These devices functioning by measuring the current going into and coming out of an electric circuit. In the ideal situation, both the currents are the same. When a current leaks, either as an electric shock to a person or through an earth fault, the current which comes out of the device is lesser than the current entering the device (this difference is called the residual current). The device senses this and trips the circuit.
These devices are alternatively known as ground fault interruptors or appliance leakage current interruptor.
Industrial versions of the RCCBs are sometimes used for situations other than electrocution. These have a higher tripping threshold of the order of 500mA.
RCCBs can also be used for three phase applications.
Residual Current circuit breakers usually have an inbuilt test function to ensure that the device is functioning. This test button needs to be operated once a month to ensure a state of readiness.
Residual current circuit breakers should not be used as a substitute for ordinary circuit breakers as they will not operate in the event of an overload or a short-circuit. This is because the residual current does not rise in these events. Therefore, an independent overcurrent protection needs to be given.