Grounding of the outer flat iron of the cable tray

The outer flat iron (side rails) of a metallic cable tray must be electrically bonded and grounded to provide a low-impedance path for fault currents, ensuring safety and compliance with NEC standards.Purpose of GroundingGrounding the outer flat iron of a cable tray ensures that any fault currents or electrical leakage are safely directed to the facility's grounding system, reducing the risk of electric shock, equipment damage, and fire hazards. It also helps minimize electromagnetic interference (EMI) and maintains system reliability, especially in installations with sensitive electronic equipment or communication circuits .Methods of GroundingBonding Between Tray Sections: Each section of the cable tray, including the side rails, should be electrically continuous. This is achieved through bolts, splice plates, clamps, or bonding jumpers that connect adjacent tray sections . Both side rails should be bonded to ensure continuity.Connection to Equipment Grounding Conductor (EGC): The cable tray can serve as the EGC in qualifying installations. If a separate EGC is used, it should be bonded to the tray sections using grounding clamps or connectors. Insulated conductors are preferred when connecting to aluminum trays to prevent electrolytic corrosion, with insulation removed at bonding points .Grounding to Building System: The tray system must be connected back to the main grounding system of the facility. This ensures that any fault current is safely carried to earth, meeting NEC Article 250 requirements .Use of Proper Materials: For aluminum trays, avoid bare copper conductors; use insulated conductors with tin or zinc-plated connectors. For steel trays, standard bonding clamps and jumpers are sufficient .Best PracticesEnsure mechanical tightness at all connections to maintain electrical continuity.Use bonding jumpers where mechanical connections alone may not provide reliable grounding.Maintain separation of power and signal cables to reduce interference.Verify grounding conductor sizing according to NEC tables to handle potential fault currents safely .For outdoor or rooftop installations, consider lightning protection and proper bonding to mitigate surge risks .SummaryProper grounding of the outer flat iron of a cable tray involves bonding all tray sections, connecting to the EGC, and linking to the building grounding system. This ensures a low-impedance path for fault currents, enhances safety, reduces EMI, and complies with NEC standards, providing a reliable and secure electrical installation .