Electrical Load Calculator: NEC 220.82 & 220.87

It has to be proven with a load calculation, not guessed. With a year of demand data, NEC 220.87: take the highest demand from 12 months of utility metering data, multiply by 125 percent, and add the charger load. A 100 A, 240 V service is 24,000 VA, so the install works when 1.25 times the metered peak plus the charger stays at or below 24,000 VA. Example: a metered peak of 8 kW gives 1.25 x 8,000 = 10,000 VA, leaving 14,000 VA, which is plenty for a 40 A (9,600 VA) charger. A peak of 18 kW leaves only 1,500 VA and fails. When it fails, a listed energy management system per NEC 625.42(A), in accordance with NEC 750.30, can set the maximum equipment load used in the service calculation instead of forcing a service upgrade.

The standard method in NEC Article 220 Part III itemizes each load with its own rule: lighting and the small-appliance and laundry circuits by Table 220.45, fastened appliances by 220.53, cooking by Table 220.55, dryers by 220.54, heat at 100 percent by 220.51, and 25 percent of the largest motor. The optional method in 220.82 is a simplified alternative for a dwelling served by a single 120/240 V or 208Y/120 V, 3-wire service or feeder of 100 A or larger: everything except heating and cooling goes into one bucket taken at 100 percent of the first 10 kVA plus 40 percent of the remainder, then the largest of the six heating and cooling options in 220.82(C) is added on top; this calculator also keeps an EV charger out of that bucket and adds its 220.57 figure at 100 percent. 220.82(A) permits it instead of Part III, so both are code methods, and they can give different service sizes for one house. The calculator runs both, shows the one you choose, and never picks between them; the authority having jurisdiction decides which calculation it accepts.

Yes, through the exception in 220.87. If a year of utility demand data is not available, you may base the calculation on the maximum demand recorded continuously for at least 30 days, defined as the highest average kilowatts reached and maintained over a 15-minute interval, using a recording ammeter or power meter on the highest loaded phase. The recording must be taken while the building is occupied, and it must include, by measurement or calculation, the larger of the heating or cooling load plus other loads that are periodic or seasonal in nature. The exception is not permitted where the service has a renewable energy system such as solar PV or wind, or uses any form of peak load shaving.

Connected load is the sum of every nameplate in the house, as if everything ran flat out at once. Demand load is what the code lets you count after applying demand factors, because the code does not expect every load in a home to run at once. In the worked example on this page, NEC 220.82 turns 34,100 VA of connected general load into 19,640 VA of demand. NEC 220.87 skips the estimate entirely and starts from the demand the meter actually recorded. Service size is always based on the calculated demand load, never on the connected total.

Per NEC 220.57, new in the 2023 edition, EVSE is calculated at 7,200 VA or the nameplate rating, whichever is larger. The 7,200 VA floor corresponds to a 30 A, 240 V circuit. So a 40 A charger counts as 9,600 VA and a 48 A charger as 11,520 VA, while a small 16 A unit still counts as 7,200 VA. The 2023 optional method (220.82) names no EVSE, so it does not settle whether the charger may ride the 40 percent second tier as an appliance fastened in place under 220.82(B)(3); and 220.82(A) is used instead of Part III, where 220.57 sits, so the 7,200 VA floor is not the optional method's own rule either. This calculator's optional method adds the charger at the 220.57 figure at 100 percent outside that tier, a load at or above any reading of 220.82, the conservative choice under 2023. The 2026 edition's 120.82(D) adds EVSE at 100 percent of its 120.57 load, which is the nameplate rating, or 7,200 VA where there is none. Under the 2023 NEC, where a listed energy management system per 625.42(A), in accordance with 750.30, controls the EVSE, the managed maximum setting can be used instead.

220.83 is a permitted way to check whether an existing service or feeder can take additional load, for a dwelling unit served by a 120/240-volt or 208Y/120-volt, 3-wire service or feeder. Per 220.83(A), when no additional air conditioning or electric space heating is being installed, existing plus new loads are taken at 100 percent of the first 8 kVA plus 40 percent of the remainder. Per 220.83(B), when air conditioning or electric space heating is being added, air-conditioning equipment is taken at 100 percent, central electric space heating at 100 percent, and fewer than four separately controlled space-heating units at 100 percent, using only the larger of the air-conditioning or space-heating load, not both; all other loads get 100 percent of the first 8 kVA and 40 percent of the remainder. Table 220.83(B) has no row for four or more separately controlled space-heating units. The calculator runs 220.83 as its existing-dwelling method, 120.83 under the 2026 edition, for the edition you choose; where four or more separately controlled units leave it without a figure, it offers its standard method for the house. If you have a year of demand data, or a 30-day recording under the exception, run 220.87 first: it uses what the house drew. Both are permitted, except that NEC 2020 does not permit 220.87 at all where the service has a renewable energy system or any peak load shaving, and the 2023 and 2026 editions (120.87 in 2026) do not permit its 30-day recording there; the authority having jurisdiction decides.

Yes, in ways worth knowing whether or not your state has adopted it; this calculator's new-service and demand-data methods answer from the 2023 edition, and its existing-dwelling method from the edition you choose (120.83 in 2026). The 2026 edition renumbers Article 220 to Article 120, so 220.82 becomes 120.82 and 220.87 becomes 120.87. Inside the optional method, the general lighting allowance drops from 3 VA to 2 VA per square foot and the 100 percent first tier drops from 10 kVA to 8 kVA, and both changes lower the calculated load: the kVA between 8 and 10 moves from 100 percent to 40 percent. New 120.82(D) adds an EV charger at 100 percent of its 120.57 load, which is the nameplate rating, or 7,200 VA where there is no nameplate, so the 7,200 VA minimum this calculator applies under 2023 is gone. And 120.87 now takes "the maximum demand at 125 percent plus the new load minus any removed load", useful when swapping resistance heat for a heat pump. See our NEC 2026 changes page for the main changes, each beside what the 2023 edition printed, and which states have adopted it.

Use 240 V for the standard single-phase, three-wire service in detached homes. Use 208 V when the dwelling is fed from two legs of a 208Y/120 V three-phase system, as an apartment or condo building can be. The choice matters: the same 24,440 VA calculated load is 101.8 A at 240 V but 117.5 A at 208 V, which can push the answer past a service size. NEC 220.82(A) permits the optional method for both service types.

A load calculation only answers whether the service capacity is sufficient. An electrician on site also weighs physical breaker space, panel age and condition, whether the panel brand is one of the known problem lines, aluminum branch wiring, available fault current, and local amendments that can be stricter than the NEC as published. This calculator is a planning and estimating tool. A permit-grade calculation, stamped where required, belongs to a licensed electrician working from your jurisdiction's adopted code edition.

There are two different ways a panel is overloaded. The first is calculated: your demand load exceeds the service rating. Run a load calculation (NEC 220.83 when adding loads to an existing home, or 220.87 from a year of metered data), and if the demand comes out above your service amps, more than 100 A of demand on a 100 A panel for example, the calculation does not support that load under that method; NEC 220.87 is also permitted and can pass where 220.83 does not, except that NEC 2020 does not permit 220.87 at all where the service has a renewable energy system or any peak load shaving, and the 2023 and 2026 editions (120.87 in 2026) do not permit its 30-day recording there. The second is physical: breakers that trip repeatedly, a panel with no open slots, two wires landed under one breaker (a double-tap), or a warm panel cover. The calculated check is what this tool answers, naming a fit, a tight result or a shortfall under the method you ran; the physical check needs a licensed electrician's eyes on the panel. Adding a large new load like an EV charger, heat pump, or electric range is one way a panel that was fine becomes overloaded.