Re: Coated vs. uncoated condutors
NEC Table 8 DC resistance information, that provides different resistance based on coated or uncoated conductors.
I think this dates back to the days when RHW was popular. The copper was always tinned. Today this is not usually an issue unless you are retrofitting an existing installation that uses the old RH or RHW conductors.
Why specify one vs. the other? You wouldn't today. THHN, THWN, etc is uncoated.
-Hal