Choosing the right breaker is one of the most important parts of a Level 2 charger installation. The breaker protects the wiring, and it must be sized for the continuous load the charger will draw. A breaker that is too small causes nuisance trips, and wiring that is not protected properly can overheat. The sizing should always be confirmed by a licensed electrician.
The 80 percent rule
Electrical practice treats an EV charger as a continuous load, which means it can run at full power for three hours or more. For a continuous load, the circuit may use at most 80 percent of the breaker rating. To find the breaker size, divide the charger's current draw by 0.8.
The math is simple. A 40-amp charger divided by 0.8 is 50 amps, so it needs a 50-amp breaker. A 48-amp charger divided by 0.8 is 60 amps, so it needs a 60-amp breaker.
Common pairings
| Charger current | Breaker size needed | Typical connection |
|---|---|---|
| 40 amps (9.6 kW) | 50 amps | NEMA 14-50 plug-in or hardwired |
| 48 amps (11.5 kW) | 60 amps | Hardwired |
A 48-amp charger cannot be used with a NEMA 14-50 outlet. A 50-amp outlet on a 50-amp breaker cannot safely carry 48 amps continuously, because 48 amps is more than 80 percent of 50. That is why 48-amp installations are hardwired on a 60-amp circuit.
Size for the maximum, not the setting
Some chargers can be set to draw less current than their maximum. Even so, the breaker and wiring should be sized for the highest current the charger can draw, not for a lower setting you use today. A future change in setting, a different charger or a different car should not overload the circuit.
Breaker, wire and outlet must match
The breaker, the wire gauge and the receptacle all have to agree. A 50-amp breaker needs conductors rated for at least 50 amps, and a NEMA 14-50 receptacle is designed for a 50-amp circuit. The correct wire size depends on the distance, the conductor material and the installation conditions, which is why your electrician will select it for your specific run.
Dedicated circuits
An EV charger should have its own dedicated circuit. Sharing a circuit with other large loads, such as a dryer or an electric range, can cause the breaker to trip and can overload the wiring. Your electrician can check which circuit has room and whether a new one is needed.
How this applies to EVIQO chargers
EVIQO's 40A (9.6 kW) NEMA 14-50 plug-in chargers, in both J1772 and NACS versions, are designed for a 50-amp circuit. The 48A (11.5 kW) hardwired chargers require a 60-amp circuit. The J1772 model that can be installed as a 40A plug-in or a 48A hardwired unit uses a 50-amp circuit for the plug-in setup and a 60-amp circuit for the 48A hardwired setup. All EVIQO chargers have a 25 ft cable and a 3-year warranty, and a 4-year extended warranty is available for an extra charge.