For any newbie researching this, I am posting following, comments I retrieved from these forums.
And I do lose sleep over thinking this.
Research -
Insightman - 7400 W/240 V = 30.83 A so 32 Amps will be more than enough. I'd choose a 25-foot cord for maximum flexibility.
Ericy - To some extent you can future proof - in 5 years you might get a different car, for example, and the cost of a 40A EVSE isn't really much more than a 32A EVSE.
IDRW - No harm future proofing the electricals with a 50 amp. The car decides what power it needs and wont draw more than 32A.
TOI - (recognizing there may be a gap in knowledge, so clarification may be required
having a 50A circuit available doesn't mean it's going to force 50A upon the charger... nay nay... think of amperage as the amount of power that can be safely pulled by the device attached... voltage is the force at which it is able to be applied... so, plugging a 16A or 32A device into a 50A plug/service, is perfectly acceptable... so long as the device in question or local regulations don't require a more closely matched circuit protection level. (always over-size your wiring whenever possible, e.g. run wires expecting the worst that circuit will ever see for a constant load, and life is good)
F14Scott -
Because car chargers draw continuously, code requires EVSE loads to be a maximum of 80% of the circuit's breaker, e.g. a 50 Amp breaker may only use a 40 Amp connector (the "charger" is actually built into the car; the box with a cable you hang in your garage is properly called a "connector" because all it does is allow the 240V, whatever Amperage, AC electricity to flow into the car, whose internal charger then converts the juice to DC and directs it into the big battery). As others have said, just because you have a 40 amp connector doesn't mean your car can or will pull that much; it pulls what its internal charger is able to pull or, in some cars with the feature, what the user sets the draw to be.
If your house supports it, I recommend a 60 Amp breaker, which could then supply up to 48 Amps. That is the draw of most Teslas, so it is, IMO, the de facto standard for high performance home charging. Plus, if your car's charger pulls less than 48 Amps (like the SE's, which pulls up to 32A), you've got even more headroom before wires get hot, etc.
Assuming your house wiring can support a 60A breaker, the material cost difference between installing and wiring for a 60A circuit and, say, a 30A circuit would probably be $100.
ingightman - I'm sure you've already read the Owner's Manual, but make sure your electrician installs at least a 40-Amp breaker if you want to use your EVSE at the 32-Amp level that will fully satisfy your SE's 7.4 kW thirst.
GvilleGuy- I am slowly coming up to speed on what it will take to become a Mini Cooper SE owner. I am grateful to this forum for assisting my armchair research. It sounds like if I -
A) Get a 50 amp circuit installed in my garage with a NEMA 14-50 outlet, then I can...
B) Purchase a 40 or 50 amp level 2 pluggable wall mount charger, which, using the PLUG and not hard-wired, would provide up to 40 amps. And the Mini needs 32 amps of that capacity. (To future proof for a Tesla down the road, I would instead install a 60-amp circuit)
C) I also need to question the electrician about whether a GFCI will be required on the circuit, which could potentially cause issues with the charging unit GFCI.
GetOffYourGass - My JuiceBox reports the Mini pulls 30.9A when charging. The EVSE can supply up to 32A. This lines up nicely with the sticker which claims a 7.4kW on-board charger.
At 240V / 30.9A (7.4kW), assuming an efficiency of 90% (anyone have a better number?), it takes 4h20m to charge that 28.9kWh (usable) battery from empty to full.
At 240V / 30A (7.2kW), it takes 4h28m to charge to full.
That's only an 8 minute difference. Only charging from 50% to full? It's only 4 minutes.
I wouldn't think twice about a 30A EVSE for this car.
Puppethead - I had wiring for 60 amp done, but currently have a 40 amp breaker for my Grizzl-E set to provide 32 amps which is the maximum my car takes. But I only wanted to pay once for the wiring, so I had the heavier gauge wiring used. Replacing a breaker is pretty easy when it comes time to upgrade.
From Amazon review:
ran a 6-3 wire through my attic, punch a hole in my main breaker box. But before snapping my 220v 50amp breaker, I connected the my ground wire to the ground bus bar, the White wire to the Neutral bus bar, then, hot wires red and black to either side of the actual breaker, snap it and ...VOILA!