Page 131 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Distribution board system: This is the most commonly used system. This system enables the appliances
connected to the system to have the same voltage. The main switch is connected to the distribution board
through suitable cables. The distribution board has a number of fuses depending upon the number of circuits
required in the installation, and the phase and neutral cable of each phase are taken from the distribution board
(Fig 4).

Fig 4

As each circuit can have power up to 800 watt, the phase wire which is taken from the circuit fuse of the distribu-
tion board is looped to the other light switches or fan switches of the same circuit by any one of the following ways.

No joint is allowed in the cable route except in switches, ceiling roses and joint boxes.
a Looping out from switch and ceiling rose: Fig 5 shows the simple looping in method which is commonly
employed. The phase wire which is connected to the terminals of the switch is looped out to the next switch
and so on, whereas the neutral wires are looped together from ceiling roses (Fig 5). Cable consumed in this
system is very high.
b Looping out from switch: This system employs special switches having two terminals and one connector
(Fig 6). Both the phase and neutral cables are taken to the switch for looping the cables. As these acces-
sories are not commonly manufactured in India such a system is not used.

Fig 5 Fig 6

c Looping out from 3-plate Ceiling roses: In this type of system, three terminal ceiling roses need to be used.
As this system uses less cables when compared to (a), this system is in use in some parts of India. (Fig 7)

d Looping out with junction box: In this system a pair of conductors from the distribution board is brought to
the junction box and tappings are taken to switches, two plate ceiling roses as well as other points from the
junction box. This method may be economical for lodges where a row of rooms are constructed on either side
of a common corridor. (Fig 8)

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CITS : Power - Electrician & Wireman - Lesson 20-25