Question 1

How do I calculate the electrical service size for a house?

Accepted Answer

The NEC 220.82 optional method sums 3 VA per sq ft of general lighting, 1,500 VA per small-appliance circuit, 1,500 VA for laundry, and the nameplate rating of every fastened-in-place appliance, range, dryer and water heater. The first 10 kVA of that total counts at 100 percent and the remainder at 40 percent. Heating or air conditioning is then added under 220.82(C).

Question 2

What is the NEC 220.82 demand factor?

Accepted Answer

First 10 kVA at 100 percent, remainder at 40 percent. Appliance loads belong inside that sum, not added afterward at full value.

Question 3

How are heating and cooling counted?

Accepted Answer

NEC 220.82(C) takes the largest applicable case: 100 percent of air conditioning, 100 percent of a heat pump compressor plus supplemental heat, or 65 percent of central electric space heating. Only the governing case is added.

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