Should a separate flat iron be installed for the cable tray

A separate flat iron is generally recommended for supporting and grounding cable trays, especially for metallic trays, to ensure structural stability and compliance with NEC standards.

Structural Support Considerations

Cable trays must be properly supported to prevent sagging, maintain cable bending radii, and handle the load of installed cables. NEC Article 392 specifies that metallic trays can serve as equipment grounding conductors if they meet grounding requirements, but they still require secure structural support. Installing a separate flat iron or steel support provides a rigid base for the tray, particularly for long spans or heavy power cables, and helps maintain proper alignment and deflection limits . For ladder-type trays, supports are typically placed at 1/4 span intervals to minimize stress at splice locations and prevent excessive deflection . Solid-bottom or ventilated trays may also benefit from additional flat iron supports to prevent sagging of small-diameter control or instrumentation cables .

Grounding and Electrical Safety

Metallic cable trays can act as grounding paths, but a dedicated flat iron or grounding bar ensures a continuous and reliable electrical connection. This is particularly important when trays are segmented with expansion joints or when multiple tray sections are connected. Proper grounding reduces the risk of electrical shock, EMI, and potential fire hazards .

Separation and EMI Considerations

When high-power and low-power cables share a tray system, NEC recommends either physical separation or separate trays with at least 12 inches of vertical separation to prevent electromagnetic interference . Installing a separate flat iron for each tray section can facilitate this separation and provide a stable mounting surface for barriers or dividers.

Practical Recommendations

• Use flat iron supports for long spans, heavy cable loads, or outdoor installations exposed to environmental stress.
• Ensure supports are securely anchored to the building structure and aligned with tray manufacturer specifications.
• Verify that grounding connections are continuous across all tray sections.
• Consider separate supports for power and signal trays to maintain proper separation and reduce EMI risks. In summary, installing a separate flat iron for cable trays is a best practice for mechanical stability, proper grounding, and compliance with NEC standards, particularly in industrial or commercial installations with heavy or mixed cable loads .