312.9 Amp Feeder

[kwired]

I don't think I can. It is a tough section to interpret.

Made even more complicated by the language in the un-enforceable Annex B.310.15(B)(3) which starts to talk about 25% of the total run specifically for burial depths in addition to the 10' / 10% "adjacent" business.

But B.310.15(B)(3) isn't about a single raceway buried all alone it is about duct banks. I think OP's application is for a single raceway. The only thing adjacent that applies is the above ground at one ambient temp being "adjacent" to the underground portion of same conductor at a different ambient temp.

 

[ptonsparky]

Fortunately, my area SED inspector feels as I do, 10' each end is good, in this case.