30Amp EV charger needs 40amp fuse?

[bdpoorte]

My friend tells me I can install a 30amp charger on the 220v outlet in my garage (but no more). But some of the specifications of the EV chargers on the market say they require a 40amp fuse to protect the 30amp charger. Will I be OK installing any of the 30amp chargers (siemens, Bosh, Blink, Clippercreek) on my 220v outlet? Can anyone help my lack of understanding on this area? Thanks!

 

[jadnashuanh]

Assuming you live in the USA, the electrical code requires you to use the 80% rule when attaching a device that can be on for more than a couple of hours continuously. This means that with say a 32A device, you'd need a 40A circuit to hard-wire it. 80% of 40 = 32A. But, you mentioned a plug. There are NO plugs or receptacles rated for 40A, and if you want to plug it in verses hardwire it, the next available receptacle and plug arrangement is a 50A one. Code requires the receptacle installed to match the supporting wiring, so if you want a plug on it, you need a 50A circuit. Crystal clear? On a 50A circuit, using that 80% rule, you could plug in something as large as a 40A device that ran continuously. Wires always have at least a little resistance in them - IOW, the wiring will warm up like a light bulb or your toaster slightly when power is flowing constantly. Using something intermittently allows the wiring to cool off in between uses. Not the case when you use it continuously, so for a safety margin, code requires you to derate the circuit to 80% of the maximum.

The difference in cost between a 30 and a 40A EVSE isn't all that much, and if you want a plug, the cost for the wiring would be the same. IF you choose to hardwire it, though, you could make the circuit for a 40A load verses a 50A one. Your i3 will work just fine with a larger EVSE, but a larger one, should you decide you have the power and want a plug, could be as big as 40A, which might make your next EV charge faster (it wont' hurt the is, but it won't help, either).

 

[alohart]

If you look at your electrical panel, what is the size of the circuit breaker for your garage outlet? If doing so is not so easy, identify your garage outlet in this image.

If your garage outlet circuit has a 30 amp capacity, you would be limited to charging at 24 amps (80% of 30 amps), so an EVSE plugged into a 30 amp circuit would need to be configured to deliver no more than 24 amps. Your i3 can charge at a maximum of 30 amps, so it wouldn't charge at its maximum speed on a 30 amp circuit, but it might be fast enough for your usage (~5 hours from empty to full).

 

[TonyWilliams]

Actually, because there is not a 40 amp outlet, NEC allows a 40 amp breaker on a 50 amp outlet.

It is dumb in the extreme, but those are the current rules.

Please use proper 50 amp rated wiring, circuit breaker, and outlet together.

If hardwired (no outlet), then it's ok and proper to use 40 amp stuff for a 25-32 amp EV charge cable.