There are numerous situations where the equipment will specify "Copper conductors only". I've had inspections where the contractor will install a lug that is CU/AL rated and attempt to use Aluminum wire. Won't pass under my watch. I recently (about 3 mo. ago) had a steamer made by Jucuzzi that specified 105° Copper wire for the hook up to the appliance. Contractor had to hustle around and find said wire in #6 awg.
