Current Unbalance Calculator — 3-Phase…

Phase-current diagnostic
Phase	Current	Deviation from average
Phase A	165.8 A	4.1 A
Phase B	152.7 A	9 A
Phase C	166.6 A	4.9 A

Three phase-current maximum-deviation model

Turn three same-condition phase-current readings into a transparent imbalance check. MAXScanner calculates average current, every phase deviation, the worst phase, full spread and percent current unbalance without pretending that current unbalance and voltage unbalance are interchangeable.

How to use this calculator

Measure Ia, Ib and Ic at the same location and representative operating condition with the same RMS method.

Enter the three phase currents in amperes and, if useful, your project, relay or equipment review limit.

Read the average, maximum deviation, worst phase and percent unbalance together; the percentage alone does not identify the cause.

Compare current and voltage readings separately when troubleshooting a motor or three-phase load because the two unbalance percentages are different measurements.

Investigate load distribution, supply voltage, connections, fuses, contactors, motor condition and measurement quality as appropriate before changing protection settings.

Where people use it

•Comparing three motor phase currents during commissioning or preventive maintenance.
•Quantifying whether one phase is carrying materially more or less current than the three-phase average.
•Recording before/after current balance when correcting unequal loading or connection problems.
•Applying a project-specific review limit without hard-coding a universal trip or derating rule.

Example: 165.8 A, 152.7 A and 166.6 A

Average = 161.70 A. The absolute deviations are 4.10 A, 9.00 A and 4.90 A. Maximum deviation = 9.00 A, so current unbalance = 9.00 ÷ 161.70 × 100 ≈ 5.566%.

A screening result is not a root-cause diagnosis or universal trip setting

•Use three currents measured under the same operating condition. Mixing readings from different load states makes the comparison misleading.
•This calculator uses the maximum-deviation-from-average method. A relay, meter, specification or standard may define or process unbalance differently; follow that required method when compliance matters.
•Do not infer voltage unbalance from current unbalance or vice versa. Motor impedance, loading and supply conditions can amplify or reshape current response.
•The editable limit is a screening input, not a universal protection setting, trip threshold or motor derating instruction.
•A current imbalance result does not by itself diagnose loose connections, winding faults, single phasing, harmonics, CT errors or unequal mechanical loading.

Frequently asked questions

How do I calculate three-phase current unbalance?+

Average Ia, Ib and Ic, find each absolute deviation from that average, take the largest deviation, divide it by the average and multiply by 100.

Is current unbalance the same as voltage unbalance?+

No. They can use a similar maximum-deviation calculation, but they describe different measured quantities and can differ greatly on the same motor or feeder.

Which phase is the worst phase?+

This calculator identifies the phase current with the largest absolute difference from the three-current average. That is a diagnostic pointer, not a root-cause diagnosis.

Can I use only two phase-current readings?+

No. The three-phase average and maximum deviation require all three comparable phase-current readings.

What current-unbalance limit should I enter?+

Use the limit required by the equipment manufacturer, protection relay philosophy, commissioning procedure or applicable specification. The calculator deliberately does not invent one universal limit.

Does a high result prove a motor winding fault?+

No. Unequal supply voltage, load conditions, connections, protection devices, measurement errors and motor faults are among several possible causes; investigate the system rather than diagnosing from one percentage.

Semantic next steps

Continue the calculation

These links move to a different input, formula or project stage rather than a keyword variation of this page.