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Size a single-family dwelling electrical service using the NEC standard calculation method (Article 220, Part III), with the Table 220.42 lighting demand factors, Table 220.55 range demand, and the noncoincident heating and cooling rule.
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The standard method in NEC Article 220, Part III, builds the service load one piece at a time. It starts with the general lighting and receptacle load at 3 volt-amps per square foot, adds the kitchen small-appliance circuits and the laundry circuit at 1500 volt-amps each, then applies the demand factors in Table 220.42 to that whole group. Larger fixed loads such as the range, dryer, fixed appliances, and heating or cooling are added on top with their own rules.
This calculator runs every one of those steps and shows the volt-amps at each stage, so you can see exactly where the final service size comes from.
The combined lighting, small-appliance, and laundry load is not counted at full value. Table 220.42 allows the first 3000 volt-amps at 100 percent, the portion from 3001 to 120000 volt-amps at 35 percent, and anything above that at 25 percent. That reflects the reality that not every light and outlet runs at once.
An electric range up to 12 kW is counted as 8000 volt-amps under Table 220.55, Column C, with 5 percent added for each kilowatt over 12. The dryer is counted at 5000 volt-amps or its nameplate, whichever is greater, under 220.54. Heating and air conditioning are noncoincident, so NEC 220.60 lets you count only the larger of the two because they never run at the same time.
The standard method is the detailed approach and is required when a dwelling does not qualify for the simpler optional calculation. For most ordinary one-family homes you can also run the optional method in NEC 220.82, which usually gives a smaller service size. Try both with the same numbers on the Service Load Calculator and compare the results.
Enter your square footage and major appliances and the calculator returns the calculated load in amps and the next standard service size. A one-family dwelling must have a service of at least 100 amps under NEC 230.79(C).
The general lighting and receptacle load is 3 volt-amps per square foot of habitable area under NEC 220.41, before the Table 220.42 demand factors are applied.
Under Table 220.55, Column C, a single range up to 12 kW is counted as 8000 volt-amps. For ranges over 12 kW, 5 percent is added for each kilowatt above 12.
NEC 220.60 treats heating and cooling as noncoincident loads because they do not operate at the same time, so only the larger of the two is included in the service calculation.
Under NEC 220.53, when four or more fastened-in-place appliances are on the same feeder or service, their total nameplate load may be counted at 75 percent. With three or fewer they are counted in full.
The standard dwelling calculation applies demand factors to the general lighting and receptacle load, because not every circuit runs at once. These factors are from NEC Table 220.42 (renumbered 220.45 in the 2023 NEC).
| Portion of general lighting load (VA) | Demand factor |
|---|---|
| First 3,000 | 100% |
| 3,001 to 120,000 | 35% |
| Remainder over 120,000 | 25% |
General lighting is figured at 3 VA per square foot of living area (NEC 220.12), plus the two 1,500 VA small-appliance circuits and one 1,500 VA laundry circuit (220.52).
General lighting demand for a 2,000 sq ft home: