A Level 2 charger is a big, steady load, so the question isn't just "is there an open breaker slot?" — it's whether your existing load plus the charger stays under the service rating. The NEC gives two ways to figure the existing load.
The charger counts at 125%
An EV charger runs for hours, so it's a continuous load: it enters the calculation at 125% of its output. A 48 A charger counts as 60 A and needs a 60 A breaker; a 40 A charger counts as 50 A. That 125% is already baked in before you compare to the service size.
Two methods to size the existing load
- NEC 220.87 — if you have 12 months of metered peak demand from the utility, take that peak × 1.25 and add the charger. The most accurate route.
- NEC 220.83 — the optional dwelling calculation: 3 VA/ft² plus small-appliance, laundry, and appliance nameplates, with the first 8 kVA at 100% and the rest at 40%, and the larger of A/C or electric heat at 100%.
Example: a 200 A service with a 12 kW (50 A) metered peak plus a 48 A charger is 1.25 × 50 + 60 = 122.5 A — comfortably under 200. The same charger on a 100 A service already carrying a 60 A peak is 135 A — over the limit.
Two things this doesn't cover
A capacity check is about amps, not physical space — confirm you actually have room for a 240 V breaker (tandems may not be allowed). And once it fits, you still need to size the wire and breaker for the run, which depends on distance and install conditions.