Cable tray expansion joint spacing

Cable tray expansion joints are designed to accommodate thermal expansion and contraction, with spacing and gap settings determined by material type, temperature differential, and installation conditions.

Expansion Joint Spacing

The spacing of expansion joints depends on the cable tray material and the temperature differential between the hottest and coldest expected conditions:

• Steel cable trays: Maximum spacing ~128 feet for a 100°F differential (VE-1 standard) or 102 feet for a 70°C differential (VE-2 standard) .
• Aluminum cable trays: Maximum spacing ~65 feet for 100°F differential or 52 feet for 70°C differential .
• Fiberglass trays: Maximum spacing ~133 feet for 70°C differential . The installation temperature also affects the gap setting, as the expansion joint must allow for movement in both directions from the fixed support point.

Gap Setting

The expansion joint gap is calculated using the expected maximum and minimum temperatures and the installation temperature:

1. Plot the maximum expected tray temperature on the vertical axis.
2. Plot the minimum expected tray temperature on the vertical axis.
3. Draw a line connecting these points.
4. Project the installation temperature onto this line and down to the horizontal axis to determine the gap setting. For example, a steel tray with a 100°F differential and installation temperature of 50°F may require a 3/8 inch gap .

Installation Guidelines

• Supports: Place a support within 2 feet of each side of the expansion joint splice plate.
• Anchoring: Anchor the tray at the midpoint between expansion joints using hold-down clamps.
• Expansion guides: Use guides at all other support locations to allow longitudinal movement without distortion .
• Splice plates: Bolted type, typically 8 nuts and bolts per plate, made of high-strength steel (ASTM A1011 HSLAS, Grade 50, Class 1) .

Material and Standards

• Standards: NEMA VE-1 and VE-2 for metallic cable trays; ASTM specifications for steel and coatings (A1011, A653, A123, B633) .
• Tray types: Ladder, trough, solid bottom, and channel types; straight sections typically 10–40 feet in length, widths 6–36 inches .
• Rungs: Minimum cable-bearing surface 7/8 inch, radius edges, spaced 6–12 inches apart; radius fittings 9 inches at center .

Key Considerations

• Expansion joints should only be installed at points where thermal movement is expected, not solely at structural expansion joints.
• Proper gap setting and support placement prevent bending, snaking, or bolt elongation due to thermal expansion .
• Material differences between tray and supporting structures require unique solutions for thermal compensation . By following these specifications and standards, cable tray systems can safely accommodate thermal expansion and contraction while maintaining structural integrity and electrical continuity.