circuit breaker

Switching device designed to protect an electric circuit from overloads such as excessive current flows and voltage failures. It has the same action as a fuse, and many houses now have a circuit breaker between the incoming mains supply and the domestic circuits. Circuit breakers usually work by means of magnetic-type relays or solenoids. Those at electricity-generating stations have to be specially designed to prevent dangerous arcing (the release of luminous discharge) when the high-voltage supply is switched off. They may use an air blast or oil immersion to quench the arc.

When a current exceeds a fixed limit as it flows through the magnetic coil of a circuit breaker, a triggering mechanism is released, pulling the contacts apart and opening the circuit, thus preventing any more current flowing. Circuit breakers have many advantages; for example, they are fast acting, can be adjusted to operate at different current values, and can be easily reset.