Reverse Connect Autotransformer

Posted by Dave Nosella on Aug 03, 2022

❓ What is an autotransformer?

Auto-transformers are transformers which have a common primary and secondary winding. Auto-transformers are often small, economical, and efficient. Autotransformers do not provide isolation between windings like an isolation transformer. If the neutral side of the input is not at a ground voltage, neither will the neutral side of the output.

An example of a use of an autotransformer: If a building has a 120/208 V three-phase supply, but 240 V is required for a single motor or load, an auto-transformer can be used to step-up the voltage.

⏪ Can you reverse connect an autotransformer?

Yes. Autotransformers may be fed in reverse to step-up voltage. Supply voltage may be connected to primary terminals marked “H” or secondary terminals marked “X.”

The same autotransformer which can be used to step down voltage, can be used to step up voltage.

(:1f4d6:) What CEC rules discuss autotransformers?

Review Canadian Electrical Code rule 26-266 or Canadian Electrical Code handbook figure 26-12 for additional information on autotransformer safety and regulations.

High voltage or low voltage

Low voltage or high voltage