Neutral Current Estimator — Calculate Current From Imbalanced Three-Phase Loads
Estimate the fundamental-frequency neutral current created by unequal single-phase loads on phases A, B and C, then compare the neutral result with the phase-current range.
Phase load currents
Why imbalanced phase loads produce neutral current
In a balanced three-phase four-wire system, the fundamental currents can cancel in the neutral because their vector sum is near zero. When the phase currents differ, that cancellation is incomplete.
The vector relationship
For three fundamental phase currents treated as 120° apart, neutral-current magnitude can be estimated from the three current magnitudes without manually drawing a phasor diagram.
Worked example
At 40 A, 25 A and 55 A, the estimated neutral current is approximately 26.5 A under the fundamental-frequency model.
Why nonlinear loads matter
Electronic equipment can introduce harmonic currents. Those components can behave differently from the fundamental current and may require a dedicated harmonic assessment.
Limitations
The result is an estimator, not a field measurement. Actual current should be checked with suitable test equipment when neutral loading is important.
Frequently asked questions
Does perfectly equal phase current produce zero neutral current?
Under the fundamental 120° model, yes.
Can neutral current exceed one phase current?
It can under some combinations of unequal phase magnitudes, especially when the phase currents have very different values.
Does the tool include harmonics?
No. It estimates the fundamental component only.