Explosion-proof standards for outdoor cable trays

Outdoor cable trays in hazardous locations must use approved cable types, proper tray materials, grounding, spacing, and mechanical protection to prevent ignition in explosive atmospheres.

Cable Types and Ratings

For hazardous locations, only cables listed for the specific class and division may be installed in cable trays. Common options include:

• Power Limited Tray Cable (PLTC) for dust locations, sometimes without spacing or single-layer requirements .
• Metal Clad (MC) or Type TC cables with gas/vapor-tight continuous sheaths and polymeric jackets for Class I, Division 1 locations .
• Instrumentation Tray Cable (ITC) for Class I, Division 2 or Class II locations, often without spacing or single-layer restrictions .
• Mineral Insulated (MI) cables for fire protection and Division 1 locations, installed with approved termination fittings .
• -ER suffix cables (e.g., TC-ER) for exposed or open wiring, providing additional crush and impact resistance . All cables must be terminated with fittings listed for the hazardous location and comply with the relevant NEC articles (e.g., Articles 501, 502, 503, 504, 725, 727).

Tray Materials and Construction

• Metallic trays (steel, aluminum) can serve as part of the grounding system if designed and labeled per NEC Article 392 .
• Fiberglass reinforced plastic (FRP) trays are preferred in areas requiring non-conductivity or corrosion resistance .
• Ventilated trays allow heat dissipation and prevent accumulation of flammable vapors .
• Covered or solid-bottom trays may be used for additional protection against debris, moisture, or EMI/RFI interference .

Installation Practices

• Support and spacing: Trays must be supported at intervals specified by the manufacturer and NEC Section 392.6(C), considering cable weight, fill, and environmental factors .
• Mechanical protection: Cables exiting trays within six feet of equipment should use ER-rated cables or additional struts, angles, or channels for protection .
• Segregation: Different cable types may require separation to prevent interference or meet NEC fill and spacing requirements .
• Height and exposure: Outdoor trays exposed to physical damage (e.g., vehicular traffic) should be installed at a minimum height of 8 feet and may require covers .
• Grounding: Metallic trays must be properly grounded, and non-metallic trays should not carry fault current .

Regulatory Compliance

• NEC compliance: Cable trays and cables must meet NEC requirements for hazardous locations (Articles 501–504, 725, 727, 392) and be installed according to listed instructions .
• OSHA and local codes: Outdoor installations must comply with OSHA 29 CFR 1910.303 and any applicable state or local regulations .
• Inspection and maintenance: Regular inspection ensures mechanical integrity, proper grounding, and absence of damage that could create ignition sources .

Summary

To achieve explosion-proof outdoor cable tray installations:

1. Use cables listed for the specific hazardous location and terminate with approved fittings.
2. Select tray materials suitable for environmental conditions and grounding requirements.
3. Ensure proper support, spacing, and mechanical protection for all cables.
4. Follow NEC, OSHA, and local codes for installation, grounding, and maintenance.
5. Consider ventilation, covers, and segregation to minimize ignition risks and maintain system integrity. By adhering to these requirements, outdoor cable tray systems can safely operate in hazardous environments while minimizing the risk of explosions.