NEC Article 220 Load Calculations: Standard vs Optional Method

Article 220 is the heart of every service-sizing decision in residential and light-commercial work. It tells you how to add up the loads in a building so you can pick the right service amperage. There are two methods: the Standard method (Part III) and the Optional method (Part IV). Both are NEC-compliant — choose whichever your AHJ accepts.

The Standard method treats each load category on its own. General lighting + small-appliance + laundry circuits get a graduated demand factor from Table 220.42 (first 3,000 VA at 100%, next portion at 35%, remainder at 25%). Fixed appliances of 4 or more on the same feeder get 75% per 220.53. Cooking equipment uses Table 220.55 (a single household range typically demand-factors to 8 kW). Electric dryer is 5,000 VA minimum per 220.54. HVAC is the larger of A/C or heat per 220.82(C). EV charger is treated as a continuous load and multiplied by 125% per 625.42. Largest motor adds 25% per 220.50.

The Optional method under 220.82 groups all the general loads together — general lighting + small-appliance + laundry + fixed appliances + cooking + dryer — and counts the first 10 kVA at 100% and the remainder at 40%. Then HVAC is added at 100%, and EV chargers at 125%. The Optional method usually produces a smaller calculated load and is often preferred for new dwellings. NJ AHJs almost universally accept it.

Which to use: When you have ONE significant continuous load like an EV charger, the Optional method usually wins. When you have multiple large fixed appliances and want explicit demand-factor accounting (e.g. a permit reviewer who wants every line itemized), the Standard method is more defensible.

The free Malfettone Load Calculator at /tools/load-calculator runs both methods side-by-side and shows every NEC reference in the output. Use it to size services for panel upgrades, EV charger installs, and additions.