How to handle cable tray bridging

Proper cable tray bridging requires secure support, correct bonding, and adherence to spacing and expansion guidelines to ensure safety and system reliability.

Support and Placement

When bridging cable trays, ensure that supports are strategically positioned so that connectors between horizontal sections fall between the support point and the quarter-point of the span, avoiding placement at the center or directly on supports. Use center-hung tray supports for easier installation and to allow cables to be deposited from each side. Maximum support spacing typically ranges up to 3.

6 meters (12 feet) depending on tray type and load capacity. For elbows or changes in direction, follow manufacturer instructions and NEMA VE 2 standards for support.

Bonding and Grounding

All bridged cable trays must maintain electrical continuity. Install bonding jumpers at expansion joints and at intervals of at least every 15 meters (50 feet) to ensure proper grounding. Conduit drop-outs should be bonded to the tray using a compression lug or grounding bushing to maintain safety and compliance.

Expansion and Movement

Cable tray bridging often spans long distances or crosses building expansion joints. Use expansion connectors at these points to accommodate thermal expansion and structural movement. Ensure that trays are fastened with guides that allow longitudinal movement to prevent stress on the cables and tray system.

Material and Tray Type Considerations

Select tray materials based on the environment: aluminum for corrosion resistance and reduced weight, stainless steel for high-corrosion areas, and fiberglass for electrically isolated or damp environments. For bridging, ventilated or ladder-type trays are preferred to allow airflow and reduce heat buildup, while solid-bottom trays may be used where aesthetics or protection from debris is important.

Practical Tips

Maintain minimum bend radius for cables at tray exits to prevent damage. Avoid overloading the tray; consider the weight and number of cables when bridging. Ensure that all trays in the bridged system are mechanically and electrically continuous.

Follow local codes such as the NEC or CEC and manufacturer installation instructions for compliance. By following these guidelines, cable tray bridging can be performed safely, maintaining both structural integrity and electrical reliability.