Three-phase load balance and neutral current calculator

Preliminary estimate

Inputs

Calculation note

Neutral current is a fundamental-frequency vector estimate for 4-wire wye screening.

Method

Average A = (A phase + B phase + C phase) / 3

Imbalance percent = largest deviation from average / average x 100

Neutral A = sqrt(A^2 + B^2 + C^2 - AB - BC - CA)

MoreLess

Formula variables

  • A, B, and C are measured or entered phase currents.
  • Line voltage is used only for the average-current kVA context.
  • Review threshold is the user-selected imbalance percent used for the result flag.
  • Neutral current is shown for 4-wire wye screening and is not a harmonic study.

Assumptions

  • Phase current imbalance is the largest phase deviation from average divided by average current.
  • Neutral current is estimated from three phase currents 120 electrical degrees apart for 4-wire wye screening.
  • The calculator does not evaluate harmonics, triplen current, transformer heating, motor derating, or equipment limits.
  • Use measured readings, load tracing, and qualified review before changing circuits or panel schedules.

Examples

208Y/120 V panel readings. Readings of 88 A, 72 A, and 80 A average 80 A with 10 percent imbalance and about 13.86 A neutral current by vector estimate.

Balancing workflow. Use the highest and lowest phase labels to decide which loads are worth tracing before moving circuits.