So if I have a single charger on my Model S, and we get given a 40amp wall unit, and I only reall yhave normal 10A 240V power points - what should I ask my electrician to install to get maximum charge possible for my Model S?
The question can only be answered by first knowing if you have single phase or three phase power in your house.
If you don't know the answer to this then go look at your switchboard / meter and see if you have breakers in gangs of 3 or just single ones and that answers this question.
For Melbourne single-phase, its typical that you have an 80A power feed into your house. (that is, the power cable from street to house is capable of at most 80A @ 230V and that is the typical size of the "service fuse" on the connection of your premises to the 'LV' network.)
There is significant derating that goes on and its common for you to have a 20% derating from this on the main circuit breaker, i.e. typical a 63A breaker in your fuse box.
This means that the total combination of everything electrical in your house cannot exceed 63A @ 230V = 14.4KW but reality is that a single 'breaker' will be less than that.
I don't know what is actually possible as "continual current" but making the assumption that its realistic to have a single breaker at 40A on your switchboard then with 20% derating on that it would mean an EVSE home charger could deliver 230A @ 32A = 7360W instantaneous. If we make an assumption that its 95% efficiency then that means for every hour plugged in it could provide around 7kWh/hr (230x32x0.95) of charge.
If you were connected to TOU metering (we are, NMI starts with 64) and you get off-peak electricity midnight-7am Mon-Fri then in the 8 hours offpeak you could 'add' approx 56kWh of energy into the battery.
If it would be possible for the EVSE to be wired up to continuously draw 40A (not sure yet, have to ask a sparky about that) then it would be closer to 70kWh and pretty much enough to go from the 'empty' to 'full' when on normal charging [rather than 'range' charging].
