Autotransformers are used where it is not a requirement to galvanically isolate the appliance from the mains. This is a type of transformer in which a common coil, called a tap, is used for both the primary and secondary windings. Therefore, the secondary winding is essentially eliminated, leaving only a single winding with taps.

They are used to power machines and for voltage conversion without galvanic isolation from the mains. The main advantage of autotransformers is less weight and lower price.