Electrical Load Calculator: NEC 220.82 & 220.87

Often yes, but it has to be proven with a load calculation, not guessed. NEC 220.87 is the cleanest path: 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, an energy management system per NEC 625.42 can limit the charger to what fits instead of forcing a service upgrade.

The standard method in NEC Article 220 Part III itemizes each load category with its own demand factor table. 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. Both methods are code-legal. The optional method usually produces the smaller number and is what most residential service calculations use.

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 real homes never run every load simultaneously. 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. NEC 2023 is genuinely ambiguous about whether EVSE inside the 220.82 optional method may ride the 40 percent second tier; this calculator adds it at 100 percent outside that tier, which is the conservative reading of 2023 and the explicit rule of the 2026 edition. Where a listed energy management system per 625.42 controls the EVSE, the managed maximum setting can be used instead.

220.83 is the optional calculation for adding loads to an existing dwelling when you have no metering data to use 220.87. Per 220.83(A), when no additional air conditioning or electric space heating is being installed, the total of existing plus new loads is taken at 100 percent of the first 8 kVA plus 40 percent of the remainder. Per 220.83(B), when new AC or electric space heating is being installed, the HVAC loads are taken at 100 percent with no demand factor and the other loads get the 8 kVA and 40 percent treatment. Published summaries agree on that structure, but verify the exact 220.83(B) wording in the code book before hanging a permit on it. This calculator implements 220.82 and 220.87; 220.87 is usually the better answer when demand data exists because measured reality beats estimates.

Yes, in ways worth knowing before your state adopts it. 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, so the two changes partially offset. New 120.82(D) settles the EV question: EVSE counts at 100 percent of nameplate with no demand factor. Secondary sources also report that 120.87 will newly allow subtracting removed loads, useful when swapping resistance heat for a heat pump, but verify that in the published book. See our NEC 2026 changes page for the full delta list 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, which is common in apartment and condo buildings. 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.