Voltage Imbalance Check

A small imbalance in the input voltage can result in a considerable amount of heat being generated in the motor windings. An imbalance of only 5%, for example, can increase the winding temperature as much as 50% above the safe level.

The voltage imbalance between any two legs of the supply voltage applied to a three-phase motor must not exceed 2%. Any voltage imbalance of more than 2% must be corrected. Examine all connections, terminals, lugs, etc. as well as the incoming power supply to the building and the distribution panels for the same things.

A voltage imbalance will produce a current imbalance as well. Use the same formula to determine the percentage imbalance. The current imbalance between any two legs must not exceed 10%.

Excerpt from Technical Institute Manual 2 available from the online store at RSES, (Refrigeration Service Engineers Society) the HVACR Training Authority.

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