How to calculate Voltage Unbalance?

Voltage Unbalance Calculator

Last Updated on March 13, 2021 by Krunal Shah

Voltage unbalance can lead to failure of motors so, it is important to know voltage unbalance. It should be within limits.

This is the Voltage Unbalance Calculator as per NEMA MG-1- 2016. You can calculate voltage unbalance at the motor terminals.


How to use the calculator?

  • First note down the Line-Line voltage i.e. RY, YB, and BR at the motor terminal with the help of a multimeter.
  • Enter those values in the calculator.

That’s it! Rest part calculator would do. Remember that as per NEMA MG-1-2016 the percentage voltage drop should not exceed more than 1% at the motor terminals.

How to calculate Voltage Unbalance?

There is simple math in Voltage Unbalance Calculation. What you have to do is –

  • Take out the average of all the line-line voltage.
  • Determine the maximum deviation of voltage.
  • Divide it by average value.
  • Multiply the value with 100 to get final result in percentage.

% Voltage Unbalance = (Maximum deviation from average voltage / Average Value) X 100

Example: For example, if the measuring line voltages are 415, 420, and 425 volts the average voltage is (415+411+410 = 1236 / 3 = 412). The maximum deviation from average voltage is 3 (412-415=[3]). The voltage unbalance is 0.73%. So here, the voltage unbalance is within the limit as per NEMA Standard.


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