Miniature circuit breaker

Normally described by abbreviation MCB.

A switching device used in the UK in electrical power distribution. It consists of a switch to turn power on and off which is connected to an automatic overcurrent detector. If the specified current is exceeded then the switch is turned off automatically.

Each device incorporates two switch off mechanisms. Internal heating caused by the current flowing will trip the MCB if the current is excessive. A very large current will initiate an electro-mechanical switch off if a threshold is exceeded.

MCB are normally supplied to a nearly standardised design in a range of standard current ratings and operating types. Current devices normally encountered are types B,C and D.

Normally several MCB will be mounted in one Consumer Unit to individually control all the circuits in one property.