Table 300.50 vs figure 310.60 Note

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310 BLAZE IT

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I am comparing Table 300.50 vs figure 310.60 and am having a hard time deciding how to bury my medium voltage cables: We have gas lines buried at 24" so we need to coordinate around them. I would loosely consider it a commercial parking lot with 13.8(15kv cable) Putting them in a horizontal concrete encased ductbank with two other low voltage conduits feeding a transformer on grade. If my ductbank is under the gas lines we do not meet 310.60, if they are above it does not meet 300.50. We are not a supervised installation so we cannot use exception 3 on table 300.50.

Separate question but possibly relevant- what type of medium voltage equipment has 105C terminals? Is this insulation mostly just meant to assist with ambient temperature correction by section 310.60(B)(4)? I understand the note is referencing the fact that ambient temperature increases at higher depths (or rather lack of cables ability to dissipate due to earth's increasing insulation component) but is there a table that lists this ambient temperature at these depths? Is there a code section that over-rides this note on a figure? are notes on a figure enforceable language?

and what I really want to ask is why the location of tables make it difficult to find important tables like 310.60(B)(2) and its reference to '(C)(2)(b)' where this code section doesn't appear to exist... why isnt 310.60(B)(2)(b) referenced in the 310.60 Note? 6% ampacity derate per 1ft isn't so bad at all but why did I have to go through all this trouble to figure it out? I don't know if I should apologize for figuring my main question out but I still have others, so I think I should still post this. Kappa.
 
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