Three-Phase Neutral Imbalance and Distro
Neutral current estimate, imbalance percent, harmonic-load warning.
Example
You enter
- Phase A current (A) 100
- Phase B current (A) 85
- Phase C current (A) 70
- Harmonic-rich loads (LED dimmers, switching supplies) false
You get
- Neutral current 25.98 A
- Imbalance % 35.29 %
Checked against published worked examples from: IEE-Business.
Details, formula, and sources
Formula or tableThree-phase neutral current (balanced linear loads) I_N = sqrt(I_A² + I_B² + I_C² − I_A·I_B − I_B·I_C − I_A·I_C). Harmonic-load warning: triplen (3rd) harmonic currents add in phase, so the neutral carries three times the per-phase 3rd-harmonic current and can exceed the phase current.
Source and editionIEEE 519 (Standard for Harmonic Control in Electric Power Systems) by name; classical three-phase electrical theory.
Free accessIEEE 519 licensed; principles free in published power-engineering texts and at IEEE-USA outreach.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesI_A, I_B, I_C, harmonic_loads, neutral_A, imbalance_percent
- Linear-load assumption true (closed-form holds; non-linear / triplen-harmonic loads can drive neutral current above the worst phase)IEEE 519 §5