The vertical safety distance should generally be no less than 300 mm between the top of the cable tray and the bottom of the ventilation duct. This spacing is important because it: In real installations, insufficient spacing often leads to airflow restriction and maintenance. 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. Cable trays should not be installed parallel above thermal pipelines. Shortest and Straightest Path: To reduce cable loss and simplify maintenance, cable routes should be as short and straight as. When installing two cable trays in parallel at the same height, the distance between them should be no less than 0.