The NEC rule requires that the cable cross-sectional areas together may not exceed 50% of the tray area (width x depth = fill). Cables will nearly completely fill the cable tray when reaching the 50% cable fill, due to empty space between the surface of the. The spacing between trays, whether horizontal or vertical, depends on various factors like cable type, environment, and tray material. Proper installation can significantly reduce electromagnetic interference, prevent fire hazards, and improve overall efficiency. This article provides an in-depth. NEC Article 392 outlines the key rules for installing and maintaining industrial cable tray systems. 16, tray fill, ampacity adjustment, voltage-drop checks, grounding, and IEC design cross-checks.