An RCD, or residual current device, is an electrical safety device that quickly breaks an electrical circuit with leakage current to ground. It is designed to prevent fatal electric shocks if you touch something live, such as a bare wire, and can also provide some protection against electrical fires. RCDs are testable and resettable devices, and they constantly monitor the electric current flowing through one or more circuits they are used to protect. If they detect electricity flowing down an unintended path, such as through a person who has touched a live part, the RCD will switch the circuit off very quickly, significantly reducing the risk of death or serious injury.

RCDs are primarily intended to give protection against the risk of injurious electric shocks and to provide an additional protective measure for insulation faults and fire hazards due to a persistent earth fault current. They do not provide overcurrent protection, which is usually provided by a fuse or a circuit-breaker. RCDs are defined by three main characteristics: the rating in amps, the rated residual operating current of the protective device in amps, known as the IΔn, and the instantaneous trip that occurs or an intentional time delay to permit discrimination. Such devices are called ‘S’ or Special/Selective.

RCDs can help protect you from electric shock in potentially dangerous areas like bathrooms and gardens, and there are various types of RCDs that can be used to make sure you are always as safe as possible. They are reliable and can reduce the risk of electric shock to you and your family, as well as protect your home against the risk of fire caused by faulty wiring or appliances.