Neutral & Grounded Conductor Sizing

Size feeder and service neutral conductors with 70% unbalance reduction (>200A), range/dryer derates, and harmonic rules per NEC 2026 §120.61.

NEC edition

Inputs

A
A
A

Subject to 0% reduction per §120.61(C)

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⚡ Test your knowledge
NEC Article 220 was renumbered in the 2026 code cycle. What is the new article number?
  • A. Art. 100
  • B. Art. 120
  • C. Art. 200
  • D. Art. 230
💡 NEC 2026 renumbered Article 220 (Branch-Circuit, Feeder, and Service Calculations) to Article 120.
Energy Management Systems were moved from Article 750 to which article in NEC 2026?
  • A. Art. 100
  • B. Art. 125
  • C. Art. 130
  • D. Art. 150
💡 NEC 2026 moved Energy Management Systems from Article 750 to Article 130.
Which NEC standard size overcurrent device comes after 90A?
  • A. 95A
  • B. 100A
  • C. 110A
  • D. 105A
💡 Per NEC §240.6(A), the standard sizes are …90, 100, 110, 125… There is no 95A standard size.

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How it works & the NEC rules behind it

Under NEC 2026 Article 120.61 (formerly NEC 2023 Article 220.61), the neutral conductor must be sized to carry the maximum calculated unbalanced load between any one ungrounded conductor and the neutral conductor.

Key Neutral Sizing Rules & Reductions:

  • 1. Basic Neutral Load (§120.61(A)): Sized for all 120V line-to-neutral connected loads (general lighting, receptacles, small appliances). 240V/208V line-to-line pure loads (water heaters, standard EV chargers, AC compressors) draw zero neutral current!
  • 2. Cooking & Dryer 70% Reduction (§120.61(B)(1)): Electric ranges and clothes dryers are permitted a 70% demand factor for the neutral calculation.
  • 3. 200-Amp 70% Feeder Reduction (§120.61(B)(2)): For large feeders and services:
    Neutral Amps = First 200A @ 100% + [Remainder over 200A × 70%].
  • 4. Non-Linear Harmonic Loads (§120.61(C)): There shall be NO reduction in neutral size for the portion of the load consisting of non-linear loads (LED drivers, servers, variable frequency drives) because triplen harmonics add directly in the neutral!
  • 5. Minimum Service Grounded Conductor (§250.24(D)): Regardless of load, the neutral conductor for a service cannot be smaller than the required grounding electrode conductor / supply-side bonding jumper from NEC Table 250.102(C)(1) based on the service phase conductor size.

Formulas & equations

Linear Neutral Amps = First 200A + [0.70 × (Unbalanced Amps − 200A)] (§120.61(B)(2)) Total Calculated Neutral = Linear Reduced Amps + (1.00 × Non-Linear Harmonic Amps) Min Service Neutral Size ≥ NEC Table 250.102(C)(1) Grounded Conductor Size

NEC reference table

Phase Conductor Size Service Amp Rating Max Unbalance (Amps) Reduced Neutral Amps (70% >200A) Minimum Cu Neutral Conductor
#2/0 AWG Cu200 A200 A200.0 A (100%)#2/0 AWG Cu (Full Size)
350 kcmil Cu300 A300 A200 + (100 × 0.7) = 270.0 A300 kcmil Cu
500 kcmil Cu400 A400 A200 + (200 × 0.7) = 340.0 A400 kcmil Cu (or #1/0 min)
2 × 350 kcmil Cu600 A600 A200 + (400 × 0.7) = 480.0 A2 × 250 kcmil Cu
2 × 500 kcmil Cu800 A800 A200 + (600 × 0.7) = 620.0 A2 × 350 kcmil Cu

Worked example, step by step

Example: Sizing Neutral for a 400A Commercial Building Service

Given: 400A 120/208V Service, 320A total line-to-neutral load (comprising 220A linear lighting/receptacles and 100A non-linear computer servers).

  • 1. Separate Loads: 220A linear load, 100A non-linear harmonic load.
  • 2. Apply 70% Reduction to Linear Portion: First 200A @ 100% = 200A. Remainder (20A) × 70% = 14A. Linear neutral = 214.0 Amps.
  • 3. Add Non-Linear Load (No Reduction per §120.61(C)): 214A + 100A = 314.0 Amps total neutral load.
  • 4. Wire Sizing: 314A @ 75°C Copper requires 400 kcmil Copper (rated 335A).
  • 5. Minimum Grounded Conductor Check (§250.24(D)): Phase conductors are 500 kcmil → Table 250.102(C)(1) requires min #1/0 AWG Cu. 400 kcmil easily satisfies this.

Frequently asked questions

EV chargers and standard central air conditioners / heat pumps operate at 240V or 208V line-to-line without utilizing a neutral conductor. Therefore, no neutral current is drawn, and on dedicated branch circuits, a neutral conductor is not even required.

Under NEC §120.61(C) / §220.61(C), non-linear loads like computers, electronic power supplies, and LED drivers draw non-sinusoidal currents rich in 3rd, 9th, and 15th harmonics. These triplen harmonics do not cancel in 3-phase neutrals; they add together arithmetically in phase, often making the neutral current exceed the phase current!

For a 200A service with 200A-rated ungrounded (hot) conductors, the neutral is sized from Table 250.102(C)(1) based on the largest ungrounded conductor — commonly 2/0 AWG copper or 4/0 AWG aluminum for a 200A service — then reduced further by the 70% demand factor of §120.61(B) where it applies. Enter your service size above for the exact minimum.

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