Patent ID: 7468871

Claim:
A residual current device (RCD) for protecting a circuit by tripping in response to an imbalance signal representative of residual current imbalance in the circuit, the RCD tripping the circuit when the imbalance signal exceeds a predetermined threshold rating, wherein the residual current device (RCD) comprises: sense means for generating said imbalance signal; test means for introducing a simulation residual current imbalance into the device so as to increase the imbalance signal; and a processor that monitors the imbalance signal and determines the simulation residual current imbalance required to increase the imbalance signal to a level that corresponds to the predetermined threshold rating so that the sense means senses the sum of any residual current imbalance in the circuit being protected and the simulation residual current imbalance in order to test operation of the residual current device (RCD) against the predetermined threshold rating.