Abstract: A device is disclosed herein for monitoring a power system for the presence of faults thereon which cause leakage currents to ground. The device includes a test impedance and bridge switching means for connecting the test impedance in different combinations to a pair of power lines. A singe test impedance is connected in four different configurations to the power lines in sequence, and this cycle is continuously repeated. Currents are measured for each connection to determine whether or not a leakage or hazard current exists which results from a fault load on one or both power lines. The device includes control means for operating the test impedance switching means, and includes current level detecting means for providing an alarm indication in the event a predetermined hazard current exists.