Must cable trays have a ground wire

Metallic cable trays must be grounded, but a separate ground wire is not always required if the tray itself is properly bonded and electrically continuous.Grounding RequirementsAll metallic cable trays must be grounded according to NEC Article 250.96, regardless of whether the tray is used as an equipment grounding conductor (EGC) or not . Grounding ensures that any stray electrical currents are safely directed to the earth, reducing the risk of electric shock, equipment damage, or fire .Using the Tray as the GroundIn some installations, the cable tray itself can serve as the EGC, provided it meets certain conductivity, strength, and continuity requirements . This is typically allowed for metal trays that are UL-classified and properly bonded at all joints. Steel and aluminum trays can serve as grounding paths, but aluminum trays require insulated conductors at bonding points to prevent corrosion .When a Separate Ground Wire is RecommendedEven if the tray can act as the EGC, installing a separate grounding conductor is often considered a best practice. This conductor can be bonded to each or alternate tray section using grounding clamps, ensuring a reliable path for fault currents and mechanically securing the EGC to prevent displacement under fault conditions . This is especially important in environments with high fault currents or where mechanical continuity of the tray may be compromised.Key Safety ConsiderationsEnsure all tray sections are electrically continuous and mechanically tight .Avoid bare copper in aluminum trays; use insulated conductors with proper bonding .Verify grounding conductor sizing according to NEC tables to handle expected fault currents .Inspect joints for paint, rust, or corrosion that could impede electrical continuity . In summary, metallic cable trays must be grounded, but whether a separate green ground wire is required depends on the tray's material, bonding, and UL classification. Using the tray as the EGC is permissible under NEC rules, but adding a dedicated grounding conductor is often recommended for enhanced safety and reliability.