What is an auto transformer and how is it different?
Auto transformers have their primary and secondary windings connected to each other electrically. The grounds of these transformers are not isolated from one circuit to the other. One ground may be at a considerably higher voltage than the ground in another section of the same circuit. For this reason local inspectors and utility companies should be consulted before installing auto transformers. Where appropriate, the auto transformer represents a cost savings over a two winding transformer. This savings varies as the ratio of windings change. After ratio windings reach approximately 4:1 or 5:1 there is little economy in using an auto transformer. Auto transformers can be single or three phase and are best used where a small percentage of voltage raising or lowering is required and isolation between two circuits is not required.
