Ungrounded cable trays pose serious safety hazards and violate NEC requirements; all metallic trays must be properly grounded and bonded.

Safety Risks of Ungrounded Cable Trays

Cable trays that are not grounded can create significant electrical hazards, including the risk of electric shock, fire, and equipment damage. Without a proper grounding path, stray currents from faults or power surges cannot safely flow to the earth, leaving personnel and equipment exposed to dangerous voltages . Ungrounded trays also increase the likelihood of electromagnetic interference (EMI) affecting sensitive control or communication circuits .

NEC Requirements

The National Electrical Code (NEC) Article 392 mandates that all metallic cable trays must be grounded, regardless of whether they are used as an equipment grounding conductor (EGC) or not . Metallic trays can serve as the EGC if they meet specific criteria, including minimum cross-sectional area and UL classification . Non-metallic trays require separate EGCs or bonding jumpers to ensure electrical continuity . Grounding ensures that the tray system is electrically continuous and bonded back to the power source .

Best Practices for Grounding and Bonding

• Bonding Between Sections: Each tray section should be electrically bonded to the next using grounding clamps, splice plates, or bonding jumpers to maintain continuity .
• Equipment Grounding Conductors: If cables in the tray contain EGCs, these should be bonded to the tray at intervals to enhance safety and mechanical stability .
• Material Considerations: Avoid bare copper conductors in aluminum trays to prevent electrolytic corrosion; insulated conductors with proper connectors are recommended .
• Resistance Levels: Grounding systems should maintain low resistance, ideally 4 ohms or less, to ensure effective fault current diversion .

Alternatives and Special Cases

• In facilities where trays carry only low-energy signal or communication circuits, grounding may focus on lightning protection and EMI mitigation rather than power fault protection .
• For non-metallic trays, a separate EGC or bonding conductor is required to meet safety standards .

Conclusion

Failing to ground cable trays is a serious safety violation and can compromise both personnel safety and equipment reliability. Proper grounding and bonding, in compliance with NEC standards, are essential for all metallic trays, while non-metallic trays require alternative grounding methods. Following these practices ensures electrical safety, reduces EMI, and maintains system integrity .