Neutral Wire Size Calculator
// SCREEN FEEDER AND BRANCH-CIRCUIT NEUTRAL CONDUCTORS FROM CALCULATED NEUTRAL LOAD, MATERIAL, RUN LENGTH, AND VOLTAGE-DROP TARGET //
Use the system family that produced the calculated neutral load.
Used for the neutral voltage-drop percentage screen.
Enter the phase or feeder load current before neutral demand reduction.
Choose the percentage of load current that applies after your code neutral-load calculation.
Add margin for harmonic-heavy electronic loads when a reduced neutral may be inappropriate.
The tool doubles this distance for neutral voltage-drop resistance math.
A 2% to 3% target is common for planning sensitive branch and feeder circuits.
Using a 100% neutral-load basis on 80.0 A, the calculated neutral current is 80.0 A. With nonlinear margin included, the ampacity screen is 80.0 A.
This is a conductor sizing screen, not a complete NEC neutral-load calculation. Confirm service, feeder, multiwire branch circuit, nonlinear load, and local amendment requirements before reducing a neutral.
- Size the neutral from the calculated maximum unbalanced load or the applicable service and feeder neutral-load method.
- Do not reduce neutrals serving circuits where nonlinear loads, harmonics, or shared neutral rules require a full-sized conductor.
- After ampacity passes, check voltage drop and raceway fill with the complete conductor set.
- Single-phase 120/240 V feeders often use the neutral only for the unbalanced 120 V load.
- Three-phase four-wire systems can carry significant neutral current when line-to-neutral loads are not balanced.
- Electronic power supplies can add triplen harmonic current that does not cancel in the neutral.
Neutral voltage drop is estimated with round-trip resistance because current leaves on an ungrounded conductor and returns on the neutral.
For complete circuit performance, check the phase conductors with the voltage drop calculator as well.
| Size | Ampacity | Resistance | Voltage Drop | Status |
|---|---|---|---|---|
| 14 AWG2.1 mm2 | 20.0 A | 3.07 ohm/kft | 36.8 V (30.70%) | Review |
| 12 AWG3.3 mm2 | 25.0 A | 1.93 ohm/kft | 23.2 V (19.30%) | Review |
| 10 AWG5.3 mm2 | 35.0 A | 1.21 ohm/kft | 14.5 V (12.10%) | Review |
| 8 AWG8.4 mm2 | 50.0 A | 0.764 ohm/kft | 9.17 V (7.64%) | Review |
| 6 AWG13.3 mm2 | 65.0 A | 0.491 ohm/kft | 5.89 V (4.91%) | Review |
| 4 AWG21.1 mm2 | 85.0 A | 0.308 ohm/kft | 3.70 V (3.08%) | Review |
| 3 AWG26.7 mm2 | 100 A | 0.245 ohm/kft | 2.94 V (2.45%) | Pass |
| 2 AWG33.6 mm2 | 115 A | 0.194 ohm/kft | 2.33 V (1.94%) | Pass |
| 1 AWG42.4 mm2 | 130 A | 0.154 ohm/kft | 1.85 V (1.54%) | Pass |
| 1/0 AWG53.5 mm2 | 150 A | 0.122 ohm/kft | 1.46 V (1.22%) | Pass |
| 2/0 AWG67.4 mm2 | 175 A | 0.0967 ohm/kft | 1.16 V (0.97%) | Pass |
| 3/0 AWG85.0 mm2 | 200 A | 0.0766 ohm/kft | 0.92 V (0.77%) | Pass |
| 4/0 AWG107.2 mm2 | 230 A | 0.0608 ohm/kft | 0.73 V (0.61%) | Pass |
| 250 kcmil126.7 mm2 | 255 A | 0.0515 ohm/kft | 0.62 V (0.51%) | Pass |
| 300 kcmil152.0 mm2 | 285 A | 0.0429 ohm/kft | 0.51 V (0.43%) | Pass |
| 350 kcmil177.3 mm2 | 310 A | 0.0367 ohm/kft | 0.44 V (0.37%) | Pass |
| 400 kcmil202.7 mm2 | 335 A | 0.0321 ohm/kft | 0.39 V (0.32%) | Pass |
| 500 kcmil253.3 mm2 | 380 A | 0.0258 ohm/kft | 0.31 V (0.26%) | Pass |
Check the full feeder or branch-circuit voltage drop with phase conductors included.
Review conductor ampacity, temperature rating, and adjustment factors.
Confirm raceway fill after adding phase, neutral, and grounding conductors.
Compare this neutral check against a broader circuit sizing workflow.
Audit the conductor resistance used in voltage-drop planning.
Estimate conductor weight for feeder pulls and material planning.