Siemens digital single phase voltage monitoring relays siemens 3ug4631 1aw30 this digital relay has a measurable voltage of 01 to 60v ac and functions as a voltage monitoring relay for single phase ac and dc voltages against a set threshold for overshoot and undershoottypical applications for this device includes protection of plant against destruction due to overvoltage switch on of plant at a defined voltage and higher protection against overloaded supply voltages particularly with ba