EV charger installations are one of the fastest-growing electrical jobs in the country, and they trip up even experienced installers for one reason: EV charging is a continuous load. That changes the math on every wire and breaker in the circuit.
The 125% Rule
NEC 625.41 requires EV charging circuits to be sized at 125% of the maximum load. A "40 amp" charger doesn't go on a 40 amp circuit — it needs 40 × 1.25 = 50 amps of circuit capacity. Wire and breaker both.
Wire Size by Charger Rating (Copper, 75°C THWN-2)
| Charger output | Circuit required | Copper wire (75°C) | Typical use |
|---|---|---|---|
| 16 A | 20 A | 12 AWG | Plug-in Level 2, light duty |
| 32 A | 40 A | 8 AWG | Common home Level 2 |
| 40 A | 50 A | 6 AWG | Home Level 2 (14-50 outlet class) |
| 48 A | 60 A | 6 AWG (hardwired, 75°C) | Fast home charging |
| 64 A | 80 A | 4 AWG | High-end home / light commercial |
| 80 A | 100 A | 3 AWG | Commercial Level 2 |
Sizes assume 75°C terminations, three or fewer current-carrying conductors, 30°C ambient, and short runs. Long runs need upsizing for voltage drop — check with our wire size calculator.
Other NEC 625 Requirements to Know
- Dedicated circuit: the EVSE gets its own branch circuit — nothing else on it
- GFCI: receptacle-fed (plug-in) chargers require GFCI protection; hardwired units follow the manufacturer's listing
- Disconnect: equipment over 60 A or over 150V to ground needs a disconnecting means within sight
- Load management: NEC 625.42 allows an energy management system to reduce the calculated load — how many panels avoid a service upgrade
- Wet locations: outdoor runs in conduit need wet-rated conductors (THWN-2, XHHW-2) — see our THHN vs THWN-2 guide
Commercial and DC Fast Charging
DC fast chargers (50 kW–350 kW) are a different scale of feeder: 480V three-phase services, conductors from 3/0 AWG up through parallel 500 MCM runs, and utility coordination. Expect:
- Feeder conductors: copper or aluminum XHHW-2 in conduit, sized per continuous-load rules plus voltage drop over often-long parking lot runs
- Flexible connections: fine-strand cable such as DLO inside cabinets and for battery-buffered chargers
- High-voltage vehicle cabling: purpose-built EV battery cable for OEM and fleet equipment
Don't Forget Voltage Drop
A detached garage 150 feet from the panel with a 48 A charger is a voltage-drop problem before it's an ampacity problem — 6 AWG won't hold 3% at that distance. Run the numbers with the calculator, and when in doubt, go up a size: EV circuits run at full load for hours, so every volt dropped is heat in your wall.
We stock THHN/THWN-2 copper in every gauge above, plus aluminum feeder options — cut to length with fast nationwide shipping.
