Expansion Joint for Cable Trays in Factory Buildings
Cable tray expansion joints are essential to accommodate thermal expansion and contraction, prevent structural stress, and ensure long-term system reliability.
Purpose of Expansion Joints
Cable trays in factory buildings are subject to thermal expansion and contraction due to temperature fluctuations. Without proper expansion joints, trays can bend, tear from supports, or cause bolt elongation, leading to misalignment or system failure . Expansion joints absorb these movements, maintaining the integrity of both the tray and the cables.
Material Considerations
- Aluminum trays expand and contract more than steel, requiring more frequent expansion joints. Aluminum is lightweight and corrosion-resistant but highly sensitive to temperature changes .
- Steel trays are heavier and more stable, requiring fewer joints but stronger supports .
- Fiberglass trays have different thermal properties and may allow longer spacing between joints .
Placement and Spacing
- Straight segments: For steel, place expansion joints every 30 meters; for aluminum, every 15 meters. If temperature differences exceed 50°C, reduce spacing to 20 meters (steel) or 10 meters (aluminum), .
- Building expansion joints: Install cable tray expansion joints within 500 mm of structural expansion or settlement joints, with compensation ≥ joint width + 20 mm .
- Maximum spacing based on temperature differential: For a 70°C differential, steel trays: 102 ft, aluminum: 52 ft, fiberglass: 133 ft .
Installation Guidelines
- Anchoring: Secure the tray at the midpoint between expansion joints with hold-down clamps. Use expansion guides at other supports to allow sliding movement .
- Gap setting: Determine the expansion joint gap using the expected maximum and minimum tray temperatures. For example, if the installation temperature is 50°F, maximum 100°F, and minimum -28°F, the gap may be set at 3/8 inch .
- Bonding jumpers: Size bonding jumpers to match the tray's fault current capacity to maintain electrical safety, even if future circuits increase load .
- Clamping: Avoid clamping trays too tightly to supports; expansion guides should allow smooth longitudinal movement .
Standards Compliance
- NEC Section 300-7(b): Requires raceways, including cable trays, to have expansion joints where necessary to compensate for thermal movement .
- NEMA VE 1: Provides detailed guidance on expansion joint installation, gap settings, and bonding requirements .
Summary
Properly designed and installed cable tray expansion joints prevent mechanical stress, maintain alignment, and ensure electrical safety in factory buildings. Material selection, spacing, anchoring, and gap settings must be tailored to the tray type, environmental conditions, and applicable standards to achieve long-term reliability .
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