NEC 625 EV Circuit — Method
Electric-vehicle supply equipment runs for hours, so the code classes it as a continuous load. NEC 210.20(A) and Article 625 require the branch-circuit conductors and the overcurrent device to be rated at not less than 125% of the EVSE rated current. So minimum circuit ampacity = charger amps × 1.25; select the next standard breaker at or above that, and choose conductors with an ampacity at least equal to the breaker rating (after any temperature/grouping derating).
Frequently Asked Questions
EVSE is a continuous load, so the breaker must be at least 125% of the charger current. A 40 A charger needs 40 x 1.25 = 50 A, so a 50 A breaker; a 32 A charger needs 40 A.
NEC 210.20(A)/Article 625 require continuous loads (3+ hours) to be sized at 125% so the conductors and breaker are not run at their full rating continuously, which would overheat them.
The conductor ampacity must be at least the breaker rating after derating. A 50 A circuit typically uses 6 AWG (about 6 mm2) copper at 75 C; confirm with ambient and grouping derating in the cable sizing calculator.
Hard-wired or dedicated-outlet circuits are required for Level 2 EVSE; it cannot share a general-purpose circuit. The dedicated circuit is sized at 125% of the charger current.
Single-phase: amps = kW x 1000 / voltage. Three-phase: amps = kW x 1000 / (root 3 x line voltage). A 7.4 kW single-phase charger at 240 V draws about 31 A.
EV Charging Circuit Sizing (NEC 625)
A home or workplace EV charger draws near its maximum current for hours at a time, which is the definition of a continuous load. The wiring rules therefore add a 25% margin so the circuit is never run at its limit continuously.
The 125% rule
Minimum branch-circuit ampacity and the overcurrent device = EVSE current × 1.25. Pick the next standard breaker, then conductors rated at least to that breaker after derating.
Putting it together
Convert the charger kW to amps if needed, apply 1.25, choose the breaker, and verify the conductor with the cable sizing calculator for the real installation method and temperature. For charge duration use the EV charging time calculator.
Related: EV Charging Time, Cable Sizing, Voltage Drop.