Requirements for cable trays used in low-voltage fire protection systems

Low-voltage cable trays must use fire-rated cables, proper firestopping at penetrations, secure cable spacing, and compliance with NFPA 70 and NEC standards to prevent fire hazards.

Low-

Voltage Cable Types and Fire RatingsFor low-voltage systems, cables must be selected based on their fire performance and application: FPL-type cables: Required for fire alarm systems; typically 18 gauge or larger, with 300-volt jacket insulation, suitable for power-limited circuits under NFPA 70 Article 760. CL2-type cables: Used for security, intrusion, video, and access control systems; rated 150 volts, compliant with Article 725. CL3-type cables: For sound and communications systems above CL2 voltage limits; also power-limited and fire-safe.

PLTC-type cables: Factory-assembled, multi-conductor cables rated 300 volts, suitable for cable trays, including outdoor, direct burial, and hazardous locations. Cables must be installed according to their classification, with riser cables (suffix “R”) for vertical runs and plenum cables for air-handling spaces.

Firestopping and Penetration Protection

Cable trays passing through walls, floors, or slabs require firestopping to prevent fire spread: Openings must be tightly sealed with fire-rated boards, firestop packs, firestop mastic, or fire-resistant mineral wool. Gap areas between firestop packs and cables should not exceed 1 cm², with a minimum packing thickness of 24 cm. Large openings require a fire-resistant backing plate before sealing, and cover plates should be square, consistent, and painted evenly.

At slab penetrations, provide 20–30 mm of firestopping and install a fire-support plate at the top; floor-level trays should have a waterstop of at least 50 mm.

Cable Tray Installation and Loading

Proper installation reduces fire risk: Tray types: Ladder, ventilated trough, solid bottom, wire mesh, or single rail, selected based on cable type, weight, and environmental conditions. Spacing and securing: Cables must be confined within trays using appropriate cable ties resistant to temperature, moisture, UV, chemicals, and fire. Avoid overloading: Excessive cable fill can cause heat buildup, insulation breakdown, and fire hazards.

Add additional trays if needed and maintain working space. Supports: Trays must be level, plumb, and securely mounted; horizontal deviation ≤2 mm/m, vertical deviation ≤3 mm/m.

Grounding and Safety

Metallic cable trays (aluminum, steel, coated steel) can serve as equipment grounding conductors if properly maintained and continuously supervised. Grounding must be completed before cable installation and tested prior to energizing circuits. Regulatory ComplianceNFPA 70 (NEC): Articles 392, 725, and 760 govern cable tray use, low-voltage circuits, and fire alarm wiring.

OSH

A Standards: 1910. 305(a)(3) and 1910. 399 require proper installation, labeling, and safe use of cable trays.

NEM

A Standards: VE 1-2002, VE 2-2006, and FG-1998 provide guidance for metal and nonmetallic cable tray systems, including installation, maintenance, and permissible loading.

Best Practices

Segregate power and signal cables to reduce interference. Remove abandoned or temporary wiring from trays after project completion. Use covers or ventilated louvers to protect cables and facilitate heat dissipation.

Plan for future expansion to avoid overloading and maintain fire safety. By following these requirements, low-voltage cable tray installations can maintain fire safety, comply with regulatory standards, and ensure reliable operation of electrical and communication systems.