MCBs and RCCBs


In some consumer units there are MCBs (miniature circuit breakers) in place of the usual fuse holders. These don’t have fuses in them: when a fault occurs, the MCB automatically switches off and the MCB switch will be in the off position on the board. Turn the main switch off, press the button or turn the switch on the MCB to on, and turn the main switch back on. If the MCB will not stay on, it means there is a fault on the circuit.


Poor practice with electricity can be fatal. A common fault is to plug a garden appliance into a nearby indoor socket. A long trailing lead from the kitchen to a lawnmower in the garden is dangerous and contravenes IEE Wiring Regulations. A socket supplying mains power to garden tools or outdoor equipment must be protected by an RCCB (Residual Current Circuit Breaker) with a trip rating of 30 milliamps. As soon as a fault occurs, the RCCB switches off the power before anyone using the appliance gets an electric shock. You can protect yourself with an RCCB by installing a socket with a built-in RCCB, by plugging an adapter-type RCCB into a standard 13-amp socket (above right), or by fitting special plugs with RCCBs built-in to attach to the leads of all the power tools used outdoors, or by fitting an RCCB near the consumer unit to protect the entire ring circuit.

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