Cable tray shrinkage joint

A cable tray shrinkage joint is a designed gap or joint in a cable tray system that accommodates thermal contraction and expansion, preventing deformation, bending, or bolt failure.

Cable trays made of metal, such as steel or aluminum, expand when heated and contract when cooled. Without proper provision for this movement, trays can bend, warp, or tear loose from supports, and bolts may elongate or break ( ). Shrinkage joints, also called expansion joints, allow the tray to move freely along its length while maintaining structural integrity and cable protection. They are particularly important in outdoor installations or areas with large temperature variations, such as rooftops or industrial facilities ( ).

• Positioning: Expansion or shrinkage joints should be installed at points where the tray is expected to experience significant thermal movement. Supports should be located within 2 feet of each side of the joint ( ).
• Anchoring: The tray should be anchored at the midpoint between joints using hold-down clamps, while other supports use expansion guides that allow sliding movement ( ).
• Gap Calculation: The size of the shrinkage joint depends on the material of the tray, its length, and expected temperature range. For example, a 100-foot aluminum tray may expand or contract by approximately 2 inches over a 100°F temperature change ( ). Proper calculation ensures the gap is neither too small (causing stress) nor too large (causing instability).
• Splice Plates and Bonding: Special expansion joint splice plates and bonding jumpers are used to maintain electrical continuity while allowing mechanical movement ( ).

• Aluminum trays expand and contract more than steel, so larger gaps or more frequent joints may be required ( ).
• Galvanized steel trays have a protective zinc coating that also affects thermal behavior slightly, but the main concern is mechanical movement ( ).

• Do not clamp the tray too tightly at supports; allow sliding movement.
• Install joints at structural expansion points rather than randomly along the tray.
• Follow NEMA VE 2 standards for spacing, guides, and expansion joint sizing to ensure compliance and long-term reliability ( ).

By properly implementing shrinkage joints, cable tray systems can accommodate thermal movement, maintain cable integrity, and prevent mechanical failures over time.