31 (C) now aligns with the Code's broader language (like Article 392), allowing these smaller conductors and detailing how to calculate ampacities, the number of conductors permissible in cable trays, how to size cable trays correctly by width, layering. The updated section 690. 305(a)(3), or comparable standards promulgated by States operating OSHA-approved State plans. In addition, this document contains several references to provisions of the National Electric Code. The primary rulebook used in the safe use of cable trays is NEC Article 392. This is a description of how to select, install, and support these metal or plastic frames, on which electrical wires are installed.