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Electromagnetism

How does a Circuit Breaker Work?

This page describes a simple circuit breaker. See the
next page for the residual current circuit breaker.

The circuit breaker acts as a safety device in the same way
as a fuse. Circuit breakers that  are used at the distribution
board in houses are called MCBs (miniature circuit breakers).
The distribution board is also called the consumer unit.
The MCBs disconnect the supply if too large a current flows.
The picture below shows a simple circuit breaker.

When the live wire carries the usual operating current, the
electromagnet is not strong enough to separate the contacts.
If something goes wrong with the appliance and a
large current flows, the electromagnet will pull hard enough
to separate the contacts and break the circuit.
The spring then keeps the contacts apart.

After the fault is repaired, the contacts can be
pushed back together by
lifting a switch on the outside of the circuit breaker.

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