Neutral Current Calculator: 3-Phase 4-Wire Unbalance Estimator+

neutral current calculator

Compute neutral current from unbalanced 3-phase line-to-neutral loads. Enter Ia, Ib, Ic (A) to get In (A) instantly—plus formula, sample table, and FAQs.

calculate neutral amperage

The 3-phase, 4-wire system is a system where the neutral current is measured as the vector sum of the phase currents. Perfectly balanced loads mean that the neutral has ~0 A; any imbalance introduces a non-zero neutral current, which you can easily determine without trial and error as a direct function of Ia, Ib, and Ic.

Formula & Table Summary:

In = sqrt( Ia^2 + Ib^2 + Ic^2 - Ia*Ib - Ib*Ic - Ic*Ia )

Inputs: Ia, Ib, Ic in amperes (RMS). Output: In in amperes (RMS).

three-phase neutral current

This neutral current calculator gives a rapid approximation of the current in the neutral of a 3-phase 4-wire system where there are unbalanced line-to-neutral loads. Give the phase currents Ia, Ib, and Ic (in amperes), and the tool carries out the vector sum using the 120 electric phase difference to yield the neutral current In. It is perfect to test panelboard loading, neutral size on the feeder, and to diagnose imbalance caused by single-phase loads on a three-phase supply. It assumes fundamental frequency currents, ignoring harmonics: adding non-linear loads, such as switch-mode power supplies, may introduce triplen harmonics that, after summation, yield more current in the neutral than the fundamental result. There is also the central formula, a small input-to-output data table, and exposition of common cases (such as when one phase is unloaded or how equal loading results in approaching zero) in the form of concise, frequently asked questions. An easy pre-check before more thorough load studies or measurements by a clamp meter or power analyzer.

distribution board neutral amps

Ia (A)	Ib (A)	Ic (A)	In (A)
20	20	20	0.00
30	10	10	20.00
25	18	12	9.00
40	0	0	40.00
16	22	19	7.75

Frequently Asked Questions - neutral current calculator:

What is neutral current in a 3-phase, 4-wire system?

It is the vector sum of the three phase currents; imbalance creates a non-zero current in the neutral conductor.

How do I calculate neutral current from Ia, Ib, Ic?

Use In = sqrt(Ia^2+Ib^2+Ic^2 - Ia*Ib - Ib*Ic - Ic*Ia).

Why is neutral current zero for balanced loads?

Equal 120°-spaced currents cancel vectorially, resulting in ~0 A in the neutral.

Does voltage matter for this calculator?

Not directly; you input currents. Voltage is implicit if you derived Ia, Ib, Ic from load and LN voltage.

What if one phase is unused?

Set that phase current to 0 A; compute In from the remaining values.

Can neutral current exceed a phase current?

With strong triplen harmonics it can, but at fundamental frequency it’s typically ≤ the largest phase current.

Do harmonics affect neutral current?

Yes. Triplen harmonics add arithmetically in the neutral and can raise In beyond the fundamental-only estimate.

Is this valid for delta systems?

No; delta has no neutral. Use this for 3-phase, 4-wire wye systems with LN loads.

How precise is the result?

It’s exact for fundamental-frequency phasors if phase angles are 120° and inputs are accurate RMS currents.

How can I reduce neutral current?

Balance single-phase loads across phases, limit non-linear loads per phase, and consider harmonic mitigation.

Tags: neutral current calculator three phase neutral current 4 wire neutral current unbalanced load neutral calculate neutral amperage neutral current formula triplen harmonics neutral single phase on three phase distribution board neutral amps neutral sizing calculator