Grounding trunk line of cable tray

A trunk line along a cable tray should be grounded using either a continuous grounding conductor or by bonding the tray itself, ensuring a safe path for fault currents and compliance with electrical standards.Purpose of Grounding

Grounding a cable tray ensures that any stray electrical currents or faults are safely directed to the earth, reducing the risk of electric shock, equipment damage, and fire hazards. It also minimizes electrical noise and interference, which is critical in environments with sensitive electronic equipment .

Methods for Grounding Along a Cable Tray

1. Continuous Grounding Conductor A bare or insulated copper conductor can be run along the full length of the cable tray. This provides a reliable path for fault currents. The conductor should be securely attached to the tray at regular intervals using grounding clamps or lugs to maintain mechanical stability and electrical continuity .
2. Using the Cable Tray as the Grounding Conductor In some installations, the metallic cable tray itself can serve as the equipment grounding conductor (EGC). This is suitable for steel or aluminum trays that meet the minimum cross-sectional area requirements specified in NEC Table 392.60(A). All tray sections must be bonded together to ensure continuous conductivity .
3. Bonding Between Tray Sections Each section of the tray should be electrically bonded to adjacent sections using tinned copper lugs, bolts, or bridging plates. For galvanized trays, the connecting plates can serve as bridging plates, while painted or coated trays require additional copper wire bridging to maintain continuity .

Material Considerations

• Copper Wire: Excellent conductivity and corrosion resistance; preferred for insulated grounding conductors.
• Galvanized Steel: Durable and corrosion-resistant; suitable for harsh environments.
• Stainless Steel: Ideal for highly corrosive or outdoor environments .

Installation Guidelines

• Ensure grounding points are planned along the tray before installation.
• Avoid placing bare copper in aluminum trays in moist environments to prevent electrolytic corrosion; use insulated conductors with exposed ends for bonding .
• Maintain grounding resistance ideally below 4 ohms to ensure effective fault current diversion .
• Follow NEC Article 250 and 392 for grounding and bonding requirements, including limitations on using trays as EGCs for circuits with high ground-fault protection ratings .

Summary

For safe and compliant grounding of a trunk line along a cable tray, either a continuous grounding conductor should be installed along the tray or the tray itself should be bonded as the EGC. Proper bonding between tray sections, use of corrosion-resistant materials, and adherence to NEC standards are essential to ensure electrical safety and system reliability .