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Frequently Asked Questions

This section is for informational purposes only and should not be used as a design tool or to generate technical specifications. For further details, please contact CTI and discuss with a representative for clarification. Search for terms or questions by entering words or phrases in the text box and clicking Search, by selecting a category from the drop-down list and clicking Show. Then simply click on the linked term or question below.

Question: What is an AutoTransformer?

Answer: An autotransformer has its primary and secondary connected to each other electrically. A portion of the energy in an autotransformer 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 autotransformers. Where the use of autotransformers 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 autotransformer. Autotransformers are most practical where a small percentage of voltage raising or lowering is required and isolation between the two circuits is not required. Autotransformers can be single phase or three phase. In neither case is any isolation provided.

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