How to ground electrical cable trays

Grounding electrical cable trays involves connecting the tray to the facility's grounding system using proper conductors and bonding methods to ensure safety and compliance with NEC standards.

Purpose of Grounding Cable Trays

Grounding cable trays provides a low-impedance path for fault currents, protecting personnel and equipment from electric shock, fire hazards, and equipment damage. It also helps dissipate lightning energy and reduces electromagnetic interference (EMI), improving system reliability and signal integrity in sensitive installations .

Methods for Grounding Cable Trays

1. Using the Cable Tray as the Equipment Grounding Conductor (EGC)
   • Metal cable trays can serve as the EGC if they meet conductivity and cross-sectional area requirements specified in NEC Table 392.60(A) and Article 250.96 .
   • All metallic trays must be grounded regardless of whether they are used as the EGC.
   • Steel trays should not be used as EGCs for circuits with ground-fault protection above 600 A, and aluminum trays above 2000 A .
2. Running a Continuous Grounding Conductor
   • A bare or insulated copper wire can run along the length of the tray, bonded at each section using UL-listed tin or zinc-plated connectors .
   • The conductor should be securely tied every 10–20 feet to prevent displacement under fault conditions.
3. Bonding Between Tray Sections
   • Use grounding clamps or bonding jumpers to electrically connect adjacent tray sections, ensuring continuity and mechanical stability .
   • For aluminum trays in moist environments, use insulated conductors to prevent electrolytic corrosion, removing insulation only at bonding points.

Material Considerations

• Copper wire: Excellent conductivity, corrosion-resistant, preferred for most installations.
• Hot-dip galvanized steel: Durable and corrosion-resistant, suitable for industrial environments.
• Stainless steel: Ideal for harsh or corrosive environments .

Installation Best Practices

• Ensure grounding connections are permanent, electrically continuous, and low impedance to facilitate proper operation of protective devices under fault conditions .
• Avoid placing bare copper in aluminum trays in moisture-prone areas; use insulated conductors instead.
• Bonding the EGC to the tray every 50–100 feet can lower voltage to ground during faults, improving safety .
• Follow NEC Article 392 and local electrical codes for compliance, including tray fill limits, cable separation, and firestop requirements .

Maintenance

• Periodically inspect grounding connections for corrosion, loosened clamps, or damaged conductors.
• Verify grounding resistance remains low (ideally 4 ohms or less) to ensure effective fault current dissipation . By following these methods and best practices, cable trays can be safely grounded, providing reliable protection for personnel, equipment, and the overall electrical system.