We are replacing a 2500kva, 21kv x 277/480 pad mount transformer. On the secondary side of the transformer, there is 373 Kcmil DLO cable (RHHW) that connects the transformer to 4000A bussduct (see attached pictures). There are (7) conductors per phase. After looking at my DLO ampacity chart (similar ampacity as 310.15(B)(16-17) but with odd DLO sizes), I don't see how they made the 373 work for a 2500kva transformer (3010A @ 480V) unless they are using the free air rating of the cable. I know that the utilities tend to use non standard cabling with they do this, but this is not utility. This is customer owned primary equipment. I'm trying to find out if the free air rating can be used in this application because the transformer is large open structure and the transition can is large and short. Once we replace the transformer, we own what is there and need to make sure we address any existing issues may be present.