The arithmetic, in one line
The existing load on the service, established from what it actually drew, taken at 125%. Plus the chargers, counted the way the code counts them. The total has to fit under the rating of the service, or the ampacity of the feeder the chargers land on.
The first term is where most of the room is, and it is the term a measurement changes. The standard calculation adds up everything in the facility as if far more of it ran at once than ever does. NEC 220.87 allows the existing load to be established from the maximum demand over 12 months of utility records, or a 30-day recording where those are not available. On an operating facility that figure is usually well below the calculated one.
How the chargers are counted
Each charger is counted at the larger of 7,200 VA or its nameplate rating, under 220.57 of the 2023 edition. A small charger does not shrink the calculation below that floor.
EV charging runs for hours, so a charger is a continuous load. The feeders and branch circuits that supply it are sized at not less than 125% of its maximum load under 625.41. That 125% is on the chargers' own circuits. It is a different rule from the 125% on the existing demand, and putting the multiplier on the wrong term is the most expensive mistake available here.
Where an energy management system that meets 750.30 limits how much the chargers can draw together, 625.42(A) allows the maximum the system permits to be used instead of the sum of the nameplates. That is the single biggest lever on whether a bank of chargers fits an existing service. Ten chargers that can draw 80 A each but are managed to 200 A together count as 200 A.
So the first question is never how many chargers
It is how much current, at once, under what control. A site that wants ten Level 2 chargers and has a load-managed system needs room for the managed maximum. A site that wants the same ten chargers unmanaged needs room for all ten at once, at the floor or the nameplate, whichever is larger, plus the continuous-load sizing on their circuits. Those are very different answers on the same panel.
Which is why a load study asks about the management system before it asks about the count, and why the answer often turns on a setting rather than on a service upgrade.
When the answer is no
When the measured existing demand at 125%, plus the managed maximum of the chargers, still lands above the rating. Then the service genuinely needs the upgrade, and the sealed study is the existing-load documentation the upgrade application asks for. The measurement was not wasted. It moved the application forward with evidence instead of an argument, and it may have shown that a smaller upgrade, or a managed system, closes the gap.
Questions people ask
How many Level 2 chargers can a 400 A service take?
There is no number without the measurement. It depends on what the service already draws at its peak, at 125%, and on whether the chargers are load-managed. Two facilities with the same 400 A service can have very different room.
Do I count each charger at its nameplate?
At the larger of 7,200 VA or the nameplate, under 220.57 of the 2023 edition. Where an energy management system meeting 750.30 limits the combined draw, the managed maximum can be used instead of the sum, under 625.42(A).
What is the 125% on EV chargers?
Charging is a continuous load, so the feeders and branch circuits supplying the chargers are sized at not less than 125% of their maximum load, under 625.41. It is separate from the 125% that NEC 220.87 applies to the existing measured demand.
Can load management avoid a service upgrade?
Often. Where the managed maximum of the chargers fits under the rating with the existing demand at 125%, the code allows the managed figure to be used, and the upgrade is not needed. Whether it fits is what the study establishes.