Allowable Fill For Outdoor Cable Trench

[EECougar]

I've looked through the NEC but I can't seem to find anything that points to the allowable fill for outdoor precast cable trench. Does anyone know the applicable guide/section for this?

 

[7anoter4]

In my opinion, if the trench is not exposed to sunshine then:
Art.390 Underfloor Raceways
(C) Trench-Type Raceways Flush with Concrete
390.6 Maximum Number of Conductors in Raceway
shall not exceed 40 percent of the interior crosssectional area of the raceway.

 

[EECougar]

Thanks for your reply! I saw that section as well but this is going to be outdoor and will definitely be exposed to sunshine/weather. I'm still struggling to locate any guidelines on this.