Answer: The NEC does not have a specific installation clearance, but indicates in section 318-6 (b) that cable trays should be exposed and accessible. Setting up an efficient cable tray access path is crucial for ensuring that maintenance personnel can safely and effectively access and maintain electrical systems. A rung spacing of 6 to 9 inches (150 to 230 mm) is preferable when. The primary rulebook used in the safe use of cable trays is NEC Article 392. You should consider it as a series of instructions that make the buildings resistant to. us-trations without notice. The information in this publication was considered.