Code reference · NEC 625.41; 625.42; 625.43; 240.6(A); Table 310.16
What breaker for a 40 A EV charger? (NEC 625)
A 40 A EV charger (9.6 kW at 240 V) is a continuous load, so its branch circuit must be rated at least 40 × 125% = 50 A (NEC 625.41/625.42). The smallest standard breaker that satisfies that is 50 A (240.6(A)).
Conductors must carry at least 50 A: minimum 8 AWG copper at the 75°C column of Table 310.16, or 6 AWG aluminum. Long runs to a detached garage should also be checked against the 3% voltage-drop recommendation — at 40 A continuous, drop adds up fast.
Two things installers miss: (1) hardwired EVSE above 60 A needs a disconnecting means within sight (625.43); (2) if the panel can't spare 50 A of calculated load, 625.42(A) lets an Energy Management System cap the charger's draw instead of forcing a service upgrade — most modern EVSEs can be current-limited in software, and the load calculation may then use the limited value.
Run the numbers yourself
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More references: What breaker for a 16 A EV charger? (NEC 625) · What breaker for a 24 A EV charger? (NEC 625) · What breaker for a 32 A EV charger? (NEC 625) · What breaker for a 48 A EV charger? (NEC 625) · What breaker for a 64 A EV charger? (NEC 625) · What breaker for a 80 A EV charger? (NEC 625) · all 97 references