Should fire protection and low-voltage electrical systems be run in the same cable tray

Fire alarm (PLFA) circuits and low-voltage communication or data cables can share the same cable tray under specific conditions, but dedicated pathways or physical separation are strongly recommended for safety and reliability.

Regulatory Perspective

According to the National Electrical Code (NEC) 760.139 (A), power-limited fire alarm (PLFA) circuits are permitted to share a cable tray, raceway, or enclosure with communications circuits or Class 3 circuits, provided the insulation and installation meet code requirements (760.139 B and D) . This allowance applies because both systems are low-voltage, reducing the risk of dangerous voltage interactions. However, circuits such as audio systems using Class 2 or Class 3 wiring may not be included under this provision unless specifically allowed .

Best Practices and Safety Considerations

Even though code permits shared trays, industry best practices recommend physical separation to protect the fire alarm system from mechanical damage, electromagnetic interference (EMI), and accidental faults during installation or maintenance . Key considerations include:

• Mechanical protection: Fire alarm cables must be secured with non-combustible supports, such as metal clips, to prevent damage from building movement or fire conditions .
• Electromagnetic interference: Data cables, especially unshielded twisted pair (UTP) Ethernet, are susceptible to EMI from nearby circuits. Fire alarm signals can also radiate low-level noise, potentially affecting sensitive data lines .
• Physical separation: If sharing a tray, a continuous grounded metallic barrier or partition is recommended to maintain separation and reduce EMI . Some guidelines suggest a minimum separation of 6 inches if no barrier is used .
• Dedicated pathways: Many fire safety standards, including BS 5839-1:2025, recommend routing fire alarm circuits independently to ensure survivability and integrity during a fire .

Practical Implementation

• Shared trays are allowed for PLFA and communication circuits if insulation and installation meet NEC requirements.
• Use dividers or compartmentalized trays to separate fire alarm and data cables physically.
• Avoid mixing fire alarm conductors with non-fire circuits in multicore cables.
• Ensure proper support and fire-resistant fixings to maintain system reliability during emergencies .

Conclusion

While code permits fire alarm and low-voltage communication cables to share a cable tray, it is strongly recommended to provide physical separation or dedicated pathways to prevent mechanical damage, EMI, and inspection failures. Following these practices ensures both regulatory compliance and long-term reliability of life safety and data systems.