Three-phase • RMS • Line-to-line
Three-Phase Voltage Unbalance Calculator
Enter simultaneous RMS line-to-line voltages. The calculator applies the NEMA maximum-deviation method and shows the complete calculation.
Step 2
Calculation result
Enter all three voltages to see the unbalance calculation.
Voltage unbalance
——- Average voltage, Vavg
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- R-Y deviation
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- Y-B deviation
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- B-R deviation
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- Maximum deviation
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100 × Dmax ÷ Vavg—Method
1. Vavg = (R-Y + Y-B + B-R) ÷ 3.
2. Find each absolute deviation from Vavg.
3. Voltage unbalance % = 100 × maximum deviation ÷ Vavg.
Band selection uses the full calculated value, not the displayed rounded percentage.
Reference bands
At or below 1%: NEMA reference for successful rated-load operation of AC polyphase motors, while performance may differ from balanced-voltage operation.
Above 1% to 5%: investigate and follow manufacturer guidance.
Above 5%: DOE guidance reports that NEMA recommends against motor use.
Limits
This result uses only three simultaneous RMS line-to-line voltage values. It does not assess other electrical quantities, harmonics, transient conditions, cause, equipment condition, protection settings, or product suitability.
Use the equipment manufacturer's requirements and applicable electrical standards for decisions. The calculator is not a substitute for qualified electrical assessment.