The EUW 3 supervises three-phase networks on under and overvoltage, in which both switching points can be independently adjusted by each other. Overranging has to be avoided. The supervision is separately carried out for every phase so that the actual asymmetry or even phase failure is recognized. In addition direction of rotation (phase sequence) and neutral wire break is monitored. Every error is shown by the corresponding red LED lighting up. In the normal operation the output relay is pulled on and the power light (green LED) lights up. In the fault case 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 the separately adjustable response and drop-out delays, short mains dips or asymmetries during switch-on processes can be deliberately ignored.