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 (minature circuit breakers). The distribution board is also called the consumer unit. The MCBs disconnect the supply if too large a current flows.
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.
Author : Dr. Colin France