Residual Current Circuit Breaker is meant for protection from earth faults and associated risk to human life such as electrical shocks.
The underlying fundamental principle behind operation of RCCB is that in ideal situations the current flowing into the circuit through live (hot) wire should be same as the returning current from the neutral.
In case of an earth fault, the current finds a passage to earth through accidental means (such as accidental contact with an open wire etc.). As a result the returning current from neutral is reduced. This differential in the current is also known as “Residual Current”.
Residual Current Circuit Breaker is designed such way that it continuously senses and compares for difference (residual current value) in current values between the live and neutral wires. Any small change in the current value on account of such event would trigger the RCCB to trip off the circuit.