For the protection of human body from the electric shock protective device like fuse or MCB are used. But generally this device are incapable of measuring small current flowing in human body, so requirement is to have a device which can sense small current and cut-off the supply instantly. The device used for this purpose is known as Earth Leakage Circuit Breaker (ELCB).
Working of ELCB
It is current operated device designed to operate when a leakage current exceeds the predefined value. It consists of a operating coil and a trip mechanism which operated the circuit when required. The coil is supplied through 1-ะค supply so current in phase & neutral wire will be same.
This current will produce flux linkages same in magnitude but of opposite direction. This will result zero net flux in tripping coil of relay. When fault or leakage current exceeds the limit higher current will flow in phase conductor than neutral current. Resultant flux now is out of balance in tripping coil of relay. Difference of flux will induce emf in the coil which opens the contact of ELCB and isolate the circuit from the supply.
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