Biggest EV charger on a 100 A circuit

An existing 100 A circuit supports at most 80 A of continuous EV charging: 100 ÷ 1.25 = 80 A (the inverse of NEC 625.41's 125% continuous-load rule). At 240 V that is about 19.2 kW of charging power.

Set the charger to 80 A or less — most hardwired EVSEs have DIP switches or a commissioning app for exactly this. A charger factory-set higher than 80 A on this circuit is a code violation even if the breaker doesn't trip immediately; continuous loading at 100% of breaker rating is what the 80% rule exists to prevent.

Also verify the existing conductors: a 100 A breaker on old wiring doesn't guarantee the wire ampacity matches today's Table 310.16 values after derates, and receptacle-connected EVSE (NEMA 14-50) adds its own requirements — including GFCI protection for the receptacle in newer code cycles (625.54).