Circuit Breaker, an electric switch designed to break (open) an electric circuit automatically when the circuit is subjected to abnormal conditions. Once the problem in the electric circuit is corrected, a circuit breaker can simply be reset, unlike a fuse, which must be replaced.

A circuit breaker operates by separating two electrical contacts. In a typical home circuit breaker, the contacts are pulled apart by a spring-loaded lever when a catch restraining the lever is released. The catch can be released by either a thermal or an electromagnetic element. The thermal element consists of a bimetallic strip that bends as it is heated. The bending that results from overheating in the circuit, as when too much electricity is being drawn from it, is sufficient to release the catch. The electromagnetic element releases the catch by means of the magnetic force that arises when there is a surge of current through the element. Such a surge will occur with a short circuit.