Method for monitoring undervoltage of the mains voltage and undervoltage release device

The method involves using a magnet for activating a power switch, and a threshold detection circuit supervising the line supply voltage, by which the hold current of the magnet is reduced at detection of an under-voltage. The threshold detection circuit is supported through a charge capacitor, and is controlled through a timer element. If the period of the timer element elapses, an off signal is provided for the magnet of the power switch at lasting under-voltage. The hold current is reduced on a fraction of the activation current, and the current is reduced during the delay time on a fraction of the hold current, at persistence of the under-voltage condition.