Voltage display, when the connection to the three phases and the neutral conductor is established, the green LEDs of the phases L1, L2 and L3 light up, if only two phases are connected, e.g. L1 and L3, the corresponding LEDs light up, even if the neutral conductor N is missing, can be used as a voltage return indicator in systems with manual mains emergency switchover operation, large operating voltage range 85-690 V AC/DC, single-phase application, or DC application possible