SAFETY DEVICE TO PREVENT FATAL SHOCK:
A residual-current device (RCD), or residual-current circuit breaker (RCCB), is a safety device that quickly breaks an electrical circuit to protect equipment and to reduce the risk of serious harm from an ongoing electric shock
An RCD is a life-saving device which is designed to prevent you from getting a fatal electric shock if you touch something live, such as a bare wire. It can also provide some protection against electrical fires. RCDs offer a level of personal protection that ordinary fuses and circuit-breakers cannot provide. An RCD is a sensitive safety device that switches off electricity automatically if there is a fault.
An RCD is designed to protect against the risks of electrocution and fire caused by earth faults. For example, if you cut through the cable when mowing the lawn and accidentally touched the exposed live wires or a faulty appliance overheats causing electric current to flow to earth.
An RCD constantly monitors the electric current flowing through one or more circuits it is used to protect. If it detects 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.
Caution: RCD does not offer protection if you touch live (red or brown wire) and neutral (black or blue wire) simultaneously.