Autotransformer Motor Controller Starter Auto-transformer motor starters are commonly used in reduced-voltage starting applications, especially with large motors. When the motor starts, two contactors pull in. One of these contactors energizes a transformer circuit and the other forces the transformer into a star configuration. The tapped output from the transformer is connected to the motor leads at the start. Watch the video and type down the correct answer in the comments below: An Autotransf