220.82 vs 220.83 vs 220.87 load calculations

When a customer adds solar, storage, an EV charger or a heat pump, the question is whether the existing service can carry it. Which method you use changes the answer, and sometimes changes the price of the job by several thousand dollars.

The three methods

220.82 — the optional method

The familiar one: 100% of the first 10 kVA of general load, 40% of the remainder, plus the largest of several heating/cooling options. It is straightforward and conservative, and it assumes a house that could use everything it has.

220.83 — adding to an existing dwelling

Purpose-built for retrofit work, and the one most solar-plus-EV jobs should use. It has two paths depending on whether air conditioning or heat is involved, and it lets you account for what is already there rather than recomputing the house from scratch.

220.87 — measured demand, and why it wins

This is the method that saves service upgrades. Instead of calculating what the house might draw, use what it did: the maximum demand over the previous year, commonly the highest 15-minute interval from utility data, with an allowance applied.

The gap is usually large. A house that calculates to 150 A on paper often peaks under 60 A in reality, because nobody runs the oven, dryer, air conditioning and EV charger simultaneously at 2 a.m.

What you need: a year of interval data from the utility, or metering installed for a suitable period. Most utilities will provide it on request, and Green Button data often suffices.

Where solar sits in this

PV is a source, not a load, so it does not appear in the load calculation. Its effect on the service is governed by 705.12 interconnection instead. Two separate questions on the same panel:

• Load calc — can the service carry the loads?
• 705.12 — can the busbar host the source?

A job can pass one and fail the other. Batteries can appear in both, depending on how they are connected and whether they can supply the premises.

EV chargers and the 750 option

An EV charger is a continuous load at 125%, which is what pushes many houses over. Load management under Article 750 is the alternative: a listed system that sheds or limits the charger when the house draws heavily, letting you count a reduced value.

On the drawing

Show the method by name, the inputs, and the arithmetic. A load calculation with a conclusion and no working is a correction. If you used 220.87, state the data source and period — a reviewer will want to know the demand figure came from the utility rather than from an estimate.

Solar Scripto builds the 220.82, 220.83 and 220.87 calculations from the project record and prints the method and inputs on the load-calc sheet, so a reviewer can check the figure rather than recompute it.

See also: what is a 200 amp service and solar and heat pumps.

> Design aid — a licensed electrician or PE must review and stamp before filing.

Educational reference, reviewed 2026-07. A design aid, not a substitute for a licensed electrician or PE. Confirm the enforced NEC edition and local amendments with your AHJ.