220V line install

It depends more on your EVSE (the charging cord) than the car. Normally the one that comes with the car is 120V 15A compatible, but apparently the Prime's EVSE can do 240V for a 15A or bigger circuit. So 15A circuit if you're using the Prime's EVSE with a 240V to NEMA 5-15 adapter.

If you're getting a different EVSE, go with whatever amperage it's designed for.

A little more info, the Prime will draw 12A on a 15A EVSE like it's own EVSE. That's because it's supposed to draw 80% of what the circuit is rated for (15A x 80% = 12A). If you get a dedicated EVSE you could go with a 240V 20A one, but again the Prime will charge at 80% of that, or 15A. (20A circuit x 80% = 15A draw). Apparently if you go with a bigger EVSE (40A, 70A, etc.) the Prime won't draw anymore than 15A. But if you installed one you still need to use the right cables for the EVSE, not the car, so that if someone ever hooks up their Tesla or Bolt they don't fry the wires.

 

Check for any rebates/tax credits available in your area to ameliorate installation costs. We decided to "future proof" to some degree by installing a ChargePoint Home Flex (NEMA 6-50 circuit) almost for free after all the credits. Our utility also allows up to $200 back per year if WiFi monitoring is allowed (they may reduce draw during peak season hours, but you can bypass when a faster charge is required).

We don't require more oomph right now, but it is nice to be able to charge to Prime in far less time than with the stock charger (now takes about 1.5 hours to fully charge), and know we can handle higher capacities for future EVs.

 

an electrician with a tesla? i'm envious

 

max the Prime takes is 16amp so 20amp breaker is fine if you dont carr about future-proof.
If your house is old with 100amp electrical panel, installing future proof line with 40-50 breaker will require to upgrade the panel as well.
In short, sometime going for 40-50 amp breaker does not make sense.