Abstract: A method and a device for impedance monitoring for a single-phase or multiphase, ungrounded power supply system. The method comprising the following steps: measuring a complex impedance against ground simultaneously for each active conductor using a measuring device; calculating a complex touch current for each active conductor; testing in the computing unit whether the corresponding complex touch current exceeds a settable body-current threshold value; generating a switch signal in the computing unit upon the body-current threshold value being exceeded; and controlling a switch element using the switch signal for shutting off or isolating the power source.