The Short Answer
EV charging is a continuous load, so the circuit must be rated for at least 125% of the charger's output. That means a 40A breaker for a 32A charger, a 50A breaker for a 40A charger and a 60A breaker for a 48A charger. The charger's current setting must never exceed 80% of the breaker rating.
Getting this right is a core part of any safe EV charger installation in Reynoldsburg, and it's one of the first things an inspector checks.
Breaker and Wire Size Chart
| Charger output | Minimum breaker | Approx. power at 240V | Typical copper wire* |
|---|---|---|---|
| 16A | 20A | 3.8 kW | 12 AWG |
| 24A | 30A | 5.8 kW | 10 AWG |
| 32A | 40A | 7.7 kW | 8 AWG |
| 40A | 50A | 9.6 kW | 8 AWG (THHN in conduit) or 6 AWG (NM cable) |
| 48A | 60A | 11.5 kW | 6 AWG (THHN in conduit) or 4 AWG (NM cable) |
*Typical sizes for short residential runs with copper conductors. Actual wire size depends on the wiring method, insulation temperature rating, terminal ratings, run length (voltage drop) and the code edition enforced locally. Your electrician makes the final call.
Why the 125% Rule Exists
Breakers and wiring are rated for loads that come and go. A charger pulling its full current for three, six or ten hours straight heats conductors and terminals more than an intermittent load. Sizing the circuit at 125% of the continuous load, so the load is 80% of the rating, keeps temperatures within safe limits and prevents nuisance trips on long charging sessions.
Bigger Isn't Always Better
A car can only accept as much AC power as its onboard charger allows. Many EVs top out around 7.2–11.5 kW. If yours accepts 7.7 kW, a 48A charger on a 60A circuit won't charge it any faster than a 32A charger on a 40A circuit. It just costs more in copper and uses more panel capacity.
- Check your vehicle's maximum AC charging rate in the owner's manual or spec sheet.
- Consider the next vehicle too. Running wire for a larger circuit now and setting the charger lower can be a smart middle ground.
- If panel capacity is tight, a smaller circuit or load management may avoid an upgrade entirely.
Other Circuit Rules to Know
- Dedicated circuit. The charger shouldn't share its circuit with other loads.
- Two-pole breaker. Level 2 uses 240 volts across two hot conductors.
- Match the setting. Chargers have a DIP switch, dial or app setting for maximum current, which must be set to match the breaker. Tesla's Wall Connector is configured during commissioning.
- GFCI. Hardwired chargers include their own ground-fault protection. Outlet-based installs often need a GFCI breaker. See NEMA 14-50 vs. hardwired.
- Breaker trips during charging? Stop and have it checked. It can mean a mismatched setting or an overheating connection. See EV charger repair.
