lux) e (lux)
Storage Rooms of Ware Football Stadium 1700
House
Cricket Stadium 2200
Inactive 50
Rough bulky 50
Medium 100
Fine 250
Table 8.1.13: Recommended Values Table 8.1.14: Recommended Values
of Illumination for of Illumination for
Outdoor open yards Roads
Illuminance Illuminance
Area or Activity Area or Activity
(lux) (lux)
Outdoor Car Parking Lot 100 Roads inside a Housing 50- 100
Area
Airport Apron 200
Roads in a Congested 50- 100
Container Yard 200
Town / City Area
Jetty 250
Wide Roads with dividers 100 - 120
Avenues 100 - 120
(d) Semi-indirect fittings: Semi-indirect fittings shall be used when a comfortable brightness ratio between the ceiling and the luminaire is desirable but an efficiency of illumination, higher than that obtainable from indirect fittings is required.
(e) Indirect fittings: Indirect fittings shall be used in situations where an environment of evenly distributed illumination is to be achieved.
(f) Angle lighting: Lighting on vertical surfaces shall be done avoiding shadows using interior or exterior light fitting of appropriate type concentrated source light fitting depending upon the place and the color tone required. However, if creating shadows is necessary then appropriate type concentrated source light fitting should be chosen depending upon the place.
1.2.7 Illumination of Exit Signs and Means of Escape
1.2.7.1 Exit signs
(a) All required exit signs shall be illuminated at night, or during dark periods within the area served.
(b) Exit signs may be illuminated either by lamps external to the sign or by lamps contained within the sign. The source of illumination shall provide not less than 50 lux at the illuminated surface with a contrast of not less than 0.5. Approved self-luminous signs which provide evenly illuminated letters having a minimum luminance of 0.2 cd/m2 may also be used.
(c) Exit signs within an area where the normal lighting may be deliberately dimmed or extinguished, such as places of entertainment, shall be illuminated either by lamps contained within the sign or by approved self-luminous signs.
1.2.7.2 Means of Escape Lighting
(a) The means of escape and exit access in buildings requiring more than one exit shall be equipped with artificial lighting. The lighting facilities so installed shall provide the required level of illumination continuously during the period when the use of the building requires the exits to be available.
(b) The intensity of illumination at floor level by means of escape lighting shall not be less than 10 lux, except that the minimum required floor level illumination of aisles in assembly halls, theatres and cinema during projection of motion or still pictures by directed light shall not be less than 2 lux.
(c) The illumination of exit signs and the lighting of the means of escape and exit access shall be powered by an alternate or emergency electrical system to ensure continued illumination for a duration of not less than 30 minutes after the failure of primary power supply.
1.2.8 Selection of Appropriate Type of Lamp
It is important to select appropriate types of lamps for each purpose. The lamps which are used for various purposes are:
(i) General Service Lamps (GLS)/Incandescent Lamps
General Service Lamps (GLS) are well known Incandescent Lamps. These are available in a number of watt ratings. However, most commonly used ratings are 40 W, 60 W, 100 W, 150 W and 200 W rated lamps are also used for special applications. These types of lamps are produce heat and should be minimized while selecting for a particular design because other better choices are available nowadays. For kitchen, cooking areas of a hotel, serving counters of a food shop or hotel, porch these are often essential because of the color temperature. For living room, toilet, corridor, veranda, bed room these have been used for long but from energy saving point of view other lamps which perform better in terms of light output to watts ratio may be used. In general, the GLS type of lamp may be used for almost all interior and exterior applications but from energy saving point of view other lamps which perform better in terms of light output to watts ratio should be used as much as possible.
(ii) Fluorescent Lamps (FL):
These are available in 20 W and 40 W ratings. These lamps are strongly recommended for reading room, educational buildings, laboratories, office room, commercial space applications, factory illumination, illumination of areas around industrial plant and machineries, exterior lighting applications.
40 W FL should be used wherever possible because a 40 W FL is more energy efficient compared to a 20 W FL. These are long life lamps, have wide applications and are advantageous in many respects.
(iii) Compact Fluorescent Lamp( CFL) Energy Saving Lamps:
CFL Lamps are available in a number of watts ratings e.g., 4 W, 7 W, 11 W, 14 W and 24 W. CFLs have been finding wide application for almost all applications because of their high Light output to watts ratio and also because of the attractive light color. CFL lamps, therefore, should be widely used for energy saving purpose.
However, for reading areas, library areas, educational buildings, laboratories fluorescent lights give better service and thus should be selected for these purposes. It is worthwhile mentioning that Fluorescent lamps with high quality ballasts closely meet the energy saving purpose.
(iv) LED Lights:
Compact light fitting formed using a cluster of white LED is currently used to replace a conventional lamp. An LED operates at very small amount of voltage. These are good for lighting, energy efficient, have almost negligible heat dissipation. These are good for relaxed environment interior lighting. LED lights are becoming more and more popular because of much lower power consumption compared to other lamps.
(v) Halogen lamp:
Halogen lamps are used for spot lights, decorative lights in shops and commercial spaces, inside show cases, stage lighting, and projection lights. Due to high temperature rise and UV light output these should be avoided for interior lighting unless needed.
(vi) Mercury Vapour Lamp These have been widely used for shops, streets, for high bay lighting, warehouse lighting and similar special lighting. Most likely, this type of lamp will be discontinued within next five to six years due some of it’s ill effects. Metal halide lamp is coming up as a better alternative to mercury vapour lamp.
(vii) Metal Halide Lamp:
These are available in a number of watts ratings e.g., 150 W, 200 W, 250 W, 500 W, 1000 W, 2000 W. Good for exterior lighting, indoor and outdoor athletic facilities, for high bay lighting, warehouse lighting. These are required where massive flood lighting is required from high altitudes for coverage of large areas.
(viii) HP Sodium Lamp:
These are available in a number of watts ratings e.g., 40 W, 50 W, 70 W, 100 W, 150 W, 250 W, 400 W, 1000 W. Good for exterior lighting, Lighting for areas where higher concentration of vehicles and people exist e.g., Street lighting, building exterior lighting, security lighting.
(ix) Low Pressure Sodium Lamp:
For outdoor lighting such as street lights and security lighting where faithful color rendition is considered unimportant. This type of lamps may be used for street lights, observatory, parking lot and similar types of areas.
(x) Solar PV Cell Powered LED Lights:
These fittings require a solar panel, a storage battery system apart from the cluster of LEDs. For outdoor lighting such as street lights, security lighting, outdoor parking area, this type of light fitting may be used.
1.3 ELECTRICAL AND ELECTRONIC INSTALLATIONS IN BUILDINGS
1.3.1 List of Symbols used for Electrical Drawings
A list of general graphical symbols used for electrical drawings is given in Table 8.1.15. These are given as guideline. In case of justified reasons a designer may modify certain symbol.
Table 8.1.15: Symbols used for Electrical Drawings
Serial No. Description Symbol
1 Main Distribution Board (MDB)
2 Floor Distribution Board (FDB)
3 Distribution Board (DB)
4 Sub-distribution Board (SDB)
5 Branch Distribution Board (BDB)
6 Switch Board (SB)
7 Telephone Outlet (PSTN)
8 Telephone Outlet (PABX)
9 Change over switch
E
10 Energy meter
A
11 Ammeter
V
12 Voltmeter
P.F
13 Power factor meter
14 Circuit breaker
15 Fuse
16 Ceiling mounted Incandescent light fitting
17 Wall mounted bracket light fitting
Serial No. Description Symbol
18 Ceiling fan
19 Exit light pendant
20 Exit light-wall mounted
21 2 pin socket Outlet (single phase)
22 3 pin 13A switched socket Outlet (single phase)
23 Weatherproof and waterproof socket outlet
SPST Single – pole, one-
24
way switch
25 DPST Two - pole, one-
way switch
TPST Three - pole, one-
26
way switch
27 SPDT Two – way switch
28 Push button switch
29 Buzzer
30 Single fluorescent lamp on ceiling
31 Double fluorescent lamp on ceiling
32 Double fluorescent lamp on wall
33 Spot light
Serial No. Description Symbol
34 Wall mounted bracket fan
35 Exhaust fan
36 Pull box
37 TV socket outlet
38 Fire Alarm bell
39 Fire detector
40 Smoke detector
41 Speaker
42 Microphone
43 Conduit, concealed in ceiling or in wall
Conduit, concealed in floor or through under
44
ground
45 Telephone conduit
46 Television antenna conduit
47 Earth Electrode
1.3.2 Estimating the Load of a Building/Complex
Estimating the total load of a building has to be started with the listing of the connected loads in a building. The steps are to list the loads in each of the rooms, in each of the flats/offices of a floor, in each of the floors and the load of the total building. In this way an account of the total building area/the total complex has to be prepared. Loads of the Lift(s), water pump(s), bulk ventilating system in the basement and any other equipment installed in the building must also be added. For completing the load calculation, practical value of appropriate diversity factors will have to be applied at each stage.
Estimating the total load of a complex consisting of a number of buildings has to be started with the listing of the connected load of each of the buildings, they are lighting load, water pump and any other equipment installed in the complex. For completing the load calculation, practical value of appropriate diversity factors among the buildings will have to be applied.
1.3.2.1 Maximum demand and diversity
Two items need to be determined, which are: (i) Maximum demand and (ii) Diversity factor. These are needed in completing the load calculation and in the computation of current. In determining the maximum demand of an installation or parts thereof, diversity shall be taken into account. Appendix A gives some information on the determination of the maximum demand of an installation and includes the current demand to be assumed for commonly used equipment together with guidance on the application of allowances for diversity.
1.3.2.2 Estimation of load in kW, in kVA and in Amperes
An estimation of loads is necessary initially for design purposes and later for keeping a track of the growth of load. Estimation of loads means estimation of watts or kilowatts in small scale. In bigger scale the kVA is assessed together with the power factor. A calculation of current is then to be performed for the selection of breakers/fuses and the current carrying cables.
1.3.2.3 Estimation of electrical load in Watts
Energy efficient and energy saving should be considered in estimating the electrical load, the watts rating of individual equipment/fittings connected to the system need to be listed and added. Typical watt ratings of some of the equipment/fittings are shown in Table 8.1.16 which may be used for estimation if the actual values are not known or specified.
Table 8.1.16: Estimated Load for Different Fittings/Fixtures
Type of Fitting/Fixture Ratings Type of Fitting/Fixture Ratings
in Watts in Watts
CFL 5-65 15 A Socket outlets 1500
LED and Solar Panel Powered 10-60 Microwave Oven (domestic) 1200-
LED Security /Street Lights 1500
Fluorescent lamp with Washing machine (domestic) 350-500
accessories:
Nominal length 600 mm 20 Television (medium size) 120-200
Type of Fitting/Fixture Ratings Type of Fitting/Fixture Ratings
in Watts in Watts
Nominal length 1200 mm 40 Computer (without printer) 200
Photo copiers 1200- Computer with printer 700-800
1500
Ceiling fans 100 Window type A.C. machine 1500
(Max) (12000 BTU/hr)
Electric 1500 Split type A.C. machine 1300
(12000 BTU/hr)
Table fans 85 (Max) Geyser (water heater, 1000-
domestic) 1200
Pedestal fans 120 Toaster (domestic) 800-1000
(Max)
Exhaust fans 100 Electric calendar 700-1000
(Max)
5A socket outlets 300
1.3.2.4 Calculation of current
For the calculation of current (for the selection of cables and breakers) of the fluorescent lamps the ratings are to be multiplied by a factor of 1.65 to take care of the power factor and the starting current situation.
For the calculation of current (for the selection of cables and breakers) of the ceiling fans, table fans, pedestal fans, exhaust fans the ratings are to be multiplied by a factor of 1.65 to take care of the power factor and the starting current situation.
For the calculation of current (for the selection of cables and breakers) of the small inductive loads (up to 1.0 kW) the ratings are to be multiplied by a factor of 1.65 to take care of the power factor and the starting current situation. The factor shall be higher for higher rated motors.
1.3.2.5 Minimum load densities
While estimating the electrical load, the minimum load densities to be considered are those shown in Table 8.1.17.
1.3.3 Fittings, Fixtures and Accessories
Switch boards with back boxes and cover plates, ceiling roses, socket outlets with back boxes, plugs, light fittings, fans, pull boxes with cover plates have been put in this category, although there may be other items which may be included under electrical accessories related to electrical and electronic installations in buildings.
1.3.3.1 Switch boards
Tumbler switches have been used for surface wiring and piano switches have been used for concealed wiring. Now a day piano switches are also used with surface wiring. Piano switches are mounted on either a plastic back box or a metal back box. These piano switches are available in gangs. The other alternative is to have piano switches mounted on a Perspex or Ebonite sheet which is then mounted on a metal back box. The Switches must conform to the relevant BS standard. The minimum ampere rating of switch shall not be below 5 A.
Switches may be Single Pole Single Throw (SPST) or Single Pole Double Throw (SPDT) depending on the operation. For some application Double Pole Single Throw (DPST) and Double Pole Double Throw (DPDT) are also available. Usually the DPST switches are made for 10 A, 15 A and 20 A rating.
The phase (Live) wire (Brown PVC insulated cable) connection to the point must go through the switch.
The metal / sheet steel back boxes of a switch board must have an earthing terminal to terminate the Earth Continuity Conductor (ECC) coming from a BDB or an SDB.
Table 8.1.17: Minimum Load Densities
Type of Occupancy Unit Load
(Watts/m2)
Non A/C A/C
Residence/ Dwelling : Single family 20 75
Residence/ Dwelling : Multi-family (other than hotels) 20 75
Hospitals 32 80
Hotels, including apartment house (excluding any provisions 24 75
for electric cooking)
Office and commercial multi-storeyed buildings 28 75
Industrial building (excluding the loads for machines) 16 -
Type of Occupancy Unit Load
(Watts/m2)
Non A/C A/C
Departmental stores 28 75
Banks 20 75
Restaurants (excluding any provisions for electric cooking) 16 75
Barber shops and beauty parlours 32 75
Schools and colleges 12 70
Parking area in commercial buildings 4 -
Warehouses, large storage areas 2 -
1.3.3.2 Socket outlets and plugs
In general, all socket outlets must be switched (combined) and shuttered.
(a) General requirements of socket outlets Socket outlets shall be 13 A switched shuttered 3 pin flat pin type. All socket outlets must be switched (combined) and shuttered and shall be for 3 pin Flat pin type (rectangular cross section) 13 A plugs fitted with tubular fuse. The corresponding plugs must be fitted with fuse. The maximum fuse rating shall be 13A for 13A Sockets. The fuse rating may be smaller depending upon the current rating of the appliances used. The phase wire (Brown cable) shall be connected to the L terminal of the socket outlet through the combined switch and the neutral wire (Blue cable) shall be directly connected to the N terminal of the socket. Earth Continuity Conductor (ECC) (Yellow + Green bi-colour cable) for such a socket outlet shall be connected to the Earth terminal of the socket.
The plug for each 13A socket outlet provided in a building for the use of domestic appliances shall be provided with its own individual fuse. The feed cables for such a circuit must have fuse or miniature circuit breaker (MCB) at the originating point in the Distribution Board or Sub-Distribution Board or Branch Distribution Board. For some high current applications, additional fuses/ circuit breakers adjacent to the sockets are recommended.
Each socket outlet shall also be controlled by a switch which shall normally be located immediately adjacent thereto or combined therewith.
The phase (Live) wire (Brown PVC insulated cable) connection to the socket outlet must be through the switch. Copper size of the Earth Continuity Conductor (ECC) for such a socket outlet shall not be smaller in size than 1.5 mm2 PVC insulated cable.
(b) 15 A/20 A rated socket outlets
(c) Round pin socket outlets of 15 A/20 A rating may be used for air conditioner outlets and water heater outlets under special circumstances, for air conditioner outlets (requiring 15 A or 20 A), 15 A/20 A rated socket outlets for round pin plugs may be used along with a circuit breaker or fuse protection in a box adjacent to the sockets.. Each 15 A/20 A socket outlet provided in a building for the use of domestic appliances such as air-conditioner, water cooler, etc. shall be provided with its own individual fuse. The feed cables for such a circuit must have fuse or miniature circuit breaker (MCB) at the originating point in the Distribution Board or Sub-Distribution Board or Branch Distribution Board. For some high current applications, additional fuses/circuit breakers adjacent to the sockets are recommended. Each socket outlet shall also be controlled by a switch which shall normally be located immediately adjacent to the Socket or shall be combined with the Socket. The corresponding plugs for 15 A should be fitted with fuse. The maximum fuse rating shall be 15 A for 15 A Sockets. For a 15 A rated socket outlet a 15 A rated fuse or a 15 A circuit breaker must be placed adjacent to the socket. For a 20 A rated socket outlet a 20 A rated fuse or a 20 A circuit breaker must be placed adjacent to the socket. Wiring for sockets shall be radial type of wiring. However, ring type wiring may be used by strictly following the rules given in IEE Wiring regulations BS 7671 and by using appropriate size of cable.
(d) Earth Continuity Conductor (ECC) for a socket The ECC for a socket outlet shall not be smaller in size than 1.5 mm2 PVC insulated annealed copper cable. The colour of the ECC cable insulation shall be Yellow + Green bi-colour.
(e) Mounting height of a three pin switched socket outlet Three pin switched shuttered socket outlets shall be mounted on a wall at a height 250 mm above floor level. Switched shuttered socket outlets are essential for safety in particular for the safety of infants. For certain applications like computers, printers, UPS, IPS such sockets may be mounted at a higher level for the ease of operation.
(f) Restriction on mounting socket outlets in wet places No socket outlets shall be provided inside bath rooms/toilets or any other place where floor may remain wet.
(g) 5 A rated 2 pin socket outlets 5 A rated 2 pin socket outlets may be used along with the light and fan switch boards only. Such sockets shall not be used as socket outlets at the skirt level.
(h) Number of socket outlets in a room/in a building The number of socket outlets in a building depends upon the specific requirements of occupants and the type of building. Adequate number of 13 A switched flat pin (rectangular cross section pin) shuttered socket outlets shall be provided and arranged around the building to cater to the actual requirements of the occupancy.
15 A round pin (rectangular cross section pin) socket outlets shall be provided for specially Air-conditioners and water heaters of such ratings only.
For residential buildings, the minimal guidelines given in Table 8.1.18 shall be used to determine the required number of 13 A switched flat pin (rectangular cross section pin) shuttered socket outlets, when actual requirements cannot be ascertained. All socket outlets shall conform to BDS 115.
Table 8.1.18: Minimum Number of 13 A flat pin Socket Outlets
Location No. of Switch Socket Outlets Bed room 2 Living room 3 Drawing room 3 Dining room 1 Toaster/Snack toaster 1 Kitchen 1 Bathroom 0 Verandah 1 Refrigerator 1 Air-conditioner one for each room
(i) Restriction on installation of two socket outlets in room fed from two phases Installation of two socket outlets in a room fed from two different phases should be avoided as far as possible. However, in unavoidable cases, the minimum distance between two such socket outlets in a room fed from two different phases must not be less than 2 m under any circumstances.
(j) Exterior/outdoor sockets Socket outlets in exposed places where chances of dripping/falling rain water exist should not be placed. In case of necessity, weather proof/waterproof covered socket outlets may be mounted with appropriate precautions. In such a case the back box should preferably be of bakelite or Acrylic or plastic material.
(k) Exterior/outdoor switches Switches in exposed places where chances of dripping/falling rain water exist should not be placed. In case of necessity, weather proof/waterproof covered switches may be mounted with appropriate precautions. In such a case the back box should preferably be of bakelite or Acrylic or plastic material.
1.3.3.3 Ceiling rose
A ceiling rose is needed for terminating the point wiring for a Light or a Fan in the ceiling.
(a) A ceiling rose shall not be installed in any circuit operating at a voltage normally exceeding 250 volts.
(b) Normally, a single pendant be suspended from only one ceiling rose using a flexible cord. A ceiling rose shall not be used for the attachment of more than one outgoing flexible cord unless it is specially designed for multiple pendants.
(c) A ceiling rose shall not contain a fuse terminal as an integral part of it.
(d) The ceiling rose shall conform to BS 67.
(e) Luminaire supporting couplers are designed specifically for the mechanical support as well as for the electrical connection of luminaires and shall not be used for the connection of any other equipment.
1.3.3.4 Light fitting
Switches shall be provided for the control of every light fitting. A switch may control an individual light point or a group of light points. Where control at more than one position is necessary for a lighting fitting or a group of lighting fittings, as many two-way or intermediate switches may be provided as the required number of control positions.
In industrial premises light fittings shall be supported by suitable pipe/conduits, brackets fabricated from structural steel, steel chains or similar materials depending upon the type and weight of the fittings. Where a lighting fitting is to be supported by one or more flexible cords, the maximum weight to which the twin flexible cords may be subject are shown in Table 8.1.19.
Table 8.1.19: Maximum Permissible Weight to which Twin Flexible Cords may be Subject Nominal Cross-sectional Area Number and Diameter Maximum Permissible of Twin Flexible Cord (mm2) (mm) of Wires Weight (kg)
0.5 16/0.2 2 0.75 24/0.2 3 1.0 32/0.2 5 1.5 48/0.2 5.3 2.5 80/0.2 8.8 4 128/0.2 14
For a Light fitting with shade, no flammable shade shall form part of the light fitting and the shade shall be well protected against all risks of fire. Celluloid shade or lighting fitting shall not be used under any circumstances.
(a) Lighting point At each fixed lighting point one of the following accessories shall be used
(i) one ceiling rose conforming BS 67
(ii) one luminaire supporting coupler conforming BS 6972 or BS 7001
(iii) one batten lamp holder conforming BS 7895, BS EN 60238 or BS EN 61184
(iv) one luminaire designed to be connected directly to the circuit wiring
(v) one suitable socket-outlet
(vi) one connection unit conforming BS 5733 or BS 1363-4. A lighting installation shall be appropriately controlled e.g., by a switch or combination of switches to BS 3676 and/or BS 5518, or by a suitable automatic control system, which where necessary shall be suitable for discharge lighting circuits.
(b) Wires/cables used inside light fittings and any other fitting Wires/cables used inside a light fitting or any other fittings are mostly flexible types. In some cases single core PVC insulated wiring cables mostly 1.5 mm2 are used. In such cases the cables must be of high quality in terms of insulation and must have appropriate copper cross section. Such cables are usually terminated in a ceiling rose.
1.3.3.5 Fans
(a) Ceiling fan Ceiling fans including their suspension shall conform to BDS 818.
With respect to the position of a lighting fitting, the positioning of a fan shall be such so that it does not throw any shadow on the working plane is not acceptable. The unit module area shall be so chosen that the required number of fans could be suitably located, to avoid creation of pockets receiving little or no air circulation.
In general, fans in large halls may be spaced at 3 to 3.5 m in both the directions in the horizontal plane. If building modules do not lend themselves to proper positioning of the required number of ceiling fans, other types of fans, such as air circulators or wall mounted bracket fans shall have to be installed for the areas uncovered by the ceiling fans. In such cases, necessary electrical outlets shall have to be provided for the purpose. Table 8.1.20 gives the recommended areas to be served by different sizes of ceiling fans where the height of fan blades is at 2.5 m above the finished floor level.
Table 8.1.20: Recommended Fan Sizes in Rooms
Room Area (m2) Fan Sweep Up to 6 915 mm Over 6 to 9 1220 mm Over 9 to 12 1442 mm
Wiring for a ceiling fan outlet from the switch board up to the ceiling fan outlet shall be done through pre-laid 18 mm dia PVC conduits using 1.5 mm2 PVC insulated 2 cables of Brown and Blue insulation. A high quality ceiling rose is to be installed at the ceiling fan point for the termination of the wiring and the connection of the two wires of the Fan.
A fan hook is required to be placed during casting of the roof. The fan hook is to be made using a 12 mm dia MS rod having at least 600 mm on both sides and shall be placed above the MS rod mesh of the roof slab.
(b) Wall mounted bracket fan For Wall mounted bracket fans shall be mounted on the wall using appropriate rowel bolts. Wiring for a Wall mounted bracket fan outlet from the switch board up to the Wall mounted bracket fan outlet shall be done through pre-laid 18 mm dia PVC conduits using 1.5 mm2 PVC insulated 2 cables of Brow and Blue insulation. A high quality ceiling rose is to be installed at the ceiling fan point for the termination of the wiring and the connection of the two wires of the Fan.
(c) Pedestal fans and table fans These items are movable and no fixed connections are necessary. Sockets will be used to energize these fans.
(d) Installation/mounting of ventilating fans or exhaust fans Exhaust fans are necessary for spaces, such as toilets, kitchens, canteens and godowns to provide the required air changes. Since the exhaust fans are located generally on the outer walls of a room, appropriate openings in such walls shall be provided right from the planning stage. The sizes and the rpm of the exhaust fans will vary according to the application and the volume for which a fan used. In some applications (such as some industries, big size gas generator room etc.) high rpm fans are essential. In all cases appropriate types of fan need to be chosen and appropriate arrangement need to be made so that rain water cannot get inside the rooms.
(e) Installation/mounting of ceiling fans Ceiling Fans shall be suspended from Fan hooks that are to be placed in position during casting of the Roof.
(f) Fan hooks Fan hooks may be concealed (hidden) or may be exposed type. Fan hooks shall be made using MS rods of 12 mm diameter. The diameter of this rod shall not be below 10 mm under any circumstances.
(g) Ceiling roses for fan points Appropriate type of ceiling roses must be provided at the fan points for the termination of the Fan point wiring cables. Connection to the Ceiling Fans will go from the ceiling roses.
(h) Cutout box/circuit breaker box If the BDB or the SDB from which a 3-pin switched shuttered socket receives power is at a significant distance away and the load connected to the socket needs special care an additional cutout box or a circuit breaker box may be placed adjacent to the socket. Such a cutout Box or a Circuit Breaker box shall be placed inside a 18 SWG Sheet Steel (coated with two coats of synthetic enamel paint) of appropriate size with appropriate Perspex cover plate. Such a box may be surface fitted or may be concealed fitted. The box shall have a brass terminal for the termination of the ECC.
1.3.4 Distribution Wiring in a Building
1.3.4.1 General
Loads are separated into known and unknown loads.
General illumination is a known load, whether derived from detailed lighting layout, or developed from watts per square meter calculation. Similarly fans are also known loads. Besides these two types, there may be some other known loads.
Number, rating and layout of outlets for general illumination, fans and other known loads should accurately be distributed among a number of branch circuits. These branch circuits should then be carefully loaded with due regard to voltage drop, operating voltage and possible increase in lighting levels in future. On the other hand the sockets are unknown loads. Socket loads will be determined from projections based on the utility of the building and type of applications.
Every installation shall be divided into small circuits (following the rules given in this document) to avoid danger in case of a fault, and to facilitate safe operation, inspection, maintenance and testing. For the establishment of the circuits appropriate type of wiring is needed and appropriate terminations/connections/junctions of these circuits are needed. At the same time appropriate types of protection against faults must be given at different levels. These are to be achieved through installation of appropriate distribution wiring in the building.
1.3.4.2 Distribution board
A Distribution Board is the junction point of the incoming line and the outgoing lines for the distribution of Electricity throughout the building. The incoming as well as the outgoing lines must have Circuit Breaker protection or Fuse protection. The junctions and terminations of the incoming and outgoing cables are made through copper bars containing bolts and nuts for cable lugs known as bus-bars. A Distribution board may be named as MDB or FDB or DB or SDB or BDB.
(a) MDB stands for Main Distribution Board. This is the distribution box where the main incoming cable enters and terminates from the main service feed connection of a large building. The FDBs get feed from MDB.
(b) FDB stands for Floor Distribution Board located in each of the floors of a multistoried building. The DBs get feed from FDB. Usually, more than one FDB are needed.
(c) DB is the abbreviation for Distribution Board. This may be the box where the main incoming cable enters and terminates from the main service feed connection. The SDBs get feed from a DB.
(d) SDB is used to represent Sub- Distribution Board. This board is located in the same floor of a building and connected to the DB. Usually more than one SDB are needed. The BDBs get feed from SDB.
(e) BDB stands for Branch-Distribution Board located in the same floor of a building and connected to the SDB. Usually more than one BDB are needed.
(f) EDB, EFDF, ESDB, EBDB Sections of DB, FDB, SDB, BDB receiving feed from the Emergency Bus-bar which in turn is getting feed from standby generator through changeover switch. These may be separate DBs placed by the corresponding normal supply DBs.
Each of these distribution boards must have busbars for Line, neutral and earthing for a single phase box. A 3-phase distribution board must have busbars for Line 1, Line 2, and Line 3, neutral and earthing.
These boxes shall be made with sheet steel of not less than 18 SWG thicknesses and must be appropriately paint finished to match the wall paint.
1.3.4.3 Circuit wiring
(a) Separate branch circuits for separate control Separate branch circuits shall be provided for different parts of a building area which need to be separately controlled. A branch circuit should be independently working and should not be affected due to the failure of another branch circuit.
The number of final circuits (also termed as sub-circuits or circuits) required and the points supplied by any final circuits shall comply with
(i) the requirement of over-current protection,
(ii) the requirement for isolation and switching, and
(iii) the selection of cables and conductors.
All final circuits shall be wired using loop wiring system; no joint box shall be used.
Sufficient number of 18 SWG sheet steel made (painted with two coats of grey synthetic enamel paint) pull boxes, with ebonite/perspex sheet cover plate, must be given on the walls near the ceiling. If brick walls are not available, pull boxes must be given in the ceilings.
(b) For domestic and office buildings 5A Light/Fan Circuits must be used for all Domestic and Residential buildings. 5A Light/Fan Circuits are also to be used for Office and commercial Buildings. The corresponding circuit wire in the BDB/ SDB/ DB then shall be not less than 1.5 mm2.
(c) For office and commercial buildings having large open floor areas Under unavoidable circumstances, in case of difficulties in forming 5 A light/fan circuits for office and commercial buildings having large open floor areas, 10 A light/fan circuits may be used. The corresponding circuit wire in the BDB/SDB/DB then shall be not less than 2.5 mm2. However, use of 5 A light/fan circuits is still emphasized.
(d) For industrial/factory buildings having large open floor areas For industrial/factory buildings having large open floor areas, 10 A light/fan circuits may be used.
(e) For industrial/factory buildings/warehouses having too large open floor areas For industrial/factory buildings/warehouses having large open floor areas, efforts should be given to use circuits not exceeding 10 A. The corresponding circuit wire in the BDB/SDB/DB then shall be not less than 2.5 mm2.
For Industrial/Factory Buildings having very large open floor areas, 15 A light/fan circuits may be used as exceptional cases only. The corresponding circuit breaker in the BDB/SDB/DB then shall be not less than 4 mm2.
Increase in the sizes of the above mentioned cables may be required if the distance is too long. Voltage drop calculation will give the guidance in that case.
(f) Separate branch circuits from Miniature Circuit Breaker (MCB) Separate branch circuits shall be provided from miniature circuit breaker (MCB) of a BDBD/SDB or fuse of the fuse distribution boards (FDB) for light/fan.
Separate branch circuits shall be provided from miniature circuit breaker (MCB) of a BDBD/SDB or fuse of the Fuse distribution boards (FDB) for automatic and fixed appliances with a load of 500 watt or more and socket outlets. Each automatic or fixed appliance shall be served by a protected socket circuit.
(g) Less than 50% loading of circuits with more than one outlet Circuits with more than one outlet shall not be loaded in excess of 50% of their current carrying capacity.
(h) Branch circuits must have spare capacity to permit at least 20% increase in load
Each branch circuit running between a DB and a SDB, between a SDB and a BDB must have spare capacity to permit at least 20% increase in load before reaching the level of maximum continuous load current permitted for that circuit
(i) One spare circuit must be allowed in the distribution board for each five circuits in use.
At least one spare circuit must be allowed in the distribution board for each five circuits in use. Additional space for a circuit breaker along with the provision for connecting a pair of outgoing cables shall be kept.
(j) Each final circuit shall be connected to a separate way in a distribution board Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent unwanted energization of a final circuit.
(k) Size of cables in a branch circuit shall be at least one size larger than that needed for the computed load current
Size of cables to be used in a branch circuit shall be at least one size larger than that computed from the loading if the distance from the over-current protective device to the first outlet is over 15 m.
(l) 4 mm2 (7/0.036) and 6 mm2 (7/0.044) wiring cable for a 15 A socket outlet branch circuit The minimum size of wiring cable used for a 15 A socket outlet branch circuit shall be 4 mm2 (7/0.036). When the distance from the over-current protective device to the first socket outlet on a receptacle circuit is over 30 m the minimum size of wire used for a 15 A branch circuit shall be 6 mm2 (7/0.044).
(m) Length of a lighting circuit The length of a lighting circuit shall be limited to a maximum of 30 m, unless the load on the circuit is so small that voltage drop between the over-current protective device and any outlet is below 1 percent.
(n) Use of common neutral for more than one circuit is prohibited Each circuit must have its own neutral cable. Use of common neutral cable for more than one circuit is not permitted.
(o) Following the appropriate new colour codes of cables During wiring, correct colour codes of the insulation of the cables must be used. Previously, for a single phase circuit red colour insulation was used for the live wire and the black colour insulation for the neutral and green + yellow bi-colour insulation was used for the ECC. Previously, for a three phase circuit red colour was used for the live (L1), Yellow colour for the live (L2), Blue colour for the live (L3) cable and the black
colour for the neutral and green + yellow bi-colour for the ECC. This colour code of cables shall now be replaced by the current IEC cable colour code standards, Table 8.1.21 and Figure 8.1.1. The current IEC colour code is recommended to be followed in Bangladesh.
Table 8.1.21: New introduced Colour Codes of Cables Following IEC Standards
Item Pre-1977 IEE Pre-2004 IEE Current IEC
Protective earth (PE) Green Green/yellow Green/yellow
bi-colour
bi-colour
Neutral (N) Black Black Blue
Single phase: Line (L) Red Red Brown
Three-phase: L1
Three-phase: L2 Yellow Yellow Black
Three-phase: L3 Blue Blue Grey
Figure 8.1.1 Existing and harmonised colour code by IEC recommended for use in Bangladesh.
The above mentioned colour coding must be indicated in the design drawing. This should also be mentioned in the specification.
(p) Balancing of circuits in three phase SDBs, DBs, FDBs, and MDBs. In a 3 phase distribution system special care must be taken during wiring to obtain balancing of loads among the three phases. In a 3 phase SDB, DB, FDB, MDB connections of the circuits to the bus-bars must be made in such a way so that the load current remains balanced among the three lines during low load as well as full load. After completing the installation balancing should be checked by clamp meter current measurement of each phase.
The above mentioned current balancing must be indicated in the SDB (if 3 phase), DB, FDB, and MDB circuit diagram of design drawing. This should also be mentioned in the specification.
1.3.5 Electrical Layout and Installation Drawings
An electrical layout drawing shall be prepared after proper locations of all outlets for lamps, fans, fixed and transportable appliances, motors etc. have been selected. This is the beginning of the electrical distribution design work. This job must be done with due importance prior to starting the construction and installation work. Strong emphasis is given on this work in this document.
1.3.5.1 Locating positions of the points on the plan of the building
At the beginning, the Light points, Fan points, Socket points, Switch Boards, BDBs, SDBs, FDBs. DBs and MDBs shall be located on each plan based on convention, suitability, application and safety view point.
Conduit layout and cable layout shall then be shown on the drawing.
1.3.5.2 Light and fan circuits must not be mixed with the socket circuits
In designing the wiring layout, power (socket) and heating (socket) sub-circuits shall be kept separate and distinct from light and fan sub-circuits. All wiring shall be done on the distribution system with main and branch distribution boards placed at convenient positions considering both physical aspects and electrical load centres. All types of wiring whether concealed or surface, shall be as near the ceiling as possible. In all types of wiring due consideration shall be given to neatness and good appearance.
1.3.5.3 Balancing of circuits in three phase distribution boxes is a must
Balancing of circuits in three phase installations shall be arranged in the drawing and also must be done during physical connection.
1.3.5.4 Single phase socket outlets receiving connection from two different phases Single phase socket outlets receiving connection from two different phases located in the same room is to be avoided. However, if it is essential to have such socket connection these must be located 2 m or more apart.
1.3.5.5 Electrical Layout drawings for industrial premises
Electrical layout drawings for industrial premises shall indicate the relevant civil structure/barrier/duct and mechanical equipment/duct.
1.3.5.6 Preparation of detailed circuit diagram
Circuit diagrams of each of the Light and Fan circuits must first be prepared based on the selection whether it is 5A or 10A circuit. The cable size of each of the circuit’s size of the ECC must be shown in the drawing. The circuit diagrams of the BDBs, SDBs, DBs, FDBs, and MDBs etc. are then to be prepared and presented in the form of single line drawings indicating the cable sizes of each interconnection and the sizes of the ECCs. The distribution of BDBs, SDBs, DBs, FDBs, MDBs etc. are two be shown in a distribution drawing indicating the cable sizes of each interconnection and the sizes of the ECCs.
1.3.5.7 Preparation of electrical distribution and wiring design drawing by an experienced Engineer
Electrical Distribution and Wiring Design drawing of building must be prepared by an eligible Engineer as mentioned in Table 2.3.4 Chapter 3 Part 2.
1.3.6 Electrical Wiring in the Interior of Buildings
1.3.6.1 Surface wiring or exposed wiring
Wiring run over the surface of walls and ceilings, whether contained in conduits or not, is termed as surface wiring or exposed wiring.
Single core PVC insulated cupper through PVC channels or through PVC conduits or through GI pipes of approved quality may be used for surface wiring.
Surface wiring using twin core flat PVC insulated cupper on wooden battens used to be used long back. This is almost discontinued and discouraged now a day.
PVC conduits or GI pipes, when used for surface wiring, shall be clamped with saddles at a spacing not exceeding 600 mm, to the wall or ceiling using plastic rowel plugs with countersunk galvanized screws.
(a) Surface wiring using wood battens The wood batten used in this method shall be of good quality wood with a minimum thickness of 12 mm. They shall be installed exposed and run straight on the ceiling or wall surfaces. Battens on walls shall be run either horizontally or vertically, and never at an angle. Battens on ceilings shall run parallel to the edges in either orthogonal direction, and not at an angle, they shall be fixed to the wall or ceiling by rowel plugs and countersunk galvanized screws. Cables shall be fixed to the battens by using galvanized steel clips or brass link clips or PVC clips of required size at a spacing not exceeding 100 mm.
(b) Surface wiring using PVC conduits PVC conduits or GI pipes, when used for surface wiring, shall be clamped with saddles at a spacing not exceeding 600 mm, to the wall or ceiling using plastic rowel plugs with countersunk galvanized screws.
The conduits placed concealed inside roof or in wall must have 20 SWG GI pull wires placed during laying of the pipes for pulling the cables later.
(c) Surface wiring using PVC channels Surface wiring may be done using single core PVC insulated cables placed inside surface fixed PVC channels of appropriate size. Fixing of channels must be done using screws in rowel plugs inserted into drilled holes on the walls/ceilings. The channels must be placed in a straight line with adequate number of screws so that no sag is observed. Cables must not be stressed in the bends. Adequate space must exist inside the channel to put the cables in position without difficulty.
Surface wiring using flexible chords, clips and nails shall not be used in general.
(d) Surface wiring using Round core flexible cable with plastic clips and nails Surface wiring using exposed Round core flexible cable with plastic clips and long nails have been used for extending a point wiring, for extending a socket wiring due to shift, for add a circuit wiring. This is not recommended for regular wiring. Instead of using this method, one should go for the recommended surface wiring using single core PVC cables with PVC channels or single core PVC cables with PVC conduits as mentioned above in this document. For a length of not exceeding 1 m this may be used only for shifting an existing Light/Fan point or for shifting an existing socket point only under unavoidable circumstances.
1.3.6.2 Concealed wiring
The wires in this type of wiring shall be placed inside GI conduits or PVC conduits that are buried in roofs and in brick/concrete walls. The conduits in the walls shall be run horizontally or vertically, and not at an angle. Conduits in concrete slabs shall be placed at the centre of thickness and supported during casting by mortar blocks or 'chairs' made of steel bars or any other approved means. All conduits shall be continuous throughout their lengths. Appropriate planning should be made in which there shall be adequate spare capacity in the conduits placed in roof slabs so that unforeseen situation during execution of the installation can be taken care of. Conduits will run through the roof and then bend downward for going up to the outlets, DBs, switch boards, sockets.
In a column structure building having no permanent walls, switch boards and socket boards, pull boxes shall be placed in columns and must be done during the casting of columns.
Concealed wiring through floors and upward mounting of PVC/GI pipes from the floor is strongly discouraged because of the occurrence of condensation and accumulation of water from condensation eventually leading to damaging of the simple PVC insulated cable insulation. This method should not be followed as a general practice.
Underground cables for electrical distribution in the premises/garden/compound of the building shall be encased in GI or PVC pipes and laid in earth trenches of sufficient depth. Armoured cables need not be encased in conduits except for crossings under road, footpath, walkway or floors. The conduits placed concealed inside roof or in wall must have 20 SWG GI pull wires placed during laying of the pipes for pulling the cables later.
1.3.6.3 Wiring inside suspended ceilings (false ceilings)
Wiring inside suspended ceilings (false ceilings) shall be surface wiring through conduits or through PVC channels mentioned under the heading of surface wiring methods.
Cables shall not be placed loosely and haphazardly on the suspended ceilings. Placing naked cables inside the suspended ceiling is not permitted.
Cable joints with PVC tape wrapping is not allowed for connection of a fitting from the ceiling rose or from a junction box inside the gap space.
1.3.6.4 Wiring through cable tray
Wiring for connections to some machines may be carried through a cable tray suspended from the ceiling. This is very rare for a domestic building. However in a commercial / office or industrial building this technique may be needed. In special circumstances Cables may be pulled through pre laid GI/ PVC pipes under the floor where there will be no chances of water accumulation in the floor or condensation.
1.3.6.5 Mounting height of light and fan switch boards
Light and fan switch boards shall be placed 1220 mm above floor level in the residential buildings (i.e, the clearance between the floor and the bottom of the switch board shall be 1220 mm).
This above mentioned height shall be 1300 mm above floor level in the office buildings, commercial buildings and industrial buildings. However, the minimum height shall not be below 1220 mm.
1.3.6.6 Restriction on the use of plastic/PVC insulated flexible chords/cables
Plastic/PVC insulated flexible chords/cables shall not be used for wiring of light/fan points or for wiring of sockets, or for wiring of any sub circuits.
1.3.6.7 Cable joints and cable joint boxes in concealed and surface wiring
Both the Brown (L) and Blue (N) cables of a final circuit shall run from a BDB/SDB up to the switch board without a joint. Similarly, both the Brown (L) and Blue (N) cables of a point shall run from the point up to the switch board. Cable joints are to be made in the switch board back box. Where the above methods are not implementable, joints shall be made using approved cable joint methods.
1.3.7 Methods of Point Wiring and Circuit Wiring
1.3.7.1 Methods of Point Wiring
Wiring between a light/fan point and its corresponding switch board is termed as Point Wiring. The load of such a point is not in excess of 100 watts in general, and in special cases this may be up to 200 watts. Wiring for a light/fan point shall be made using one of the following two methods: (i) Surface wiring or (ii) Concealed wiring. For wiring of a point one brown and one blue PVC insulated copper cable shall run between a point and its switch board. Cable joints inside conduits or within channels are forbidden. The current carrying capacity for such a circuit shall not be more than 5 A for a residential or a commercial (business/mercantile) building. The minimum size of a cable for such wiring shall be 1.5 mm2. Common neutral shall not be used under any circumstances.
1.3.7.2 Methods of Circuit Wiring
Wiring between a switch board and a BDB/SDB/DB will be called Circuit Wiring. Circuit wiring shall be done with a live cable a neutral cable and an ECC cable for a single phase circuit. Sometimes this circuit is also referred to as sub-circuit. An ECC must be provided with each circuit. The ECC at the switch board end shall be terminated in the earth terminal of the metal part of the switch board using a brass screw/bolt and a nut. The BDB/SDB/DB end of the ECC shall be terminated in the earthing busbar of the BDB/SDB/DB.
The ECC in this case shall be PVC insulated copper cable of appropriate size but with yellow + green bi-colour insulation.
For each circuit, the live cable must be drawn using brown colour insulated PVC cable and the neutral cable shall be drawn using blue colour insulated PVC cable. Common neutral shall not be used under any circumstances.
The minimum sizes of cable for various uses shall be as follows:
(a) For a 5 A circuit protected by a 5 A circuit breaker or fuse shall not be below 1.5 mm2
(b) For a 10 A circuit protected by a 10 A circuit breaker or fuse shall not be below 2.5 mm2.
(c) For a 15 A circuit protected by a 15 A circuit breaker or fuse shall not be below 4 mm2.
(d) For a 20 A circuit protected by a 20 A circuit breaker or fuse shall not be below 6 mm2. The above mentioned sizes must be increased for long cables as mentioned elsewhere in this document. In general, the minimum size of cable for a particular circuit shall depend on the rating of the fuse or circuit breaker used for the protection of that circuit. A voltage drop check is to be made for each length of the circuit to ensure that the voltage drop at the farthest end of the load from the main distribution point does not exceed 2.5 percent. Sockets shall get direct connection from the BDB/SDB through breaker/fuse protection. Depending on the assessed requirements sockets may be grouped/looped at the socket end. Such grouping shall not exceed 3 numbers of sockets in one circuit.
1.3.8 Feeder Wiring between SDB and BDB, DB and SDB, FDB to DB, MDB to
FDB etc. Wiring between a BDB and an SDB, an SDB and a DB, a DB and an FDB, an FDB and an MDB needs special attention and the rules are similar to Circuit Wiring. ECC must be present for each of the feed connections. The ECC in this case also shall be PVC insulated copper cable of appropriate size but with Green + Yellow bi-colour insulation. At both ends the ECC must be terminated at the earthing busbar.
Appropriate cable lugs/cable sockets must be used for terminating the L1, L2, L3, N and E connections on the busbars of both the boards. The sizes of the cables must be chosen to match with the rating of the circuit breaker/fuse ratings as mentioned above.
Circuit breakers/fuses must be provided at the outgoing and incoming sides of each of the busbars of each BDB/SDB/DB/FDB boxes.
1.3.9 Conduits, Channels, Cables, Conductors and related Accessories
Conduits, Cables, Conductors and Accessories are important parts of an electrical distribution installation.
1.3.9.1 Conduits and conduit fittings
Cables of an electrical distribution installation are drawn through electrical conduits. For the installation of conduits various types of fittings are needed. For the two types of commonly used conduits, PVC and Metal, fittings should be as under.
(a) PVC conduits
(i) PVC conduits and conduit fittings shall be of heavy wall water grade type. All bends shall be large radius bends formed by heat or by mechanical bending machine. The cross-section of the conduit shall remain circular at the bend and the internal diameter shall not be reduced due to bending. PVC pipe fittings shall be sealed with PVC solvent cement or adhesive for PVC of approved quality.
(ii) Conduits installed in floors, if installed, shall have a slope of at least 1:1000 towards floor mounted pull box or cable duct.
(iii) Conduits placed concealed inside roof or in wall must have 20 SWG GI pull wires placed during laying of the pipes for pulling the cables later.
(iv) Water grade PVC conduits must be used for both concealed and surface wiring. Water grade PVC conduits of different diameters shall be used as per necessity.
(v) Appropriate high grade bends and circular boxes must be used with the PVC pipes.
(vi) 18SWG metal sheet made and synthetic enamel paint coated quality boxes of matching sizes shall be used as pull boxes and junction boxes. Appropriate pull-box covers of ebonite or perspex sheet shall be fitted with GI machine screw and washer.
(vii) The PVC conduits placed concealed inside roof or in wall must have 20 SWG GI pull wires placed during laying of the pipes for pulling the cables later.
(b) PVC channels PVC channels should be used only for extension work in an already installed building. A design drawing should not show use of such wiring except inside a false ceiling. Even inside the false ceiling this item should be used for lengths. For long distances PVC conduits should be used. High quality PVC channels of sufficient thickness should be used and fixed in a neat manner. For large number of cables and for thick cables PVC channels should not be used.
(c) PVC flexible pipes/conduits PVC flexible conduits shall be used with surface wiring only and only in places where PVC bends cannot be used. Except special circumstances flexible PVC conduits shall not be used.
(d) Metal/steel conduits Galvanized Iron (GI) conduits shall be made using at least 16 SWG sheet. The conduits shall have seamless joint along the length and must be suitable for making bends. No projections are allowed inside the conduits. Metal conduits must be threaded for end to end joints using sockets. In case of necessity, threads will be cut at the end of short pieces. Sharp edges at the ends must be properly treated so that cable injury does not take place during cable pulling.
(e) Pull boxes
(i) Pull boxes/Joint boxes must be placed closed to the ceiling where conduits from the ceiling are going downward toward a switch box or are going toward a socket box or are going toward a BDB/ SDB/ DB / FDB.
(ii) Pull boxes are extremely essential for pulling the cables without injuring the cables and thus should not be avoided under any circumstances. These are also essential for future maintenance and extension work.
(iii) Pull boxes/Joint boxes must be placed in the ceiling of office/factory building where conduits are running over a long distance between two walls (terminal points) and where fixed walls are not available and also where heavy beams are used. In case of big cross section beams pull boxes/joint boxes shall be placed closed to the beams.
(iv) Pull boxes/Joint boxes must be made with 18 SWG GI sheet or with 18 SWG MS sheet but coated with two coats of Grey Synthetic Enamel paint.
(v) Covers of pull boxes should be ebonite or perspex sheet of not less than 1/8 inch thickness.
(f) Metal Boxes for Switch Boards Metal Boxes for Switch Boards must be made with 18 SWG GI sheet or with 18 SWG MS sheet but coated with two coats of Grey Synthetic Enamel paint. A Switch Board Metal Box must have a small Copper / Brass earthing busbar for terminating the ECCs.
(g) Switches for operating light and fan points Switches for operating Light and Fan points must be of 5A rating. These switches are usually SPST type. However, for special applications like stairs and some other places these may be SPDT type.
Switches for operating Light and Fan points may be of Gang type or may be isolated type. The isolated types are to be mounted on an ebonite top plate which is again fitted on the above mentioned Metal boxes for Switch Boards.
(h) Mounting regulators of ceiling fans Metal Boxes for Mounting Inductor Regulators of Ceiling Fans must be made with 18 SWG GI sheet or with 18 SWG MS sheet but coated with two coats of Grey Synthetic Enamel paint. Metal Boxes for mounting regulators of ceiling fans must have a small copper/brass earthing busbar for terminating the ECCs. However, such regulators may be placed inside the 18 SWG GI sheet or MS sheet made Metal Boxes for Switch Boards. In such a case arrangements must be made so that the PVC insulated point and circuit wiring cables and their joints inside the switch board do not touch a regulator. This may be done by appropriately dressing the cables and fastening the cables by using polymer cable fasteners.
1.3.9.2 Cables and conductors
For application in building wiring, PVC insulated stranded cables shall be used for Live and Neutral Wires for single phase and 3-lines (L1, L2, L3) and one neutral for 3-phase. For ECC also PVC insulated stranded cables shall be used. As a result, use of bare conductors is non-existent.
(a) Cables Conductors of a PVC insulated cable, thin or thick, shall be copper. Cable containing Aluminum conductors may be used for thick cable of size more than 35 mm2 but copper is always preferred.
Cables for power and lighting circuits shall be of adequate size to carry the designed circuit load without exceeding the permissible thermal limits for the insulation. The voltage drop shall also be within the specified limit of 2.5 percent from a distribution point up to their farthest end of the load point. Recommended sizes (in mm2) of copper conductors are as follows:
1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500, 630, 800, 1000
For final circuit/sub-circuit and for Light/fan point wiring the cable nominal cross-section of the cable shall not be less than 1.5 mm2 for copper conductors.
Standard copper conductor sizes of cables which should be used for electrical installations/distribution in buildings are given below. Conductors of sizes other than the sizes listed below are not recommended.
(b) Phase and neutral cables shall be of the same size In the wiring of the sub-circuit/circuit and all other circuits inside a building the Phase cable and the neutral cable shall be of the same size.
(c) Flexible cables/flexible cords The minimum cross-sectional area of conductors of flexible cables/flexible cords shall be 0.5 mm2 for copper conductors. Flexible cable or cords shall not be used as fixed wiring unless contained in an enclosure affording mechanical protection.
Flexible cables/flexible cords may be used for connections to portable equipment. For the purpose of this regulation an electric cooker of rated input exceeding 3 kW is not considered to be portable. The flexible cord shall be of sufficient length so as to avoid undue risk of damage to the outlet, cord or equipment and of being a hazard to personnel.
(d) Treatment of cable ends/cable terminations All stranded conductors must be provided with cable sockets/cable lugs of appropriate size fitted using appropriate hand press tool or hand crimp tool or hydraulic press tool depending on the size of the cable. This is necessary for termination of the cable ends on bus-bars.
(e) Jointing of cables in wiring Cable joints for the PVC insulated cables used in circuit wiring (thin cables) are to be made through porcelain/PVC connectors with PIB tape wound around the connector before placing the cable inside the box joint/pull box.
1.3.10 Conduits through the Building Expansion Joints
Conduits shall not normally be allowed to cross expansion joints in a building. Where such crossing is found to be unavoidable, special care must be taken to ensure that the conduit runs and wiring are not in any way put to strain or are not damaged due to expansion/contraction of the building structure. In unavoidable situations, PVC conduit through an oversize flexible PVC conduit may be used with pull boxes on both sides of expansion joints.
1.3.11 Types of Electrical Wiring for Exterior Lighting and other exterior purposes
1.3.11.1 Electrical wiring for garden lighting
For garden lighting PVC insulated PVC sheathed underground cables shall be used. For protection purpose these may be drawn through PVC pipe of appropriate dimension so that adequate clearance remains for the ease of pulling. In general, no junction of cables shall be provided in underground level. However, in case of necessity, metal sleeve cable ferrule joints using Crimp Tool or hydraulic press and heat shrink insulated sleeve shall be used on top.
1.3.11.2 Electrical wiring for street lighting
For street lighting PVC insulated PVC sheathed underground cables shall be used. For protection purpose these may be drawn through PVC pipe of appropriate dimension so that adequate clearance remains for the ease of pulling. In general, no junction of cables shall be provided in underground level. However, in case of necessity, metal sleeve cable ferrule joints using Crimp Tool or hydraulic press and heat shrink insulated sleeve shall be used on top. Joining the cables at the bottom of a street pole must be done inside a metal joint box located sufficiently above the street level so that water cannot reach the box even during the worst rain/flood situation.
1.3.11.3 Electrical wiring for boundary light
For boundary lighting PVC insulated PVC sheathed underground cables shall be used. For protection purpose these may be drawn through PVC pipe of appropriate dimension so that adequate clearance remains for the ease of pulling. In general, no junction of cables shall be provided in underground level. However, in case of necessity, metal sleeve or cable ferrule joints using Crimp Tool or hydraulic press and heat shrink insulated sleeve shall be used on top. However, for the portion of the cable running concealed through a wall, PVC insulated cables through PVC conduits may be used.
1.3.12 Branch Distribution Boards, Sub-distribution Boards, Distribution Boards, FDBs and MDBs 1.3.12.1 Enclosure/box Enclosures for sub-distribution boards located inside the building shall be dust-proof and vermin-proof using sheet steel fabrication of a minimum thickness of 20 SWG. The boards shall be safe in operation and safe against spread of fire due to short circuit.
1.3.12.2 Size of the enclosure of a BDB/SDB/DB/FDB/MDB
Table 8.1.22 provides a guidance of sizes of enclosures for SDB containing miniature circuit breakers or fuses. However, the size will depend on the number and size of the circuit breakers or the fuses the number of outgoing cables and their sizes, the size of the busbars and the type of insulators used for the busbars.
Table 8.1.22: Recommended Enclosure Sizes for MCB's and Fuses Dimensions (mm) No. of MCB's or Fuses
Height Width Depth 350 390 120 up to 12 480 390 120 up to 24 610 390 120 up to 36 740 390 120 up to 48
1.3.12.3 Location
A Sub-distribution board (SDB) shall be located as close as possible to the electrical load centre for that SDB. This is also applicable for determining the locations of FDBs, DB and BDBs. These boards shall never be located on water soaked or damp walls.
1.3.12.4 Wiring of sub-distribution boards
(a) In wiring a sub-distribution board, total load of the consuming devices shall be distributed, as far as possible, evenly between the numbers of ways of the board, leaving the spare way(s) for future extension.
(b) All connections between pieces of apparatus or between apparatus and terminals on a board shall be neatly arranged in a definite sequence, following the arrangements of the apparatus mounted thereon, avoiding unnecessary crossings.
(c) Cables shall be connected to terminals only by soldered or welded lugs, unless the terminals are of such form that it is possible to securely clamp them without cutting away the cable strands.
1.3.13 Electrical Services Shafts, Bus Ducts, L.T. Riser Cables and L.T. Busbar Trunking 1.3.13.1 Vertical service shaft for electrical risers For buildings over six-storey or 20 m high there shall, in general, be a minimum of one vertical electrical service shaft of (200 mm x 400 mm) size for every 1500 m2 floor area. The electrical service shaft shall exclusively be used for the following purposes:
(a) Electric supply feeder cables or riser mains
(b) Busbar Trunking
(c) telephone cables
(d) Data Cables
(e) fire alarm cables
(f) CCTV cables
(g) Other signal cables
(h) Area fuse/circuit breakers
(i) Floor Distribution board/sub-distribution boards for individual floors. The construction of the floors of the duct area shall be constructed in such a way so that the remaining empty open space after putting the cables/busbar trunking/ pipes/ conduits in position is filled up with RCC slab(s) or any other non-inflammable material so that fire or molten PVC cannot fall from one floor to the next lower floor(s). For this purpose arrangements need to be made during floor casting.
Free and easy access to the electrical shaft room in each floor must be available for operation, maintenance and emergency shut downs.
Vertical cables other than electrical cables shall be placed at a sufficient distance from the nearest electrical cable. A vertical separating brick wall between electrical and non-electrical wall is preferable.
Vertical Service Shaft for Electrical Risers as mentioned above must not be placed adjacent to the Sanitary Shafts. They should be placed at significant separation in order to ensure that the Vertical Service Shaft for Electrical Risers remains absolutely dry.
1.3.13.2 LT Riser main cables
(a) For low rise building riser main cables will serve to bring L.T. connection to the floor distribution boards (FDBs) of each floor from the main distribution board. For a 5 storied building or lesser having a floor space of less than 600 m2 in each floor the riser cables may be PVC insulated cables through PVC or GI pipes.
(b) For bringing the riser main cables a common vertical wall and holes or slots in the floors must be given by the building construction people.
(c) However, for larger floor area or for higher buildings PVC insulated PVC sheathed underground cables must be used with protection and spacing.
(d) For more than 9 storied building Busbar preferably sandwiched copper busbar trunking should be used for safety reasons.
(e) PVC insulated PVC Sheathed underground cables must be used as Riser Main Cables. These cables shall be placed in or pulled through a PVC pipe of higher diameter so that the cable can be easily pulled through it. The PVC pipes must be fixed vertically in a straight line on the wall of the shaft using appropriate saddles. However, in some cases PVC insulated PVC Sheathed underground cables may be directly fixed on the wall using appropriate saddles with 37mm spacing between two adjacent cables. Sheet metal made Joint Boxes (with ebonite cover plates) must be placed at each floor tapping point.
(f) The cable work shall be done neatly so that no suspended cables are seen around the place and no suspended flexible pipes are seen.
(g) Each riser cable must have appropriate fuse or circuit breaker protection at the source busbar junction and also at the tap off point.
1.3.13.3 LT Busbar Trunking
For high rise buildings, LT (0.4KV TP&N) busbar trunking sytem is used instead of riser main cables to minimize space in the vertical electrical shaft, to minimize the risk of spreading of fire from one floor to another due to electrical short circuit in one of the cables or sparks, to have a neat distribution system. Most part of the busbar trunking shall be installed vertically. The horizontal portion of the busbar trunking shall usually connect the vertical portion with the Substation LT panel.
(a) Busbar trunking are specially useful to minimize space and to minimize risks of spreading fire (during accidents) which may happen with bundles of insulated cables. The conductors supported by insulators inside the busbar trunking shall be copper of solid rectangular cross-section. The copper bars are insulated. A busbar trunking system shall be laid with minimum number of bends for distribution system. Typical rating of feeder busbar trunking for 3-phase- 3-wire or 3-phase- 4-wire system shall range from 200 amperes to 3000 amperes although lower amperes are not impossible.
(b) Horizontal busbar trunking of suitable size may be provided along the roads for a group of buildings to be fed by a single substation but with heavy weather (moisture and water) protection and covered with appropriate weather resistant water proof material. Extreme care need to be taken in these cases for protection against moisture, water and outside weather.
(c) Busbar trunking shall be placed in a dry place and must not be installed in a place which is even slightly exposed to weather/moisture/ spray or sprinkle of water.
1.3.13.4 LT Busducts
In certain applications, especially in factory lighting and factory power distribution of large area factories Busducts are used. In most cases, these Busducts are suspended from ceiling. Busducts offer safe, reliable, neat distribution system in these cases. The choice will depend on the floor area, type of machineries, type of jobs and other factors.
Appropriate circuit protection using adequate number of circuit breakers of appropriate rating is needed. In most cases these busducts are horizontally mounted/suspended. The busbars shall be copper. The rating shall depend on the current on each segment and the current carried by each segment.
1.3.14 L T Main Incoming Cable and Service Connection
(a) Overhead service connection to a building shall be achieved with PVC insulated Cables with GI support wire (similar to catenary) or catenary wire (mainly for single phase consumers). The overhead service connection shall be led into buildings via roof poles or service masts made of GI pipe at least 38 mm in diameter having a goose neck bend at the top and installed on the outer wall. The alternative is to have underground cable connection.
(b) Underground PVC insulated PVC sheathed water proof cables shall be placed in underground cable trench or pulled through a PVC pipe of higher diameter placed in a cable trench so that the cable can be easily pulled through it. PVC insulated stranded annealed copper ECC cables matching with the main cable size shall run along the Main incoming cable with termination at the earthing busbar at both end. Each of the PVC pipes must have 18 SWG GI pull wires placed during laying of the pipes for pulling the cables later.
(c) For main incoming thick underground cables joints are strongly discouraged and should be avoided as far as possible. However, for unavoidable cases joints must be made through sleeve or ferrule of appropriately matched size fitted with hydraulic press following neat processing of the cable ends. Appropriate fusible heat shrink cover must be used over such junction. For thick cables running through conduits as vertical risers, these joints must be put inside metal joint/pull boxes with covers.
(d) Special forms of construction, such as flame proof enclosures, shall be adopted where risk of fire or explosion exists near a place where thick incoming cable or riser cables are placed.
(e) The Underground service cable shall be laid in conformity with the requirements of Sec 1.3.24 titled “Laying of LT underground Cables”, of this Chapter.
(f) The power and telecommunication or antenna cables must be laid separately maintaining sufficient distance.
(g) The fire alarm and emergency lighting circuits shall be segregated from all other cables and from each other in accordance with BS 5839 and BS 5266. Telecommunication circuits shall be segregated in accordance with BS 6701 as appropriate.
(h) Where a wiring system is located in close proximity to a non-electrical service both the following conditions shall be met:
• The wiring system shall be suitably protected against the hazards likely to arise from the presence of the other service in normal use, and
• Appropriate protection against indirect contact shall be taken.
(i) A wiring system shall not be installed in the vicinity of a service which produces heat, smoke or fume likely to be detrimental to the wiring, unless protected from harmful effects by shielding arranged so as not to affect the dissipation of heat from the wiring.
(j) Where a wiring system is routed near a service liable to cause condensation (such as water, steam or gas services) precautions shall be taken to protect the wiring system from deleterious effects.
(k) No cable shall be run in a lift (or hoist) shaft unless it forms part of the lift installation as defined in BS 5655.
1.3.15 Design for Electrical Wiring
Design of Electrical wiring must be done following the provisions provided in this Chapter. Detailed design drawings must be prepared by eligible Engineer for complete execution of the electrical works mentioned in this document and any other new items arising because of the evolution of new technologies in the near future. Typically, there must be conduit layout drawing(s) indicating the conduit layouts, the locations of the switch boards, locations of the sockets, locations of the BDBs, locations of the SDBs, locations of the DBs, locations of the FDBs, location of the MDB, location of the Main incoming cable. A distribution diagram of the BDBs, SDBs up to MDBs as applicable indicating the ampere rating of the incoming MCB/MCCB, interlinking cable sizes and the ECCs must be presented. Detailed circuit diagrams of the circuits and the BDBs, SDBs, MDBs as applicable must be presented.
Detailed drawings of earthing and earth inspection pits and any other complicated parts must be presented. The contractor shall prepare as built drawings after completing a project.
1.3.15.1 Design for electrical wiring in bedrooms and drawing rooms
The location of a switch board must be near the entrance door of a bedroom like any other room. The location of the wall mounted light fittings must be chosen based on the possible locations of furniture which is also needed in other rooms. Sufficient number of 3-pin 13 A switched shuttered flat pin sockets must be provided in a bed room. The same principles are applicable for a Living room.
Design must be made in such a way that sufficient clearance (space) is left inside the concealed conduits (i) for the ease of pulling the cables and also for adding few more cables in case of necessity during future modification.
For bedrooms and drawing rooms the light plus fan sub circuits for shall not be of more than 5A rating.
Generally, single core PVC insulated stranded electrolytic annealed copper cables shall be used in concealed wiring technique or in the other methods.
1.3.15.2 Design for electrical wiring in a kitchen. The sensitive item in a kitchen is placing 3-pin 13 A switched shuttered flat pin sockets on wall of the kitchen side table near the wall. Good distance must be maintained between the kitchen water tap and the socket. The socket for the refrigerator (if any) shall also be a 3-pin 13 A switched shuttered flat pin socket, and may be placed at the same level as the other socket. For the ease of operation a 3-pin 13 A switched shuttered flat pin socket for this purpose may be placed at the bottom level height of a switch board provided this is acceptable in terms of aesthetics.
For kitchens, the light plus fan sub circuits for shall not be of more than 5A rating.
1.3.15.3 Switches for toilets and bath rooms
Switches for toilet lights and toilet ventilating fans must be placed outside the toilets adjacent to the entrance door but must not be placed inside the toilet. The same rule should be followed for bath rooms. Using ceiling mounted chord switch at the entrance path of the door of a toilet is a good idea for small toilets attached to bed rooms. Ceiling mounted chord switches may be used with a chord suspended from the ceiling near the opening of the door.
1.3.15.4 Design for electrical wiring in office rooms
The location of a switch board must be near the entrance door of an office room. The location of the light fittings must be chosen based on the possible locations of work table, furniture. Sufficient number of 3-pin 13 A switched shuttered flat pin sockets must be provided in each office room. In this regard special consideration needs to be given on the possible location of computers and other office equipment.
Sufficient conduits and cables must be left for future modification as often rearrangement of cables needs to be made.
Generally, single core PVC insulated stranded electrolytic annealed copper cables shall be used for wiring by using the concealed wiring technique or the other two methods mentioned in the wiring section.
In case of special requirements, PVC insulated PVC sheathed Stranded Electrolytic Annealed Copper Cables may be used for wiring through conduits or other methods.
For Offices the sub circuits for shall not be of more than 5 A rating.
1.3.16 Temporary Electrical Connection for a Building Construction Site
Temporary connections are needed for a building construction site. A fuse distribution board containing incoming cut out fuse, outgoing cutout fuses plus busbars or distribution boards containing in coming circuit breakers, outgoing circuit breakers plus busbars of appropriate rating must be installed for such connections. Such boards shall be installed in a dry place so that rain water or waters coming from a construction zone cannot reach such boards.
1.3.17 Temporary Electrical Connection for an Outdoor Concert
Temporary connections are needed for an outdoor concert stage for special lighting, for various display systems, for high power audio systems. A fuse distribution board containing incoming cut out fuse, outgoing cutout fuses plus busbars or a distribution board containing in coming circuit breakers, outgoing circuit breakers plus busbars of appropriate rating must be installed for such connections. Such boards shall be installed in a dry place and shall be mounted at a safe height above ground so that rain water or waters coming from anywhere cannot reach such boards. Such boards shall not be installed near flammable materials.
Cables of appropriate types and appropriate ratings must be used for such applications. Appropriate type of sockets, preferably flat 3-pin switched shuttered 13 A sockets should be used for distribution.
1.3.18 11 kV/ 0.4 kV Electrical Substation in a Building
1.3.18.1 General
According to the rule of the distribution companies of Bangladesh, 11 kV/ 0.4 kV Electrical substations shall be required for a building if the load requirement of the building exceeds 50 kW. In most cases, substations are required for Multi-storied residential, Multi-storied Commercial buildings, Multi-storied Office building and Industries. To determine the rating of the substation required, a load factor of at least 80% shall be applied to the estimated load of the building. The future expansion requirements should definitely be taken into consideration.
1.3.18.2 Location of an electrical substation
In a multi-storied building, the substation shall preferably be installed on the lowest floor level, but direct access from the street for installation or removal of the equipment shall be provided. The floor level of the substation or switch room shall be above the highest flood level of the locality. Suitable arrangements should exist to prevent the entrance of storm or flood water into the substation area.
The location of a substation will depend on (i) the feed point of the 11 kV Supply Authority line and (ii) the location of the LT vertical riser cables.
It is preferable to locate the air-conditioning plant room (if any) adjacent to the electrical substation in such a way that the distance from the controlling switchboard of the air-conditioning plant rooms and corresponding switches in the electrical substation are kept minimum.
In case of a building complex, or a group of buildings belonging to the same organization, the substation should preferably be located in a separate building and should be adjacent to the generator room, if any. Location of substation in the basement floor and on the floors above ground floor level (GFL) preferably be avoided. If Sub- Station it to be installed on the basement floor or the floors above ground floor level (GFL) special safety measures is to be taken by the user or owner. Measures are as follows:
(i) No objection certificate stating the Sub-Station safe by the Fire Service and Civil Defense Department.
(ii) Certification of the building consultant stating safe, proper ventilation, easy entrance and exit and safe load bearing capacity of the floors above the ground floor level (GFL).
(iii) Proper undertaking of the Sub-Station user or owner as the case may be, Stating safety and liability will be ensured by them. In case the electric substation has to be located within the main building itself for unavoidable reasons, it should be located on ground floor or assessment floor or the floors above the ground floor (GFL) with easy access from outside.
1.3.18.3 Height, area, floor level and other requirements of a substation room
(a) The minimum height of a substation room should be 3.0 m to 3.6 m depending upon the size of the transformer.
(b) The recommended area required for substation and transformer rooms for different capacities are given in Table 8.1.23 for general guidance. Minimum recommended spacing between the transformer periphery and walls should be :
(i) 0.75 m for Transformer installed in a room with wall on two sides.
(ii) 1.0 m for Transformer installed in a room with wall on three sides.
(iii) 1.25 m for Transformer installed in an enclosed room.
(iv) 1.5 m distance from one to another transformer for multiple transformers in room for 11 kV voltage level and 2.5 m distance for higher level of voltage.
(c) For transformers having large oil content (more than 2000 litres), soak pits are to be provided.
The areas given in Table 8.1.23 hold good if they are provided with windows and independent access doors in accordance with local regulations.
All the rooms shall have significant ventilation. Special care should be taken to ventilate the transformer rooms and where necessary louvers at lower level and exhaust fans at higher level shall be provided at suitable locations in such a way that cross ventilation is maintained. Fans should be provided so that the transformer gets air supply from the fans.
The floor level of the substation should be high. Arrangement shall be made to prevent storm water entering the transformer and switch rooms through the soak pits, if floor level of the substation is low.
Substation of higher voltage may also be considered to the basement floor having proper and safe building design.
Table 8.1.23: Recommended Area for Transformer and Substation of Different Capacities
Capacity of Transformer Area Total Substation Area (with HT, LT
Transformer 2
(m ) Panels & Transformer Room but
(kVA) without Generators), (m2)
1 × 150 12 45
1 × 250 13 48
2 × 250 26 100
1 × 400 13 48
2 × 400 30 100
3 × 400 40 135
2 × 630 26 100
3 × 630 40 190
2 × 1000 40 180
3 × 1000 45 220
1.3.18.4 11kV/0.4kV Distribution transformer for the substation of a building An 11 kV/0.4kV indoor distribution Transformer is a major part of an indoor substation. These Substations may be installed inside the building itself or may be housed in a separate building adjacent to the building. For small to moderate power rating up to 2 MW, two types of indoor transformers have been widely used in recent years. These are (i) Oil Type Natural Cooled transformer and
(ii) Cast Resin Dry Type Natural Cooled transformers. In most cases Oil Type Natural Cooled transformer may be used for substations if adequate space is available to accommodate the transformer. Cast Resin Dry Type Natural Cooled transformers should be used (i) in places where stringent protection against spread of fire is needed and (ii) in places where space saving is of utmost importance. Choice of oil type or dry type transformers Dry type transformer should be installed where risk of spreading of fire is high and where flammable materials are to be kept around the substation. For Hospital buildings, Multistoried Shopping Centers Dry type transformers should be used to for minimizing fire risks. An industrial buildings containing inflammable materials, chemical and having the substation in the same building dry type transformers should be used for minimizing fire risks.
1.3.18.5 Type of connection between a substation transformer and its LT panel
Connection between a substation transformer and its LT panel can be established a) by using NYY underground LT Cables or b) by using ceiling suspended busbar trunking. For small size transformers the first method should be used although there is no restriction in using the second method. However, for big substations the second method is safer and at the same time gives a neat solution.
1.3.18.6 Ventilation of a substation
In an electrical substation significant amount of forced ventilation is very much needed apart from natural ventilation. Exhaust fans (minimum 450 mm dia) must be provided in sufficient numbers on all sides of the substation above the lintel level. Grill fitted windows having window panes must be provided on all sides for natural ventilation. The windows must have sun sheds so that no rain water can enter inside the substation.
If due to space constraint or due to any other difficulties, sufficient number of windows and ventilating fans cannot be installed, high velocity forced ventilation using ducts must be provided.
1.3.18.7 Layout of a substation
(a) In general, substation HT to LT transformer shall be placed in one corner of the room so that the HT side remains away from the passage of the persons.
(b) The HT metering panel shall be located near the exterior of the substation room near the exit gate and also shall be convenient for the HT cable entry.
(c) The HT Panel shall be located near the exterior, just after or adjacent to the HT panel.
(d) LT panel shall remain at a sufficient distance from the transformer but not too far away from the transformer. On the other hand, the location of the LT panel should such that the riser main cable can have their way upward or outward within very short distance.
(e) In allocating the areas within a substation, it is to be noted that the flow of electric power is from supply company network to HT room, then to transformer and finally to the low voltage switchgear room. The layout of the rooms shall be in accordance with this flow.
(f) All the rooms shall have significant ventilation. Special care should be taken to ventilate the transformer rooms and where necessary louvers at lower level and sufficient number of high speed exhaust fans at higher level shall be provided at suitable locations in such a way that cross ventilation is maintained. Sufficient numbers of ceiling fans must be provided so that the transformer gets air supply from ceiling fans.
(g) The 11 kV/0.4 kV substation shall not be placed in a basement.
(h) The substation shall preferably be placed in ground floor. Placing a substation on any other floor other than ground floor shall be avoided.
(i) The substation room and the areas adjacent to cable routes must have adequate fire alarm and fire extinguishing/fighting system appropriate for extinguishing fire due to electrical system, cable burning and oil burning.
1.3.19 Standby Power Supply
1.3.19.1 Provision for standby power supply
Provision should be made for standby power supply, in buildings, where interruption of electrical power supply would cause significant discomfort, result in interruption of activities, major production loss, cause hazard to life and property and cause panic. The standby power supply may be a petrol engine or diesel engine or gas engine generator or an IPS or a UPS.
1.3.19.2 Capacity of a standby generating set
The capacity of standby generating set shall be chosen on the basis of essential light load, essential air-conditioning load, essential equipment load and essential services load, essential lift (s), one or all water pumps and other loads required as essential load. Table 8.1.24 shows recommended room area for different sizes of generators as a general guidance. Minimum recommended spacing between the generator periphery and walls need to be included:
(i) 1.0 m for generator installed in an enclosed room.
(ii) 1.25 m distance from one to another generator for multiple generators in the room.
1.3.19.3 Generator room
The generating set should preferably be housed in the substation building or should be placed adjacent to the substation room to enable transfer of electrical load (Change over) with negligible voltage drop as well as to avoid transfer of vibration and noise to the main building. The generator room should have significant amount of ventilation and fitted with a number of ceiling fans. Appropriate type and number of firefighting equipment must be installed inside the generator room. The generator engine exhaust should be appropriately taken out of the building and should preferably be taken out through any other side except South. The generator oil tank should be place away from the control panel side. In case of gas engine generator extra precaution must be taken regarding ventilation, leakage to prevent explosion.
The standby generator room should preferably be located outside the building. In the case of a gas engine driven generator, the generator must be located outside the building with adequate ventilation and windows. In general the generator room must have adequate ventilation and fans for continuous cooling.
The generator shall be placed either on the ground floor or in the first basement. Location of generator in the basement floor preferably be avoided. If generator is to be installed on the basement floor special safety measures is to be taken by the user or owner as per manufacturer’s safety specification. A continuous running generator must be located outside the building. Other rules mentioned above for standby generator are strictly applicable for this case.
For both the standby and continuous running generators the generator room and the areas adjacent to cable routes must have adequate fire alarm and fire extinguishing/fighting system appropriate for extinguishing fire due to cable burning and fuel burning. Generators must be installed on shock absorbing mounting bases.
1.3.19.4 Changeover switch of a generator
A standby generator, if needed, is to be connected at the supply input point after the energy meter and after the main incoming switch or the main incoming circuit breaker, but through a changeover switch of appropriate rating. The rating of such a switch shall be at least 1.25 times the rating of the main incoming circuit breaker. The changeover switch shall be of such a type so that when moved to the mains position, there is no chance that the generator will be connected and vice versa.
The Changeover Switch may be manual type with knife switch type switching or may be automatic type with magnetic contactors. In both the cases the Changeover Switch shall be properly made so that there is no chance of loose connection or spark.
The wiring for this purpose shall be made following the standard practices mentioned under the heading of wiring using cables of appropriate size.
Table 8.1.24: Recommended Area for Standby Generator Room
Capacity (kW) Area (m2)
1 × 25 20
1 × 48 24
1 × 100 30
1 × 150 36
1 × 300 48
1 × 500 56
1.3.19.5 Installation of an IPS or a UPS
(a) For safety purpose size of a UPS should be kept as small as possible.
(b) For the installation of a 200 - 600 VA IPS a 5A circuit must be made with the light points and fan points of different rooms to be brought under the control of the IPS. This circuit must have 3A Fuse protection using fuse cutout box. Wiring and connection has to be made following the wiring rules given in the wiring sections of this document. Cables of appropriate size must be used for wiring.
(c) For the installation of a 600 - 700 VA IPS a 5A circuit must be made with the light points and fan points of different rooms to be brought under the control of the IPS. This circuit must have 5A fuse protections or 5A circuit breaker protection. Wiring and connection has to be made following the wiring rules given in the wiring sections of this document. Cables of appropriate size must be used for wiring.
(d) For the installation of an IPS of higher capacity, a BDB with multiple outgoing circuits each not exceeding 5 A shall be used with cutout - fuse protection at both incoming and outgoing sides. Cables of appropriate size must be used for wiring of each circuit.
(e) Battery maintenance (checking water level, temperature rise and the condition of the terminals) should be done at least every 15 days. Connection of the Battery terminals should be made properly and checked periodically for loose connection and deposition of sulphate. Battery of an IPS must be kept in a safe place so that short circuit between the battery terminals does not occur. Inflammable materials must not be kept in the vicinity of the IPS or battery.
(f) Safety issues must be taken into consideration in placing an IPS in a room. Same points shall apply for the installation of an UPS.
1.3.19.6 Installation of a solar photovoltaic system on top of a building
Building should be provided with solar photovoltaic system. For installation of a solar photovoltaic system, necessary precaution needs to be taken. Separate wiring and protection system must also be ensured.
Installation of solar water heaters on the roof tops of the residential and commercial buildings: Buildings or apartments where hot water will be required, use of solar water heaters instead of electric and gas water heaters should be made mandatory. Flat plate heat collectors or vacuum tube solar water heaters of various capacities are available in the market. The integral parts of a conventional solar photovoltaic system are:
(a) Solar photovoltaic panel(s)
(b) Battery charge controller
(c) Inverter
(d) Cables between the solar photovoltaic panel(s) and the battery charge controller
(e) Cables between the battery and the battery charge controller
(f) Cables between the inverter and the distribution board (DB/SDB/BDB)
(g) Other cables and accessories. For the installation of a solar photovoltaic system of higher capacity, a DB with multiple outgoing circuits each not exceeding 5 A shall be used with cutout - fuse protection at both incoming and outgoing side. Copper cables of appropriate size must be used for wiring of each circuit.
Battery maintenance (checking water level, temperature rise and the condition of the terminals) should be done at least every 15 days. Connection of the battery terminals should be made properly and checked periodically for loose connection and deposition of sulphate.
Batteries of a solar photovoltaic system must be kept in a safe place so that short circuit between the battery terminals does not occur. Inflammable materials must not be kept in the vicinity of the IPS or battery. In most cases for roof top solar panels, the battery room shall be placed inside a roof top room with adequate natural ventilation and forced cooling using ceiling fans. Because of the roof top location of the Solar panels, the room temperature is expected to be higher.
Safety issue must be taken into consideration in placing the batteries of a solar photovoltaic system. For a residential flat system building, one or two circuits for each flat shall come from the DB of the photo-voltaic source at roof top to each flat depending on the requirement. Connection to load in each flat will be done through a changeover switch for each circuit. For a commercial/office building, one or two circuits for each office/office area shall come from the DB of the photo-voltaic source at roof top to each flat depending on the requirement. Connection to load in each flat will be done through a changeover switch for each circuit. Conduit based riser system must carefully be installed, separately for this system only, during the construction of the building to bring down the cables from the roof top DB room up to each flat/office/office area. Special care must be taken during installation so that rain water can under no circumstances get into the conduit and cable system.
1.3.19.7 Installation of a Solar Photovoltaic System on the exterior Glass of a Building having Large Glass area Facade For semitransparent solar panels mounted on exterior glass of multistoried building similar process and precautions mentioned above must be followed.
1.3.20 Electrical Distribution System
1.3.20.1 Design, selection and choice of the type of connection
(a) In the planning and design of an electrical wiring installation, due consideration shall be given to prevailing conditions. Advice of a knowledgeable and experienced electrical design engineer must be sought from the initial stage up to the completion of the installation with a view to have an installation that will prove adequate for its intended purpose, and which will be safe and will be efficient.
(b) All electrical apparatus shall be suitable for the voltage and frequency of supply of this country mentioned earlier.
(c) The number and types of connection required e.g., single-phase two-wire AC or three-phase four-wire AC shall be assessed, both for the supply source and for the internal circuits needed within the installation.
(d) The following characteristics of the supply shall be ascertained :
(i) nominal voltage(s)
(ii) current and frequency
(iii) prospective short circuit current at the origin of the installation
(iv) type and rating of the over-current protective device acting at the origin of the installation
(v) suitability for the requirements of the installation, including the maximum demand
(vi) expected maximum value of the earth loop impedance of that part of the system external to the installation.
(e) In case of connected loads of 50 kW and above, HT 11 kV three-phase supply line with substation must be installed because of the requirement of the distribution companies although the use of HT supply will involve higher expenses due to installation of a distribution transformer, HT metering Panel, HT panel and LT Panel at the consumer's premises. In this respect, the rules of the electrical distribution authorities will be the ultimate deciding factor.
1.3.20.2 Equipment and accessories
(a) High Voltage Switchgear The selection of the type of high voltage switchgear for any installation should consider the following:
(i) voltage of the supply system,
(ii) the prospective short circuit current at the point of supply,
(iii) the size and layout of electrical installation,
(iv) the substation room available, and
(v) the types machineries of the industry (if applicable).
(b) Guidelines on Various Types of Switchgear Installation
(i) Banks of switchgears shall be segregated from each other by means of fire resistant barriers in order to prevent the risk of damage by fire or explosion arising from switch failure. Where a bus-section switch is installed, it shall also be segregated from adjoining banks in the same way.
(ii) In the case of duplicate or ring main supply, switches with interlocking arrangement shall be provided to prevent simultaneous switching of two different supply sources.
(c) Low Voltage Switchgear
(i) Switchgear and fusegear must have adequate breaking capacity in relation to the capacity of the transformers.
(ii) Isolation and protection of outgoing circuits forming the main distribution system may be effected by means of circuit breakers, or fuses or switch fuse units mounted on the main switchboard. The choice between alternative types of equipment will take the following points into consideration:
(iii) In certain installations supplied with electric power from remote transformer substations, it may be necessary to protect main circuits with circuit breakers operated by earth leakage trips, in order to ensure effective earth fault protection.
(iv) Where large electric motors, furnaces or other heavy electrical equipment are installed, the main circuits shall be protected by metal clad circuit breakers or conductors fitted with suitable instantaneous and time delay overcurrent devices together with earth leakage and backup protection where necessary.
(v) In installations other than those mentioned above or where overloading of circuits may be considered unlikely, HRC type fuses will normally afford adequate protection for main circuits separately as required; the fuses shall be mounted in switch fuse units or with switches forming part of the main switch boards.
(vi) Where it is necessary to provide suitable connection for power factor improvement capacitors at the substation bus, suitable capacitors shall be selected in consultation with the capacitor and switchgear manufacturer and necessary switchgear/feeder circuit breaker shall be provided for controlling the capacitor bank(s).
1.3.21 Transformers
(a) Where two or more transformers are to be installed in a substation to supply an LT distribution system, the distribution system shall be divided into separate sections each of which shall normally be fed from one transformer only unless the LT switchgear has the requisite short circuit capacity.
(b) Provision may, however, be made to interconnect busbar sections through bus couplers to cater for the failure or disconnection of one transformer which need to be executed with much care using locking system.
(c) The transformers, which at any time operate in parallel, shall be so selected as to share the load in proportion to their respective ratings. Appropriate protection must be provided and appropriate arrangements need to be made.
(d) When a step-up transformer is used, a linked switch shall be provided for disconnecting the transformer from all poles of the supply, including the neutral conductor.
1.3.22 Precautions regarding Rotating Machines
(a) All equipment including cables, of every circuit carrying the starting, accelerating and load currents of motors, shall be suitable for a current at least equal to the full load current rating of the motor. When the motor is intended for intermittent duty and frequent stopping and starting, account shall be taken of any cumulative effects of the starting periods upon the temperature rise of the equipment of the circuit.
(b) The rating of circuits supplying the rotors of slip ring or commutator of a motor or an induction motor shall be suitable for both the starting and loaded conditions.
(c) Every electric motor having a rating exceeding 0.376 kW shall be provided with control equipment incorporating means of protection against overcurrent.
(d) Every motor shall be provided with means to prevent automatic restarting after a stoppage due to drop in voltage or failure. This requirement does not apply to any special cases where the failure of the motor to start after a brief interruption of the supply would be likely to cause greater danger. It also does not preclude arrangements for starting a motor at intervals by an automatic control device, where other adequate precautions are taken against danger from unexpected restarting.
1.3.23 LT Energy Meters
LT energy meters shall be installed in residential buildings at such a place which is readily accessible to the owner of the building and the Authority. Installation of digital energy meters at the users’ premises is a requirement of the distribution Companies.
LT energy meters should be installed at a height where it is convenient to note the meter reading but should not be installed at a level less than 1.5 meter above the ground.
The energy meters should either be provided with a protective covering, enclosing it completely except the glass window through which the readings are noted, or shall be mounted inside a completely enclosed panel provided with hinged or sliding doors with arrangement for locking. Earthing terminal must be provided if a metal box is used. Such an earthing terminal must be connected to the ECC.
1.3.24 Laying of LT underground Cables
PVC-PVC NYY underground LT cables shall be laid using one of the three methods.
(a) In the first method, brick wall prepared 900 mm deep trenches with cover plates shall be used for placing the cables at the bottom of the trench.
(b) In the second method, 900 mm deep trenches prepared by ground excavation (underground direct burial method) shall be used for placing the cables on top of a 75 mm sand layer. In this second method (underground direct burial method), two layers of brick on top, marking tape and then back filling the trench will have to be done. The depth of the trench in general shall be 900 mm.
(c) In the third method, pre-laid PVC pipes having sufficient clearance compared to the cable size (s) may be required at places. The PVC pipes must be laid in trenches of the 900 mm depth. For pre-laid PVC pipe ducts, brick wall made underground inspection pits will be required at an interval of at least 10 m for cable pulling and future extensions or alterations.
1.3.25 Laying of HT Underground Cables
The HT underground armoured cables shall be laid using one of the three methods. In the first method (i) brick wall prepared 900 mm deep trenches with cover plates shall be used for placing the cables at the bottom of the trench. In the second method, 900 mm deep trenches prepared by ground excavation (underground direct burial method) shall be used for placing the cables on top of a 75 mm sand layer. In this second method (underground direct burial method), two layers of brick on top, marking tape and then back filling the trench will have to be done. The depth of the trench in general shall be 900 mm. In the third method, pre-laid PVC pipes having sufficient clearance compared to the cable size(s) may be required at places. The PVC pipes must be laid in trenches of the 900 mm depth. For pre-laid PVC pipe ducts, brick wall made underground inspection pits will be required at an interval of at least 10 m for cable pulling and future extensions or alterations. PVC pipe having sufficient clearance may be used for bringing the cable up to the trench of the metering panel or HT panel. The PVC pipes must have 18 SWG GI pull wires placed during laying of the pipes for pulling the cables later. Methods of installation of cables and conductors in common use are specified in Table 8.1.25.
1.3.26 Main Switch and Switchboards
1.3.26.1 Metal clad enclosed type
All main switches shall be either metal clad enclosed type or of any other insulated enclosed type and the circuit breakers shall be fixed at close proximity.
1.3.26.2 Circuit breakers on each live conductor
There shall be circuit breakers or miniature circuit breakers or load break switch fuses on each live conductor of the supply mains at the point of entry. The wiring throughout the installation shall be such that there is no break in the neutral wire in the form of a switch or fuse unit or otherwise.
1.3.26.3 Location
(a) The location of the main board shall be such that it is easily accessible for firemen and other personnel to quickly disconnect the supply in case of emergencies.
(b) Main switchboards shall be installed in boxes or cupboards so as to safeguard against operation by unauthorized personnel.
(c) Open type switchboards shall be placed only in dry locations and in ventilated rooms and they shall not be placed in the vicinity of storage batteries or exposed to chemical fumes.
(d) In damp situation or where inflammable or explosive dust, vapour or gas is likely to be present, the switchboard shall be totally enclosed or made flame proof as may be necessitated by the particular circumstances.
(e) Switchboards shall not be erected above gas stoves or sinks, or within 2.5 m of any washing unit in the washing rooms or laundries.
(f) In case of switchboards being unavoidable in places likely to be exposed to weather, to drip, or in abnormally moist atmosphere, the outer casing shall be weather proof and shall be provided with glands or bushings or adapted to receive screwed conduit.
(g) Adequate illumination shall be provided for all working spaces about the switchboards, when installed indoors.
Table 8.1.25: Different ways of Installation of Cables and Conductors in Common Use
Type Description Example
A Cables enclosed in conduit
B Cables enclosed in trunking
C Cables enclosed in underground
conduit, ducts, and cable ducting.
D Two or more single-core cables
contained in separate bores of a
multi-core conduit and intended
to be solidly embedded in
concrete or plaster or generally
incorporated in the building
structure.
E Sheathed cables clipped direct to
a nonmetallic surface.
F Sheathed cables on a cable tray.
G Sheathed cables embedded direct
in plaster.
Single-core Mutli-core
Type Description Example
H Sheathed cables suspended from
or incorporating a catenary wire.
J Sheathed cables in free air. Vertical surface of a wall
or open cable trench
For cables in which the
20 mm min.
conductor cross-sectional area 20 mm min.
does not exceed 185 mm2, S is
equal to twice the overall
diameter of the cable. For cables s
in which the conductor cross-
sectional area exceeds 185 m2, S
s
is about 90 mm. For two cables
in horizontal formation on
brackets fixed to a wall, S may
have any lesser value. Single-core Multi-core
K Single and multi-core cables in Two single-core cables with
enclosed trench 450 mm wide by surfaces separated by a
600 mm deep (minimum distance equal to one
dimensions) including 100 mm diameter; three single-core
cover. cables in trefoil and
touching throughout. Multi-
core cables or groups of
single-core cables separated
by a minimum distance of
50 mm.
L Single and multi-core cables in Single-core cables
enclosed trench 450 mm wide by arranged in flat groups of
600 mm deep (minimum two or three on the vertical
dimensions) including 100 mm trench wall with surfaces
cover. separated by a distance
equal to one diameter with
a minimum separation of
50 mm between groups.
Multi-core cables installed
singly separated by a
minimum* distance of 75
mm. All cables spaced at
least 25 mm from the
trench wall.
Type Description Example
M Single and multi-core cables in Single-core cables
enclosed trench 600 mm wide by arranged in groups of two
760 mm deep (minimum or three in flat formation
dimensions) including 100 mm with the surfaces separated
cover. by a distance equal to one
diameter or in trefoil
formation with cables
touching. Groups
separated by a minimum*
distance of 50 mm either
horizontally or vertically.
Multi-core cables installed
singly separated by a
minimum* distance of 75
mm either horizontally or
vertically. All cables
spaced at least 25 mm
from the trench wall.
* Larger spacing to be used where practicable.
1.3.27 Mounting of Metal clad switchgear
A metal clad switchgear shall be mounted on hinged type metal boards or fixed type metal boards.
(a) Hinged type metal boards shall consist of a box made of sheet metal not less than 2 mm thick and shall be provided with a hinged cover to enable the board to swing open for examination of the wiring at the back. The joints shall be welded. The board shall be securely fixed to the wall by means of rag bolt plugs, or wooden plugs and shall be provided with locking arrangement and an earthing stud. All wires passing through the metal board shall be protected by a rubber or wooden bush at the entry hole. The earth stud should be commensurate with the size of the earth lead(s).
(b) Fixed type metal boards shall consist of an angle or channel steel frame fixed on the wall at the top, if necessary.
(c) There shall be a clearance of one meter at the front of the switchboards.
1.3.28 Wooden Boards as Main Boards or Sub-Boards Containing Fused Cutouts and Main Switches
Use of Wooden Board is discouraged because of the fear of break out of fire from a spark or from an overheated cable. However, for small installations, not exceeding 15A SP, connected to a single-phase 230 V supply, wooden boards may be used as main boards or sub-boards containing fused cutouts and main switches of appropriate ratings may be used. Such a board shall be made using seasoned teak or other approved quality timber.
1.3.29 Location of Distribution Boards
The distribution boards shall be located as near as possible to the centre of the load they are intended to control.
(a) They shall be fixed on suitable stanchion or wall and shall be accessible for replacement of fuses. All switches and circuit breakers used as switches shall be located so that they may be operated from a readily accessible place. They shall be installed such that the center of the grip of the operating handle of the switch or circuit breaker, when in its highest position, is not more than 2.0 m and the bottom of the panel shall be more than 0.45m above the floor or working platform.
(b) They shall be either metal clad type, or all insulated type. But if exposed to weather or damp situations, they shall be of the weather proof type and if installed where exposed to explosive dust, vapour or gas, they shall be of flame proof type. In corrosive atmospheres, they shall be treated with anticorrosive preservative or covered with suitable plastic compounds.
(c) Where two or more distribution fuse boards feeding low voltage circuits are fed from a supply of medium voltage, these distribution boards shall be:
(i) fixed not less than 2 m apart, or
(ii) arranged so that it is not possible to open two at a time, namely, they are interlocked, and the metal case is marked "Danger 415 Volts" and identified with proper phase marking and danger marks, or
(iii) installed in rooms or enclosures accessible to authorized persons only.
(d) All distribution boards shall be marked "Lighting" or "Power", as the case may be, and also be marked with the voltage and number of phases of the supply. Each shall be provided with a circuit list giving diagram of each circuit which it controls and the current rating for the circuit and size of fuse element.
(e) Distribution boards must be easily accessible for the ease of maintenance and switching off during accidents.
1.3.30 Over-current and Short Circuit Protection of Circuits
(a) Appropriate protection shall be provided at the distribution boards for all circuits and sub-circuits against short circuit and over-current. The installed protective devices shall be capable of interrupting any short circuit current that may occur, without causing any danger. The ratings and settings of fuses and the protective devices shall be coordinated so as to obtain absolute certain discrimination of the faulty area only during a fault.
(b) Where circuit breakers are used for protection of main circuit and the sub-circuits, discrimination in operation shall be achieved by adjusting the protective devices of the sub-main circuit breakers to operate at lower current settings and shorter time-lag than the main circuit breaker.
(c) A fuse carrier shall not be fitted with a fuse element larger than that for which the carrier is designed.
(d) The current rating of fuses shall not exceed the current rating of the smallest cable in the circuit protected by the fuse.
1.3.31 Fire Alarm and Emergency Lighting Circuits
Fire alarm and emergency lighting circuits shall be segregated from all other cables and from each other in accordance with BS 5839 and BS 5266. Telecommunication circuits shall be segregated in accordance with BS 6701 as appropriate.
1.3.32 Earthing
1.3.32.1 General
Earthing refers to connecting the exposed conductive part of electrical equipment and also the extraneous conductive parts of earthed bodies like water pipe to the general mass of the earth to carry away safely any fault current that may arise due to ground faults. The object of an earthing system is to provide a system of conductors, as nearly as possible at a uniform and zero, or earth, potential. The purpose of this is to ensure that, in general, all parts of equipment and installation other than live parts shall be at earth potential, thus ensuring that persons coming in contact with these parts shall also be at earth potential at all times.
1.3.32.2 Earthing used in electrical installation for buildings
The usual method of earthing is to join the exposed metal work to earth via a system of earth continuity conductors (ECC) connected to an earth electrode buried in the ground through a system of earth lead wires. In conjunction with a fuse, or other similar device, this then forms a protective system.
Thus, if a live conductor accidentally comes into contact with an exposed metal, the fuse or protective device operates. As long as the overall resistance of the protective system is low, a large fault current flows which blows the fuse. This cuts off the supply and isolates the faulty circuit, preventing risk of shock, fire, or damage to equipment/ installation. In Electrical installation for buildings, following types of earthing systems are required to be installed:
(i) L.T. circuit/system earthing,
(ii) Equipment earthing (LT side),
(iii) Substation neutral earthing,
(iv) Substation LT system earthing, and
(v) H.T. circuit earthing for a substation. The purpose of L.T. circuit/system earthing is to limit excessive voltage from line surges, from cross-overs with higher voltage lines, or from lightning, and to keep noncurrent carrying enclosures and equipment at zero potential with respect to earth. Earthing the system helps facilitate the opening of overcurrent protection devices in case of earth faults. Earthing associated with current carrying conductors is normally essential for the protection and safety of the system and is generally known as circuit/ system earthing, while earthing of non-current carrying metal work and conductor is essential for the safety of human life, animals, and property and it is generally known as equipment earthing.
1.3.32.3 Arrangements of earthing systems:
(a) The value of resistance from the consumer's main earthing terminal to the earthed point of the supply, or to earth, is in accordance with the protective and functional requirements of the installation, and expected to be continuously effective.
(b) Earth fault currents and earth leakage currents likely to occur are carried without danger, particularly from the point of view of thermal, thermo-mechanical and electromechanical stresses.
(c) Where a number of installations have separate earthing arrangements, protective conductors running between any two of the separate installations shall either be capable of carrying the maximum fault current likely to flow through them, or be earthed within one installation only and insulated from the earthing arrangements of any other installation.
1.3.32.4 Integral parts of an earthing system
The integral parts of an Earthing System are:
(a) Earth electrode(s) buried under the ground
(b) Earth lead cables/wires connecting the earth electrode(s) with the earthing busbar system. Earth lead cables/wires are also need to interconnect the earth electrodes when there are more than one earth electrode.
(c) Earth continuity conductors (ECC) for linking earthing busbar at the substation LT panel or main distribution DB of a building.
(d) Earth electrode clamp. Connections of (i) Earth continuity conductors (ECC), (ii) Earth lead cables/wires and
(iii) Earth electrode(s) must be made in appropriate and long lasting manner because poor connection or loss of connection will render the earthing system ineffective.
1.3.32.5 Earth continuity conductors (ECC)
ECC runs along the circuits/sub-circuits, socket circuits, interlinking circuits between a BDB and a SDB, between a SDB and a DB, between a DB and a FDB, between a FDB and a MDB, between a MDB and the LT panel earthing busbar of the substation. At each point an ECC shall be terminated in a copper earthing busbar. In metal switch boards back boxes and in metal socket back boxes appropriate copper or brass bolt nut termination shall be provided. ECC of an earthing system joins or bonds together all the metal parts of an installation. PVC insulated wiring copper cables of appropriate size having Green + Yellow bi-colour insulation shall be used as ECC. The minimum size of the ECC shall be same as cross-sectional area of the phase conductor for the PVC insulated wiring copper cables of appropriate size having Green + Yellow bi-colour insulation.
1.3.32.6 Earth lead cable/wire
Earth Lead cable/wire runs between an earth electrode and the earthing busbar of the MDB/DB or between an earth electrode and the LT panel earthing busbar of the substation. Often more than one earth electrodes are needed. In such a case duplicate earth lead cables/wires from each earth electrode must be brought to the MDB/DB or to the LT panel earthing busbar of the substation and properly terminated. In addition, in the case of multiple earth electrodes, they must be interlinked by additional earth lead cables/wires. PVC insulated wiring copper cables of appropriate size having Green + Yellow bi-colour insulation shall be used as earth lead wire. At both ends of the earth lead cable/wire, copper cable lugs must be fitted using crimp tools or hydraulic press.
The minimum size of the earth lead wire shall be 2 numbers of 1.5 mm2 PVC insulated wiring copper cables of appropriate size having Green + Yellow bi-colour insulation.
The ends of the earth lead wires shall be terminated using crimp tool fitted cable lugs for fitting on the busbar or with the Earth Electrode Clamp.
(a) An earth lead cable/wire establishes connection between the main earthing busbar and the earth electrode(s). The earth lead wire shall be brought to one or more connecting points, according to size of installation; the copper wire earthing leads shall run from there to the electrodes. Usually more than one earth lead wires are needed for one earth electrode to make sure that this link never fails.
(b) Earth lead cable/ wires shall one of the following types:
(i) PVC insulated cable
(ii) stranded copper cables without insulation
(iii) copper strips (copper bars)
(iv) PVC insulated cable is preferable in most cases.
(v) Earth lead wires shall run through PVC pipe from the earth electrode up to the earthing busbar of the MDB/DB or LT Panel.
(c) Earth lead cables/ wires shall run, at least, 2 in parallel (at least) down to the earth electrode so as to increase the safety factor of the installation. The two cables shall be terminated in two seperate cable lugs and bolts at both ends. Copper wire used as earthing lead must not be smaller than single core stranded 2 × 4 mm2 PVC insulated cables (i.e. 2 nos. of single core 4 mm2 PVC insulated cables in parallel). Depending on the current capacity of the Main incoming line the size will have to be raised.
Earth lead cables/wires shall be pulled from the earth electrode up to the terminating earthing busbar through PVC conduits or GI pipes of appropriate dimension.
Table 8.1.26: Minimum Cross-sectional Area of Copper ECCs in Relation to the Area of Associated Phase Conductors Cross-sectional Area of Phase Minimum Cross-sectional Area of the Conductor(s) (mm2) Corresponding Earth Conductor (mm2)
Less than 16 Same as cross-sectional area of phase
conductor
16 or greater but less than 35 16 mm2
35 or greater Half the cross-sectional area of phase
conductor
1.3.32.7 Earth electrodes and their installation
The earth electrode shall, as far as practicable, penetrate into moist soil (which will remain moist even during the dry season) preferably below ground water table. The resistance of an earthing system after measured after the installation of earth electrodes (individually or combined as a single group) shall be around one ohm.
The types of earth electrodes are to be used for earthing of electrical installations of a building and their sizes shall be as under:
(a) Copper rod earth electrode: shall have a minimum diameter of 12.5 mm of minimum length of 3.33 m. Multiple copper rod earth electrodes may have to be installed to achieve an acceptable value of earthing resistance of around 1 ohm.
(b) Copper plate earth electrodes: shall be 600 mm x 600 mm x 6 mm minimum in size. The copper plate shall be buried at least 2 m below the ground level. Multiple Copper plate earth electrodes may have to be installed to achieve an acceptable value of earthing resistance of around 1 ohm.
(c) Galvanized Iron (GI) pipes: GI pipe earthing shall have a minimum diameter of 38 mm and of minimum length of 6.5m. Multiple GI pipes Earth Electrode may have to be installed to achieve an acceptable value of earthing resistance of around 1 ohm.
Schematic drawings of typical earthing systems are shown in Figures 8.1.2 to 8.1.4. For the installation of the earthing system the following points shall be considered.
(a) For installing a copper rod earth electrode, a 38 mm GI pipe shall be driven below ground up to a depth of 5 m and shall be withdrawn. The 12 mm dia copper rod earth electrode of 4 m length shall then be easily driven into that hole up to a depth of 3.6 m and 0.33 m shall be left for placing inside the earthing pit described below.
(b) For installing a 600 mm x 600 mm x 6 mm Copper plate 2 m below the ground level earth excavation will have to be done. The earth lead wire shall come via an earthing pit.
(c) GI pipe earth electrodes driven by tube well sinking method are suggested. For this purpose 38 mm dia GI pipes are recommended for domestic buildings. For large plinth area buildings and multi-storied buildings 50 mm dia GI pipes are recommended. The length of GI pipe to be driven below the ground level depends on the earthing resistance which in turn depends on the availability of water table during the dry season in this country. However, except the high land and mountains, this depth varies between 12 m to 25 m.
(d) Multiple numbers of GI pipe earth electrodes need to be used and connected in parallel in order to lower the earthing resistance measured with an earth resistance measuring meter. This is applicable for copper rod earyhing and plate earthing also.
(e) If multiple rod, pipe, or plate electrodes of one grounding system are installed to meet the earth resistance requirements, they shall not be less than 1.8 m apart. Two or more grounding electrodes that are bonded together shall be considered a single grounding electrode system.
(f) If multiple rod, pipe, or plate electrodes of one grounding system are installed to meet the earth resistance requirements, they shall not be less than 1.8 m apart. Two or more grounding electrodes that are bonded together shall be considered a single grounding electrode system.
Figure 8.1.2 Copper Rod Earthing Figure 8.1.3 Copper Plate Earthing
(a) (b) Figure 8.1.4 Pipe Earthing; (a) Type 1; (b) Type 2
1.3.32.8 Brass clamps/terminals on earth electrodes (earth electrode clamp)
(a) A brass clamp must be fitted on top of a GI pipe earth electrode to terminate the earth lead wire and to maintain electrical contact with the earth electrode and also to terminate the earth lead wire coming from the earthing busbar of the LT panel/ MDB/DB. This is needed to establish long lasting and firm connection between the earth electrode and earth lead wire, which in turn means connection between the earth electrode and earthing busbar of an LT panel or MDB/DB.
(b) The Brass clamp shall be made using at least 9.5 mm thick and at least 50 mm wide Brass plate bent and shaped properly to fit tightly around the GI pipe earth electrode and shall have sufficient length (at least 35 mm) on both sides for fixing bolts and cable lugs. This clamp shall have two hexagonal head 9.5 mm bolts on one side and two hexagonal head 9.5 mm bolts on the other side, Figure 8.1.4(a). Sufficient space should be available for fixing the cable lugs of the earth lead wires. After fitting the lugs of the earth lead cables the brass clamp and the GI pipe head should be coated with two coats of synthetic enamel paint on top of one undercoat paint layer.
(c) An alternative to this clamp is to use a 9.5 mm (at least) thick brass plate having 4 holes for fitting four hexagonal brass bolts on the four corners for fitting the cable lugs of the earth lead wires as shown in Figure 8.1.4(b). The brass plate is welded to a GI pipe socket and threaded on top of the earth electrode (pipe).
1.3.32.9 Earthing busbars
A copper earthing busbar shall be provided inside the LT Panel or MDB/DB of a building. The earth lead wire coming from the Earth Electrode (s) shall be terminated on this busbar using cable lugs (cable lugs must be fitted using crimp tools or hydraulic press) and brass bolts and nuts. Copper earthing busbar shall also be provided inside the DBs, FDBs, SDBs and BDBs. Hexagonal head brass screw, nuts and washers are needed for fixing the ECC and earth lead cables with this busbar 1.3.32.10 Earthing pit An earthing pit shall be constructed around the top of the Earth Electrode, below the ground level using 250 mm brick walls on a CC floor with a 150 mm thick RCC slab cover on top having lifting hooks. The top of the earth electrode (in case of pipe earthing) shall remain 375 mm above the top of the bottom CC floor of the pit. The minimum inside dimension of the earthing pit shall be 600 mm × 600 mm × 600 mm. The outside as well as the inside of the walls of the pit and the floor of the pit shall be cement mortar plastered. The inside shall be net cement finished. The top of the RCC slab pit cover shall remain 38 mm above the ground level. The pit shall be made in such a way that water cannot get in to the pit. One earthing pit is needed for one earth electrode.
1.3.33 Lightning Protection of Buildings
Whether a building needs protection against lightning depends on the probability of a stroke and acceptable risk levels. Assessment of the risk and of the magnitude of the consequences needs to be made. As an aid to making a judgment, a set of indices is given in Table 8.1.27 below for the various factors involved.
Table 8.1.27 (a): Index Figures Associated with Lightning Protection Design
Index A: Use of Structure Index Index B: Type of Construction Index
Houses and similar buildings 2 Steel framed encased with 1
nonmetal roofa
Houses and similar buildings 4 Reinforced concrete with 2
with outside aerial nonmetal roof
Small and medium size 6 Brick, plain concrete, or 4
factories, workshops and masonry with nonmetal roof
laboratories
Big industrial plants, telephone 7 Steel framed encased or 5
exchanges, office blocks, hotels, reinforced concrete with metal
blocks of flats roof
Places of assembly, for 8 Timber formed or clad with any 7
example, places of workshop, roof other than metal or thatch
halls, theatres, museums,
exhibitions, department stores,
post offices, stations, airports,
stadiums
Schools, hospitals, children's 10 Any building with a thatched 10
homes and other such structures roof
a A structure of exposed metal which is continuous down to ground level is excluded from the table as it requires no lightning protection beyond adequate earthing arrangements.
Table 8.1.27 (b): Index Figures Associated with Lightning Protection Design Index C : Contents or Index Index D : Degree of Isolation Index Consequential Effects
Ordinary domestic or office 2 Structure located in a large area having 2
building, factories and workshops structures or trees of similar or greater
not containing valuable materials height, e.g. a large town or forest
Industrial and agricultural 5 Structure located in an area with a 5
buildings with specially few other structures or trees of
b
susceptible contents similar height
Power stations, gas works, 6 Structure completely isolated or 10
telephone exchanges, radio exceeding at least twice the height of
stations surrounding structures or trees
Industrial key plants, ancient 8 Index E : Type of Terrain Index
monuments, historic buildings,
museums, art galleries
Schools, hospitals, children's and 10 Flat terrain at any level 2
other homes, places of assembly
b
This means specially valuable plant Hilly terrain 6
or materials vulnerable to fire or the
Mountainous terrain 300 m and above 8
results of fire.
Table 8.1.27 (c) : Index Figures Associated with Lightning Protection Design
Index F : Height of Structure Index Index G : Lightning Prevalence Index
Up to 9 m 2 Number of thunderstorm days
per year:
9-15 m 4 Up to 3 2
15-18 m 5 4-6 5
18-24 m 8 7-9 8
24-30 m 11 10-12 11
30-38 m 16 13-15 14
38-46 m 22 16-18 17
c
46-53 m 30 19-21 20
c
Structures higher than 53 m require Over 21 21
protection in all cases
1.3.33.1 Degree of Isolation
The relative exposure of a particular building will be an element in determining whether the expense of lightning protection is warranted. In closely built-up towns and cities, the hazard is not as great as in the open country.
1.3.33.2 Type of terrain
In hilly or mountainous areas, buildings are more susceptible to damage due to lightning than buildings in the plains or flat terrain. In hilly areas, a building upon high ground is usually subject to greater hazard than one in a valley or otherwise sheltered area.
1.3.33.3 Height of structure
Height of the structure is an important factor for the purpose of lightning protection. Taller structures are subject to greater hazards than smaller structures and, therefore, lightning protection is more desirable for tall structures.
1.3.33.4 Lightning prevalence
The number of thunderstorm days in a year varies in different parts of a country. However, the severity of lightning storms, as distinguished from their frequency of occurrence, is usually much greater in some locations than others. Hence, the need for protection varies from place to place, although not necessarily in direct proportion to the thunderstorm frequency.
1.3.33.5 Risk assessment
"Risk Index" is the sum of the indices for all the factors, as given in Table 8.1.27. A few examples of calculation of Risk Index are given in Table 8.1.28, based on a marginal Risk Index of 40.
1.3.33.6 Integral parts of a lightning protection system
A smallest complete lightning protection system shall consist of (i) An air spike or air terminal, (ii) A down conductor, (iii) A roof conductor and (iv) An earth electrode. An air spike or air terminal is that part which is intended to intercept lightning discharges. It consists of a vertical thick conductor of round cross section mounted on the highest part of the building to protect the required area. However, in general there may be more than one air spike or air terminal. In such a case roof conductors (made with copper strips or PVC insulated Annealed Stranded copper cables) need to be used to interconnect the Air Spikes or Air Terminals. Usually, for each Air Spike or Air Terminal there shall be one down conductor (made with copper strips or PVC insulated Annealed Stranded copper cables) going down up to the Earth Electrode pit and connected to the Earth Electrode. In all junctions, appropriate type of copper or brass junction plates or brass clamps must be used to ensure low resistance, firm and long lasting connection.
Table 8.1.28: Example of Calculation of Risk Index Total Example A B C D E F G Index Recommendations Figure
Small residential building 2 4 2 2 2 2 21 35 No protection
in a thickly populated needed, in general
locality (height less than
10 m)
Office building in a 7 2 2 2 2 5 21 41 As the figure is
locality (height 20 m) around 40, need
of protection will
depend upon the
importance of the
building
Hotel building (height 7 2 2 10 2 16 21 60 Protection
31m) exceeding twice the essential
height of surrounding
structures
Building of historical 8 4 8 10 2 30 21 83 Protection
importance completely essential
isolated (height > 55 m)
Structure of high historical - - - - - - - - Protection essential
importance as the height
(height > 55 m) exceeds 53 m
Structure, such as hydro- 7 2 6 2 6 4 21 48 Protected by
electric power stations, surroundings
sufficiently protected by
means of surrounding
structures, for example,
high vertical cliffs, high
metallic structures or earth
wire of transmission
system (height 15 m)
(a) Air spike/air terminal An air spike or air terminal shall be made with copper rod of minimum 12 mm diameter with tin coating on top. The terminal shall have a copper/brass base plate for mounting on top of roof, column, parapet wall using rowel bolts. The minimum dimension of such a base plate shall be 152 mm x 152 mm x 13 mm. The length and width may need to be increased depending on the number of connection of the down conductors and the roof conductors. Such connections are to be made using hexagonal head brass bolts and nuts of 10mm diameter with brass washers. Minimum height of the air terminal shall be 300 mm above the highest point of the building fulfilling all the conditions of NFPA 780.
(b) Down conductor A Down Conductor shall be made with copper strip or Stranded PVC insulated annealed copper cable.
(c) Roof conductor A Roof Conductor shall be made with copper strip or Stranded PVC insulated annealed copper cable. This shall run along the periphery of the roof to link all air spikes and all down conductors installed on top of a building. The joints shall be made using clamps made of copper strips (of 1/8 inch minimum thickness) and appropriate brass bolts and washers of 3/8 inch minimum diameter.
(d) Earth electrode The Earth Electrode is exactly of the same type as the Earth Electrode of the Electrical Distribution (Electrical Installation for Buildings) system described earlier in this document. Considering the practical situation in this country and Pipe Earth Electrodes are suggested. For each Air spike one Earth Electrode is an ideal solution.
(e) Earth inspection boxes A 18 SWG GI sheet made Earth Inspection Box must be provided for each down conductor 1000 mm above the plinth level of the building (concealed inside the wall) which will contain a copper strip made clamp on the insulation peeled down conductor to check the continuity of the Earth Lead Down Conductor and the Earth Electrode and also to measure the Earth Resistance of the system. The box shall have a GI sheet made cover plate.
(f) Earthing pit Earthing pits shall be provided as described in the earthing topic above.
1.3.33.7 Number of lightning arrestors required and their installation
Number of Lightning Protection Air Spikes in a building will depend on the nature of the roof top, on the total area of the roof top, on the height of the building, height of the adjacent buildings, height of the nearby towers or other similar structures. However, as a thumb rule, for every 80 m2 area at least one air spike should be chosen at the beginning. During placement of the air spikes the total number may have to be increased or adjusted.
1.3.33.8 Protection zone
The zone of protection is the space within which an air spike provides protection by attracting the stroke to itself. It has been found that a single vertical conductor attracts to itself strokes of average or above average intensity which in the absence of the conductor would have struck the ground within a circle having its centre at the conductor and a radius equal to twice the height of the conductor. For weaker than average discharges the protected area becomes smaller. For practical design it is therefore assumed that statistically satisfactory protection can be given to a zone consisting of a cone with its apex at the top of the vertical conductor and a base radius equal to the height of the conductor. This is illustrated in Figure 8.1.5. A horizontal conductor can be regarded as a series of apexes coalesced into a line, and the zone of protection thus becomes a tent-like space (Figure 8.1.6).
(a) When there are several parallel horizontal conductors the area between them has been found by experience to be better protected than one would expect from the above considerations only. The recommended design criterion is that no part of the roof should be more than 9 m from the nearest horizontal conductor except that an additional 0.3 m may be added for each 0.3 m or part thereof by which the part to be protected is below the nearest conductor.
(b) The earth termination is that part which discharges the current into the general mass of the earth. In other words, it is one or more earth electrodes. Earth electrodes for lightning protection are no different from earth electrodes for short circuit protection systems. The total resistance of an electrode for a lightning protection system must not exceed 10 ohms for buildings up to 10 storied and 2 ohms for high rise buildings.
Figure 8.1.5 Protected zone for Figure 8.1.6 Protected zone for horizontal
vertical conductors conductors
(c) The down conductor is the conductor which runs from the air termination to the earth termination. A building with a base area not exceeding 100 m2 shall be provided with one down conductor. For a larger building, there shall be one down conductor for the first 80m2 plus a further one for every 100 m2 or part thereof in excess of the first 80 m2. Alternatively, for a larger building one down conductor may be provided for every 30 m of perimeter. Ideally, every air spike should have a down conductor going down up to the earth electrode.
(d) The material used for lightning conductors must be copper. The criterion for design is to keep the resistance from air termination to earth electrode to a negligible value.
(e) Recommended dimensions for various components of lightning arrester are given in Table 8.1.29. Larger conductors should however be used if the system is unlikely to receive regular inspection and maintenance.
Table 8.1.2 9: Sizes of the Components of Lightning Protection Systems
Components Minimum Dimensions
Air terminals 12 mm dia
Copper strip 20 mm W x 3 mm T Copper and phosphor bronze rods 12 mm dia
PVC insulated stranded annealed copper cable (minimum size) 19 strands of 1.8 mm dia
Down Conductors Copper strip 20 mm x 3 mm
PVC insulated stranded annealed copper cable (minimum size) 19 strands of 1.8 mm dia
Earth Electrode
Hard drawn copper rods for driving into soft ground 12 mm dia Hard drawn or annealed copper rods for indirect driving 12 mm dia or laying in ground
Phosphor bronze for hard ground 12 mm dia Copper clad steel for hard ground 50 mm dia GI pipe 38 mm/50 mm dia
(f) External metal on a building should be bonded to the lightning conductor with bonds at least as large as the conductor.
(g) When a lightning conductor carries a stroke to earth, it is temporarily raised to a potential considerably above that of earth. There is, therefore, a risk that the discharge will flash over to nearby metal and cause damage to the intervening structure. This can be prevented by either, (i) providing sufficient clearance between conductor and other metal or (ii) by bonding these together to ensure that there can be no potential difference between them. The necessary clearance is obtained from : H D 0.3 R (8.1.1) 15 n
Where,
D = Clearance in metres
R = Resistance to earth in ohms
H = Height of building in metres n = Number of down electrodes
Since it is often impracticable to provide the necessary clearance, the alternative technique of bonding is preferred.
(h) Surge arrester selection A surge arrester is a protective device for limiting surge voltages by discharging, or bypassing, surge current through it. It also prevents continued flow of follow-through current while remaining capable of repeating these functions. It is used to protect overhead lines, transformers and other electrical apparatus mostly in an outdoor substation from lightning voltages traveling through the overhead lines.
(i) Horn-gap lightning arresters Horn-gap lightning arresters are commonly used for low and medium voltage overhead lines. The rating of the surge arrester shall be equal to or greater than the maximum continuous phase to ground power frequency voltage available at the point of application.
(j) Design of lightning arrester using rolling sphere method Lightning arrester (including number and height) can also be designed and installed by using rolling sphere method following NFPA 780. Minimum height of the air terminal shall be in accordance with Sec 1.3.33.6.
1.3.34 Telecommunications in Buildings
1.3.34.1 General
Placing concealed 2 pair indoor cables is needed to get (ii) telephone lines of the wired telephone companies inside rooms of a building and (ii) to get the PABX lines of the building /offices in the building to the respective rooms under the PABXs. In addition to this, 10/20/50 pair telephone cables are required to be brought in to the PABX room(s) of the building. Conduits are to be installed for both of these two categories. For the entry of 10/20/50 pair cables, conduits through straight and easy path (in most cases, through one side of the vertical electrical duct) need to be brought in.
1.3.34.2 Concealed telecommunication cable wiring
2 pair PVC insulated PVC sheathed annealed copper telecommunication cable shall be drawn through sufficient number of pre-laid 19/25/38 mm PVC conduits to establish telecommunication network inside a building. A clearance of at least 40 percent must be maintained inside the PVC conduits. Sufficient number of 18 SWG GI sheet made pull boxes (with Perspex sheet / ebonite sheet cover plates) at all suitable places must be placed for the ease of pulling these cables.
2 pair PVC insulated PVC sheathed annealed copper telecommunication cable shall be used for wiring between a Telephone DP/Patch panel and a telecommunication outlet. The extra pair shall remain for future maintenance. The minimum size of the copper wire of this cable shall be 0.5 mm. The copper shall be preferably tinned.
1.3.34.3 Surface telecommunication cable wiring
Surface wiring should not be a choice during designing a building wiring. However, if the building is already constructed or under compulsory conditions or for extension of an existing network one may go for surface wiring. The same 2 pair PVC insulated PVC sheathed annealed copper telecommunication cable shall be used for this purpose. Wiring shall be done either by using channels or by using PVC conduits following the power line surface wiring methods mentions earlier.
1.3.34.4 Telecommunications outlets
Wall mounted Telecommunication outlets shall contain RJ11 or RJ45 connectors/jacks (shuttered). For simple telephone connection RJ11 shuttered jacks are sufficient. The outlet box shall have a back-box which may be made of the same polymer material as the front panel or shall be made using 18 SWG GI sheet or 18 SWG MS sheet but painted with two coats of synthetic enamel paint.
1.3.34.5 Telephone DP room, patch panel room and digital PABX room
Telephone DP room, Patch Panel Room and PABX room should be located near the vertical riser duct of the building so that the incoming 50/100 pair underground telephone cable can be terminated in the DP/MDF or patch panel for distribution among the flats of a multistoried residential building or among the offices of a multistoried commercial/office building.
If a digital telephone PABX is to be installed then this can be installed in the same room. A separate earth electrode with earth lead wire will be required for the PABX.
1.3.35 Television Antennas/Cable Television system
In a multistoried residential/office building, television antennas shall be placed at one suitably sited antenna location on roof top and connect these to individual flats/ residences/offices in the same building by coaxial cables through concealed conduits.
1.3.35.1 Cable work for television antennas/cable television system
Vertical duct and easy entry to each flats/ offices must be provided as sharp bending of these cables is difficult and harmful to the cables. These cables must not be placed in the same conduit with power cables. A distance of at least 350 mm must be maintained if a portion runs in parallel with the power cable conduits. RF and Video cables shall be PVC sheathed Co-axial Cables shall be made with solid Copper centre conductor, foamed polythene insulated and further sealed Alluminium foil taped and Copper wire braided.
1.3.35.2 Television antenna outlets/cable television system outlets
Wall mounted television coaxial cable outlets shall contain high quality coaxial connectors/jacks. The outlet box shall have a back-box which may be made of the same polymer material as the front panel or 18 SWG GI sheet or 18 SWG MS sheet made but painted with two coats of synthetic enamel paint.
1.3.36 Data Communication Network for LAN and Internet Services inside a
Building
Data Communication Network for LAN and Internet Services inside a Building may be installed using Cat 6 unshielded twisted pair (UTP) cables in a concealed manner following the concealed wiring power cables installation procedure mentioned in the wiring methods section of this document. Each of the cables will be terminated at one end at the 8P8C (RJ45) connector based data socket outlet board in the required rooms at the power socket level. On the other end, the cable will be terminated in the patch panel. From the patch panel up to the data socket outlet the cable shall be in one piece i.e., no
joints will be allowed. As a result the concealed conduit work needs to be done carefully to have a straight line path and without any bend in the roof slab. Sufficient pull boxes will be required in the roof slab. Pull box will also be needed close to the vertical bend near the bend and ceiling at any downward drop of the conduit. The conduits must have 20 SWG GI pull wires during laying for pulling the cables later.
Because of the nature of these cables more clearances are needed inside the PVC conduits compared to the power cables. If the conduits are running parallel to the power cables then there should be at least a distance of 410 mm between these two.
Recently Cat. 7 cables are emerging as a better choice in place of Cat. 6 cables.
1.3.37 Fire Detection and Alarm System inside a Building
The major parts of a Fire Detection and Alarm System inside a Building may be listed as
(a) A number of different types of Fire Detectors/ detection devices wired in a number of radial circuits
(b) Manual call points
(c) A central control panel for fire detection
(d) A number of alarm sounders/alarm devices wired in a number of radial circuits
(e) Cables for wiring the fire detectors/detection devices
(f) Cables for wiring the alarm sounders/alarm devices
Control Panel
The control panel will indicate in which detection circuit (zone) an alarm or fault condition has been generated and will operate common or zonal sounders and auxiliary commands (for example door release or fire brigade signaling).
Detectors
A number of types of detectors (smoke detectors, heat detectors, ionization smoke detectors, optical beam smoke detectors, opto-heat detectors) for the installation
Alarm Devices
Alarm devices fall into two types, audible and visual. The audible types are most common, with a variety of types being available from bells to all kinds of different electronic sounders including those containing pre-recorded spoken messages. The choice of device is dependent on local preference, legal requirement and the need to have a tone distinct from all other building audible alarms.
Speech alarms or links to PA systems overcome some of the complacent responses to warning tones and can be used to good effect when carrying out regular fire tests in buildings where there are many people unfamiliar with the regular routines - such as hotels. Finally visual alarms are to be used where the hard of hearing may be occupying a building or where the ambient noise is such (above 90 dBA) that audible warning may not be heard, where hearing protectors are in use or where the sounder levels would need to be so high that they might impair the hearing of the building occupant.
Audible and Visual Alarm Devices
The audible types are most common, with a variety of types being available from bells to all kinds of different electronic sounders including those containing pre-recorded spoken messages. The choice of device is dependent on local preference, legal requirement and the need to have a tone distinct from all other building audible alarms.
Cables for Fire Detectors
BS 5839-1 introduced more onerous requirements for the types of cables used in fire detection and alarm systems. Fireproof cables should now be used for all parts of the system and enhanced fire resistance cables should be used where there is a requirement to ensure cable integrity over a longer period of time. For example when connecting to alarm sounders or where connection between sub-panels provides any part of alarm signal path.
Fire alarm cables should be segregated from the cables of other systems; they should be clearly marked, preferably coloured red and should be routed through parts of the building that provide minimum risk. This latter point is particularly relevant where the use of the building is being changed - for example if a fuel store is being moved.
Specific Areas of Application for Fire Detection and Alarm Equipment
The BS 5839 suite of standards relate to specific areas of application for fire detection and alarm equipment. Specifically part 1 relates to public premises and part 6 relates to residential premises. BS5839-1 is a comprehensive code of practice for fire detection and alarm systems, the requirements relate to both life and property protection and the standard includes much advice and comment with is very useful in informing the building owner or system specifier of the background to the requirements.
Codes of Practice for Different Types of Fire Protection Systems
The parts of BS7273 are codes of practice for different types of fire protection systems. Generally this is considered separately to fire alarm systems but there may be occasions where a tradeoff can be made between the two systems, or where the two systems interact and must be interfaced.
Standards Related to Design and Performance of Items of Equipment that Make up a Fire Detection and Alarm System The EN 54 suite of standards relates to the design and performance of items of equipment that make up fire detection and alarm system. Each part relates to a different piece of equipment, for example part 3 relates to alarm devices, part 11 to call points, part 4 to power supplies etc. Fire Detection Zones Fire detection zones are essentially a convenient way of dividing up a building to assist in quickly locating the position of a fire. BS 5839-1 has some specific recommendations with respect to detection zones. Wiring of the fire detection and alarm system will be done using the concealed wiring and the surface wiring methods described in the power line wiring section of this document.
1.3.38 CCTV System inside a Building
Installation of cable network for CCTV System inside a Building shall be done following the guidelines given for cable work for television antennas/cable television system earlier in this document. For wiring of the power lines required for the Installation of CCTV system inside a building will be done using the concealed wiring and the surface wiring methods described in the power line wiring section of this document.
1.3.39 Design and Installation of Access Control System
Wiring of the Installation of access control systems will be done using the concealed wiring and the surface wiring methods described in the power line wiring section of this document.
1.3.40 Installation of Electronic Security Systems
Wiring of the installation of electronic security systems will be done using the concealed wiring and the surface wiring methods described in the power line wiring section of this document.
1.3.41 Qualification of the Contractor of Electrical and Electronic Engineering
Works in a Building A Contractor who will be working with the electrical and electronic engineering works in a building must have appropriate ABC license from the electrical licensing board of government of Bangladesh. The contractor must have sufficient number of well trained and experienced technicians to execute the job. For big volume of work, the contractor must have at least one Electrical Engineer assigned for the job.
1.3.42 Inspection and Testing
1.3.42.1 General
Every installation shall, on completion and before being energized, be inspected and tested. The methods of test shall be such that no danger to persons or property or damage to equipment occurs even if the circuit tested is defective.
1.3.42.2 Periodic inspection and testing
Periodic inspection and testing shall be carried out in order to maintain the installation in a sound condition after putting it into service. Where an addition is to be made to the fixed wiring of an existing installation, the latter shall be examined for compliance with the recommendations of the Code.
1.3.42.3 Checking the conformity with the Bangladesh Standard
The individual equipment and materials which form part of the installation shall generally conform to the relevant Bangladesh Standard (BDS) wherever applicable. If there is no relevant Bangladesh standard specification for any item, these shall be approved by the appropriate authority.
(i) Inspection of the colour identification of cables of wiring For single phase, Brown for Live, Blue for Neutral, Green + Yellow bi-colour for ECC. For three phase, Brown for L1, Black for L2, Grey for L3, Blue for Neutral and Green + Yellow bi-colour for ECC and Earth Lead Wire.
(ii) Inspection of earthing terminal, earthing bus Inspection should be made to check whether brass made earthing terminals have been provided inside the metal back boxes of the switchboards and socket boards (welded or screwed to the metal back box) and whether the ECCs of the sub circuit have been terminated in these terminals. Inspection should be made to check whether at least one copper earthing busbar has been provided in the BDBs, SDBs, FDBs, DBs, MDBs and the LT panel and whether ECCs have been appropriately terminated in these busbars using hexagonal head brass bolt and nuts. Also it should be checked whether the Earth Lead Wires have been properly terminated in the LT Panel / MDB / DB as appropriate.
(iii) Insulation Tests Insulation test is one of the most important tests for Electrical Installations in a Building.
Insulation resistance test shall be made on all electrical equipment, using a self-contained instrument such as the direct indicating ohm-meter of the generator type. DC potential shall be used in these tests and shall be as follows or an appropriate Meggar:
Circuits below 230 volts 500 volts Meggar
Circuits between 230 volts to 400 volts 1000 volts Meggar The minimum acceptable insulation resistance value is 5 mega ohms for LT lines. Before making connections at the ends of each cable run, the insulation resistance measurement test of each cable shall be made. Each conductor of a multi-core cable shall be tested individually to all other conductors of the group and also to earth. If insulation resistance test readings are found to be less than the specified minimum in any conductor, the entire cable shall be replaced. All transformers, switchgears etc. shall be subject to an insulation resistance measurement test to ground after installation but before any wiring is connected. Insulation tests shall be made between open contacts of circuit breakers, switches etc. and between each phase and earth.
(iv) Earth Resistance Test and the Continuity Resistance Test Earth resistance tests shall be made on the system, separating and reconnecting each earth connection using earth resistance meter. The electrical resistance of the Earth Continuity Conductor of different segment shall be measured separately using sensitive digital Ohm meter or by means of resistance bridge instrument. The resistance of the Earth Lead Wire shall be measured from the earthing busbar of the LT Panel/MDB/DB and the earth electrode(s). The electrical resistance of any section shall not exceed 1 ohm. Where more than one earthing sets are installed, the earth resistance between two sets shall be measured by means of sensitive digital Ohm meter or by means of resistance bridge instrument. The earth resistance between two sets shall not exceed 1 ohm.
Operation Tests Current load measurement shall be made on equipment and on all power and lighting feeders using Clamp on Ammeters.
The current reading shall be taken in each phase wire and in each neutral wire while the circuit or equipment is operating under actual load conditions.
Clamp on Ammeters are required to take current readings without interrupting a circuit.
All light fittings shall be tested electrically and mechanically to check whether they comply with the standard specifications.
Fluorescent light fittings shall be tested so that when functioning no flickering or choke singing is felt.
(v) Inspection of the Installation On completion of wiring a general inspection shall be carried out by competent personnel in order to verify that the provisions of this Code and that of the Electricity Act of Bangladesh have been complied with. A certificate may be issued on satisfactory completion of the work in a format as shown in Appendix C. Items to be inspected are detailed in the following sections.
Inspection of Substation Installations In substation installations, it shall be checked whether:
• The installation has been carried out in accordance with the approved drawings;
• Phase to phase and phase to earth clearances are provided as required;
• All equipment are efficiently earthed and properly connected to the required number of earth electrodes;
• The required ground clearance to live terminals is provided;
• Suitable fencing is provided with gate with lockable arrangements;
• The required number of caution boards, firefighting equipment, operating rods, rubber mats, etc., are kept in the substation;
• In case of indoor substation sufficient ventilation and draining arrangements are made;
• All cable trenches have covers of noninflammable material;
• Free accessibility is provided for all equipment for normal operation;
• All name plates are fixed and the equipment are fully painted;
• All construction materials and temporary connections are removed;
• Oil level , busbar tightness, transformer tap position, etc. are in order;
• Earth pipe troughs and cover slabs are provided for earth electrodes/earth pits and the neutral and LA earth pits are marked for easy identification;
• Earth electrodes are of GI pipes or CI pipes or copper plates. For earth connections, brass bolts and nuts with lead washers are provided in the pipes/plates;
• Earth pipe troughs and oil sumps/pits are free from rubbish, dirt and stone jelly and the earth connections are visible and easily accessible;
• HT and LT panels and switchgears are all vermin and damp-proof and all unused openings or holes are blocked properly;
• The earth busbars have tight connections and corrosion free joint surfaces;
• Control switch fuses are provided at an accessible height from ground;
• Adequate headroom is available in the transformer room for easy topping-up of oil, maintenance, etc.;
• Safety devices, horizontal and vertical barriers, busbar covers/shrouds, automatic safety shutters/door interlock, handle interlock etc. are safe and in reliable operation in all panels and cubicles;
• Clearances in the front, rear and sides of the main HT and LT and subswitch boards are adequate;
• The switches operate freely; the 3 blades make contact at the same time, the arcing horns contact in advance; and the handles are provided with locking arrangements,
• Insulators are free from cracks, and are clean;
• In transformers, there is no oil leak;
• Connections to bushing in transformers are light and maintain good contact;
• Bushings are free from cracks and are clean;
• Accessories of transformers like breathers, vent pipe, buchholz relay, etc. are in order;
• Connections to gas relay in transformers are in order;
• In transformers, oil and winding temperature are set for specific requirements to pump out;
• In case of cable cellars, adequate arrangements exist to pump off water that has entered due to seepage or other reasons; and
• All incoming and outgoing circuits of HT and LT panels are clearly and indelibly labeled for identifications.
Inspection of Low Tension (LT) Installation In Low Tension (LT) or Medium Voltage (MV) Installations, it shall be checked whether:
• All blocking materials that are used for safe transportation in switchgears, contactors, relays, etc. are removed;
• All connections to the earthing system have provisions for periodical inspection;
• Sharp cable bends are avoided and cables are taken in a smooth manner in the trenches or alongside the walls and ceilings using suitable support clamps at regular intervals;
• Suitable linked switch or circuit breaker or lockable push button is provided near the motors/apparatus for controlling supply to the motor/apparatus in an easily accessible location;
• Two separate and distinct earth connections are provided for the motor apparatus;
• Control switch fuse is provided at an accessible height from ground for controlling supply to overhead travelling crane, hoists, overhead busbar trunking;
• The metal rails on which the crane travels are electrically continuous and earthed and bonding of rails and earthing at both ends are done;
• Four-core cables are used for overhead travelling crane and portable equipment, the fourth core being used for earthing, and separate supply for lighting circuit is taken;
• If flexible metallic hose is used for wiring to motors and other equipment, the wiring is enclosed to the full lengths, and the hose secured properly by approved means;
• The cables are not taken through areas where they are likely to be damaged or chemically affected;
• The screens and armours of the cables are earthed properly;
• The belts of belt driven equipment are properly guarded;
• Adequate precautions are taken to ensure that no live parts are so exposed as to cause danger;
• Installed Ammeters and voltmeters work properly and are tested; and
• The relays are inspected visually by moving covers for deposits of dusts or other foreign matter.
Inspection of Overhead Lines For overhead lines, every care must be taken so that:
• All conductors and apparatus including live parts thereof are inaccessible;
• The types and size of supports are suitable for the overhead lines/conductors used and are in accordance with approved drawing and standards;
• Clearances from ground level to the lowest conductor of overhead lines, sag conditions, etc. are in accordance with the relevant standard;
• Where overhead lines cross the roads suitable grounded guarding shall be provided at road crossings,
• Where overhead lines cross each other or are in proximity with one another, suitable guarding shall be provided at crossings to protect against possibility of the lines coming in contact with one another;
• Every guard wire shall be properly grounded/earthed;
• The type, size and suitability of the guarding arrangement provided shall be adequate;
• Stays cables must be provided suitably with the overhead line carrying poles as required and shall be efficiently earthed at the bottom and shall be provided with suitable stay insulators of appropriate voltages;
• Anti-climbing devices and Danger Board/Caution Board Notices are provided on all HT supports;
• Clearances along the route are checked and all obstructions such as trees/branches and shrubs are cleared on the route to the required distance on either side;
• Clearance between the live conductor and the earthed metal parts are adequate; and
• For the service connections tapped off from the overhead lines, cutouts of adequate capacity are provided. Inspection of Lighting Circuits The lighting circuits shall be checked to see whether:
• Wooden boxes and panels are avoided in factories for mounting the lighting boards, switch controls, etc.;
• Neutral links are provided in double pole switch fuses which are used for lighting control, and no fuse is provided in the neutral;
• The plug points in the lighting circuit are all 3-pin type, the third pin being suitably earthed;
• Tamper proof interlocked switch socket and plug are used for locations easily accessible;
• Lighting wiring in factory area is enclosed in conduit and the conduit is properly earthed, or alternatively, armoured cable wiring is used;
• A separate earth wire is run in the lighting installation to provide earthing for plug points, fixtures and equipment;
• Proper connectors and junction boxes are used wherever joints are in conductors or cross over of conductors takes place;
• Cartridge fuse units are fitted with cartridge fuses only;
• Clear and permanent identification marks are painted in all distribution boards, switchboards, sub-main boards and switches as necessary;
• The polarity has been checked and all fuses and single pole switches are connected on the phase conductor only and wiring is correctly connected to socket outlets;
• Spare knockouts provided in distribution boards and switch fuses are blocked;
• The ends of conduits enclosing the wiring leads are provided with ebonite or other suitable bushes;
• The fittings and fixtures used for outdoor use are all of weatherproof construction, and similarly, fixtures, fittings and switchgears used in the hazardous area are of flameproof application;
• Proper terminal connectors are used for termination of wires (conductors and earth leads) and all strands are inserted in the terminals;
• Flat ended screws are used for fixing conductor to the accessories;
• Flat washers backed up by spring washers are used for making end connections. Accessibility of Connections and Cable joints for Inspection Except for the following, every connection and joint shall be accessible for inspection, testing and maintenance:
• A compound-filled or encapsulated joint
• A connection between a cold tail and a heating element (e.g. a ceiling and floor heating system, a pipe trace-heating system)
• A joint made by welding, soldering, brazing or compression tool
• A joint formatting part of the equipment complying with the appropriate product standard.
1.4 Related Codes and Standards
Significant modification, upgradation and additions of the previous electrical engineering section of BNBC of 1993 have been incorporated in this updated version. While making changes and additions, the following documents/regulations/codes have been taken as reference/guiding sources:
(a) Bangladesh Electricity Act.
(b) IEE wiring Regulation (17th edition) BS: 7671 2008 including all parts.
(c) British Standards (BS). In addition to these, the following documents/regulations/codes have also been taken as references as required:
(a) National Building Code of India - 2005.
(b) Building Code of Pakistan - latest version.
(c) National Electrical Code of USA.
(d) International Electrotechnical Commission (IEC) Standards.
(e) ISO 50001 Standard for Energy Management System.
(f) Verband Deutscher Elektrotechniker (Association of German Electrical Engineers) (VDE). However, efforts have been be given to accept a significant part of rules and practices mentioned in IEE wiring Regulation (17th edition) BS: 7671 2008 including all parts with necessary modifications for our system and suitable for our country. While preparing this document the following Standards and practices are kept in mind.
(a) For having safe domestic electrical systems, domestic electrical installations shall be designed and installed according to the "fundamental principles" given in British Standard BS 7671 Chapter 13. These are similar to the fundamental principles defined in international standard IEC 60364-1. It is necessary to apply British Standard BS 7671 (the "Wiring Regulations"), including carrying out adequate inspection and testing to this standard of the completed works.
• To meet the above mentioned requirements the following rules and guidance shall be followed.
• The rules of the IEE wiring regulations (BS 7671), colloquially referred to as "the regs" (BS 7671: 2008, 17th Edition).;
• The rules of an equivalent standard approved by a member of the European Economic Area (e.g., DIN/VDE 0100);
(b) Guidance given in installation manuals that is consistent with BS 7671, such as the IEE On-Site Guide and IEE Guidance Notes 1 to 7.
(c) Installations in commercial and industrial premises must satisfy the requirements set in Electricity at Work Regulations 1989 (UK) and must follow recognised standards and practices, such as BS 7671 "Wiring Regulations".
Apart from these, some modifications had to be made considering the weather and other local conditions, practices and previous experiences in this country.
1.5 List Of Related Appendices
Appendix A Maximum Demand and Diversity
Appendix B Useful Tables Relating to Conductor Sizes
Appendix C Completion Certificate Form
Source: Bangladesh National Building Code 2020, S.R.O. No. 55-Law/2020, Bangladesh Gazette (Extraordinary), 11 February 2021. Tables, figures and equations: refer to the linked gazette pages.