The EUW 3 monitors three-phase networks on under and overvoltage, in which both switching points can be indepen¬dently adjusted by each other. To recognize asymmetry or even phase failure, the supervision is separately carried out for every phase. In addition the direc-tion of rotation (phase sequence) and neutral wire break is controlled. Every error is shown by the corresponding LED lighting up. However, in the normal operation the output relay is pulled on and the power light (green LED) lights up. In case of a fault as well as at loss of the supply voltage the relay drops off and the operating light goes out. The inserted hysteresis prevents the permanent condition change by varying measuring voltage around a switching point. With adjustable response and release delays, which are separated from each other, short net break downs or asymmetries can be avoided specific on switching on actions.