Grounding treatment at the end of cable trays

Cable trays must be properly grounded and bonded to provide a low-impedance path for fault currents, ensure personnel safety, and maintain system reliability.

Key Grounding Principles

1. Use of Cable Tray as Equipment Grounding Conductor (EGC) Metallic cable trays can serve as the EGC in installations where qualified personnel service the system. This allows the tray itself to carry fault currents safely to the grounding system, provided the tray meets the minimum metal cross-sectional area requirements specified in NEC Table 392.60(A) and is electrically continuous .
2. Bonding Between Tray Sections All metallic sections of a cable tray should be bonded to maintain electrical continuity. Grounding clamps or bonding jumpers are commonly used to connect adjacent tray sections, ensuring a continuous path for fault currents and preventing voltage differences that could cause arcing .
3. Use of Separate EGC Conductors In addition to using the tray as an EGC, a bare or insulated copper conductor can be installed in or on the tray. This conductor should be bonded to each or alternate tray sections to enhance safety and mechanical stability under fault conditions. For aluminum trays, insulated conductors are preferred to prevent electrolytic corrosion .
4. Material Considerations
   • Steel trays: Should not be used as EGCs for circuits with ground-fault protection above 600 A.
   • Aluminum trays: Should not be used as EGCs for circuits with ground-fault protection above 2000 A.
   • Corrosion prevention: Use tin- or zinc-plated connectors when bonding to aluminum trays .
5. Grounding to Facility System Cable trays must be connected to the facility's main grounding system to provide a low-impedance path for fault currents. This protects personnel from electric shock, prevents equipment damage, and reduces fire hazards .
6. Compliance with Standards Grounding and bonding practices must comply with NEC Article 392, NEC Section 250, and other applicable standards. This includes ensuring electrical continuity, proper sizing of conductors, and maintaining a permanent, low-impedance path for fault currents .

Additional Benefits of Proper Grounding

• Minimizes electromagnetic interference (EMI), improving signal integrity for data and control cables.
• Enhances system reliability by reducing the risk of equipment malfunctions and downtime.
• Protects against lightning strikes by safely dissipating surge currents to ground .

Best Practices

• Inspect bonding connections regularly to ensure continuity.
• Avoid placing bare copper conductors in aluminum trays in moist environments.
• Use high-quality connectors and clamps from trusted suppliers.
• Maintain separation between power and data cables to prevent interference. Proper grounding and bonding of cable trays are essential for safety, compliance, and long-term reliability in industrial and commercial electrical installations .