METHOD INCORRECT METHODSConduit set

out to clear wall

Conduit

Bend Box buried too deep

The Regulations require that at the switch points the conduit is terminated a box or similar enclosure. When run buried, taking the conduit out to the surface through a bend or a set in the conduit is not appropriate. On the other hand the sunk box shall not be buried too deep leaving a gap between the box and the switch plate.

When conduits are run to switches or other positions on a wall, they are usually run in chases cut into the wall. These chases, which will be filled after the conduits are laid, must be deep enough to allow at least 10 mm of plaster covering the conduit, to avoid plaster cracks appearing in a later stage. Sunk boxes fitted to these conduits should be placed allowing for the plaster cover. These will be applicable to conduits and sunk boxes on ceiling soffit as well.

Conduits for socket-outlets

Socket-outlets near the skirting level shall be preferably be fed from floor above rather than from floor below, in order to avoid traps where moisture could get collected. On reinforced concrete floors conduits have to be laid on shuttering and secured in position before the concrete is poured. Care must be taken while concrete is being poured, because, if not securely fixed, conduit may move out of position or lift and then, once the concrete is set, it will be too late to rectify matters. Whenever conduits are to be buried in cement, special care should be taken to see that the joints are tight. Otherwise liquid cement may enter the conduit and form a solid block inside.

Fig. 29 - Conduit connection to socket outlets at skirting level Junction Box Junction Box

Floor

Floor above Incorrect Method Trap for Moisture

Looping Box Looping Box

Box for S/O Box for S/O _{Floor Below}



Conduits for distribution boards

When surface mounted distribution boards are used with a buried conduit system, the best method to take the cables from the conduits to the DB is to fit an adaptable box in the wall to take the conduits into it. The conduits can be taken out of the plaster and enter the DB direct with a set on the conduits but this method is not recommended. Alternatively adapter boxes can be mounted on top or bottom or both on the DB to take the cables. Adapter box can be mounted partially buried so that the conduit can enter it easily.

Before drawing the cables, the installation of the conduits must be complete and also must be clean and dry. No attempt should be made to wire conduits which are buried in concrete until the building has been dried out and conduits swabbed out to remove any moisture and obstructions which may have entered the conduits. A draw wire with a swab at the end should be drawn through the conduit for this purpose. It is a good practice to keep the open ends of the conduits plugged as soon as they are laid before concreting to prevent any foreign matter entering them.

Wiring

Wiring is carried on each conduit run from draw-in box to draw-in box in sequence usually starting from a mid-point in the conduit system so as to reduce the length of cables which have to be drawn-in. A draw-wire has to be inserted into the conduit run to draw in the cables. It is a good practice to keep a draw-wire drawn inside the conduit whilst it being laid. However, if the number of bends do not exceed the stipulated equivalent of two 90o bends and the length is not excessive, it is not difficult to insert the wire at a later stage. If it is difficult, two wires from either end of conduit run, with small hooks at the ends could be inserted. Once the two ends reach each other wires could be twisted so that the two hooks get entangled and one wire could be pulled out from one end until the draw-wire fed from the other end comes out. Obviously two persons are required to do this operation.

Fig. 30 - Conduit Entries to Surface Mounted Distribution Boards Flush mounted box

Distribution Board Best Method Conduit set-out to enter DB Distribution Board

Not Recommended Recommended Partially sunk Adapter box

Distribution Board

Once the draw-wire is inserted and the conduit is cleaned if necessary, the required number of cables should be tied to one end of the draw-wire. The ends of the cables to be tied must be bared for a distance of about 50 mm and threaded through a loop in the draw wire for this purpose. When drawing in a number of cables, they must be carefully fed in from the sending end whilst one pulls them at the receiving end.

Before drawing in the cables into the conduits they must be run off the reels. If the cables are allowed to spiral off the reels they would become twisted and kinked inside the conduits.

The cables should be fed into the conduits in such a manner as to prevent any cables crossing and also to avoid them being pulled against the sides of the openings of the draw-in boxes. Always some slack has to be left at the draw-in boxes and it has to be ensured that the cables are fed to the conduit in such a way that no twisted cables will be left at the draw-in point. This is particularly applicable when the cables have to be pulled out from one conduit and fed to another connected to the same draw-in box.

Fig. 31 - Method of connecting cables to draw wire

Draw wir e

Cables



This operation needs care and synchronization between the persons who are feeding and pulling. Sometimes a third person may be required to be stationed mid-way to relay messages if the persons at both ends are not within earshot. If the cables are not drawn carefully in this manner, they are almost certain to become crossed and might result in the cables becoming jammed inside the conduit. Also the insulation of the cable is liable to get damaged in the process.

Example

Let us now consider wiring of the two-storied house shown in Fig. 33 as an example. This house has 9 lighting points in the ground floor and 5 in the upper floor. The light in the staircase is to be controlled by two-way switches in both floors. The obvious choice of lighting circuits will be to have one for the ground floor nine lights and another for the five lights in the upper floor. There are four 13A socket-outlets in the kitchen and another sixteen in other areas. Thus the logical distribution of the socket-outlets will be to have one final circuit for the kitchen and to have another for other areas. Allowing another circuit for future expansions the distribution board can consist of five final circuits. Thus the final circuits of the house would be as follows:

Lighting circuits with lamps No. 1 to No. 9 wired using 1 mm2 cable fed through a 5 or 6A MCB

Lighting circuits with lamps No. 10 to No. 14 wired using 1 mm2 cable fed through a 5 or 6A MCB

Four socket-outlets in the kitchen wired using 4 mm2 _{cable in a} radial circuit fed through a 30 or 32A MCB

Other socket-outlets wired using 2.5 mm2 _{cable in a ring circuit} fed through a 30A MCB. (This would be possible only if the floor

area served by the socket-outlets other than the kitchen is not more than 100 m2_).

This will usually be fed from a 30 or 32A DP MCB or an isolator and a 40A DP 30mA RCCB (because 30A RCCB is a non standard unit) using

Fig. 33 - Wiring points in a house

6 mm2 _{cable. (Use of an isolator is not recommended. Actual required capacity} of the main switch need to be determined by estimating the maximum demand considering the equipment to be used in the house.)

Single line diagram

The arrangement can be shown in a single line diagram as in Fig. 34.

Conduit layout

A suitable method of wiring the lighting circuits and connected conduit layout is shown in Fig. 35 and 36. Numbers of cables between respective points are shown in by the number of lines in the Fig. 35 and the number inside the parenthesis in Fig. 36. A three dimensional view of the conduits for the lighting circuits are shown in Fig.37.

Fig. 34 - Single Line Diagram 30 A DP MCB 40 A DP 30 mA LIGHTS 10-14 (6A) 2 x 1 _{LIGHTS 1-9} (6A) 2 x 1 (30A) 2 x 4 Radial

SOCKET OUTLETS IN KITCHEN