NEC 310.60 (C) (2)(b) permitted cable derating

[wgmacfarlane]

Why does the NEC article 310.60(c)(2)(b) say where the burial depths are deeper than shown in a specific underground ampacity table or figure, an ampacity derating of 6% per ft increase in depth for all values of rho shall be "permitted".
Should it not say required?
The consequenses are a reduction of cable life.

 

[charlie b]

Good question. You have seven more days to submit a suggested revision to the NFPA (for the 2017 edition).

My only guess is based on the fact that the entire article addresses the determination of ampacity under engineering supervision. I think they are simply giving us a process that has their blessing, without actually telling us how to do our jobs.

Welcome to the forum.