Undervoltage monitoring in three-phase networks (each phase against neutral conductor) with a fixed threshold value, fixed hysteresis and integrated test button. It was specially developed for emergency lighting systems in accordance with DIN VDE 0108. The device can also be used to monitor a single phase. All unused inputs must be connected to the connected phase. If there is a reverse voltage caused by the consumer that is greater than the set threshold value, no error message is issued. Good message: Relay is energized (contacts 11-14 and 21-24 closed), LED is off. Fault message: Relay is de-energized (contacts 11-14 and 21-24 open), LED is on. Press button: Relay de-energizes (contacts 11-14 and 21-24 open), LED goes on. Connection with screw terminals