22 (A) (1) (a) through 392. 22 (A) (1) (c) outlines the rules for placing multiple conductor cables within a cable tray. The capacity does not depend on size only but also on cable type, diameter, and allowable fill capacity to allow safe and efficient operation. This comprehensive guide will take you. When dealing with any mixture of cables, it is crucial to follow the National Electrical Code (NEC) regulations, specifically 392. This is a description of how to select, install, and support these metal or plastic frames, on which electrical wires are installed. Formula 1: Cable Tray Fill Ratio Where: Total Cable Area (mm²) = Sum of.