Properly calculating cable tray fill capacity is essential to avoid overheating, equipment damage, and code violations. You can determine the fill by dividing the total cable area by the tray's usable area (Width × Depth). NEC 392 recognizes several cable tray types, each. NEC Article 392 outlines the key rules for installing and maintaining industrial cable tray systems. These systems, made from metal or plastic, are open structures designed to support electrical conductors, ensuring proper organization and safety. Select Fill. Proper separation helps reduce electromagnetic interference (EMI), prevent data corruption, and minimize the risk of system downtime, resulting in more reliable and efficient installations.