kVA to amps calculator

An electrical load calculation totals a building's connected load, applies the NEC Article 220 demand factors, and returns the minimum service or feeder size in amps. It accounts for the fact that no building runs every load at once, so the diversified demand sizes the gear, not the sum of all nameplates.

A demand factor is the fraction of a connected load you may count toward the service, because that load will not run at full output with everything else. The Article 220 tables set them by category from metered data. The dwelling general-lighting demand, for example, takes the first 3000 VA at 100 percent and the rest at 35 percent.

The optional method, NEC 220.82, lumps general lighting, small-appliance, laundry, and appliance nameplates together, then takes 100 percent of the first 10,000 VA and 40 percent of the remainder. It is allowed for a single 120/240 V service rated 100 A or more and usually yields a smaller service than the standard method.

Use NEC 220.87 to find the existing load from the metered annual peak, or a 30-day recording, taken at 125 percent. Subtract that from the service rating for the spare capacity. The EV charger, a continuous load under Article 625, enters at 125 percent of its rating and has to fit inside the headroom.

No. You count only the larger of the two, because heating and air conditioning are noncoincident under NEC 220.60 and cannot run at the same time. Compare the heat load against the AC load and carry the larger into the total. Counting both is a common error that oversizes the service.