Fire cable trays for low-voltage electrical rooms

Fire-rated cable trays in low-voltage electrical rooms must be properly installed, supported, and firestopped to ensure safety, code compliance, and maintainability.

Cable Tray Selection and Material

For indoor low-voltage applications, painted steel or galvanized steel trays are commonly used, while aluminum or fiberglass-reinforced plastic trays may be selected for corrosive or high-humidity environments . The tray type should match the cable load and allow adequate airflow to prevent overheating. Ladder trays are preferred for heavy power cables as they provide ventilation, while solid-bottom trays are used where electromagnetic interference (EMI) or cable concealment is required .

Installation Guidelines

• Support and Alignment: Trays must be level, plumb, and securely mounted on supports, with horizontal deviation ≤2 mm per meter and vertical deviation ≤3 mm per meter .
• Clearances: Maintain at least 12 inches of vertical clearance above trays for installation and maintenance access .
• Cable Segregation: High-power and low-power cables should be separated to prevent EMI, and solid dividers may be used if mixed circuits are unavoidable .
• Fill Limits: Power cables should not exceed 40% of the tray cross-sectional area, and control cables should not exceed 50% .
• Grounding: Metallic trays must be grounded according to NEC Article 250.96, either as an equipment grounding conductor (EGC) or with a separate conductor .

Firestopping Requirements

Fire-rated cable trays must be properly sealed at wall, floor, and slab penetrations to prevent fire spread . Key points include:

• Use fire-rated boards, firestop packs, firestop mastic, or fire-resistant mineral wool to seal gaps.
• Gap area between firestop packs and cables should not exceed 1 cm², with a minimum packing thickness of 24 cm .
• For large openings, install a fire-resistant backing plate before sealing.
• At slab penetrations, provide 20–30 mm of firestopping and a fire-support plate at the top.
• Ensure all gaps inside and around metal trays are sealed both internally and externally, and cover plates are square, consistent, and painted evenly .

Safety and Maintenance

• Only use cables rated for open-air environments, such as Tray Rated (Type TC) or Metal-Clad (Type MC) cables .
• Secure cables with appropriate ties to maintain spacing and prevent movement .
• Regular inspection and maintenance are essential to ensure firestopping integrity and tray stability.
• Avoid using cable trays in hoistways or fully enclosed spaces to maintain accessibility . By following these guidelines, fire-rated cable trays in low-voltage electrical rooms will provide safe, code-compliant, and maintainable cable management, minimizing fire hazards and ensuring reliable operation .