Connecting jumper wires to cable trays

Bonding jumpers are installed across cable tray sections to ensure electrical continuity and proper grounding, especially at expansion joints, painted trays, or adjustable fittings.

When Jumpers Are Required

Bonding jumpers are necessary in the following situations:

• Expansion joints or adjustable fittings where the tray may move or flex .
• Painted or powder-coated trays, as coatings can block electrical continuity .
• High-vibration environments where standard splice plates may loosen over time .
• If the connection resistance exceeds 0.0003 ohms, a jumper ensures compliance and safety . For standard, stationary, uncoated trays with UL-classified splice plates, jumpers may not be required if the metal is tightly bolted and electrically continuous .

Materials and Types

• Copper bonding jumpers are preferred for conductivity and flexibility .
• Common sizes include 2 AWG soft drawn tin-plated copper or smaller braided straps like #6 AWG for shorter spans .
• Insulation is often flame-retardant PVC (VW-1), resistant to oil, acid, and abrasion .
• Standard lengths vary from 7–36 inches, depending on the tray configuration and gap to be bridged .

Installation Steps

1. Identify connection points: Use the 5/16-inch square holes at the ends of the tray channel, not the splice plate bolts .
2. Attach lugs: Bolt each end of the jumper securely to the tray channel. Ensure metal-to-metal contact by removing paint or coating at the connection point if necessary .
3. Span the gap: The jumper should bridge the discontinuity of expansion splices or adjustable fittings without tension .
4. Verify continuity: Measure resistance to ensure it is below 0.0003 ohms for safety .
5. Optional hardware: Use serrated nuts or star washers to improve electrical contact and prevent loosening .

Additional Considerations

• Aluminum trays: Avoid bare copper jumpers in moist environments to prevent electrolytic corrosion; use insulated conductors with tin or zinc-plated connectors .
• Wire mesh trays: If used as an equipment grounding conductor, a separate jumper may be recommended to maintain low impedance and reduce noise .
• Ground network integration: All metal parts of the building, including trays, beams, and conduits, should be bonded to maintain equipotential grounding . Properly installed bonding jumpers ensure electrical safety, code compliance, and reliable grounding across the cable tray system, particularly in dynamic or coated installations.