Installation of secondary electromechanical cable trays

Secondary electromechanical cable trays should be installed with proper support, spacing, and material selection to ensure safe, code-compliant routing from main trays to equipment.

Planning and Material Selection

Secondary cable trays, often called branch or lateral trays, extend from the main cable tray system to electrical devices or equipment. The choice of tray type—ladder, ventilated trough, or solid-bottom—depends on the cable type, environmental conditions, and load requirements. For corrosive or high-moisture environments, fiberglass-reinforced plastic (FRP) trays are recommended due to their corrosion resistance and non-conductive properties.

Steel or aluminum trays are suitable for general industrial applications, with galvanization or stainless steel finishes providing additional corrosion protection.

Support and Mounting

Secondary trays must be mechanically supported to prevent sagging and maintain proper alignment. Support elements include wall brackets, suspended supports, and center suspensions, which attach trays to ceilings, walls, or structural beams. The support span should follow manufacturer recommendations, typically ranging from 1.

5 to 3 meters for ladder trays, depending on load and cable weight. Mounting elements, such as plates or clamps, secure junction boxes or devices to the tray system.

Routing and Clearance

Trays should maintain adequate clearance for installation and maintenance, generally at least 12 inches above the tray for access. Secondary trays must avoid prohibited areas like hoistways or enclosed spaces and remain accessible for inspection and cable management. Horizontal and vertical bends, T-pieces, and crossovers allow proper routing while maintaining cable separation to prevent electromagnetic interference (EMI) between high-power and low-power cables.

Cable Management and Fill

Cables should be arranged to prevent sagging and overheating. Fill limits are typically 40% for power cables and 50% for control cables of the tray's cross-sectional area. Proper cable tying and bundling ensure even weight distribution and reduce mechanical stress on the tray system.

Ventilated trays provide better heat dissipation, while solid-bottom trays offer additional protection for sensitive instrumentation cables.

Grounding and Safety

Metallic trays can serve as equipment grounding conductors (EGC) if installed according to NEC requirements. All connections, supports, and fittings should be bonded to maintain electrical continuity and reduce the risk of shock or fire. Installation should comply with NEC Article 392 and relevant standards such as BS EN 61537 for cable tray systems.

Best Practices

Use trays and fittings from the same manufacturer to ensure compatibility and system integrity. Plan secondary tray routes to minimize sharp bends and excessive length. Consider environmental factors such as temperature, humidity, and chemical exposure when selecting materials.

Ensure all personnel performing installation are trained and familiar with electrical safety and cable tray standards. By following these guidelines, secondary electromechanical cable trays can be installed safely, efficiently, and in compliance with industry standards, ensuring reliable cable support and long-term system performance.