Cable trays generally require bridging for grounding and conductive continuity, but the method depends on the tray material and installation standards.

Purpose of Bridging

Bridging in cable trays is primarily used to ensure electrical continuity and proper grounding across sections of metallic trays. This helps prevent potential differences between tray sections, reduces the risk of electrical shock, and allows the tray to serve as an equipment grounding conductor (EGC) if compliant with NEC requirements . Bridging also maintains structural integrity in some installations, though its main function is electrical safety.

Material-Specific Guidelines

• Galvanized Steel Trays: Bridging can be achieved using anti-loosening nuts or washers on connecting bolts to ensure a conductive connection between tray sections .
• Stainless Steel and Aluminum Alloy Trays: These require dedicated grounding bolt holes for bridging, rather than relying on standard connection plates .
• Connection Practices: For metallic trays, connectors should use at least two sets of galvanized steel bolts with anti-loosening gaskets or insulated multi-strand copper wires with crimped tinned copper connectors. The copper wire cross-section should be greater than 4.0 mm² to ensure proper conductivity .

NEC Compliance

According to NEC Article 392, metallic cable trays can serve as grounding conductors if properly installed. Bridging ensures that all tray sections are electrically continuous, which is critical for safety and compliance . Nonmetallic trays, such as fiberglass or plastic, do not require bridging because they are not conductive.

Practical Recommendations

• Always follow the manufacturer's instructions for bridging and grounding.
• Use anti-loosening hardware to maintain reliable connections over time.
• Ensure that bridging does not interfere with cable installation or violate minimum bend radii.
• For stainless steel or aluminum trays, use special grounding bolt holes rather than standard connection plates to achieve proper grounding . In summary, bridging is necessary for metallic cable trays to maintain electrical continuity and grounding, but the exact method depends on the tray material and installation standards. Nonmetallic trays do not require bridging. Proper bridging ensures safety, compliance with NEC Article 392, and reliable operation of the electrical system.