Residual current devices

A residual current device, RCD, comprising:

• first circuit means for detecting a differential current in a supply to a load indicative of a residual current and providing a fault signal when said residual current exceeds a given threshold,
• an electrical switch having load contacts in the supply to the load, and
• second circuit means responsive to said fault signal persisting beyond a certain duration to disconnect the load from the supply by opening the load contacts,
• the second circuit means issuing intermittent first test pulses during an operative state of the RCD, each first test pulse causing a simulated residual current exceeding said given threshold to flow, and a corresponding fault signal to be provided, for the duration of each first test pulse, the duration of each corresponding fault signal being less than said certain duration so that the load contacts do not open, the second circuit means attempting to force the load contacts to open if a corresponding fault signal is not received in respect of a first test pulse,
• the second circuit means further issuing intermittent second test pulses during the operative state of the RCD at a frequency less than that of the first test pulses, each second test pulse causing a simulated residual current exceeding said threshold to flow, and a corresponding fault signal to be provided, for the duration of each second test pulse, the duration of each corresponding fault signal being greater than said certain duration to allow the load contacts to open, the second circuit means detecting if the load contacts do not open in response to a corresponding fault signal exceeding said certain duration and attempting to force the load contacts to open in response thereto.