Classification of Cable Tray Expansion Joints

Cable tray expansion joints are classified based on material type, design, and function to accommodate thermal expansion and contraction in cable tray systems.

1. Classification by Material

• Metallic Expansion Joints: Used with steel or aluminum cable trays. Steel expands less than aluminum, requiring fewer joints over a given length, while aluminum expands more and needs closer spacing .
• Non-Metallic Expansion Joints: Used with fiberglass or plastic trays. These materials have higher thermal expansion rates, so expansion joints are spaced more closely than metallic trays .

2. Classification by Design

• Expansion Splice Plates: These are metal plates that connect two tray sections while allowing longitudinal movement. They are commonly used in metallic trays and are paired with bonding jumpers to maintain electrical continuity .
• Snap Track Expansion Guides: These guides allow the tray to slide longitudinally from a fixed point, preventing distortion or bending. Two guides are typically attached to each side rail, and the tray is anchored at the midpoint between expansion joints .
• Hold-Down Clamps with Expansion Guides: Used to secure the tray at specific points while allowing movement at other supports. This prevents tray deformation due to thermal changes .

3. Classification by Function

• Thermal Expansion Joints: Designed to absorb length changes due to temperature fluctuations. The spacing depends on the material and expected temperature differential. For example, steel trays may require joints every 128 feet for a 100°F differential, while aluminum requires joints every 65 feet .
• Structural or Mechanical Joints: These joints accommodate movement caused by building vibrations, seismic activity, or structural shifts, in addition to thermal expansion .

4. Installation Considerations

• Expansion joints must be installed with proper gap settings based on the maximum and minimum expected temperatures at the site .
• Cable trays should be anchored at the midpoint between expansion joints and secured with expansion guides at other supports to allow smooth longitudinal movement .
• Bonding jumpers around expansion splice plates should match the fault current capacity of the tray to maintain electrical safety .

Summary

Cable tray expansion joints are classified primarily by material (metallic vs non-metallic), design (splice plates, expansion guides, hold-down clamps), and function (thermal vs structural). Proper selection and installation ensure the system accommodates thermal expansion and contraction, maintains structural integrity, and complies with NEC and NEMA standards .