Calculators · NEC Article 220, standard method

Service load

The demand load of a dwelling after the NEC 220 factors, and the smallest standard service that carries it. Enter the nameplates; the service size updates as you type.

Free. No sign-up. Not sealed engineering. By Ali Mazloum, P.Eng.

Inputs

Enter a floor area above 0.
NEC 210.11(C)(1) requires at least two.
Enter 0 or more.
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Defaults: a 2,000 sq ft house on 240 V with the usual appliances.
Minimum service size –
Demand load–VA
Demand current–A
Connected load–VA
General lighting–VA

Standard method, NEC 220 Part III. Space heating, EV charging, pool and spa equipment are not included. Educational use; not sealed engineering.

Method  General lighting at 3 VA per sq ft, plus 1,500 VA per small-appliance and laundry circuit. The first 3,000 VA at 100 %, the rest at 35 % (Table 220.42). Range per Table 220.55 Column C. Dryer at the nameplate or 5,000 VA, whichever is larger (220.54). Fixed appliances at 75 % when there are four or more (220.53). Divide by the service voltage and round up to the next standard size.

Sizing a residential service

Five minutes

Service sizing is one of the first calculations in a house design, and one of the easiest to get wrong by adding up nameplates. NEC Article 220 gives a standard method that starts from the connected load and applies demand factors, because a house never runs every light, receptacle and appliance at once.

The standard method

General lighting is taken at 3 VA per square foot of living space. The kitchen needs at least two small-appliance circuits at 1,500 VA each (210.11(C)(1)) and the laundry one circuit at 1,500 VA (210.11(C)(2)). Those three loads together take the first 3,000 VA at 100 % and the remainder at 35 %.

Appliances

A range up to 12 kW counts as 8 kW of demand under Table 220.55 Column C. A dryer counts at its nameplate or 5,000 VA, whichever is larger. Fixed appliances such as the water heater and dishwasher are added in full, or at 75 % when there are four or more of them. Air conditioning is added at 100 %; where there is also electric heat, the larger of the two is used (220.60).

The service size

The demand load in VA divided by the service voltage gives the current, which is rounded up to the next standard size: 100, 125, 150, 200, 225, 250, 300, 350 or 400 A. Most new houses land at 200 A, and the trend to heat pumps and EV charging is pushing more of them to 400 A.

What it does not do

This is a simplified standard method. A full calculation adds space heating (220.51), the heat-versus-cooling comparison (220.60), EV charging, pool and spa equipment and any other special loads. The optional method (220.82) often gives a lower number and is worth running beside this one.

FAQ

Straight answers
What size electrical service do I need for my home?

Most homes of 1,500 to 3,000 sq ft with standard appliances land at 200 A. Smaller homes and condos can work on 100 A or 125 A. Electric heating, more than one EV charger or other large loads can push a house to 400 A. This is a starting point; your utility and inspector may ask for more.

What is the difference between connected load and demand load?

Connected load is the sum of every nameplate in the house. Demand load applies the NEC factors that recognize not everything runs at once. The demand load is always lower, and it is the number that sets the service size.

Why does the NEC require at least two small-appliance circuits?

NEC 210.11(C)(1) requires two 20 A circuits for the kitchen counter, pantry, breakfast and dining receptacles, so toasters, kettles and microwaves do not share one circuit. Each counts as 1,500 VA in the calculation.

How does NEC Table 220.55 work for ranges?

Column C gives 8 kW of demand for one range up to 12 kW. Above 12 kW, add 5 % of the column value (400 W) for each extra kW. All the elements of a range rarely run at full power together.

Standard method or optional method?

NEC 220.82 is the optional method for a dwelling unit served at 100 A or more, new or existing, and it usually gives a lower number than the standard method. NEC 220.83 is the optional method for adding load to an existing dwelling. Either is acceptable where the conditions of the section are met; this tool runs the standard method of Part III.

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