Triad autotransformers are single winding transformers in which the primary coil is a fraction of the entire winding for voltage step-up or the secondary coil is a fraction of the entire winding for voltage step-down. In ordinary double wound power transformers, the primary and secondary are isolated and all the power is transferred by induction. In autotransformers, part of the power is transferred conductively through the windings. Triad autotransformers come in a variety of configurations, case types and output watts (VA) ratings in excess of 2,000 watts. A universal isolation/autotransformer/voltage control model is available with up to a 4,000 output watts rating when operated as an autotransformer.