Voltage Unbalance Calculator

Enter three phase voltages to compute % unbalance using common industry definitions. Includes Show Work and share links.

How to Use

  1. Select an input mode (Line-to-Line or Line-to-Neutral).
  2. Enter three measured voltages (e.g., Vab, Vbc, Vca).
  3. Choose units (V or kV) and optional rounding.
  4. Open “Show Work” to see the average, deviations, and formulas.
3-Phase Snapshot
Average, max deviation, and percent unbalance readout.
Avg
—
Max Dev
—
% Unbal
—
Status: —
Phase A Phase B Phase C V1: — V2: — V3: — Overlay intensity increases with higher % unbalance (informational).
Inputs & Settings
Enter three voltages. Results update instantly. Share link is explicit.
Example L-L: Vab. Example L-N: Va.
Example L-L: Vbc. Example L-N: Vb.
Example L-L: Vca. Example L-N: Vc.
Controls display rounding (calcs use full precision).
Show Work (step-by-step)
—
Work is shown in base volts for clarity. Percent unbalance uses: (max deviation ÷ average) × 100.

Reference

Voltage unbalance is a condition where the three phase voltages are not equal. Higher unbalance can increase motor heating and reduce efficiency.

  • Average voltage: Vavg = (V1 + V2 + V3) / 3
  • Max deviation: Vdev = max(|V1−Vavg|, |V2−Vavg|, |V3−Vavg|)
  • % Unbalance (common): % = (Vdev / Vavg) × 100

Note: Different standards may define unbalance differently. This tool includes the most commonly used “max deviation from average” percent form.

FAQ

Should I use line-to-line or line-to-neutral readings?

Use the same type you measured. For typical motor checks, line-to-line readings are common in the field.

What if one reading is missing?

This calculator needs three voltages. If you only have two, re-measure or verify metering.

Is this the same as current unbalance?

No. Current unbalance can be larger than voltage unbalance depending on the load and motor characteristics.

Does this tool diagnose the cause?

No. It quantifies the imbalance. Causes can include utility supply issues, loose connections, single-phasing, or unbalanced loads.

Tool Info

Last updated:

Updates may include improved definitions, validation messages, and edge-case handling.