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Safety of Cable Trays in Low Voltage Shafts and Vertical Shafts

Fiber optic splice closure knowledge brief Published 09 Sep 2021

Prepared for preliminary research by the RIVO OPTICAL knowledge desk. Confirm cable count, splice capacity, sealing class, tray layout, protection sleeves and installation requirements against current standards and product documentation.

Cable trays can be safely installed in low voltage and vertical shafts if they comply with NEC Article 392, IEC 61537 standards, and proper mechanical and fire safety practices are followed.Regulatory and Standard Guidelines

NEC Article 392 provides the primary guidance for cable tray installation in buildings, including vertical and low voltage shafts. It defines cable trays as support structures, not raceways, and emphasizes proper selection, installation, and support to prevent fire hazards and mechanical failure . Compliance ensures that cables are adequately supported, accessible for maintenance, and protected from damage. IEC 61537:2023 specifies requirements for cable tray systems, including mechanical strength, load capacity, and environmental suitability. It applies to steel, stainless steel, aluminum, and fiber-reinforced plastic trays, ensuring they can safely support cables in vertical or confined spaces . The standard also addresses grouping of cables and protective measures, which is critical in vertical shafts where gravity and vibration can affect cable stability.

Installation Considerations
  • Mechanical Support: Vertical shafts require secure anchoring of trays at regular intervals to prevent sagging or collapse. Support spacing should follow manufacturer recommendations and IEC 61537 load testing procedures .
  • Cable Type and Segregation: Only cables rated for open-air exposure should be used in trays. Low voltage cables should be separated from high voltage or power cables to reduce interference and fire risk .
  • Fire Safety: In vertical shafts, fire-resistant trays or covers may be required to prevent flame propagation. Proper ventilation and spacing help dissipate heat from bundled cables .
  • Accessibility: Trays should allow easy access for inspection, maintenance, and future upgrades. Vertical installations must consider safe access points and fall protection for personnel .
Practical Recommendations
  1. Use ladder or ventilated trays in vertical shafts to allow airflow and reduce heat buildup.
  2. Ensure secure anchoring at top, bottom, and intermediate points to handle cable weight.
  3. Follow NEC and IEC standards for spacing, load, and cable type.
  4. Consider fire-rated materials or enclosures in shafts that serve as fire barriers.
  5. Maintain clear labeling and segregation of low voltage and high voltage cables to prevent accidental contact or interference. By adhering to these standards and installation practices, cable trays in low voltage and vertical shafts can provide a safe, durable, and maintainable solution for cable management in commercial and industrial buildings .

Safety of Cable Trays in Low Voltage Shafts and Vertical Shafts - RIVO MULTITRADE OPTICAL SYSTEMS [PDF]

Safety of Cable Trays in Low Voltage Shafts and Vertical Shafts

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This reference is intended for preliminary fiber optic splice closure research. Compatibility, splice capacity, sealing class, tray layout, protection sleeves, installation methods, test limits and applicable standards must be verified for the specific project.

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