Earth Leakage Circuit Breaker(ELCB) - Construction and Working

Touching the live wire of a working circuit, playing with the socket-outlet installed close to the floor, etc. are common habits of small innocent children.

Not only children, but even elderly persons can get an electric shock from faulty electric appliances like iron, mixer etc. because one is unable to see the leakage current with the human eye.

This electric shock can prove fatal for human beings and can also result in fire, Devices like fuses and circuit breakers are there, which provide protection against overloads and short-circuits. However, these devices are incapable of detecting the extremely small currents which pass through the human body
and produce electric shock.

So what is required now is a protective device which can sense the extremely small current magnitudes and if the leakage current exceeds such small values, will cut off the electric supply instantly.

The Earth Leakage Circuit Breaker (ELCB) is one such device that senses the extremely small leakage currents and thus prevents death, injury, or fire arising from the electric shocks. The device also called a Residual Current Circuit Breaker (RCCB) cuts off the supply before any real danger arises.

The ELCB or the RCCB operate very quickly with extremely small leakage currents i.e. the time in which they operate is far less as compared to that of the fuse or the MCB. These breakers are extensively used in residential, commercial, and industrial premises.

Construction & Working of an ELCB:
The ELCB consists of an operating coil and a trip mechanism which in turn trips the supply to the circuit. 

It will operate if a live terminal or conductor is touched by an earthed object or person provided the leakage current exceeds the rated operating current of the ELCB.

The construction of an ELCB is as under:
The phase and neutral wires of the circuit being protected are led through one winding of a transformer. 

A second winding controls the tripping mechanism. Under normal conditions, when there is no leakage current the tripping mechanism is not energized and the relay contacts are kept closed using a spring mechanism.

When the earth leakage occurs from either the phase or the neutral side of the circuit, the currents are unbalanced by an amount equal to the leakage current and if this current reaches the rated tripping current of the ELCB, the tripping mechanism will operate opening the ELCB contacts.

A test button is included in the ELCB for testing its trip mechanism. This test should be carried out periodically to ensure its satisfactory working. 

The ELCB can be reset manually after its operation. But it cannot be reset, as long as the leakage persists.

The ELCB is provided near the main switchboard to protect the whole of the residence installation from leakage in any circuit or appliance, by switching off the supply.

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