- (600 volts nominal, or less.) A device designed to open and close a circuit by nonautomatic means and to open the circuit automatically on a predetermined overcurrent without injury to itself when properly applied within its rating.
- (Over 600 volts, nominal.) A switching device capable of making, carrying, and breaking currents under normal circuit conditions, and also making, carrying for a specified time, and breaking currents under specified abnormal circuit conditions, such as those of short circuit.
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by current in excess of that which the equipment can safely carry (overcurrent). Its basic function is to interrupt current flow to protect equipment and to prevent fire. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
 A two-pole miniature circuit breaker | |
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Circuit breakers are commonly installed in distribution boards. Apart from its safety purpose, a circuit breaker is also often used as a main switch to manually disconnect ("rack out") and connect ("rack in") electrical power to a whole electrical sub-network.
Circuit breakers are made in varying current ratings, from devices that protect low-current circuits or individual household appliances, to switchgear designed to protect high-voltage circuits feeding an entire city. Any device which protects against excessive current by automatically removing power from a faulty system, such as a circuit breaker or fuse, can be referred to as an over-current protection device (OCPD).
English
Pronunciation
Noun
circuit breaker (plural circuit breakers)
- (electricity) An electrical switch capable of opening and closing an electrical circuit in all operating conditions, including fault situations.
- (electricity) More specifically, a circuit breaker that automatically breaks overcurrent conditions; a type of overcurrent protective device.
- (finance) Synonym of trading curb.
- (chiefly Singapore) Quarantine measures intended to prevent spread of pandemics, especially COVID-19.
- (programming) A design pattern used to detect failures
