Ob- The original post was evolved and it was an attempt to see if the rules for roof top temperature could be followed and if the rule for 310.15(A)(2) could be also incorporated.
Picture this: Ambient temperature based on ASHRAE is 89 degrees F in Detroit. Add to that 40 degrees F for the adder mentioned in T. 310.15(B)(2)(c) for a conduit installed 4" above the roof. Now we have 129 degrees and we need a THWN conductor that will be adjusted to that temperature and still be rated for 34 amperes. Since 10' of wiring in the 100' run example exceeds the limit we can not ignore the temperature correction factor.
