Abstract: The protection of potentially incendiary circuits is achieved by a power system which comprises a power supply connected by power distribution wiring to one or more modules, the one or more modules each comprising an intrinsically safe circuit including a load, a sensor to detect the voltage supplied to the load, and a fast-acting switch arranged, in response to the detection of a decrease in the supplied voltage, to disconnect the load in such manner as to prevent any series break upstream from the switch from becoming incendiary.