An RCD (residual current device), has been designed to protect you from fatal electric shocks as it automatically switches off electricity when there is a fault. This potentially life-saving device protects against electrocution in instances where there is a bare wire, over-heating or earth faults.

RCDs are also known as an RCCB (residual-current circuit breaker) in the UK but in the United States and Canada they are referred to as a GFCI (ground fault circuit interrupter).

If RCDs are regularly tested, they are reliable life-saving devices, reducing the risk of electric shock and protecting your home against electrical fires. You can find out more in our complete RCD guide.

How does an RCD work?

An RCD is placed within the circuits it has to protect. By monitoring the electric current, it can quickly detect when a circuit fails and electricity is flowing incorrectly. When the fault is detected, the RCD switches off the circuit so that the person handling the wires comes to no harm.

RCDs are often integrated with a fuse or MCB (miniature circuit breaker) adding protection when there are excessive current causing spikes or surges in the circuit.

Types of RCD

Fixed RCDs: they are installed in a fuse box and are used for both industrial and domestic applications. They protect lots of circuits and provide an excellent level of protection. RCDs located within a consumer power distribution unit are mostly passive. This allows household appliances to re-establish normal operation when the circuit power is restored.
Socket-Outlet RCDs: they provide individual protection to the person who is in contact with the equipment. They can be used in place of a standard socket outlet. Socket-outlet RCDs are either active or passive. They are latching in operation so are not ideal for power tools which do not require a restart when the circuit is restored.
Portable RCDs: they also only provide individual protection to the person who is in contact with the equipment. They plug into any standard socket, and the appliance is then plugged into the RCD. Portable RCDs are mostly active and unlatch when any abnormality is detected. People who use outside power tools would benefit from a portable RCD as their equipment could become dangerous if they were suddenly reactivated.