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.