MikeD wrote:jjeff: It is my understanding (anyone please correct me if I'm mistaken) that EVSE's are designed such that the load carrying (stranded) copper wires in its charging cord are as thin as allowed (to improve its safety as thinner copper wires tolerate frequent flexing better, to reduce cost, reduce weight, etc) but as a result must use high temperature tolerant insulation (typically 105 C?). This means that at maximum rated load the EVSE cord runs hot (close to the insulation rating) and so the circuit wires connected to it must function not only as the current conductor but also as a "heat sink", i.e. they must be of thick enough gauge so that their (equilibrium?) running temperature does not exceed the rating of their insulation AND this temperature does not exceed the rating of the breaker that they are connected to (typically 75 C). Hence the special 80% rule for EVSE circuits.
Does this understanding help clarify things?
I looked at a couple of my EVSEs. My OEM '12 has 105c wiring on both input and output, 12 gauge capable of 20a continuous(mine was upgraded by EVSEupgrade.com).
My '13, also upgraded by EVSEupgrade.com has 90C wiring on both input and output, 12 gauge and again capable of 20a continuous.
My 30a(continuous) GE EVSE has 10g 80c output wiring and a 60c 8g input pigtail 14-50 I installed.
I'm not really sure why the differences in C but AFAIK all 10g wiring should be able to handle 30a continuous. Of course stranded wire does vary in the diameter of the individual wires that make up the bundle, the finer the wire the more flexible it would be and the more amperage it should be able to carry for a given diameter of the bundle, the C rating is the rating of the jacket around the wire.