We have multiple runs where a portion of the run is under ground in concrete encased ductbank and then it transitions to the overhead within the facility. Only about 20% of the run is under ground, the rest is overhead. Right now I am basing an entire run on the ampacity requirements for the underground, are there any references in the NEC other than 310.15(A)(2) that would allow me to use a free air ampacity if there is only a certain % of the run is installed under ground?
Thank you.
Thank you.