Miniature circuit breakers (MCBs) are fitted in newer consumer units in place of fuses. They
have the advantage that they can be manually reset without having to replace wire as in the
case of the traditional fuse. The MCBs have either a button or lever that can be flicked to
The MCB tripping is an indication either that the circuit has been overloaded or that a
short circuit has occurred somewhere in the system. Before resetting the MCB it is important to
identify what has caused it to trip. Switch off all the appliances connected to the circuit to
ensure it is not overloading. Now see Identifying a faulty circuit for more details on
finding the problem.
First switch off the main switch on the consumer unit, this is very important. Reset the
MCB by either pushing the button or by flicking the lever.
Finally flick the main switch of the consumer unit back on. If the MCB immediately resets
itself once power is restored, then a fault is still occurring, see Identifying a faulty circuit
to try to identify the fault.