HPWC instructions different than NEC rules?

[davewill]

This is done in residential homes usually only for the range in the kitchen. This specific instance (50A outlet on 40A breaker with 8 ga wire) is allowed because:

1. There is no such thing as a 40A outlet. Available NEMA outlets jump from 30A to 50A.
2. 8 ga wire is rated for 40A, and breaker is 40A, thus protecting the wire.
3. The appliance nameplate rating is 40A, so it will not attempt to draw more current than that.
4. The appliance is permanently installed, so it's highly unlikely someone would plug a different device into the 50A outlet.
5. The appliance is not classified as a "continuous load", so it's not subject to the 80% rating rule.

If any of those things are not true, then you cannot use the 50A outlet on a 40A breaker.

Small correction, number 5 has nothing to do with it. Many 30a or 32a EVSEs are installed on 40a circuits with 14-50 or 6-50 outlets.

 

[SomeJoe7777]

Small correction, number 5 has nothing to do with it. Many 30a or 32a EVSEs are installed on 40a circuits with 14-50 outlets.

You're right, but I was also thinking that what you cannot do is take a device rated for 50A, but because it is classified as a continuous load would not draw more than 40A due to the 80% rule, and use it on this setup.

Of course, that would also break rule #3 as well (nameplate rating > 40A).

 

[davewill]

You're right, but I was also thinking that what you cannot do is take a device rated for 50A, but because it is classified as a continuous load would not draw more than 40A due to the 80% rule, and use it on this setup.

Of course, that would also break rule #3 as well (nameplate rating > 40A).

#3 is the only real issue. There are also a lot of 6-50s with 40a breakers (I've even heard of 30a breakers) in people's garages for welders. The upshot is and always has been that you cannot simply assume that any random 50a outlet is backed by a 50a circuit. That's one of the problems with the adapter method the UMC uses. I thought hard about getting a Jesla, but I have one of the 40a 6-50 installations, and couldn't use it.

I think a switch arrangement would have been a much better solution. It would also make third-party adapters safer to use. That's why I went with an OpenEVSE for portable use instead, despite it being much bulkier. I can set it for whatever amperage is safe in the particular circumstance.