Power cable quantity depends on tray width, cable size, and fill percentage. Maintaining 50% capacity improves airflow and future expansion. Tray-rated power and control cables simplify compliance. Proper grounding and bonding are mandatory for metallic trays. Fill Rules for Single-Conductor Cables 4. Ampacity Derating. Several factors determine the number of cables a cable tray can hold: Cable Tray Size: The width and depth of the tray determine its total area. This is a description of how to select, install, and support these metal or plastic frames, on which electrical wires are installed. You should consider it as a series of instructions that make the buildings resistant to. Halfway through, the cable tray is full.