What is the maximum allowable voltage imbalance between any leg of a 3-phase power supply?

The maximum allowable voltage imbalance between any leg of a 3-phase power supply is 2%. This ratio is significant because an imbalance in voltage can lead to various operational issues in three-phase motors and equipment, including overheating, reduced efficiency, and even premature failure of components.

A voltage imbalance occurs when the voltages across the three phases of a power supply do not remain proportional. Ideally, in a balanced system, each leg should carry either equal voltage or voltages that differ within a specific limit. Exceeding the 2% imbalance threshold can result in uneven loading, leading to increased currents in the over-volted phases, which subsequently causes excessive heat generation in motors and transformers.

Standards set forth by organizations such as the Institute of Electrical and Electronics Engineers (IEEE) specify this 2% maximum in order to promote safe and reliable operation of electrical equipment. Balancing the voltage across all phases not only ensures optimal performance but also diminishes the risk of damaging electrical systems.