A relay (10) has contacts (44,46) to control delivery of AC power to a load, and includes a sensor (64) mounted for observing any arc at the relay contacts, and a control circuit (70) which controls the time of subsequent actuation or deactuation of the relay with respect to the AC power supply so that the relay contracts open or close substantially at a zero crossing point of the AC current, so as to minimize relay contact arcing. The sensor and control circuit (70) are mounted within the relay housing (32,34) to make a simple plug-in unit.