Mains monitoring relays are used to monitor voltage and sequence of 1-phase to 3-phase mains supplies. The switching threshold can be adjusted freely in the range 150 to 230 V or can be set to a fixed value of 196 V(DIN VDE). The NKR 5 indicates the status of the phase voltage and sequence with four LEDs. The relay returns to normal operating mode either automatically when the voltage returns or only after it has been acknowledged with an internal or external button.