Technical specification for Electrical wiring in multistory buildings

Technical specification for Electrical wiring in multistory buildings

This section covers, definition of point wiring, system of wiring and supply, installation, connection, testing and commissioning of point wiring for light points, ceiling fan points, exhaust fan points, convenience socket outlet points, power socket outlet points, bell outlet points etc. including fixing of light fixtures, ceiling fan, exhaust fan, wall fan, bell etc

The following standards and rules shall be applicable:

  1. Code of practice for electrical wiring installation (System voltage not exceeding 650 V) IS 732
  2. Code of practice for fire safety of buildings (General) Electrical installation. IS 1646
  3. Rigid steel conduits for electrical wiring. IS 9537 (Part - 2)
  4. Fittings for rigid steel conduits for electrical wiring. IS 2667
  5. Flexible steel conduits for Electrical wiring. IS 3480
  6. Accessories for rigid steel conduit for electrical wiring. IS 3837
  7. PVC insulated cables. IS 694
  8. Rigid non-metallic conduits for electrical wiring. IS 9537 (Part - 3)
  9. Flexible (Pliable) non-metallic conduits for electrical installation. IS 6946
  10. 3 pin plugs and sockets.IS 1293
  11. Specifications of conduits for electrical installation. IS 8130
  12. Switches for domestic purpose. IS 3854
  13. Fittings for rigid non-metallic conduits. IS 3419
  14. Guide for electrical layout in residential buildings Indian electricity act and rules. IS 4648

All the equipment and components provided in the transformer and accessories shall be suitably designed for installation and satisfactory operation as specified below.

Site conditions
Location MUMBAI
Site altitude 50 M above mean sea level
Maximum Ambient temperature and Relative humidity
Minimum Ambient temperature and Relative humidity
Design Ambient temperature and Relative humidity

Seismic factor Zone III as per IS 1893 Rainfall 1000 mm/year
Environmental Tropical/humid/corrosive conditions
Location of Equipment Indoor
Wind speed 80 kmph maximum

Electrical system data:
Power supply for Equipment
Voltage 415 V ± 5 % Frequency 50 Hz ± 3 %
Permissible combined voltage & frequency variation ± 6 % System design faults level (Symmetrical) 35 kA for 1 sec. max.
System earthing LV side neutral solidly earthed Wiring 3 phase, 4 wire on 415V system
Auxiliary power supply : Power supply 240V AC, 1-Ph, 50Hz
Control Supply
Space heater power supply = 240V AC, 1-Ph, 50Hz
Illumination power supply = 240V AC, 1-Ph, 50Hz
Plug-socket power supply = 240V AC, 1-Ph, 50Hz


  • A point shall consist of the branch wiring from the distribution board together with a switch as required, including the ceiling rose or pendant holder or swan holder, or ceiling fan box or socket or suitable termination. A point shall include, in addition, the earth continuity conductor/wire from the distribution board to the earth pin/stud of the outlet/switch box and to the outlet points
  • Supply, installation, fixing of conduits with necessary accessories, junction/pull/inspection/switch boxes and outlet boxes
  • Supplying and drawing of wires of required size including earth continuity wire
  • Supply, installation and connection of flush type switches, sockets, cover plates, switch plates, and fixing fan regulator etc
  • The point shall be complete with the branch wiring from the distribution board to the outlet point, through switch board, conduit with accessories, junction, pull, inspection boxes, control switch, socket, outlet boxes, ceiling roses, button/swan holder, connector etc


The rate per point shall include supply, installation, connection, testing and commissioning of point as described under “point wiring”. The measurements of the points will be enumerated


Unless otherwise mentioned on the drawings, the system of point wiring shall be as follows:
The system of wiring shall consist of single core, FRLS insulated, 650/1100 volt grade, copper conductor wires/cables laid through exposed (surface mounted) PVC conduits as directed & wherever required, conduits shall be concealed in walls and slabs


Prior to laying of conduits, the contractor shall submit for approval, the shop drawing for conduit layout indicating the route of the conduits, number and size of the conduits, location of junction/inspection/pull/outlet boxes, size and location of switch boxes, number and size of wires pulled through each conduit and all other necessary relevant details. Only after the drawings are approved, the contractor shall proceed with the work of laying of conduits.

PVC Conduit

All non-metallic PVC conduits shall conform to IS: 9537 ( Part - 3 ). The conduit shall be planed and of type as specified in IS: 9537 and shall be used with the corresponding accessories (Refer IS: 3419 specification for fittings for rigid non metallic conduits). PVC conduits shall be rigid unplasticised, heavy gauge having 2.0 mm. wall thickness upto 20 mm. diameter conduit and 2.5 mm. wall thickness for all sizes above 20 mm. diameter

M.S. Conduit

Conduits shall conform to IS: 9537 ( Part - 2 ), finished with galvanized surface. No steel conduit less than 25 mm. in diameter shall be used. Conduits shall be solid drawn of lap welded type, with minimum wall thickness for conduits having 25 mm. and above diameter
The conduits shall be delivered to the site of construction in original bundles and each length of conduit shall bear the label of manufacturers
The conduit accessories such bends, coupling etc. shall be conforming to the relevant Indian Standard specification

All the boxes for switches, sockets and other receptacles, junction boxes, pull boxes and outlet boxes shall be fabricated from 2.0 mm. thick mild sheet painted with two coats of red-oxide and then two coats of enamel paints as called for. Colour of the paints shall be as approved by the client. The boxes shall have smooth external and internal finished surface
Boxes in contact with earth or exposed to the weather shall be of 2 mm. mild steel and hot dip galvanized after fabrication
Separate screwed earth terminal shall be provided in the box for earthing purpose
All boxes shall have adequate no. of knock out holes of required diameter for conduit entry
Switch boxes to receive switches, socket outlets, power outlets, telephone outlets, fan regulators, etc. shall be fabricated to the approved shape and size to accommodate all the devices without overcrowding.
Outlet boxes to receive ceiling fan shall be fitted with adequately sized rod
Hook to fix ceiling fan. The boxes shall be of minimum depth of 65 mm.
Boxes installed for concealed wiring shall be provided with suitable extension rings or plaster covers as required. Boxes for use in masonry block or tiled walls shall be square cornered tile type, or standard boxes having square cornered tile type covers. These boxes shall be installed in the center of the masonry block or tiles
Cast metal boxes installed in wet locations and boxes installed flush with the outside of exterior surface shall be gasketed

Cover Plate
The cover of the boxes to receive outlet points shall be of best anodized sheet cut to shape and size or plate of approved manufacturers of switches


The cables shall conform to IS: 694. For all internal wiring FRLS insulated cables of 650/1100 volts grade, single core shall be used
The conductors shall be plain annealed copper conductors complying with IS 1554
The conductors shall be circular copper conductor
The insulation shall be FRLS compound complying with the requirements of IS 694. It shall be applied by an extrusion process and shall form a compact homogeneous body.
The thickness of FRLS insulation shall be as set out in the relevant standards

The cores of all cables shall be identified by colors in accordance with the following sequence.
Single phase = Red
Three phase = Red, Yellow, Blue
Neutral = Black
Earth = Green or Green/Yellow

Means of identifying the manufacturer shall be provided throughout the length of cable Unless otherwise specified in the drawings the size of the cables used for internal wiring shall be as follows:
In case of circuit wiring for lights, exhaust fans, ceiling fans, bell, convenience socket outlet points (P+N+E):
2.5 sqmm = From D.B. to switch boards.
1.5 sqmm = From switch boards to outlet points

In case of power socket outlet circuit having not more than two 15 A power outlet (P+N+E):
4.0 sqmm = From D.B. to first power outlet
2.5 sqmm = From first power outlet to second power outlet

In case of power socket outlet circuit having single 15 A power outlet (like water heater) (P+N+E):
4.0 sqmm = From D.B. to power outlet.

In case of 15 A. power outlet for window Air conditioner or other likewise appliances (P+N+E):
4.0 sqmm = From D.B. to power outlet.

The earth continuity conductor shall be similar to circuit cables and shall be drawn through conduit along with other circuit cables. The size of the earth continuity conductor shall be as follows:



Nominal cross-section area of largest associated copper circuit conductor should be same as to Nominal cross-sectional area of earth continuity conductor in sqmm for following sizes;
1.5 Sqmm
2.5 Sqmm
4.0 Sqmm

Separate circuit shall run for each water heater, kitchen equipment, window air conditioner, and similar outlets at location as shown on drawing

Switches shall conform to IS 3854, IS 1293 and IS 4615. The switches shall be single pole, single or two way as shown on the drawings or as specified. They shall be of moulded type rated for 250 volt, and of full 5/15 A capacity. They shall be provided with insulated dollies and covers
The switches shall be rocker operated with a quiet operating mechanism with bounce free snap action mechanism enclosed in an arc resistant chamber.
The switches shall have pure silver and silver cadmium contacts.
The switches shall be flush modular type.
The make of the switches shall be as indicated in the drawings or BOQ or make of material or as suggested and approved by the client.
The switches installed in outdoor area shall be industrial, metal clad type, and shall be provided in weather proof enclosures, complete with weather proof gasketed covers.

The sockets shall conform to IS 1293. Each socket shall be provided with control switch of appropriate rating. The sockets shall be moulded type, rated for 250 volts, and either of full 5 A or 15 A capacity, as mentioned on the drawings.
Sockets shall be of three pin type, the third in being connected to earth continuity conductor.
The socket shall be flush modular type.
The sockets installed in machine room, plant room or wet/damp area shall be metal clad weather proof type.
The finishing and make of all the sockets shall be same as light switch.
The socket shall have fully sprung contacts and solid brass shrouded
Terminals to ensure positive electrical connections.
The sockets shall be provided with automatic shutters, which open only when earth pin of the plug inserts in the socket.
The socket shall be provided with three pin plug top suitable to the socket and of the same make as socket.



The insulation resistance shall be measured by applying 500 volt megger with all fuses in places, circuit breaker and all switches closed
The insulation resistance in megohms of an installation, measured shall not be less than 50 megohms divided by the number of points on the circuit
The insulation resistance shall be measured between

The earth continuity conductors shall be tested for electrical continuity and the electrical resistance of the same along with the earthing lead but excluding any added resistance or earth leakage circuit-breaker, measured from the connection, with the earth electrode to any point in the earth continuity conductor in the completed installation and shall not exceed one ohm

A test shall be made to verify that every no-linked, single pole switch is connected to one of the phase of the supply system

All the above tests shall be carried out in presence of client and the results shall be recorded in prescribed forms. Any default during the testing shall be immediately rectified and that section of the installation shall be re tested. The completed test result form shall be submitted to the client for approval On completion of an electric installation a certificate shall be furnished by the contractor, countersigned by the certified supervisor under whose direct supervision the installation was carried out. This certificate shall be in a prescribed form as required by the local electric supply authority.


All the rigid PVC conduit used for concealed installation shall be as per IS ; 9537 and its accessories shall be as per IS: 3419 (Small Wire Ropes).
Whenever necessary bends or diversion may be achieved by bending the conduits with the help of bending spring. No other method of bending is allowed Conduit pipes shall be joined with the help of plain coupler fixed at the end with the help of vinyl solvent cement. No other method of joining is permissible All other methods, no wires through conduit, bunching, etc. Shall be as specified in the concealed installation Prior to fixing the conduits, the complete route shall be marked on site for the approval of consultant

The rigid PVC conduits shall be used for concealed wiring system. The conduits shall be concealed in the concrete slab, floor, walls, beams, columns etc

Conduits embedded in concrete shall be installed in the frame work before pouring concrete. The conduits shall be installed above the bottom reinforcing bars, and shall provide positive wire fastening of the conduit to the reinforcing rods at an interval of not more than one meter, but on either side of couplers or bends or putlet/pull/junction boxes or similar fittings, proper hold fast shall be fixed at a distance of 30 cm from the center of such fittings. Conduits embedded in the wall shall be fixed inside the chase. The chase in the wall shall be neatly made and be fixed in the manner desired. In the case of building under construction, chase shall be provided in the wall at the time of their construction and shall be filled up neatly with cement mortar 1:4 after erection of conduit and brought to the original finish of the wall. Cutting of horizontal chases in walls is prohibited. The conduits shall be fixed inside the chase by means of staples or by means of saddles not more than 60 cm apart.
Conduits shall be so arranged as to facilitate easy drawing of wires through them. Entire conduit layout shall be done in such a way as to avoid additional junction boxes other than light points. The wiring shall be done in a looping manner. All the looping shall be done in either switch boxes or outlet boxes. Looping in junction or pull boxes are strictly not allowed. Where conduits cross building expansion joints, adequate expansion fittings or other approved devices shall be used to take care of any relative movement
All conduits shall be installed so as to avoid steam and hot water pipes
Conduits shall be installed in such a way that the junction, derivation and pull boxes shall always be accessible for repairs and maintenance work. The location of junction/pull boxes shall be marked on the shop drawings and approved by the client
A separation of 200 mm shall be maintained between electrical conduits and hot water lines in the building
No run of conduit shall exceed ten mtr. between adjacent draw in points nor shall it contain more than two right angle bends, or other derivation from the straight line
Caution shall be exercised in using the PVC conduits in location where ambient temperature is 50 degree cel. or above. Use of PVC conduits in places where ambient temperature is mote than 60 deg. cel. Is prohibited. The entire conduit system including boxes shall be thoroughly cleaned after completion of installations and before drawing of wires. Conduit system shall be erect and straight as far as possible. Traps where water may accumulate from condensation are to be avoided and if unavoidable, suitable provision for draining the water shall be made
All jointing method shall be subject to the approval of the client

Separate conduits shall be provided for the following system.
15 A power outlets.
5 A outlets and lighting system.
Low voltage system.
Telephone/intercom system.
C.C.T.V. system
Sound system
Computer data cabling system
Equipment wiring

Conduits shall be joined by means of plain couplers vinyl and/or solvent cement. Where there are long runs of straight conduit, inspection type couplers shall be provided at intervals , as approved by the client
The conduits shall be thoroughly cleaned before making the joints
In case of plain coupler joints, proper jointing material like a vinyl solvent cement (gray in color) or any material as recommended by the manufacturer shall be used.

Wherever necessary, bends or diversions may be achieved by bending the conduits or by employing normal bends. No bends shall have radius less than 2.5 times outside dia. of the conduit

Heat may be used to soften the PVC conduit for bending, but while applying heat to conduit, the conduit shall be filled with sand to avoid any damage to the conduit

All the outlets for fittings, switches etc. shall be boxes of substantial construction In order to minimize condensation or sweating inside the conduits, all outlets of conduit system shall be properly drained and ventilated, but in such a manner as to prevent the entry of insects , etc. Fixing between conduit and boxes, outlet boxes, switch boxes and the like must be provided with entry spouts and smooth PVC bushes. Joints between conduit and any type of boxes shall be affected by means of conduit couplers in to each of which shall be coupled smooth PVC bush from inside the box. In any case all the joints shall be fully water tight.

Cables of AC supply of different phase shall be bunched in separate conduits. The number of insulated wires/ cables that may be drawn into the conduits shall be as per the following table. In this table, the space factor does not exceed 40%. However, in any case conduits having lesser than 19 mm dia. shall not be used.

All conduits and it’s accessories shall be of threaded type and under no circumstances pin grip type or clamp type accessories be used

Conduit pipes shall be fixed by heavy gauge spacer bar saddles. The saddles shall be of 3 mm x 19 mm galvanized mild steel flat, properly treated and securely fixed to support by means of nuts and bolts raw bolts, brass machine screws, as mentioned, at an internal of not more than one meter but on either side of couplers, or bends, or junction/pull/outlet boxes or similar fittings, saddles shall be fixed at a distance of 30 cm from the center of such fittings.
Draw boxes shall be located at convenient location for easy drawing of wires
Every mains and sub mains shall run in independent conduits with an independent earth wire of specified capacity along the entire length of conduit
The conduits to be installed shall be of ample cross section area to facilitate the drawing of wires. The diameter of the conduit shall be selected as per table specified in these specifications. But in no case it shall be less than 25 mm diameter
Entire conduit layout shall be done such as to avoid additional junctions boxes other than for outlet points. Conduits shall be free from sharp edge and burrs. Conduits shall be laid in a neat and organized manner as directed and approved by the client. Conduit runs shall be planned so as not to conflict with any other services pipe, lines/duct
The entire conduit system shall be electrically and mechanically continuous and shall be bonded, together by means of approved type earthing clamp and earthed through a bare copper conductor of 14 SWG to the earthing terminals on the nearest distribution board
If required, connection between PVC and steel conduits shall be through a junction box. Direct connection between PVC and steel conduits are not allowed
Where exposed conduits are suspended from the structure, they shall be clamped firmly and rigidly to hangers of design to be approved by client. Where hangers are to be anchored to reinforced concrete, appropriate inserts and necessary devices for their fixing shall be left in position at the time of concreting, making holes and opening in the concrete will generally not be allowed. In case, it is unavoidable, prior permission of the client shall be obtained

Conduit pipes shall be joined by means of screwed couplers and screwed accessories, as per IS 2667
The threads shall be free from grease or oil
In long distanced straight runs of conduit, inspection type couplers two way junction boxes at reasonable intervals shall be provided or running threads with couplers and lock nuts shall be provided. The bare threaded portion shall be treated with anti-corrosive paints. Threads on conduit pipes in all cases shall be between 11mm to 27mm long, sufficient to accommodate pipes to full threaded portion of couplers or accessories. Cut ends of conduit pipes shall have no sharp edges nor any burrs left, to avoid damage to the insulation of conductors while pulling them through such pipes
Brass female bushes shall be used in each conduit termination in a switch box, outlet box, electrical panel or any other box
Conduit shall be secured in each outlet box switch box, electrical panel or any other ox by means of one brass hexagonal lock nut and bush, outside and inside the box
At each building, expansion joints approved oil tight double wire wound flexible steel conduit or any other approved method shall be used. This shall be united on both sides with the rigid conduits by suitable union
Conduits installed in the plant room for mechanical equipment shall be properly clamped with the mechanical supports, but in no case, it shall be fixed with the body of the equipment
The connection of conduit to the mechanical equipment shall be through oil tight double wire wound flexible steel conduit. In any case the length of the flexible conduit shall not exceed one meter. The flexible conduit shall be properly clamped with the body of the equipment. They shall not in any case be clamped with any cover or any removable parts of the equipment


All necessary bends in the system including diversion shall be done by bending pipes or by inserting suitable solid or circular inspection type normal box or similar fittings. Conduit fittings shall be avoided as far as possible on conduit system exposed to weather, where necessary, solid type fittings shall be used. Radius of such bends in conduit pipes shall be not less than 75 mm. No length of conduit shall have more than the equivalent of four quarter bends from outlet, the bends at the outlets not being counted

In order to minimize condensation or sweating inside the conduit, all outlets of conduit system shall be properly drained and ventilated, but in such a manner as to prevent the entry of insects, as far as possible

The outer surface of the conduits including bends, junction boxes, etc., forming part of the conduit system shall be adequately protected against rust, particularly when such system is exposed to weather. In all cases, no bare/threaded portion of conduit pipe shall be allowed unless such bare threaded portion is treated with anti-corrosive coating or covered with approved plastic compound


Unless otherwise specified, insulated conductors of different phases shall be bunched in separate conduit.
Wires carrying current shall be so bunched in the conduit that the out going and return wires are drawn into the same conduit. Wires originating from two different phases shall not be run in the same conduit


Switches shall be installed at 900 mm above finished floor level unless otherwise indicated on the drawings
The switch controlling the light point or fan shall be connected on to the phase wire of the circuit and neutral shall be continuous, having no fuse or switch installed in the line except at the D.B. All fan regulators shall be fixed inside the switch boxes on adjustable flat M.S. strips/plates with tapped holes and brass machine screws, leaving ample space at the back and side for accommodating wires
The cover plates to the switch box shall be fixed by means of sunk head brass cadmium screws
Where two or more switches and fan regulators are installed together, they shall be provided with one gang cover plate with knockouts to accommodate required number of switches, sockets and regulators
The switch controlling the socket outlet shall be on the phase wire of the circuit. The third pin of the socket shall be connected to the earth continuity conductor of the circuit
The switch boxes, installed back-to-back in the same wall shall be offset from each other, 150 mm horizontally, to preclude noise transmission


The drawing and joining of copper conductor or wires shall be executed with due regard to the following precautions. While drawing insulated wires into the conduits, care shall be taken to avoid scratches and kinks which may cause breakage of conductors. There shall be no sharp bends
Insulation shall be shaved off for a length of 15 mm at the end of wire like sharpening of a pencil and it shall not be removed by cutting it square or ringing
FRLS insulated copper conductor wire ends before connection shall be properly soldered (at least 15 mm length) with soldering flux/copper solder, for copper conductor. Strands of wires shall not be cut for connecting to the terminals. All strands of wires shall be soldered at the terminals. All strands of wires shall be soldered at the end before connection. The connecting brass-screws shall have flat ends. All looped joints shall be soldered and connected through terminals block/connectors. The pressure applied to tighten terminal screws shall be just adequate, neither too much nor too less. Conductors having nominal cross section exceeding 4 sq. mm shall always be provided with crimping type cable sockets. At all bolted terminals, brass flat washer of large area and approved steel spring washers shall be used. Brass nuts and bolts shall be used for all connections
Only certified wire men and cable jointers shall be employed to do joining work
For all internal wiring FRLS insulated wires of 650/1100 volts grade shall be used. The sub-circuit wiring for point shall be carried out in looping system and no joint shall be allowed in the length of the conductors. No wire shall be drawn in to any conduit, until all work of any nature that may cause injury to wire is completed. Care shall be taken in pulling the wires so that no damage occurs to the insulation of the wire. Before the wires are drawn into the conduits the conduits shall be thoroughly cleaned of moisture, dust, and dirt or any other obstruction by forcing compressed air through the conduits


The wiring shall be by looping back system, and hence all joints shall be made at main switches, distribution boards, socket outlets, lighting outlets and switch boxes only. No joints shall be made inside conduits and junction boxes.
Contractors shall be continuous from outlet to outlet. For joints where unavoidable, due to any specified reasons, prior permission in writing shall be obtained from the client before making such connections. Joints by twisting conductors are prohibited.


Balancing of circuit in three phase installation shall be planned before the commencement of wiring and shall be strictly adhered to.


All earthing systems shall be in accordance with IS: 3043 - 1985 code of practice for earthing

All the items will be measured as mentioned in Bill of quantity.

The wire shall be supplied in the actual length as per detailed purchase order
The wire shall be dispatched at client’s stores or at site as per detailed instructions given by client at later stage.
The wire shall be loaded from the main vendor’s store and properly stacked as per instruction of client’s local representative. All such labour and transportation charges shall be clearly mentioned in the offer.

The quotes values of parameters shall be within given tolerance for given period of service life.
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