Abstract: A residual current device (RCD) protects a circuit by tripping in response to an imbalance signal representative of residual current imbalance in the circuit. The RCD trips the circuit when the imbalance signal exceeds a predetermined threshold rating. The RCD includes a sense coil for generating the imbalance signal and a test coil for introducing a simulation residual current imbalance into the device so as to increase the imbalance signal. A processor 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 coil 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 RCD against the predetermined threshold rating.

Abstract: A combined toroid/shunt device for detecting residual current in an electrical installation comprising a plurality of conductors such as a live conductor (2) and a neutral conductor (3) is described. The device comprises a toroid means (1, 4) for detecting an AC residual current within a first range and a plurality of resistive shunts (6a) to (6d) for connection in respective ones of the plurality of conductors. A current detection means (5, 7, 13) responsive to current flowing in each of said shunts for detecting a DC residual current and/or an AC residual current within a second range is described. The first range of AC residual current is an AC residual current resulting from earth leakage or cross-leakage between conductors up to a saturation level at which the toroid or electronic means associated means therewith becomes saturated. The second range includes an AC residual current of said saturation level.