Article Overview
An expansion joint in a cable tray is a specially designed connection that allows the tray to safely expand and contract due to temperature changes, preventing structural stress and damage to cables.
Purpose and Function
Cable trays, typically made of metal, expand and contract with temperature fluctuations. Without proper accommodation, this movement can cause bending, misalignment, or even tearing of the tray and cables. Expansion joints are installed to absorb these movements, allowing the tray to slide or expand without causing strain on the system, ensuring long-term reliability and safety of the electrical installation .
How Expansion Joints Work
Expansion joints usually consist of splice plates, sliding guides, and bonding jumpers. The tray is anchored at specific points, while expansion guides allow sections to move back and forth. This setup ensures that the tray can expand or contract freely without distorting or damaging the cables . The correct placement and sizing of expansion joints depend on the material of the tray, the length of the run, and the expected temperature variations .
Installation Guidelines
- Spacing: For steel trays, expansion joints are typically installed every 30 meters, and for aluminum trays, every 15 meters. Shorter intervals may be required if temperature differences exceed 50°C .
- Support: Supports should be placed within 2 feet of each side of the expansion joint, but the tray should not be clamped so tightly that it cannot move .
- Standards: Installation should follow NEC Section 300-7(b) and NEMA VE 1 guidelines, which emphasize compensating for thermal expansion and contraction to maintain system integrity .
Importance
Properly installed expansion joints prevent structural stress, bolt elongation, and cable damage, especially in environments with large temperature swings, such as rooftops or outdoor industrial settings. They are essential for maintaining the safety, alignment, and longevity of cable tray systems .
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It is important that cable tray installations incorporate features which provide adequate compensation for their thermal
