13.3 Neutral Load and Service Sizing

Why This Matters for the TX Journeyman Exam

The final step of a dwelling service calculation ties together every load category from Sections 13.1 and 13.2, adds the neutral-load rules from NEC 220.61, and lands on a service-entrance conductor size from Table 310.12(A). The exam typically asks you to carry a full calculation through to the conductor size, so every arithmetic step must be right. This section references Chapter 4 for the service-disconnect rules (230.70–230.79) and Chapter 7 for OCPD selection (240.6(A)) — it does not re-teach them.

NEC 220.61 — Feeder or Service Neutral Load

NEC 220.61 defines the neutral load as the maximum unbalanced load: the greatest load between the neutral conductor and any one ungrounded conductor. On a 120/240 V single-phase, 3-wire service, 240 V loads (line-to-line) do not contribute to the neutral; only 120 V loads (line-to-neutral) do.

220.61(B) — Permitted Neutral Demand Factors

There is no separate "Table 220.61" in the 2023 NEC — the reductions are in 220.61(B) as text:

The practical result for a single-family dwelling: the first 200 A of unbalanced neutral load is taken at 100%, and the portion above 200 A is taken at 70%.

220.61(C) — Prohibited Reductions

No neutral reduction is permitted for:

• Any portion of a 3-wire circuit consisting of 2 ungrounded conductors and the neutral of a 4-wire, 3-phase wye-connected system
• That portion consisting of nonlinear loads on a 4-wire, wye-connected, 3-phase system (harmonic current concerns)

NEC 220.60 — Net Computed Load (Recap)

As covered in Section 13.2, where noncoincident loads (heating vs. air-conditioning) will not run simultaneously, 220.60 permits only the larger load to be included in the total. This applies to the total ungrounded-conductor load and indirectly to the neutral (since the 240 V heating or cooling load contributes little or nothing to the neutral).

Table 310.12(A) — Single-Phase Dwelling Service Conductors

Table 310.12(A) applies to service conductors supplying the entire load of a one-family dwelling on a single-phase, 120/240 V system rated 100–400 A. Conductors sized per this table must have an ampacity not less than 83% of the service or feeder rating, and the table may only be used where no adjustment or correction factors (310.15) apply.

Table 310.12(A) — Excerpt (Service-Entrance Conductors)

Per 310.12(D), the neutral conductor may be smaller than the ungrounded conductors if the requirements of 220.61 (and 230.42(C) for services) are met.

Complete Worked Example — Single-Family Dwelling Service Load

Given: A 2000 sq ft single-family dwelling, 120/240 V single-phase service, with:

• 2 small-appliance branch circuits, 1 laundry branch circuit
• 10 kW electric range
• 5500 VA electric clothes dryer
• 4 fastened-in-place appliances with a combined nameplate of 9000 VA
• 12 kW electric furnace (no air-conditioning)
• 100% neutral treatment (no 220.61(B) reductions applied)

Step 1 — General-Lighting Demand Load (from 13.1)

Apply Table 220.45:

• First 3000 VA × 100% = 3000 VA
• Remaining 7500 VA × 35% = 2625 VA
• General-lighting demand load = 5625 VA

Step 2 — Range Load (220.55, Table 220.55 Column C)

10 kW ≤ 12 kW → Column C direct = 8000 VA

Step 3 — Dryer Load (220.54)

max(5000 VA, 5500 VA) = 5500 VA

Step 4 — Fastened-in-Place Appliances (220.53)

4 or more qualifying appliances → 75% demand factor:

9000 VA × 0.75 = 6750 VA

Step 5 — HVAC (220.51, 220.60)

Electric furnace: 12 kW × 100% = 12000 VA (220.51) Air-conditioning: none → 0 VA Per 220.60, use the larger: 12000 VA

Step 6 — Total Computed Load (Ungrounded Conductors)

Step 7 — Service Current

Formula: I = Total VA / V

Substitution: 37875 VA / 240 V = 157.8 A

Step 8 — Select the Service Rating

The computed load is 157.8 A. The service-disconnect rating must be selected from the 240.6(A) standard ampere ratings at or above this value. Standard ratings include 150 A and 175 A — 150 A is below 157.8 A, so the minimum standard service rating is 175 A.

Step 9 — Select Service-Entrance Conductors (Table 310.12(A))

For a 175 A single-family dwelling service, Table 310.12(A) gives:

• Copper: 1/0 AWG
• Aluminum or copper-clad aluminum: 3/0 AWG

Step 10 — Neutral Load

With 100% neutral treatment (no 220.61(B) reductions), the neutral carries the maximum unbalanced 120 V load. The general-lighting demand load (5625 VA) is the primary 120 V load. The range and dryer have 120 V components (controls, lights, 120 V heating elements) but their neutral contribution is typically reduced per 220.61(B)(1); this example uses 100% treatment, so the neutral is sized to carry the full unbalanced load.

Neutral current = 5625 VA / 240 V = 23.4 A

Per 310.12(D), the neutral may be smaller than the ungrounded conductors, provided it meets 220.61. A 4 AWG copper neutral (rated for 100 A per Table 310.12(A)) is more than adequate for 23.4 A.

Summary of Results

This is the natural endpoint of the load calculation. The service-disconnect rules (230.70–230.79), conductor ampacity adjustments, and OCPD selection are covered in Chapters 4 and 7.