Abstract: An apparatus for selectively stepping up/down the voltage applied from an input to any load in an alternating current power system. The apparatus comprising an auto transformer having a series winding with a plurality taps for the selection of different output load voltages and a common winding. The series winding being connected between said input of the alternating current power system and said common winding. The common winding being connected between the series winding and common or neutral terminal of an alternating current power system. The load is being connected between one tap of the series winding and the common or neutral terminal of the alternating current power system.