Cable tray expansion joint installation requirements

Cable tray expansion joints must be installed at designated locations with proper gap settings, supports, and bonding to accommodate thermal expansion and contraction.Placement and SupportExpansion joints should be installed only at structural expansion joint locations or where thermal movement is expected due to temperature variations . A support should be located within 2 feet of each side of the expansion joint splice plate. Cable trays must not be clamped too tightly at these supports, allowing free expansion and contraction without distortion . The tray should be anchored at the support closest to the midpoint between expansion joints using hold-down clamps, while expansion guides at other supports allow sliding movement .Gap SettingThe expansion joint gap depends on the expected temperature range and the material of the tray. For example, for a 100°F temperature differential, steel trays require an expansion joint every 128 feet, and aluminum trays every 65 feet . The installation temperature determines the initial gap setting. A nomograph can be used to calculate the correct gap:Plot the maximum expected tray temperature on the vertical axis.Plot the minimum expected tray temperature on the opposite vertical axis.Draw a line connecting these points.Project the installation temperature onto this line to determine the required gap on the horizontal axis (e.g., 3/8 inch gap at 50°F installation temperature), .Bonding and GroundingBonding jumpers should be installed around the expansion joint splice plates to maintain electrical continuity. They should be sized to match the fault current capacity of the tray side rails or the cross-section of a one-piece tray . This ensures that future increases in circuit ratings or protective device sizes do not require resizing the bonding jumpers.Material ConsiderationsSteel trays expand less than aluminum, so expansion joints are spaced farther apart.Aluminum trays have higher thermal expansion and require closer spacing of expansion joints .Temperature extremes, such as rooftop installations, require careful consideration of both tray and structural material differences to prevent bending, snaking, or bolt hole elongation .Compliance and StandardsInstallation should follow NEMA VE2 guidelines, which provide detailed instructions for support spacing, expansion joint placement, and installation practices for all types of cable trays, including ladder, trough, center rail, and wire basket trays in aluminum, steel, or fiberglass . Proper adherence ensures safety, structural integrity, and electrical continuity. By following these specifications, cable tray systems can safely accommodate thermal expansion and contraction while maintaining mechanical stability and electrical grounding.