The winding of an autotransformer is done on the same coil for each phase. By design, the auto transformer is an economical solution and offers more compact dimensions. Autotransformer are used in applications that don’t require a neutral on the secondary phase. It is a reliable and acceptable power source for heating, air conditioning etc … Just like our other transformers, this one can be installed both indoors and outdoors.
Schematic of connecting an autotransformer