Abstract: The monitoring device simultaneously senses the voltage at the interconnection points between a plurality of series connected current interrupting devices. When current is interrupted by any one of the devices, the conductivity statuses of all devices are latched and stored until reset in a storage device which provides a signal indicating which of the devices caused current flow to be interrupted. The monitoring device thus detects both intermittent and sustained faults. The monitoring device employs optically isolated digital electronic circuitry for direct interconnection with AC control circuits.