It depends on the car’s energy use and on whether the onboard charger can draw the current. Power is straightforward: at 240 V, 32 A is 7.68 kW and 40 A (the usual continuous current on a 50 A circuit) is 9.60 kW. Converting power into miles per hour requires a watt-hour-per-mile assumption. This page uses one published illustration, not a typical-car claim: the Alternative Fuels Data Center’s Q2 2024 charging-infrastructure trends report describes Level 2 as about 25 miles of range per hour, assuming 6.6 kW of power. That implies 264 watt-hours per mile (6.6 kWh ÷ 25 miles). At that same energy use, 7.68 kW is about 29 miles per hour and 9.60 kW is about 36.
| Continuous current at 240 V | Power | Miles per hour at 264 Wh/mi |
|---|---|---|
| 16 A (typical 20 A circuit) | 3.84 kW | 14.5 |
| 24 A (typical 30 A circuit) | 5.76 kW | 21.8 |
| AFDC L2 illustration | 6.60 kW | 25.0 |
| 32 A (typical 40 A circuit) | 7.68 kW | 29.1 |
| 40 A (typical 50 A circuit) | 9.60 kW | 36.4 |
| 48 A (typical 60 A circuit) | 11.52 kW | 43.6 |
AFDC’s home-charging page also works an example at 27 kWh per 100 miles (270 Wh/mile), which would shave a little off each of those mile-per-hour figures. Highway winter driving can be much hungrier than 264–270 Wh/mile; efficient suburban driving can be leaner. The 40 A circuit is 25% more power than 32 A, not a doubling, and it only helps if the car can use it and if the panel has the headroom — see the 40-amp versus 50-amp page and the calculator.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.