Neutral Current Calculator – 3-Phase Load Balancing (Per-Phase & Neutral)

Single-phase loads spread across the three phases of an LV system should be balanced so no phase is overloaded and the neutral current stays low. This calculator checks the per-phase currents and the resulting neutral current from your load distribution, and flags the imbalance, following NEC.

When loads are unequal, the phase carrying the most current runs hottest and the neutral carries the vector difference of the phase currents - which can be significant, and with harmonic-rich loads even exceed a phase current. Good practice keeps phase imbalance within about 10-20% by redistributing single-phase circuits across the phases at the distribution board.

Example: Phase currents of 80 A, 60 A and 40 A give an average of 60 A, so the imbalance is (80−60)/60 = 33% - too high. The neutral current is √(80²+60²+40² − 80·60 − 60·40 − 40·80) = √3600 ≈ 35 A. Redistributing circuits to even the phases reduces both the hottest-phase loading and the neutral current.

Effects of phase imbalance and target limits:

Why Balance Matters

Imbalance overloads the heaviest phase, increases losses, raises the neutral current and can trip protection or overheat the neutral conductor. With single-phase non-linear loads (IT, LED lighting), triplen harmonics add in the neutral, so it may need to be full-sized or oversized. Distribute single-phase circuits evenly across phases when wiring the distribution board.

Formula assumes linear loads at similar power factor; harmonics increase the actual neutral current.