Cable tray expansion joints are installed to accommodate thermal expansion and contraction, ensuring structural integrity and preventing stress on cables and trays.

Understanding Thermal Expansion in Cable Trays

Cable trays, especially metal ones, expand and contract with temperature changes. Steel and aluminum trays have different expansion rates; for example, a 100-foot aluminum tray can expand or contract by approximately 2 inches with a 100°F temperature change, while steel expands less . Without proper expansion joints, trays can bend, tear from supports, or cause bolt elongation at splice points .

Components of an Expansion Joint

1. Expansion Joint Splice Plates: These connect two tray sections while allowing movement. They should be installed at calculated intervals based on tray material and expected temperature variation .
2. Bonding Jumpers: Ensure electrical continuity across the joint.
3. Expansion Guides: Allow the tray to slide back and forth at support points, preventing distortion .
4. Hold-Down Clamps: Used at the midpoint between expansion joints to anchor the tray while allowing movement at other supports .

Installation Guidelines

• Support Placement: Place supports within 2 feet of each side of the expansion joint splice plate . Do not clamp the tray too tightly; it must be free to expand and contract.
• Joint Spacing: Follow NEMA VE 1 standards for maximum tray lengths between expansion joints. For a 100°F differential, steel trays require joints every 128 feet, aluminum every 65 feet .
• Gap Setting: Determine the expansion gap based on the highest expected tray temperature at installation. Use nomographs or manufacturer guidelines to calculate the correct gap .
• Environmental Considerations: Install expansion joints in areas with significant temperature fluctuations, such as rooftops or outdoor industrial settings .

Best Practices

• Evaluate the type of cable and environmental conditions to determine joint placement .
• Ensure proper alignment and secure bonding to maintain electrical continuity.
• Use expansion guides at all supports except the hold-down clamp location to allow smooth movement.
• Regularly inspect joints for wear or misalignment, especially in high-temperature or outdoor installations. By following these guidelines, cable tray expansion joints can effectively absorb thermal movements, maintain system integrity, and prevent damage to both the trays and the cables they support .