Cable tray expansion joints require jumper wires
Yes, cable tray expansion joints generally require flexible copper jumper wires to maintain electrical continuity and ensure safety.
Why Jumper Wires Are Needed
Cable tray expansion joints are installed to accommodate thermal expansion and contraction of the tray system due to temperature fluctuations, preventing stress, misalignment, or damage to the cables and tray structure . Because expansion joints allow movement, the metal parts of the tray may not maintain continuous electrical contact. Flexible copper bonding jumpers are required to bridge the gap and ensure proper grounding across the moving sections .
Installation Guidelines
- Placement: Bonding jumpers should be installed around the expansion joint splice plates and sized to match the fault current capacity of the cable tray side rails or cross-section .
- Support: Cable tray supports should be located within 2 feet of each side of the expansion joint, and expansion guides should allow the tray to slide without distortion .
- Material Considerations: If the tray is painted, powder-coated, or made of materials that reduce conductivity, jumpers are essential because coatings can block electrical continuity .
- NEC Compliance: NEC Section 300-7(b) requires cable trays to accommodate thermal expansion and contraction, and proper bonding jumpers help maintain compliance by ensuring electrical continuity across joints .
When Jumpers May Not Be Required
For standard rigid metallic splice plates in stationary, uncoated trays, bonding jumpers may not be necessary if the plates provide sufficient electrical continuity and are tightly bolted . However, in the case of expansion joints, the movement of the tray makes jumpers a critical safety measure, regardless of plate type.
Summary
In practice, any cable tray expansion joint should include flexible copper bonding jumpers to maintain grounding and meet safety standards. This ensures that the system remains electrically continuous, prevents inspection failures, and accommodates thermal movement without compromising safety .
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