Residual current circuit breaker, diagram. Residual current circuit breakers, RCCBs, are used to protect some circuits. They detect a difference in the current between the live and neutral wires. Any difference can indicate a short circuit or another electrical anomaly, such as current leakage, which can indicate a shock hazard. A difference between currents in the live and neutral wires induces a magnetic field in the core and causes separation of the relay contacts, breaking the circuit.