90C apparently means 90C only. The equipment might draw enough current through that lug to raise the lug temperature to 90C. So conductor insulation with a 60C or 75C insulation rating might be damaged.
Thank you. That makes sense.
But what if you stay below the 60C or 75C ampacity limits? It seems to me that this would present no risk of overheating.
Lug temperature will be driven by heat coming in from the field terminated wire side as well as heat coming in from the equipment side. Your statement is looking only at the former. I'm suggesting that a lug marked "90C conductors only" would be telling you that the latter may cause temperatures at the lug to exceed 75C regardless of the conductor size used for the field terminated wires.
That is what I was thinking also but imagine a panel and all the breakers are using 90C wire at a higher ampacity then wouldn't the bus bar get hot and cause the 60C insulation to go above it's temp. rating
