NEC Article 220 (Parts III and IV)7 min read

Worked Example: NEC 220 Dwelling Service Size — Standard vs Optional Method

A 2,000 ft² house works out at 150 A by the standard method but 125 A by the optional method — here is where the difference comes from.

Open NEC 220 Residential Electrical Load Calculator calculator

Scenario

Floor area	2,000 ft²
Small-appliance and laundry circuits	2 × 1,500 VA and 1 × 1,500 VA
Other fixed appliances	3 appliances totalling 4,500 VA
Range and dryer	10 kW range, 5,000 VA dryer
HVAC	4,800 VA cooling, 10,000 VA heat pump heating (larger of the two used)
Supply	240 V single-phase

Step-by-step calculation

Step 1: Standard method: general loads with the Table 220.42 demand factors

Lighting 3 VA/ft² × 2,000 = 6,000 VA; + 4,500 VA small appliance and laundry = 10,500 VA

3,000 × 100% + 7,500 × 35%

5,625 VA

Step 2: Standard method: add the other loads

Load	Rule	VA
General loads	Table 220.42	5,625
Fixed appliances (fewer than 4)	220.53 — 100%	4,500
Range, 10 kW	Table 220.55 Column C	8,000
Dryer	220.54 — 5,000 VA minimum	5,000
Heating (larger than cooling)	220.60	10,000
Total		33,125

Step 3: Optional method (220.82)

All general loads and appliances at nameplate: 10,500 + 4,500 + 10,000 (range) + 5,000 (dryer) = 30,000 VA. The first 10 kVA at 100% and the rest at 40% gives 18,000 VA. The heat pump is added at 100% under 220.82(C).

Result summary

Check	Requirement	Actual	Status
Standard method	n/a	33,125 VA → 150 A	✓ PASS
Optional method	n/a	28,000 VA → 125 A	✓ PASS

The optional method allows a 125 A service, the standard method 150 A. Either is code-compliant for a single dwelling; many designers still choose 200 A for future loads such as an EV charger.

Key insight: The optional method's single 40% factor above 10 kVA is more generous than the separate standard-method factors, which is why it usually gives a smaller service for a typical house.