This type of circuit breaker works by comparing the Current going in to an appliance with the current coming out. When an appliance is working correctly all of the current entering the appliance through the live wire is returned to the power supply through the neutral wire. If something goes wrong with the appliance some of the electric current will flow through the earth wire. The amount of current flowing through the neutral wire decreases and now there is a difference between the current entering the appliance through the live wire and the current returned to the power supply through the neutral wire. This difference is called the residual current.

Residual Current Circuit Breaker (RCCB)

residual current circuit breaker (RCCB), is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor. Such an imbalance is sometimes caused by current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit.

A residual current circuit breaker cannot remove all risk of electric shock or fire. In particular, an RCD alone will not detect overload conditions, phase to neutral short circuits or phase-to-phase short circuits.