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Voltage Unbalance Calculator — 3-Phase NEMA Method

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Vab line-to-line Measured RMS voltage between phases A and B.Vbc line-to-line Measured RMS voltage between phases B and C.Vca line-to-line Measured RMS voltage between phases C and A.Nominal voltage (optional) Enter 0 to omit the separate nominal-voltage comparison.

Calculated result

1.961% voltage unbalance

Average line voltage: 459 V

Maximum deviation: 9 V (Vca)

Highest-to-lowest spread: 17 V

Above the commonly referenced 1% NEMA motor threshold; investigate the supply/load and consult the motor manufacturer for applicable derating guidance.

Average vs entered nominal: -0.22%

Show the working

1. Average = (460 + 467 + 450) ÷ 3 = 459 V.
2. Absolute deviations = 1, 8, 9 V; maximum = 9 V.
3. NEMA percent voltage unbalance = 9 ÷ 459 × 100 = 1.961%.

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