The short answer
A 40 amp EV charger needs a 50 amp breaker and 6 AWG copper NM-B cable (8 AWG copper in conduit), and it can plug into a NEMA 14-50 outlet. A 48 amp charger needs a 60 amp breaker and 4 AWG copper NM-B cable, and it must be hardwired. A 40 amp charger adds about 34 miles of range an hour.
Charger amps, breaker and wire
The smallest copper wire for each charger, from NEC 2023 Table 310.16 as commonly published. It ignores the run length, so a long run may need one size more. Range assumes 3.5 miles per kWh.
| Charger | Breaker | NM-B | THHN | kW | Mi/hr | Plug? |
|---|---|---|---|---|---|---|
| 16 A | 20 A | 12 AWG | 12 AWG | 3.8 | 13 | Yes |
| 24 A | 30 A | 10 AWG | 10 AWG | 5.8 | 20 | Yes |
| 32 A | 40 A | 8 AWG | 8 AWG | 7.7 | 27 | Yes |
| 40 A | 50 A | 6 AWG | 8 AWG | 9.6 | 34 | Yes |
| 48 A | 60 A | 4 AWG | 6 AWG | 11.5 | 40 | No |
| 64 A | 80 A | 3 AWG | 4 AWG | 15.4 | 54 | No |
| 80 A | 100 A | 1 AWG | 3 AWG | 19.2 | 67 | No |
NM-B is cable in walls (60°C column). THHN is wire in conduit (75°C column). "Plug?" means a NEMA 14-50 plug can be used; otherwise the charger is hardwired.
How it works
The formula
An EV charger runs for hours, so the code treats it as a continuous load. We size the breaker for 125% of the charger's amps, pick the smallest wire for that breaker, then check the voltage drop.
wire = smallest gauge rated for the breaker
drop (V) = 2 × K × charger amps × feet ÷ circular mils
power (kW) = amps × 240 ÷ 1,000
range per hour = kW × 3.5
Assumptions
- NEC 625.41 and 625.42 require EV supply equipment to be sized as a continuous load: the breaker and wire carry at least 125% of the charger's rated amps.
- The circuit is 240 V single-phase. Voltage drop is held to 3%. K is 12.9 for copper and 21.2 for aluminum.
- NM-B cable uses the 60°C column of Table 310.16 (NEC 334.80). THHN in conduit uses the 75°C column and needs breakers and terminals marked 75°C.
- A NEMA 14-50 receptacle is rated 50 A, so it allows 40 A of continuous charging. A charger above that is hardwired. Receptacles for EV charging need GFCI protection (210.8, 625.54).
- Range uses 3.5 miles per kWh, which is typical for a mid-size EV in mixed driving. Charging losses and cold weather lower it. Your car may charge slower than the charger allows.
- Aluminum wire is allowed, but the terminals must be rated for it.
- Local code, the utility and your electrician decide. You may need a permit and a load calculation to show the panel can carry the charger.
Worked example: 48 amp charger, 80 ft
48 A charger at 240 V, 80 ft one way, copper NM-B cable.
- Continuous load: 48 × 1.25 = 60 A, so the breaker is 60 A.
- NM-B uses the 60°C column. 6 AWG copper is only 55 A, so the smallest wire is 4 AWG (70 A).
- Drop: 2 × 12.9 × 48 × 80 ÷ 41,740 = 2.4 V, or 1%. That is under 3%.
- Power: 48 × 240 ÷ 1,000 = 11.5 kW. Range: 11.5 × 3.5 = 40 miles an hour.
- A 48 A charger is above 40 A, so it is hardwired, not plugged in.
Too big or too small
- Breaker too small: it trips during a long charge, and the charge stops overnight. Size it at 125% of the charger's amps.
- Wire too small: it runs hot for hours and can overheat the wire, the outlet or the breaker. The code rating is the floor, not a target.
- Long run, small wire: voltage drop makes the charger work harder and some chargers fault. Go up a gauge when the run is long.
- Wire bigger than needed: it costs more now, but it lets you swap in a faster charger later without redoing the walls.
- Charger bigger than the car: many cars charge at 40 to 48 amps at most, so a bigger charger adds cost and no speed.
Questions people ask
What size breaker do I need for a 48 amp EV charger?
A 60 amp breaker. EV charging is a continuous load, so the breaker must be at least 125% of the charger's amps (NEC 625.41 and 625.42): 48 × 1.25 = 60. The same rule gives a 40 amp breaker for a 32 amp charger and a 50 amp breaker for a 40 amp charger.
What size wire do I need for a 40 amp EV charger?
A 40 amp charger needs a 50 amp breaker, so use 6 AWG copper NM-B cable or 8 AWG copper THHN in conduit. On a longer run the voltage drop may call for more: at 200 ft, 4 AWG copper NM-B keeps the drop under 3%.
Can I plug my EV charger into a NEMA 14-50 outlet?
Yes, up to 40 amps. A 14-50 receptacle is rated 50 amps, and 125% of 40 is 50. A 48 amp charger or bigger must be hardwired to the circuit. Plug-in chargers wear out the outlet over time, so use a good quality receptacle and check it for heat.
Does an EV charger outlet need GFCI protection?
Yes. The NEC requires ground-fault protection for personnel on receptacles used for EV charging (625.54), and 210.8 requires it on 240 V receptacles in garages and outdoors. A GFCI breaker does it, and many chargers have it built in. Ask your electrician which one you have so you do not pay for it twice.
How many miles of range does a Level 2 charger add per hour?
About 13 miles an hour from a 16 amp charger, 27 from a 32 amp charger and 40 from a 48 amp charger. We assume 3.5 miles per kWh, a typical mid-size EV. Heavy SUVs get less and small cars get more. Your car may also limit its charge rate to less than the charger offers.
Is a bigger charger worth it?
Only if your car can use it and you drive enough to need it. Many cars accept 40 to 48 amps at most. A 32 amp charger adds about 27 miles an hour, which refills a day of driving overnight. Wire costs more as the amps rise: 8 AWG for 32 amps, 4 AWG for 48.