Cable tray and conduit grounding

Metallic cable trays can serve as an equipment grounding conductor (EGC) if properly installed, bonded, and inspected according to NEC standards.Grounding PrinciplesCable tray grounding ensures safety by providing a low-resistance path for stray electrical currents, preventing electric shock, equipment damage, and fire hazards . The NEC mandates that all metallic cable trays must be grounded, regardless of whether they are used as the EGC . Grounding can be achieved either by using the tray itself as the EGC or by installing a separate grounding conductor within or alongside the tray .Using Cable Trays as EGCUL-Classified trays: Only trays marked as suitable for use as an EGC can serve this purpose .Material considerations: Aluminum trays are excellent conductors but may corrode if bare copper is used; insulated conductors with tin or zinc-plated connectors are recommended in moist environments . Steel trays are strong but less conductive, requiring thicker sections or additional bonding to maintain a reliable grounding path .Bonding: Adjacent tray sections should be bonded using grounding clamps or jumpers to ensure continuity. This prevents separation at joints from interrupting the grounding path .Equipment Grounding Conductor (EGC)An EGC is a dedicated conductor that safely returns stray electricity to the power source, tripping protective devices in case of faults . If a separate EGC is installed in the tray, it should be mechanically anchored and bonded to the tray sections to prevent displacement under fault currents . Bare copper should generally be avoided in aluminum trays to prevent electrolytic corrosion .Conduit-to-Tray ConnectionsWhen cables drop from trays to enclosures or conduit systems, bonding must be maintained using:Bolted connections to channel dropouts (minimum two bolts)Grounding conductors in the cableConduit-to-tray adapters or bonding jumpers if adapters are not listed for grounding Inspection and ComplianceGrounding inspections should be performed before energizing the system and ideally before cable installation . Inspectors verify:Tray sections are UL-classified for EGC useMinimum cross-sectional area of the tray is adequateAll bonding connections are secure and continuousDropouts and conduit connections maintain proper bonding Best PracticesMaintain low grounding resistance (ideally ≤4 ohms) for effective fault current diversion .Remove paint or coatings at bolted connections to ensure electrical continuity .Avoid exposure to corrosive environments or moisture without proper insulation .Steel trays should not be used as EGCs for circuits with ground-fault protection above 600 A . By following these guidelines, cable tray and conduit systems can provide a safe, reliable grounding path, ensuring compliance with NEC standards and protecting personnel and equipment from electrical hazards.