I was looking at the ampacity ratings chart - NEC Table 310.16:
There are 3 ratings for each sized wire. Using #2 THHN wire as an example:
Allowable Ampacity: 95 Amps at 60ºC / 115 Amps at 75ºC / 130 Amps at 90ºC
I have also seen wet rating and dry rating.
Is there a bottom line to which rating you use to know the rating of the particular wire? Is it at 60, 75 or 90 degrees? Does it depend on where you live and what the air temperature is?