But, if it supports 40A charging it'll charge at 40 amps unless you back off the charging rate (which nobody does, typically). You'd always assume 40 amps for circuit purposes.

I’m not disputing that you have to derate conductors based on excess temperature according to NEC. I’m saying that no EVSE exists that will pull 37A. It’ll pull either 32A or 40A and needs wiring and a breaker backing it that either is 40 or 50 amp rated, respectively.

Also, Romex (NM-B) is always considered to be 60C rated, and you cannot assume 90C rated conductors (in the case of a properly rated 90C conductor like THHN) because the outlet and breaker must also be matched and capable of 90C. No 40-50A breaker I’m aware of is 90C rated. They’re typically 75C, and sometimes 60. Likewise, no NEMA 14-50 outlet I’ve ever seen is 90C rated. They’re all 75 or 60C. The crappy Leviton one mentioned in the article is 60C. That means everything is essentially treated as 60C for derating purposes besides derating factors for things like bundled conductors.

In comparison, Bryant and Hubbell outlets (the more expensive ones EV forums tend to recommend) are 75C rated, so you can usually use the 75C derating tables for everything, since breakers are THHN are typically capable of 75C. MC cable would also be 75C rated, as well.

Thanks! The further clarification and use of terminology is much needed here. Plus I needed that citation!