Monitoring of direct or alternating voltages in live systems. If the set values are exceeded or not reached, this is indicated and a switching process is triggered. The integrated 7-segment display provides information about the causes of the error. The type of voltage to be measured (AC or DC), two measuring ranges, an upper and a lower threshold value, the response delay and the error memory (on or off) can be set using a manual input on the device. Errors can be acknowledged directly on the device or via an external contact. Connection with screw terminals