Automatic Electronic Phase Selector (single-phase automatic throw-over breaker) is designed to supply an industrial/ appliance single phase 220V/50Hz load from three phase four wire mains 3 x 380 + N in order to maintain uninterrupted power supply of essential single-phase loads and protect them against un-allowable voltage variations in the mains. For this purpose, a single-phase load is switched into a three phase circuit. Depending on voltage presence and voltage quality on phases the healthy phase selector will automatically select the optimum phase and promptly switch the single phase load supply to this phase. A phase prioritization is foreseen, i.e. the device restores the supply circuit to the user-selected priority phase after switching to reserve phases and regenerating the voltage on the priority phase.