The standard bottom configuration for ventilated trough cable tray is a corrugated bottom with 27/8 inch bearing surfaces - 6 inches on centers and 21/4 inch x 4 inch ventilation openings. They are commonly used where cable support uniformity and cable containment are more important than maximum airflow. Standard Widths: Sidewall Heights: Standard Lengths: Material Thickness by. The primary rulebook used in the safe use of cable trays is NEC Article 392. Note that wider rung spacings and wider cable tray widths decrease the overall strength of the cable tray. Cables Smaller than 4/0 AWG/Kcmil (120 Sq. 10 (B) (1), the smallest size single conductor allowed to be installed in a cable tray is 1/0 AWG.