Study Materials

Edition flag (important): The 2023 NEC reorganized Article 220. The general- lighting demand-factor table that the 2017/2020 editions numbered Table 220.42 is, in the 2023 arrangement, Table 220.45 (dwelling demand factors), and the dwelling general-illumination unit-load section is 220.41 [2020: Table 220.12]. Non-dwelling unit loads move to Table 220.42(A). Section numbers below are given for the 2023 NEC with the 2020 number in brackets where they moved. Confirm against your adopted edition — this is the single most renumbered area on the exam.

The standard method, step by step

The dwelling standard calculation (220 Part III) is a fixed recipe. Learn the order:

1. General lighting & receptacles — 3 VA/ft² of floor area (220.41), using outside dimensions, excluding open porches/garages/unused spaces.
2. Small-appliance branch circuits — at least two, 1500 VA each (220.52(A)).
3. Laundry branch circuit — 1500 VA (220.52(B)).
4. Apply the general-lighting demand factors to the sum of 1–3: first 3000 VA at 100%, 3001–120,000 VA at 35%, remainder at 25% (Table 220.45 [2020: 220.42]).
5. Add appliances at nameplate — fixed appliances get the four-or-more 75% demand factor (220.53); the range uses Table 220.55; the dryer uses the larger of 5000 VA or nameplate, then Table 220.54.
6. Heating vs. A/C — include the larger of the two noncoincident loads (220.60).
7. Convert to amperes and select service size.

The range and dryer tables

• Range (Table 220.55, Column C): one range not over 12 kW → 8 kW demand. For ranges over 12 kW, increase the 8 kW column by 5% per kW (or major fraction) that the nameplate exceeds 12 kW (Note 1). Columns A and B handle smaller ranges and multiple units.
• Dryer (220.54 + Table 220.54): each dryer at 5000 VA or nameplate, whichever is greater; for multiple dryers, apply the Table 220.54 demand percentages.

The optional method — often the master's shortcut

For a one-family dwelling (220.82), the optional method is simpler and usually yields a smaller service:

• General load (lighting/receptacles/appliances, small-appliance and laundry circuits, and most fixed appliances at nameplate): first 10 kVA at 100%, remainder at 40% (220.82(B)).
• Heating/cooling — take the largest applicable per 220.82(C) (e.g., 100% of A/C, or 65% of central electric heat, etc.).

The neutral load

The feeder/service neutral (220.61) carries only the unbalanced load. You may take the range and dryer neutral at 70% of their calculated demand (220.61(B)(1)), and further reduce the portion of a 3-wire neutral load over 200 A by an additional 70% (220.61(B)(2) — with exclusions for nonlinear loads).

Multifamily — the optional method

For three or more dwelling units (220.84), the optional multifamily method applies the Table 220.84 demand factors to the total connected load per unit (23 units → 41%, etc.). This almost always beats the standard method for larger buildings and is a common master-exam calculation.

Key numbers & facts (Chapter 5 cram box)

• General lighting: 3 VA/ft² (220.41).
• Small-appliance circuits: ≥2 × 1500 VA (220.52(A)); laundry 1500 VA (220.52(B)).
• Dwelling general-lighting demand: 3000 @ 100% / next to 120,000 @ 35% / remainder @ 25% (Table 220.45 [2020: 220.42]).
• Four+ fixed appliances: 75% (220.53).
• Range: 8 kW for one ≤12 kW; +5%/kW over 12 (Table 220.55, Note 1).
• Dryer: 5000 VA or nameplate, greater (220.54).
• Optional 1-family: first 10 kVA @ 100%, remainder @ 40% (220.82(B)).
• Noncoincident heat/AC: use the larger (220.60).
• Neutral: range/dryer at 70% (220.61(B)).
• Optional multifamily: 3+ units, Table 220.84.

Worked example — optional-method one-family service

A 2400 ft² dwelling has a 12 kW range, a 5 kW dryer, a 4.5 kW water heater, a 1.2 kW dishwasher, a 9 kW A/C and 10 kW of electric thermal-storage heat (a continuous heating system, noncoincident with cooling). Size the service by the optional method (240 V).

1. General load: 2400 × 3 = 7200 VA lighting + 2 × 1500 (small appliance) + 1500 (laundry) + 12,000 (range) + 5000 (dryer) + 4500 (WH) + 1200 (DW) = 34,400 VA.
2. Optional demand (220.82(B)): first 10,000 @ 100% = 10,000; remainder 24,400 @ 40% = 9,760 → 19,760 VA.
3. Heating/cooling (220.82(C)): compare the 9 kW A/C (220.82(C)(1), 100% = 9,000 VA) against the 10 kW electric thermal-storage heat (220.82(C)(3), a heating system whose load is continuous at full nameplate, taken at 100% = 10,000 VA); use the larger = 10,000 VA. (Had this instead been central electric space heating, 220.82(C)(4) would apply 65% — a different result; the load type dictates the percentage.)
4. Total: 19,760 + 10,000 = 29,760 VA → I = 29,760 ÷ 240 = 124.0 A → a 125 A service meets it, though 150 A is common for growth. (220.82)

Named exam traps (Chapter 5)

• Using the 2020 section numbers on a 2023 exam (or vice versa). Table 220.42 ↔ Table 220.45; the whole article renumbered.
• Forgetting the laundry and second small-appliance circuits.
• Applying 8 kW to a range over 12 kW without the 5%-per-kW bump.
• Mixing standard and optional methods in one calculation. Pick one lane.
• Taking A/C and heat instead of the larger (220.60).