Lightning Protection for Non-Metallic Cable Trays

Non-metallic cable trays require specialized lightning protection through bonding, grounding, and overhead shielding to comply with NFPA 780 and IEC 62305 standards.

Key Considerations

Non-metallic cable trays, such as those made from fiberglass or PVC, are inherently non-conductive and cannot carry lightning currents directly. Therefore, they cannot serve as a grounding path like metallic trays. Lightning protection for these trays focuses on external measures to prevent direct strikes and minimize induced surges in the cables they carry .

Grounding and Bonding

• While non-metallic trays themselves are non-conductive, any metallic components (supports, fasteners, or covers) should be bonded to the building's grounding system to provide a path for lightning currents .
• Overhead cable systems or metallic shielding can be installed above non-metallic trays to intercept lightning strikes and safely divert currents to ground .
• Surge protection devices (SPDs) can be installed at cable entry points to protect sensitive equipment from transient overvoltages caused by nearby lightning strikes .

Shielding and Separation

• For sensitive signal or communication circuits, EMI/RFI shielding may be necessary. Solid-bottom trays or metallic covers can provide partial shielding against electromagnetic disturbances induced by lightning .
• Separation of power and signal cables is recommended to reduce coupling of lightning-induced surges into sensitive circuits. Using separate trays or barriers is the most effective approach .

Compliance with Standards

• NFPA 780 provides criteria for the installation of lightning protection systems, including the use of air terminals, conductors, and grounding electrodes to protect building structures and cable pathways .
• IEC 62305 outlines risk assessment, protection levels, and design requirements for lightning protection systems, including surge protection for energy, data, and control circuits .
• Risk assessments should consider local lightning frequency, building height, and exposure to determine the level of protection required .

Practical Implementation

1. Install metallic overhead protection above non-metallic trays in exposed areas.
2. Bond all metallic supports and covers to the main grounding system.
3. Use surge protection devices at cable entry points to protect connected equipment.
4. Separate power and signal circuits to minimize induced surges.
5. Follow NFPA 780 and IEC 62305 guidelines for grounding, bonding, and surge protection. By combining these measures, non-metallic cable trays can be effectively protected from lightning hazards while maintaining compliance with international standards .