Requirements for grounding wires for cable trays

Grounding wires are recommended in cable trays, even if the tray itself can serve as an equipment grounding conductor, to ensure safety, compliance, and reliability.Using Cable Trays as Grounding ConductorsMetallic cable trays can serve as Equipment Grounding Conductors (EGC) if they meet NEC requirements for conductivity and cross-sectional area ( ). Steel trays are suitable for circuits with ground-fault protection up to 600 amperes, while aluminum trays are limited to 2000 amperes ( ). All metallic trays must be grounded according to NEC Article 250.96, regardless of whether they are used as EGCs ( ).Benefits of Installing Grounding WiresEven when the tray itself is conductive, installing a dedicated grounding wire provides several advantages ( ):Enhanced safety: Provides a reliable path for fault currents, reducing the risk of electric shock or fire.Mechanical stability: Bonding the grounding wire to tray sections prevents the wire from being displaced by magnetic forces during fault conditions.Corrosion prevention: In aluminum trays, using an insulated conductor avoids galvanic corrosion that can occur with bare copper wires in moist environments ( ).Redundancy: Some installations use both the tray and a separate EGC in the cable for added reliability ( ).Installation GuidelinesBonding: Grounding wires should be bonded to each or alternate tray sections using mechanical clamps or listed connectors ( ).Material selection: Use copper, stainless steel, or hot-dip galvanized steel for durability and conductivity ( ).Inspection: Grounding should be inspected before energizing the system and after all tray sections are installed to ensure continuity ( ).Resistance: Maintain low grounding resistance, ideally 4 ohms or less, to ensure effective fault current diversion ( ).ConclusionWhile metallic cable trays can function as grounding conductors, installing a dedicated grounding wire is a best practice for safety, mechanical stability, and compliance with NEC standards. Proper bonding, material selection, and inspection are essential to ensure the grounding system performs reliably under fault conditions ( ).