Cable tray gap

The connection gap between cable tray sections is primarily determined by thermal expansion, material type, and installation temperature, with typical gaps ranging from 3/8 inch for steel to larger values for aluminum.

Thermal Expansion Considerations

Cable trays expand and contract with temperature changes. Steel trays typically require an expansion joint every 128 feet for a 100°F temperature differential, while aluminum trays require one every 65 feet. The gap at the expansion joint is calculated based on the expected maximum and minimum temperatures, as well as the installation temperature.

For example, if a steel tray is installed at 50°F with an expected range from -28°F to 100°F, the gap may be set at approximately 3/8 inch. Proper gap sizing prevents structural stress and maintains alignment.

Installation and Bonding

At expansion joints, bonding jumpers should be installed to maintain electrical continuity. These jumpers are sized to match the fault current capacity of the tray side rails or cross-section. If future upgrades involve higher-rated circuits, the bonding jumpers may need adjustment, but following NEC Table 250-95 ensures compliance for standard installations.

Spacing Between Trays

When installing multiple trays in parallel, maintain a minimum horizontal spacing of 0. 6 meters for maintenance access and airflow. For power and signal trays, a minimum separation of 0.

5 meters is recommended to reduce electromagnetic interference, which can be reduced to 0. 3 meters if shielding is used. Vertical spacing between stacked trays should be at least 150 millimeters to allow heat dissipation and future cable additions.

Material and Environmental Factors

The type of tray material affects gap requirements. Aluminum, being more prone to thermal expansion than steel, requires closer attention to gap sizing. Environmental factors such as direct sunlight, indoor vs. outdoor installation, and ambient temperature fluctuations should also be considered when determining the connection gap.

Summary

Steel trays: Expansion joint gap ~3/8 inch for typical temperature ranges. Aluminum trays: Require more frequent expansion joints due to higher thermal expansion. Parallel trays: Minimum 0.

6 meters horizontal spacing; 0. 5 meters for power vs. signal trays. Stacked trays: Minimum 150 mm vertical clearance.

Bonding jumpers: Ensure electrical continuity across gaps. Properly accounting for these factors ensures structural integrity, electrical safety, and ease of maintenance in cable tray installations.