A residual current circuit breaker, briefly called RCD circuit breaker, is a residual current protection device that can be found in almost any distribution and is usually connected upstream of overcurrent protection devices, such as circuit breakers. An RCD does not protect the wires from overload or short circuit, as the circuit breaker does, but serves as personal or fire protection. For personal protection, FI circuit breakers with a tripping current of 30 mA are used.