Cable trays passing through expansion joints

Cable trays passing through building expansion joints must include properly designed expansion joints and guides to accommodate thermal expansion, contraction, and structural movement.

Key Considerations

Thermal Expansion and Contraction: 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 about 2 inches with a 100°F temperature change, while steel expands less, around 1 inch for the same conditions . Without proper accommodation, trays can bend, “snake,” or tear from supports . Expansion Joints Placement: Expansion joints should be installed at or near building expansion joints, typically within 500 mm (about 20 inches) on both sides . The joint must allow movement equal to the building joint width plus an additional 20 mm to ensure full compensation . For long straight runs, NEMA VE 1 and VE 2 standards recommend spacing based on material and temperature differential: steel trays every 128 feet and aluminum trays every 65 feet for a 100°F differential . Support and Anchoring: Supports should be located within 2 feet of each side of the expansion joint splice plates. Trays must not be clamped too tightly; expansion guides should be used at all other support points to allow sliding movement. The tray should be anchored at the midpoint between expansion joints with hold-down clamps . Splice Plates and Hardware: Standard splice plates are insufficient for expansion. Slotted or elongated holes in expansion plates allow bolts to slide as the tray moves, preventing stress and deformation . Bonding jumpers are recommended to maintain electrical continuity across expansion joints . Material-Specific Considerations: Aluminum trays expand more than steel, so joint spacing and guide design must account for the material's thermal coefficient. Environmental factors, such as rooftop installations or outdoor exposure, may require closer spacing or additional expansion guides . Standards Compliance: Installation should comply with NEC Section 300-7(b) and NEMA VE 1 guidelines, ensuring that trays can safely accommodate thermal and structural movements without compromising system integrity .

Summary

When cable trays pass through building expansion joints, it is essential to:

• Install expansion joints near the building joints with sufficient movement allowance.
• Use expansion guides and proper anchoring to allow sliding and prevent distortion.
• Select material-appropriate spacing and hardware, including slotted splice plates.
• Follow NEC and NEMA standards to ensure long-term reliability and safety. Properly designed expansion provisions prevent mechanical stress, maintain alignment, and protect both the tray and the cables from damage due to thermal or structural movement .