Friday, April 26, 2019


Phase wise Load Distribution may possibly during Final DB (Distribution Board) wiring. Equally load distribution in final DB or physically load connection to an electrical circuit is important to keep the load balanced in each of three phases.

Importance of Load Distribution in Final DB

3 phase Final Distribution Board Wiring DiagramAll loads of a premises become connected in electrically through final DB. Equally distributing the load on phase Read, Yellow and Blue; it’s promising better performance of others accessories like protective devices RCD, Circuit Breaker, switches, fusses and cables etc.

RCD for Earth Leakage Protection

Earth Leakage: Electricity is carried by conductors that are supported above the earth or inside the earth but are electrically isolated by insulators which prevent the electricity from neutralizing itself as it would if it shorted to earth. However, there is some very small leakage across these insulators, especially aerial insulators during wet or humid conditions. This is called earth leakage.

RCD for three phase system should have a residual current device (RCD-TP) of sensitivity not exceeding 100 mA. If there is no three phase load in the installation, it is better to use three units (RCD-SP) of single phase RCCBs be installed. This will reduce the interruption when single phase fault occurs.

Properly rated Residual Current Devices (RCD) must be used for protection from earth leakage currents to prevent electric shocks. For power circuit RCD sensitivity should be 30mA, for sensitive load like water heater RCD sensitivity should be 10mA.

Any place of public entertainment, children school, where the floor is likely to be wet or where the wall or enclosure is of low electrical resistance, protection against earth leakage current must be provided by a RCD of sensitivity 10mA.

Any hand-held equipment, apparatus or appliance installation must ensure protection against earth leakage current provided by a RCD of sensitivity 30mA.


Main and Earth Conductor and Accessories

For light circuit load should keep within 1800 watts, if contactor control is use for lighting circuits, loading may be increased to 7 KW per circuit. Both of main and earth conductor should be same sizes, normally used sizes are 1.5 & 2.5 sqmm cable.

For connection between the ceiling rose and lamp holders for pendant type light fittings should be used heat resisting flexible cords, this cords may insulated with butyl rubber, EP, rubber, silicone rubber or glass fiber.

Typically used Circuit Breaker (CB) capacity for final circuit is 6A, 10A, 16A etc.

Every domestic wiring installation need final DB wiring with load distribution, ensuring control and protection separating/isolating and switching together with the protection of the system.


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