Your cable tray length must always be longer than or equal to the support span you have selected. Here's a simplified overview: These figures may vary by manufacturer, material, and design. However, manufacturers. Choosing the appropriate size and dimensions for a cable tray is critical for performance, maintenance, and potential future improvements. In this. 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. NEC 392 recognizes several cable tray types, each. National Electrical Code (NEC) specifies the capacities of cables rated at 2000 volts or less in cable trays.