Should cable trays be fitted with expansion joints

Cable trays are not always equipped with expansion joints; they are installed only where necessary to accommodate thermal expansion and contraction.

When Expansion Joints Are Required

Expansion joints in cable trays are used to absorb thermal expansion and contraction caused by temperature fluctuations, preventing deformation, misalignment, or damage to the tray and cables . According to the National Electrical Code (NEC) Section 300-7(b), raceways, including cable trays, must have expansion joints where necessary, but there is no requirement to install them in every tray run . The need depends on factors such as:

• Material of the tray: Aluminum expands nearly twice as much as steel for the same temperature change .
• Length of the tray run: Longer runs are more susceptible to thermal movement. NEMA VE-1 and VE-2 standards provide tables for maximum lengths between expansion joints based on material and temperature differential .
• Environmental conditions: Areas with large temperature swings, such as rooftops or outdoor installations, are more likely to require expansion joints .

Installation Considerations

When expansion joints are used, proper installation is critical:

• Supports should be placed within 2 feet of each side of the expansion joint splice plate .
• Expansion guides allow the tray to slide and expand without distortion, while the tray is anchored at a midpoint between joints .
• Gap settings must account for the expected temperature range at the time of installation to ensure proper movement .

Practical Implications

In many installations, especially shorter runs or areas with minimal temperature variation, expansion joints may not be necessary. Instead, trays can be installed with slight gaps and expansion guides to accommodate minor movement . Overuse of expansion joints is not recommended, as they add cost and complexity without providing additional benefit if thermal movement is minimal. Conclusion: Expansion joints are not mandatory for all cable tray installations. They are required only when the tray length, material, and environmental conditions indicate significant thermal expansion or contraction that could compromise the system's integrity . Proper planning and adherence to NEC and NEMA guidelines ensure safe and reliable cable tray performance.