Cable tray bridging locations must be supported at recommended spans, typically 1/4 of the tray length, to minimize deflection and stress, following NEC, NEMA, and manufacturer guidelines.

Support and Span Guidelines

Cable trays must be supported at regular intervals to maintain structural integrity and prevent excessive deflection. According to NEMA BI 50015 and BI 50016, the recommended support location for bridging or splice points is at 1/4 of the tray span. This ensures that stress and deflection are minimized at splice plates or fittings, which are common bridging points in a tray system .

• Straight sections: Support should be placed at both ends and at intermediate points according to the tray's load rating.
• Splice plates: Use vertical adjustable or heavy-duty expansion splice plates at bridging locations to accommodate thermal expansion and maintain alignment .
• Rung spacing: For ladder-type trays, a rung spacing of 6 to 9 inches (150–230 mm) is recommended to support cables and prevent sagging .

Load and Material Considerations

• Ensure the tray material (steel, aluminum, or FRP) is suitable for the expected load and environmental conditions .
• Avoid placing excessive cable weight at bridging points; adhere to fill limits: 40% for power cables, 50% for control cables .
• For metallic trays used as equipment grounding conductors, verify that the cross-sectional area of side rails meets NEC requirements for the specific circuit rating .

Thermal Expansion and Environmental Factors

• Bridging locations should account for thermal expansion and contraction, especially in outdoor or sun-exposed installations. Expansion splice plates or adjustable supports help prevent stress on the tray and cables .
• Nonmetallic trays may require additional support or spacing adjustments due to lower rigidity .

Best Practices

• Maintain clearances for maintenance access (minimum 12 inches above trays) and avoid prohibited areas such as hoistways .
• Separate high-power and low-power cables to prevent electromagnetic interference at bridging points .
• Ensure proper bonding and grounding at bridging locations, using insulated conductors and grounding clamps where necessary . By following these guidelines, cable tray bridging locations will remain structurally sound, electrically safe, and compliant with NEC and NEMA standards, while minimizing maintenance issues and potential system failures.