Article Overview
Cable tray expansion joints are sized based on the tray width and thermal expansion requirements, with typical widths matching the tray (6–48 inches) and gap settings determined by temperature differentials.
Width of Expansion Joints
The width of a cable tray expansion joint generally matches the width of the cable tray it connects, which can range from 6 inches to 48 inches for ladder-type trays, depending on the application and cable load . Wider trays may require stronger rungs or load reductions to maintain structural integrity. The expansion joint must accommodate the full tray width to allow smooth longitudinal movement without stressing the cables or tray supports .
Length and Gap Setting
The length of the expansion joint splice plate is determined by the thermal expansion and contraction of the tray material. The gap setting is calculated based on the maximum and minimum expected temperatures at the installation site. For example, using a nomograph or NEMA VE-1/VE-2 tables:
- For a steel tray with a 100°F temperature differential, an expansion joint is typically required every 128 feet .
- For an aluminum tray, the spacing is approximately 65 feet .
- For a 70°C differential, steel trays require joints every 102 feet, aluminum every 52 feet, and fiberglass every 133 feet . The installation temperature also affects the initial gap setting. For instance, if the tray is installed at 50°F with a maximum of 100°F and minimum of -28°F, the expansion gap may be set to 3/8 inch to allow proper movement .
Installation Considerations
- Supports should be placed within 2 feet of each side of the expansion joint .
- The tray should be anchored at the midpoint between expansion joints and secured with expansion guides at other supports to allow sliding movement .
- The expansion joint must allow longitudinal movement without distortion, preventing bending, tearing, or bolt elongation .
Summary
- Width: Matches cable tray width (6–48 inches typical).
- Length/Gap: Determined by material, temperature differential, and installation temperature (e.g., 3/8 inch gap for moderate conditions).
- Spacing: Steel 102–128 ft, Aluminum 52–65 ft, Fiberglass 133 ft depending on temperature range.
- Supports: Within 2 ft of joint, with midpoint anchoring and expansion guides. Proper sizing and installation of expansion joints ensure safe thermal movement, prevent structural damage, and maintain cable integrity.
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