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Common Questions About Isolation Transformers and Autotransformers


1. What is the difference between an isolation transformer and an autotransformer?

Whether an isolation transformer or an autotransformer, a transformer typically steps the supply or line voltage coming into the unit up or down to whatever voltage the load or downstream component or circuit requires. While sometimes confused, there is a critical difference between the isolation transformer and the autotransformer:

By definition, the input and output windings of an isolation transformer are separate windings—physically isolated and electrically insulated from each other by distance, an insulation barrier, or both.

An autotransformer, on the other hand, is uniquely designed to accommodate the range of both the available input and required output voltages in a single winding. And because the "common" section of that single winding is shared between the input and output of the unit, there is no physical isolation or electrical insulation between them.


2. Where and why are isolation transformers used?

An autotransformer can be a remarkably efficient and versatile solution, particularly when the ratio of voltage transformation between input and output is low. Advantages of weight and overall size typically yield a lower cost design than an isolation transformer designed to the same electrical parameters.

In contrast, the isolation transformer, by its very nature, affords a degree of electrical safety/protection to people and equipment alike that the autotransformer cannot provide. And, unlike an autotransformer, an isolation transformer can accommodate an electrostatic shield between input and output, which a) prevents electrical noise on the load side from filtering back onto the line side, b) provides an additional degree of isolation between input and output windings, and c) can provide for an electrical path to ground, or protective earthing, in the event of a fault. Isolation transformers, like autotransformers, can be used to create a step up or step down. The isolation transformer can also mitigate potentially damaging effects of poor power quality on sensitive equipment over time.

Our engineering team will help you determine which type—isolation or autotransformer—is best suited to your unique application. Contact us online or call us at 715.627.4367.