The standard NEMA lengths for cable tray are 12, 20, 24 and 30-feet, although some manufacturers like Eaton offer cable tray in lengths up to 40 feet. 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. Selecting the appropriate cable tray dimensions and size is essential for many kinds of reasons: The size of the cable tray has to be suitable on account. When choosing the size of cable tray, it is a tradeoff between the existing volume of cable and the future volume of cable. A tray that is too small will overheat and physically damage, and too large tray will drain the project budget. It is grounded on 40 years of experience in the manufacturing. National Electrical Code (NEC) specifies the capacities of cables rated at 2000 volts or less in cable trays.
[PDF Version]