Cable sizing for cable with different installation medium

[xyz123]

hye

I have got a case, where i have few cables which pass through different installaiton mediums e.g. above ground, direct buried.

On what basis shall i size the cable i.e. on above ground or direct buried. Both cases have different ampacity derating factor and hence final cable size might be different.

Thank you in advance.

 

[don_resqcapt19]

300.15(2) Selection of Ampacity Where more than one calculated or tabulated ampacity could apply for a given circuit length, the lowest value shall be used.
Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

 

[xyz123]

thanks for the reply. i looked at the extract that you sent me but frankly speaking couldnt get my head around it.

first of all it says to use lower value, which means cable might have a weak point so to speak, which can easily lead to a fault or breakdown in cable.

Secondly as per the exception, for one single cable you would have more than one sizes with junction boxes or cable joints in between. this is not practical at all..

what are your thoughts?