Select a calculation method, then enter the connected loads from the project plans and specifications to determine the required service size per NEC 2023 Article 220.
Optional Method
The Optional Method allows a simplified calculation for single dwelling units served by a single 120/240V or 208Y/120V, 3-wire set of service or feeder conductors with an ampacity of 100A or greater (NEC 220.82(A)). It totals general and fixed loads, applies 100% to the first 10 kVA and 40% to the remainder, and then adds the larger of the heating or cooling load per NEC 220.82(C).
NEC Load Calculator (Single Family Using Optional Method)
Standard Method
The Standard Method (NEC 2023 Article 220, Part III) calculates the dwelling service load item by item: general lighting and receptacles at 3 VA/sq ft (220.41) plus small-appliance and laundry circuits at 1,500 VA each (220.52), reduced per Table 220.45; fastened-in-place appliances at 75% when four or more (220.53); the clothes dryer at 5,000 VA or nameplate, whichever is larger (220.54); cooking appliances per Table 220.55; the larger of the heating or cooling load (220.60); and 25% of the largest motor (220.50). It typically produces a more conservative (larger) calculated load than the Optional Method (220.82).
NEC Load Calculator (Single Family Using Standard Method)
