Generally, standard trays require supports every 6 to 10 feet, while heavy-duty, long-span trays can handle distances of up to 20 feet between supports. This guide covers the critical steps, from selecting the right electrical cable tray and performing accurate cable fill. Ladder cable tray: The interior usable width of the tray must be at least as wide as the total of the cables' individual layer-installed diameters. Solid bottom cable tray: The sum of cable diameters must not be greater than 90% of the allotted cable tray width. The systems are installed on ceilings, walls or floors. Various galvanisation surfaces can be applied to improve corrosion.