So there's no such thing as a charging cable that would only pull 24 amps (and so be ok w/ 30amp circuit) ?
Clipper Creek makes a 30 amp 240v connectable EVSE Model LCS-30 that connects to a 30 amp Supply and pulls max 24 amps. It will provide a decent rate L2 charge at about 5.8 kw.
Thanks for these pointers (you and @mkettner). They are several hundred dollars. The only reason to try to go to a smaller amperage cable would be to be able to use with a 30amp receptacle at her son's house, the idea being it's easier to find one of those. But I think she's better off sticking with the 3XB3 that'll come with the car (i.e. free), and put that money into another 40amp outlet at her son's house if need be (he or I can install it).
I am curious though: if I bought that 30amp cord, how does the car know to pull less juice ? I'm thinking the other conductors in the connector allow the car to handshake with some kind of logic in the box in the cord, and tell it "you're actually connected to a car and not some kid's fingers" while the cord tells the car "you can only draw 24 amps from this charger (dunno why it insists on making this a hyperlink)"; do I have that about right ?
Yes. Most electric ranges require 40 amp 240v supply and come with a cord with a 14-50P plug that plugs into a 14-50R receptacle protected by a 40 amp breaker.
Duh, I actually installed one of those when we remodeled kitchen 3 years ago (with 40amp breaker and 8/3 NM-B).