6 AWG vs 4 AWG for EV Chargers: Which Wire Size is Best?
A complete guide to sizing your electrical wire for 40 Amp and 48 Amp electric vehicle charging stations.
The 125% Continuous Load Rule
When deciding between 6 AWG and 4 AWG, the first thing you need to understand is how the National Electrical Code (NEC) views EV chargers. Because they run for several hours at a time, they are considered continuous loads.
The NEC requires the circuit and breaker to be sized at 125% of the charger’s maximum output. For a popular 48-amp charger, you need a 60-amp breaker (48A × 1.25 = 60A). For a 40-amp charger, you need a 50-amp breaker (40A × 1.25 = 50A).
When to Use 6 AWG
6 AWG is the most common wire used for EV installations, but it comes with a major caveat regarding the type of wire you buy.
- 6 AWG NM-B (Romex): Rated for 55 amps (60°C). This means it is perfect for a 50-amp breaker and a 40-amp charger. It cannot be used for a 60-amp breaker/48-amp charger setup.
- 6 AWG THHN/THWN-2 in Conduit: Rated for 75 amps (90°C), but typically clamped at 65 amps (75°C) for most terminations. This means if you pull individual THHN wires through a conduit, 6 AWG is fully compliant for a 60-amp breaker and a 48-amp charger.
When to Use 4 AWG
4 AWG is a thicker, more expensive wire, but it solves a very specific problem for DIYers and electricians.
- 4 AWG NM-B (Romex): Rated for 70 amps (60°C). If you want to install a 48-amp charger (requiring a 60A breaker) and you want to use standard NM-B wire inside your walls without running conduit, you must upsize to 4 AWG.
- Long Distance Runs: If your panel is located far away from your garage (e.g., over 100 feet), upgrading from 6 AWG to 4 AWG is often necessary to prevent voltage drop, ensuring your car charges efficiently.
Keep Your EV Cables Organized
Whether you choose 6 AWG THHN in conduit, 4 AWG Romex, or just need to secure the charging cord itself, our parametric cable cleats keep installations clean and professional. Customize the exact diameter and 3D print in durable PETG.
