Cable tray tee expansion joint

Cable tray tees require expansion provisions to accommodate thermal contraction and expansion, typically using expansion splice plates and guides to allow longitudinal movement.

Understanding Thermal Expansion in Cable Trays

All cable tray materials, including steel, aluminum, and fiberglass, expand and contract with temperature changes. The amount of movement depends on the material type, the length of the tray run, and the temperature differential between the hottest and coldest days at the installation site . Without proper expansion provisions, cable trays can bend, tear loose from supports, or cause bolt hole elongation at splice points .

Expansion in Tee Fittings

For tee fittings, such as horizontal or ladder-style tees, expansion must be considered at the junctions where the main run meets the branch. Expansion splice plates are installed at these points to allow the tee to move longitudinally without stressing the tray or cables . The tray should be anchored at the support nearest the midpoint between expansion splice plates, while expansion guides at other supports allow sliding movement in both directions .

Installation Guidelines

1. Determine Temperature Differential: Calculate the maximum and minimum site temperatures to find the total temperature differential (∆T). This will dictate the spacing of expansion joints .
2. Select Expansion Splice Plates: Use manufacturer-recommended splice plates compatible with the tray class and material. Steel, aluminum, and fiberglass have different maximum spacing limits (e.g., steel: 102 ft, aluminum: 52 ft, fiberglass: 133 ft for a 70°C differential) .
3. Set Proper Gap: At installation, set the gap between expansion splice joints to accommodate expected thermal movement .
4. Anchor and Guide: Anchor the tray at the midpoint between expansion joints and use expansion guides at other supports to allow free movement .
5. Avoid Over-Clamping: Do not clamp the tray too tightly at supports near expansion joints, as this prevents proper expansion and contraction .

Standards and References

• NEMA VE-2 Section 3.4.2 provides guidance on expansion joint spacing and installation.
• NEC Section 300-7(b) requires raceways to have expansion joints where necessary to compensate for thermal movement . By following these practices, cable tray tees can safely accommodate thermal expansion and contraction, ensuring long-term reliability and preventing mechanical stress on both the tray and the cables.