Grounding Requirements for Composite Cable Trays

Composite (non-metallic) cable trays cannot serve as equipment grounding conductors and require a separate grounding conductor to ensure electrical safety.

Key Grounding Principles for Composite Trays

Non-metallic or composite cable trays are inherently non-conductive, meaning they cannot carry fault current and therefore cannot function as an Equipment Grounding Conductor (EGC) under NEC standards . Unlike metallic trays, which may serve as the EGC if they meet cross-sectional area and continuity requirements, composite trays require a dedicated grounding wire to maintain safety and compliance .

NEC Compliance

• NEC Article 392 governs cable tray installations, including grounding and bonding requirements .
• Metallic trays can be used as EGCs if they meet minimum metal area requirements and are electrically continuous, but composite trays are excluded from this provision .
• For composite trays, a separate insulated or bare copper grounding conductor must be installed along the tray to provide a low-impedance path to ground .

Grounding Conductor Installation

• The grounding conductor should run the entire length of the tray and be securely attached using UL-listed clamps or connectors to ensure continuity .
• In environments prone to moisture or corrosive conditions, insulated conductors are preferred to prevent degradation. Connections should be made with tin- or zinc-plated connectors to maintain reliable bonding .
• The grounding system should achieve a low resistance to earth, ideally 4 ohms or less, to ensure effective fault current dissipation .

Best Practices

• Bonding at intervals: Even though composite trays are non-conductive, bonding the grounding conductor to equipment and metallic components at regular intervals ensures safety and compliance .
• Avoid bare conductors in corrosive environments: Use insulated conductors to prevent chemical or electrolytic damage.
• Material selection: Copper is preferred for conductivity, while stainless steel or galvanized steel may be used in harsh environments for mechanical strength .
• Mechanical security: Ensure the grounding conductor is firmly anchored to prevent movement under fault conditions or vibration .

Summary

For composite cable trays:

1. Do not use the tray itself as a conductor.
2. Install a separate grounding conductor along the tray.
3. Ensure proper bonding and low resistance to ground.
4. Use corrosion-resistant materials and secure connections. Following these practices ensures that composite cable tray installations are safe, NEC-compliant, and capable of handling fault conditions effectively.