When vertically installed, the height of cable trays from the ground should not be lower than 1. If the above standards cannot be met, metal covers must be added for protection. NEC cable tray sizing follows Article 392, which. In practice, cable tray dimensions are a system of interrelated measurements —width, depth, length, and material thickness—that directly affect cable fill compliance, heat dissipation, structural loading, and long-term expandability. The standard provides formulas to calculate the working load and safety margin. However, manufacturers. This publication is intended as a practical guide for the proper and safe* installation of cable ladder systems, cable tray systems, channel support systems and associated supports.