There is no single wire size for every Level 2 EV charger. The right gauge depends on how many amps your charger draws, how the wire is run, and how far it travels from the panel. Getting it right is a safety issue, so it is worth understanding how the sizing works, even though the actual installation should be done by a licensed electrician.
Here is how to figure out what wire gauge a Level 2 EV charger needs.
Start with the charge rate and the 125 percent rule
EV charging is a continuous load, meaning it can run at full current for hours. The National Electrical Code requires circuits with continuous loads to be sized at 125 percent of the load. In practice, that means the breaker is 25 percent larger than the charger’s output, and the charger draws no more than 80 percent of the breaker rating.
So a 40-amp charger needs a 50-amp breaker, and a 48-amp charger needs a 60-amp breaker. The wire is then sized to safely carry that circuit.
Typical copper wire sizes by charge rate
The table below shows common pairings for copper wire. These are typical starting points, not a substitute for an electrician’s calculation:
| Charge rate | Breaker | Typical copper wire |
|---|---|---|
| 16 amps | 20 amps | 12 AWG |
| 24 amps | 30 amps | 10 AWG |
| 32 amps | 40 amps | 8 AWG |
| 40 amps | 50 amps | 8 AWG (in conduit) or 6 AWG (cable) |
| 48 amps | 60 amps | 6 AWG |
Most home Level 2 installs land at 32, 40, or 48 amps, so 8 AWG and 6 AWG copper are the sizes you will hear about most often.
Why the wiring method changes the answer
This is where many DIY plans go wrong. The same gauge does not carry the same current in every situation, because the wiring method changes the wire’s allowed ampacity:
- THHN or similar conductors in conduit use a higher temperature rating, so 8 AWG copper can serve a 50-amp circuit.
- NM-B cable, often called Romex, is rated more conservatively, so 8 AWG NM-B tops out at 40 amps. A 50-amp circuit run in NM-B needs 6 AWG.
That single difference is why an electrician might use 8 AWG in one home and 6 AWG in another for the same charger. The wiring method matters as much as the amperage.
Copper, not aluminum, in most cases
Most EV chargers specify copper conductors, commonly rated for 90 degrees Celsius. Aluminum can sometimes be used, but it generally has to be upsized and the terminals must be rated for it. Many chargers have terminals that accept up to 6 AWG wire, which is another reason larger installs are often hardwired at that size. Always follow the charger manufacturer’s wire specifications.
Distance and voltage drop
Over a long run, some voltage is lost in the wire, which can reduce charging performance. For longer distances, such as a panel in the basement feeding a detached garage, an electrician may upsize the wire, for example moving to 4 AWG on a 60-amp circuit, to keep voltage drop in check. A voltage drop calculation is part of a proper installation.
Do not forget the panel
The wire and breaker are only part of the picture. Your panel needs an open double-pole slot and enough capacity to handle the new circuit. Older or full panels may need an upgrade, or load management may let you add the charger without a service upgrade.
