What is an auto transformer?
An auto transformer has its primary and secondary connected to each other electrically. A portion of the energy in an auto transformer comes from this connection while the balance comes directly from the supply. Building inspectors often object to auto transformers because they do not isolate one circuit from the other. One ground may be at a considerably higher voltage than the ground in another section of the same circuit. Local inspectors and utility companies should be consulted before installing auto transformers. Where the use of auto transformers is not objectionable, they do represent a considerable saving in price over that of a regular separate winding transformer. This saving varies as the ratio of windings changes. After the ratio of windings reaches approximately 4:1 or 5:1, there is very little economy in using an auto transformer. Auto transformers are most practical where a small percentage of voltage raising or lowering is required and isolation between the two circuit
