The residual current device (RCD) or residual current circuit breaker (RCCB) enables the rapid disconnection of electricity, thereby avoiding prolonged and potentially serious shocks. An RCD device complete with overcurrent protection is called an RCBO, or residual current circuit breaker with overcurrent protection.
The primary functions of RCBOs are to ensure protection against earth fault currents, overload, and short circuit currents. It is recommended that an RCBO be attached to each separate circuit, meaning that a fault in one circuit will not affect the functioning of the others. Such devices allow for disconnection of the circuit for the protection of people and equipment in the event that the current becomes unbalanced. They can be operated exclusively of other overcurrent protective devices within the rated short-circuit capacity.
Design and testing requirements for RCBOs are outlined in the set of standards: IEC/EN 61009: Residual current circuit-breakers with integral overload protection for household and similar uses (RCBO).