AmpSizerWhat circuit does an EV charger need?
EV charger circuit
6 AWG copper
on a 60 A device · 10 AWG ground · 3/4" conduit at 23% fill
1% drop at 40 ft
- Ampacity wants6 AWG
- Voltage drop wants10 AWG
- Current the conductor has to carry
- 60 A
- Usable ampacity after derating
- 65 A (table 65)
- Longest run before the drop passes 3%
- 122 ft
- In metric sizes
- 13.3 mm²
— had the ampacity and 240.4(D) still rejected it, at 0 A.
Enter the charger output current, not the breaker. The 125% of 625.41 is applied for you.
A sizing aid from the published NEC tables, not a design — have it signed off by a licensed electrician against the code your inspector enforces. Calculations follow the US NEC; outside the US, follow your local electrical code.
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MonthlyOne thing a month worth measuring, testing or recalculating on a home electrical system — the part of sizing that happens after the install. No product pitches, and nothing that needs a live panel.
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What size circuit does an EV charger need?
The AmpSizer EV charger circuit for a 48 amp charger on 240 volts is 6 AWG copper on a 60 amp breaker, with a 10 AWG ground, in three-quarter inch EMT. Voltage drop over 40 feet is 1%.
The 60 amps is not a rounding-up of 48. Charging equipment is a continuous load under 625.41, so the circuit is sized at 125% of the charger’s output — 48 × 1.25 is 60, and that is a standard rating.
It also works backwards, which is the more useful direction: a 50 amp breaker supports a 40 amp charger, and a 60 amp breaker supports 48. A charger set to draw the full rating of its breaker is the most common fault in this whole subject.
The chargers people actually buy, with the circuit each one legally needs.
| Charger output | Circuit at 125% | Breaker | Copper | Aluminium | Ground | Approx. miles per hour |
|---|---|---|---|---|---|---|
| 16 A | 20 A | 20 A | 12 AWG | 12 AWG | 12 AWG | ~13 |
| 24 A | 30 A | 30 A | 10 AWG | 10 AWG | 10 AWG | ~19 |
| 32 A | 40 A | 40 A | 8 AWG | 8 AWG | 10 AWG | ~25 |
| 40 A | 50 A | 50 A | 8 AWG | 6 AWG | 10 AWG | ~31 |
| 48 A | 60 A | 60 A | 6 AWG | 4 AWG | 10 AWG | ~37 |
| 64 A | 80 A | 80 A | 4 AWG | 2 AWG | 8 AWG | ~49 |
| 80 A | 100 A | 100 A | 3 AWG | 1 AWG | 8 AWG | ~61 |
Copper at 75 °C on a short run. Range added assumes 240 V and about 3.5 miles per kWh, which is a mid-size sedan in mild weather.
The three ways this goes wrong
Sizing the charger to the breaker. A 60 A breaker is a 48 A charger. Setting the charger to 60 because the breaker says 60 puts a continuous load at 100% of the device, and it will hold — for a while.
Forgetting the panel. Adding 60 amps of continuous load to a house is a load calculation, not a circuit. Where the service will not take it, load management is the answer and it is a fraction of the cost of an upgrade.
Assuming the far garage is the same as the near one. A charger at the end of a 150 ft feeder is a voltage-drop problem, and a charger that sees low voltage draws its rated current anyway — so the loss lands in the conductor as heat rather than in the car as range.
Frequently asked questions
What size wire for a 48 amp EV charger?
6 AWG copper on a 60 A breaker for a normal garage run. At 100 ft, voltage drop is still only 2.5% so 6 AWG holds; past about 120 ft you want 4 AWG. Aluminium is 4 AWG in place of the 6, and it is a legitimate choice on a long run out to a detached garage.
Can I put a 48 amp charger on a 50 amp breaker?
No. 48 × 1.25 is 60, so a 48 A charger needs a 60 A circuit. What you can do is turn the charger down: almost every unit has a current setting, and setting it to 40 A makes it legal on a 50 A breaker. That setting is in software, so it needs to be checked after any firmware update.
Is a NEMA 14-50 receptacle a 50 amp circuit?
The receptacle is rated 50 A, and a charger plugged into it may draw no more than 40 A continuously — 50 ÷ 1.25. Most portable chargers sold with a 14-50 plug are set to 32 A or 40 A for exactly that reason. The four conductors are two hots, a neutral and a ground, even though the charger itself does not use the neutral.
Do I need a neutral for an EV charger?
A hardwired Level 2 charger almost never needs one — it is a 240 V load with no 120 V circuits inside it, so two hots and a ground. A 14-50 receptacle does need one, because the receptacle is a general-purpose outlet and something else might be plugged in. Hardwiring saves a conductor and a connection.
How many miles per hour of charging does each size add?
Roughly 3 to 4 miles of range per kWh delivered, so a 32 A charger at 240 V adds about 25 miles an hour, a 40 A about 30, and a 48 A about 37. Doubling the charger rarely halves anything useful in practice, because most cars sit overnight — the argument for 48 A is a short window, not a faster car.
How we calculate this
Worked example
With Charger output current 48, One-way run 40, System voltage 240 V, Metal Copper, Terminal rating 75 °C — the usual breaker, Ambient 86, Current-carrying conductors in the raceway 3, this page works out 6 AWG copper. on a 60 A device · 10 AWG ground · 3/4" conduit at 23% fill
- Current the conductor has to carry60 A
- Usable ampacity after derating65 A (table 65 )
- Longest run before the drop passes 3%122 ft
- In metric sizes13.3 mm²
Sources:
Sizing decisions that are not about wire
The panel may be the constraint, not the circuit. A 60 A charger circuit in a house with a 100 A service usually needs a load calculation, and often a load-management device that throttles charging when the rest of the house is busy. That is cheaper than a service upgrade.
Hardwired beats a plug for high currents. Above 40 A a receptacle is a wear point carrying a continuous load for hours, and receptacle failure on 14-50 outlets is a well documented problem.
A GFCI or breaker with self-test may be required depending on where the charger is and which code edition applies. Garage and outdoor receptacles have GFCI rules of their own that a hardwired unit avoids.