Code reference · NEC 625.41; 625.42; 240.6(A)
NEC 625: EV charger circuit sizing
EVSE is a continuous load: the branch circuit must be rated at least 125% of the charger's maximum current (625.41/625.42). The standard ladder: 16 A charger → 20 A circuit · 24 A → 30 A · 32 A → 40 A · 40 A → 50 A · 48 A → 60 A.
Working backwards (the installer's 80% rule): an existing 50 A circuit supports at most 40 A of continuous charging; a 60 A circuit supports 48 A (~11.5 kW at 240 V).
An Energy Management System (625.42(A)) may limit the calculated load — useful when panel capacity is tight.
Run the numbers yourself
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More references: NEC Table 310.16 ampacity, explained · The NEC 705.12 120% rule, actually explained · What wire size for a 100 A sub panel? · NEC 706: battery energy storage disconnects · NEC 240.4(D): the small-conductor overcurrent caps · Voltage drop and the NEC: what's required vs recommended · all 97 references