A consumer unit or fusebox is a particular type of distribution board comprising a co-ordinated assembly for the control and distribution of electrical energy, principally in domestic premises. A consumer unit incorporates a manual means of isolation on the incoming circuit(s) – a main switch, and an assembly of one or more fuses, circuit-breakers or residual current devices.
Circuit breakers, fuses and RCDs are protective devices that will interrupt the flow of electrical current if the circuit concerned develops a fault. Instead of a modern unit like the one shown above with circuit breakers and RCDs, some older houses have fuseboxes with rewireable fuses.
Rewireable fuses have a piece of special fuse wire running between two screws. The fuse wire generates heat when a fault current flows through it and it melts when the heat exceeds the acceptable level. The melted fuse breaks the circuit and stops the electricity supply.
A circuit-breaker is an automatic switch fitted to each circuit in the consumer unit which switches off in the event of a short circuit, an overload or a fault to earth on the circuit. It is not usually required to operate very often.
A circuit-breaker is much the same size as a fuseholder, but give more precise protection than cartridge fuses. When they 'blow' or 'trip', they are simply reset instead of needing replacement or rewiring.
A residual current device is a mechanical switching device or association of devices intended to cause the opening of the contacts when the residual current attains a given value under specific conditions, such as under earth fault conditions.
The main switch allows you to turn off the electricity supply to the electrical installation. Note that some electrical installations may have more than one main switch. For example, if your house is heated by electric storage heaters, you will probably have a separate main switch and consumer unit arranged to supply them.
It is important to know where the consumer unit is located and that it is accessible. It is also important that you know where the main switch(es) are in order to turn it (them) off in the event of an emergency.
If your electrical installation includes one or more residual current devices (RCDs), it is important that they are checked regularly. You can do this by following the instruction label, which should be located near the RCD. The label will read as follows:
Information supplied by NICEIC