EV Charger Circuit Sizing Calculator
NEC 625 branch-circuit sizing for Level 2 EV charging equipment (EVSE) — breaker and wire size from the charger's continuous current rating.
How this is calculated
NEC 625.42 classifies EV charging equipment loads as continuous loads — expected to run at maximum current for 3 hours or more, which a typical Level 2 home charging session does. NEC 625.41 and NEC 210.19(A)(1) both require the branch-circuit overcurrent protection and conductors to be sized at not less than 125% of that continuous load:
Minimum breaker / conductor ampacity = charger amps × 1.25
The breaker is rounded up to the next standard size at or above that minimum, and the wire is then sized to support that breaker (not just the raw 125% figure), which also satisfies NEC 240.4 for the overcurrent device chosen.
Dedicated circuit requirement
NEC 625.42 also requires each EVSE to be supplied by its own dedicated branch circuit with no other outlets, unless the installation uses an approved energy management system (EMS) to actively manage shared load — for example, a system that can throttle or pause charging to stay within panel capacity when other large loads are running. This calculator assumes a standard dedicated circuit, not an EMS-managed shared circuit.
How this calculator works
NEC 625.42 (continuous load, dedicated circuit), 625.41 (overcurrent protection at 125%) and 210.19(A)(1) for conductors; wire sizes from Table 310.16.
EV charger breaker and wire size by charger rating (copper)
Computed with the calculator above: breaker = next standard size at or above 125% of the charger rating; wire sized to that breaker.
| Charger rating | 125% minimum | Breaker | Wire (60°C terminals) | Wire (75°C terminals) |
|---|---|---|---|---|
| 16 A | 20 A | 20 A | 12 AWG | 14 AWG |
| 24 A | 30 A | 30 A | 10 AWG | 10 AWG |
| 32 A | 40 A | 40 A | 8 AWG | 8 AWG |
| 40 A | 50 A | 50 A | 6 AWG | 8 AWG |
| 48 A | 60 A | 60 A | 4 AWG | 6 AWG |
| 50 A | 62.5 A | 70 A | 4 AWG | 4 AWG |
| 60 A | 75 A | 80 A | 3 AWG | 4 AWG |
| 80 A | 100 A | 100 A | 1 AWG | 3 AWG |
Worked example
A Level 2 charger with a 48 A continuous rating, on copper wire with 60°C terminals.
The minimum is 48 × 1.25 = 60 A, which is itself a standard breaker size, so the breaker is 60 A. At 60°C, the smallest copper wire rated for 60 A is 4 AWG. If the panel and charger terminals are listed for 75°C, 6 AWG copper (65 A) is enough.
A 40 A charger works out to a 50 A breaker with 6 AWG copper at 60°C or 8 AWG at 75°C.
Frequently asked questions
What size breaker do I need for a 40 A EV charger?
A 50 A breaker: EV charging is a continuous load, so the circuit must be rated at least 125% of the charger's 40 A output.
Why is the breaker bigger than the charger rating?
NEC 625.42 treats EV charging as a continuous load (3 hours or more), and NEC 625.41 and 210.19(A)(1) require continuous loads to be sized at 125%. That keeps the breaker and wire from running at their limit for hours.
Can I share the circuit with other outlets?
Not normally. Each EVSE needs its own dedicated branch circuit unless an approved energy management system controls the load.
Does this check whether my panel has room?
No. Adding a 50–60 A continuous load can exceed an older service. Run a dwelling load calculation (NEC Article 220) to confirm the panel and service can carry it.
Common mistakes
- Sizing to the charger's output instead of 125%. EV charging is a continuous load (NEC 625.42), so the circuit is sized at 125% of the charger's rated current: a 48 A charger needs a 60 A circuit.
- Reading the 75 °C column with 60 °C terminals. The wire size depends on the terminal temperature rating of the breaker and the charger. With 60 °C terminals a 60 A circuit needs 4 AWG copper; with 75 °C terminals 6 AWG.
- Using NM cable at the THHN rating. Type NM cable is limited to the 60 °C ampacity of its conductors (NEC 334.80), even though the individual wires are rated 90 °C.
- Ignoring the panel. The circuit can be correct and the service still too small. Check the dwelling load calculation with the charger added.
What it does not cover
Panel capacity, multiple chargers on one circuit and energy management systems.
Sources
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