Hitachi Energy autotransformers have a single winding with two end terminals and one or more terminals at intermediate tap points or a transformer in which the primary and secondary coils have part or all of their turns in common. The primary voltage is applied across two of the terminals, and the secondary voltage is taken from two terminals, almost always having one terminal in common with the primary voltage.
An autotransformer does not provide electrical isolation between its windings as an ordinary transformer does; if the neutral side of the input is not at ground voltage, the neutral side of the output will not be either.
