Electrical grounding connection cable tray

Metallic cable trays must be properly grounded and bonded to provide a continuous fault current path, ensuring safety and NEC compliance.

Purpose of Grounding Cable Trays

Grounding a cable tray provides a safe path for stray electrical currents to flow into the earth, protecting personnel and equipment from electric shocks, fires, or equipment damage. It ensures that any fault current is quickly diverted, maintaining system stability and safety (Apex Tray Guide), .

NEC Requirements

• Article 392 of the National Electrical Code (NEC) governs cable tray grounding and bonding. All metallic trays must be electrically continuous and properly bonded at splice points (ShowMeCables), .
• Cable trays can serve as the Equipment Grounding Conductor (EGC) if they meet minimum metal cross-sectional area requirements and are installed according to NEC Table 392.60(A) (IDC Online), .
• Steel trays should not be used as EGCs for circuits with ground-fault protection above 600 A, and aluminum trays above 2000 A (IDC Online), .

Grounding and Bonding Practices

• Mechanical Continuity: Ensure all tray sections are tightly connected to maintain electrical continuity. Use bonding jumpers where mechanical connections alone do not guarantee continuity (ShowMeCables), .
• Connection to Building Ground: The tray system must be securely connected to the building's grounding electrode system to complete the fault current path (ShowMeCables), .
• EGC Conductor: If an EGC cable is installed in or on the tray, it should be bonded to each or alternate tray sections using grounding clamps. This also mechanically anchors the conductor to prevent displacement under fault conditions (IDC Online), .
• Material Considerations: Avoid bare copper conductors in aluminum trays to prevent electrolytic corrosion. Use insulated conductors with insulation removed only at bonding points, and use tin or zinc-plated connectors (IDC Online), .

Best Practices

• Verify grounding conductor sizing according to NEC tables to safely carry potential fault currents (ShowMeCables), .
• Maintain low grounding resistance, ideally 4 ohms or less, to ensure effective fault current diversion (Apex Tray Guide), .
• Ensure all tray sections, fittings, and splice points maintain a conductive connection across the entire system to prevent shock hazards and equipment malfunction (ShowMeCables), .

Summary

Proper grounding of cable trays involves ensuring electrical continuity, bonding at splice points, connecting to the building grounding system, and following NEC requirements for material and conductor sizing. These measures protect personnel, prevent equipment damage, and ensure reliable operation of the electrical system.