Jadnashua
Retired Defense Industry Engineer xxx
40A circuit, 50A receptacle is code compliant...not a great idea to then plug in an actual 50A device, which may not trip the breaker, as it may be only drawing 40A. Unlike where they prohibit putting a 20A receptacle on a 15A circuit, but you can install a 15A one on a 20A circuit...there, the receptacle does limit what can be plugged in, and both the wiring and receptacle should be fine. IOW, on a 40 or 50A circuit with a receptacle, both the plug and receptacle are exactly the same, so you CAN overload it (by not abiding by the 80% rule).That is the way it should be.
And the reason the plugs have different blade contacts.
Good Luck.
Many EVSE's are available in 32 and 40A versions, and if you buy one with a plug attached, BOTH have the same 50A one...only one of those should be installed on a 40A branch circuit...there's nothing to prevent the unknowing user to plug in something that is too large for the circuit, unlike a 15A receptacle installed on a 20A circuit. Good for one, good for all? Seems like a disconnect to me! A common connection point for many is to share the electric dryer socket, and it just may be a 40A circuit and they're trying to install a 40A device that will fit, but shouldn't be used.
Mine is installed correctly, so I'm not concerned about it, but still wonder about the wisdom of allowing a 50A receptacle on a 40A circuit. Obviously, if the load actually was a real 50A, the 40A CB would trip, probably fairly quickly. But, it would not trip quickly, if at all, on a 40A load, which had the same plug, but should not be installed (nothing obvious to the average user since it fits).