Cable Tray Expansion Joint Installation Method

Cable tray expansion joints should be installed at designated points with proper support, gap settings, and expansion guides to accommodate thermal movement and prevent structural stress. Key Steps for Installation1. Identify Expansion Joint Locations Expansion joints must be installed where the cable tray passes through building expansion joints or areas subject to significant temperature variations.

Placement should follow approved shop drawings and consider environmental conditions such as rooftop exposure or large seasonal temperature changes. 2.

Support Placement

Position cable tray supports within 2 feet of each side of the expansion joint splice plates. Avoid clamping the tray too tightly; it must be able to slide freely to accommodate expansion and contraction. Anchor the tray at the support closest to the midpoint between expansion joints using hold-down clamps, while other supports use expansion guides to allow sliding movement.

3.

Gap Setting

Determine the expansion joint gap based on the temperature at installation and the expected temperature range. Use a nomograph or calculation method as per NEMA VE 1 standards to set the correct gap. For example, a steel tray with a 100°F differential may require an expansion joint every 128 feet, while aluminum may require one every 65 feet.

Adjust the gap according to the metal temperature at the time of installation to ensure proper thermal compensation. 4.

Installation of Splice Plates and Bonding Jumpers

Install expansion joint splice plates and bonding jumpers as provided by the manufacturer. Ensure electrical continuity across the joint by connecting bonding jumpers properly. 5.

Fire and Barrier Considerations

Where trays pass through floors or fire barriers, use approved sleeves and seal with fire-resistant materials to maintain fire integrity. 6.

Final Checks and Testing

After installation, perform a continuity test to ensure electrical integrity. Verify that all supports, clamps, and expansion guides are correctly positioned and allow free movement of the tray. Ensure that the tray covers are secured, especially for rooftop installations exposed to sunlight.

7. Compliance with StandardsFollow NEC Section 300-7(b) and NEMA VE 1 guidelines for thermal expansion and contraction. Evaluate environmental conditions, tray material, and cable type to determine proper joint placement and configuration.

By following these steps, cable tray expansion joints will effectively accommodate thermal movement, prevent stress on the tray and cables, and ensure long-term system reliability.