Cable Tray Expansion Joint Manufacturing Method

Cable tray expansion joints are manufactured and installed to accommodate thermal expansion and contraction, using splice plates, expansion guides, and bonding jumpers, with material and gap settings determined by temperature differentials.

Materials and Fabrication

Cable tray expansion joints are typically made from the same material as the tray itself, such as steel, aluminum, or fiberglass, to ensure compatible thermal expansion properties ( ). The expansion joint consists of splice plates that connect two tray sections while allowing longitudinal movement. These plates are fabricated to precise dimensions to maintain structural integrity and electrical continuity.

Bonding jumpers are incorporated around the splice plates to match the fault current capacity of the tray side rails or cross-section, ensuring safety and compliance with electrical standards ( ).

Manufacturing Process

Material Selection: Choose tray-compatible metals or composites with appropriate corrosion resistance and mechanical strength ( ). Cutting and Shaping: Splice plates are cut and formed to match the tray profile, including holes for bolting and slots for thermal movement. Surface Treatment: Steel trays may be pre-galvanized or hot-dip galvanized, while aluminum trays rely on natural oxide layers for corrosion resistance ( ).

Assembly: Splice plates are pre-assembled with expansion guides and bonding jumpers to allow sliding movement while maintaining electrical continuity ( ).

Gap Setting and Installation

The expansion gap is calculated based on the maximum and minimum expected temperatures at the installation site.

Using NEM

A VE-1 or VE-2 standards, the gap is set to allow the tray to expand and contract without distortion or stress ( ). For example, a steel tray with a 100°F temperature differential may require an expansion joint every 128 feet, while aluminum requires one every 65 feet ( ). The installation process includes: Anchoring the tray at the midpoint between expansion joints with hold-down clamps.

Securing all other supports with expansion guides to allow sliding movement. Ensuring bonding jumpers are properly sized and connected to maintain electrical continuity ( ).

Standards and Guidelines

Manufacturing and installation must comply with NEC Section 300-7(b) and NEMA VE-1/VE-2 standards, which provide guidance on spacing, gap settings, and environmental considerations to prevent structural stress and maintain long-term reliability ( ).

Summary

The manufacturing of cable tray expansion joints involves material selection, precise fabrication of splice plates, incorporation of expansion guides and bonding jumpers, and careful gap setting based on thermal calculations. Proper adherence to standards ensures the system accommodates thermal movement, maintains electrical safety, and prevents mechanical damage to the tray or cables.