The green LED lights up when the supply voltage is applied. If each phase voltage , exceeds 195 V (US1) or exceeds the preset threshold (US2) with respect to the neutral conductor, including the hysteresis when the device is switched on, the relay , immediately switches to the operating position. The yellow LED lights up. If at least one phase voltage , falls below the threshold, the relay returns to its normal position and the yellow , LED goes out. If phase 2 also fails, the green LED also goes out., The neutral conductor must be connected!
