How to ground cable trays

Grounding a cable tray involves connecting it to the facility's grounding system to provide a low-impedance path for fault currents, ensuring safety and system reliability.

Key Principles of Cable Tray Grounding

Purpose of Grounding: Grounding a cable tray ensures that any fault current is safely directed to the earth, protecting personnel from electric shock, preventing equipment damage, and reducing fire hazards caused by overvoltage or insulation failure. Using the Cable Tray as an Equipment Grounding Conductor (EGC): In qualifying facilities where only trained personnel service the system, the metal of the cable tray itself can serve as the EGC. This requires that the tray meets minimum metal cross-sectional area requirements based on the circuit's protective device rating.

Aluminum trays should not use bare copper conductors due to corrosion risks; insulated conductors with exposed ends at bonding points are recommended. Bonding Between Tray Sections: Each section of the cable tray should be electrically bonded to adjacent sections using grounding clamps. This ensures continuity and mechanical stability, preventing the EGC from being displaced under fault conditions.

Alternative Grounding Methods: Dedicated EGC Wire: Run a continuous grounding conductor along the length of the tray, connecting it to each tray section and to the facility ground.

Individual Cable EG

Cs: Each multi-conductor cable may include its own EGC, which should be bonded to the tray at intervals to maintain continuity. Compliance with Codes and Standards: All metallic cable trays must be grounded according to NEC Article 250. 96, regardless of whether the tray is used as an EGC.

Ensure that grounding connections use tin- or zinc-plated connectors to prevent corrosion and maintain low resistance. Maintenance and Inspection: Regularly inspect grounding connections for corrosion, loose clamps, or damaged conductors. Proper maintenance ensures the grounding system remains effective over time.

Best Practices

Avoid using wire mesh trays as EGCs unless a dedicated grounding wire is installed, due to reduced current-carrying capability. Ensure grounding resistance is low (ideally 4 ohms or less) to provide an effective path for fault currents. Keep grounding conductors clear of flammable materials and corrosive environments to maintain safety and longevity.

By following these principles and practices, a cable tray system can be safely grounded, providing protection for both personnel and equipment while maintaining compliance with electrical codes.