What Size Breaker and Wire for an EV Charger? 32, 40 and 48 Amp

An EV charger is a continuous load, so its circuit is rated at 125% of the charger's current. A 32 amp charger needs a 40 amp breaker, a 40 amp charger a 50 amp breaker, and a 48 amp charger a 60 amp breaker, all on 240 volts. The wire has to carry the breaker's current: 8 AWG copper in conduit for the 40 amp circuit, and 8 AWG copper for the 50 amp one (6 AWG if you use NM-B cable, which is rated for a lower temperature). The breaker size calculator and the wire size calculator do the math for your own charger and run.

Breaker and wire size by charger

For a 240 volt single-phase circuit with copper wire. The wire is sized for the ampacity (the breaker's rating at 125% of the charger) and checked for a 3% voltage drop on a long run:

The NM-B column is for Romex-type cable, which is rated for 60°C, so it needs larger wire than THHN in conduit. Long runs may need larger wire to limit the voltage drop; the 100 and 150 foot columns are for wire in conduit.

How the sizes work

• 125% for continuous loads. A load that runs for three hours or more, as a car charging overnight does, is rated at 125%. A 40 amp charger is 40 × 1.25 = 50 amps.
• Charger current, not the circuit. Chargers are set to a current, often adjustable (16, 24, 32, 40 or 48 amps), and the circuit is sized for the setting. A 48 amp charger delivers about 11.5 kW at 240 volts.
• Plug or hardwire. A NEMA 14-50 outlet on a 50 amp breaker suits a plug-in charger set to 40 amps or less. A hardwired charger can use up to 48 amps on a 60 amp breaker.
• Voltage drop. Over a long run, a bigger wire keeps the voltage up. Aim for 3% or less (see the voltage drop calculator).
• Wire type. THHN wires in conduit are rated for 75°C, and Romex (NM-B) for 60°C, so a longer or hotter run changes the choice.

How fast does each charger charge?

At about 4 miles of range per kWh, which is typical for an efficient car:

For what charging costs, use the EV charging cost calculator.

Before you install

• Check the panel. A new 50 or 60 amp circuit adds a big load to the service. An electrician can run a load calculation and tell you if the panel has room, or if you need a load management device.
• GFCI and permits. The NEC requires ground-fault protection for receptacles that connect an EV charger, and most places require a permit and inspection. Follow the charger's manual and your local code.
• Use a licensed electrician. A 240 volt circuit in a panel is not a casual job.

These sizes follow the NEC rules for continuous loads and the copper ampacity table. Your local code and the charger's instructions decide what is required.

Frequently asked questions