Most EV owners work from the standpoint of what kind of charging capability they WANT, and then wire their EVSE outlet from there. My shoe is on the other foot: I want to work with the wiring I have, and choose the highest amperage ESVE I can safely use.
I have a new-to-me 2013 Leaf S. The car has (apparently, from the dashboard time-to-charge display) all the charge options: 120v, 240v/3kW, and 240v/6 Kw. It even has the optional CHAdeMO port, though the little stripper does not even have cruise control! But what of that...
FWIW, I have the LeafSpy diagnostic app, and though all 12 bars of battery health show on the dash, LeafSpy indicates a battery SOH just shy of 90%.
That's the background on my car. Now onto the specifics of my garage's capability.
I have a 100 amp sub panel in my garage, with two 15-amp circuits, one 20-amp circuit (all three are 120 V) and room left for one 240 v breaker. One of the 15/120 circuits is dedicated to a fish pond pump that runs full-time, but its draw is very small--probably less than one amp. The other two 120 circuits are for lighting and occasional use outlets--power tools, compressor, etc.
The sub panel is about 120 feet from the main service entrance, which is 200 amp, and currently (no pun intended) feeds the garage through a 240 v/30 amp breaker.
I measured the diameter of the service wire (black, white, and bare ground) at the sub panel, and the copper conductor is about 3 mm in diameter. I think that corresponds to either 8 or 10 gauge wire. (Knowing the previous owner who ran the wire, I am going to guess it is more likely to be 10 than 8 gauge.)
I know the proposed circuit for the Leaf is going to have to be 125% of the actual charge rate.
So, can anyone out there calculate the maximum charging load--and hence amperage output of the EVSE--I can safely use?