And to add more confusion, even if you have 90c rated conductors and 90c rated terminals, you would still need 90c rated equipment to use the 90c ampacity in the circuit. 90c terminals are common but 90c equipment is not.
Correct. It is generally when you terminate on separately-installed connectors in an otherwise-empty enclosure, that you get to take credit for a 90C rating of the terminals. Or in an enclosure that contains nothing but busbars. Everything inside the enclosure needs a 90C rating to take credit for 90C terminations.
It is very common that the lug is marked for 90C, but built within equipment that isn't. 75C is the most common rating of equipment. There is a line drawn at 100A and less, such that 60C is the default for 100A and less, while 75C is the default over 100A. Think of it as a burden of proof, for the manufacturer to have listing and labeling that spells out the 75C rating. Cases where the 60C rating governs a design are usually more academic than practical, because most equipment carries a 75C listing to override this default.
