Fire protection electrical and low-voltage electrical cables share the same cable tray

Fire protection (FPL-type) and low-voltage or power-limited cables can share the same cable tray under specific conditions, provided code requirements for separation, insulation, and circuit type are met.Regulatory Guidance

NEC Article 760 allows power-limited fire alarm circuits (PLFA) and Class 2 circuits to be installed in the same cable tray if the insulation of the Class 2 circuit is equal to or greater than that of the fire alarm cable. This ensures safety and prevents electrical interference or hazards (NEC 760.139(B)), . Similarly, low-powered network communication circuits can share trays with PLFA cables if insulation requirements are met (NEC 760.139(C)), . However, audio system circuits using Class 2 or Class 3 wiring should not share the same tray with fire alarm circuits unless specifically allowed by the fire alarm control system design . In the UK, BS 5839-1:2017 and IET guidance indicate that LV and fire alarm loop cables may share containment depending on the fire alarm manufacturer's EMC advice and cable choice . Separation distances may also be required to reduce electromagnetic interference, particularly for data or unscreened cables.

Practical Considerations

• Separation Distance: While some codes permit shared trays, a minimum separation of 50 mm is often recommended for indoor copper data cabling near LV power cables to prevent interference, with longer parallel runs potentially requiring up to 150 mm .
• Cable Type: Fire-resistant cables (FPL, FPLP, FPLR) are designed to maintain operation during a fire, whereas flame-retardant cables (FRT) only limit flame spread and may not maintain circuit operation . Only fire-resistant cables should be prioritized for life-safety systems.
• Containment: Using metallic or earthed containment can help reduce electromagnetic interference and provide additional safety when different voltage bands share a tray .
• Code Compliance: In the US, PLFA and communications circuits are explicitly permitted to share trays under NEC 760.139(A), provided insulation and separation requirements are met .

Summary

• Fire alarm and low-voltage cables can share the same cable tray if:
  1. Insulation ratings meet or exceed the fire alarm cable requirements.
  2. Separation distances are maintained to prevent interference.
  3. Circuit types are compatible (e.g., Class 2 with PLFA, but not audio Class 2/3 with PLFA).
• Fire-resistant cables should be used for circuits that must operate during a fire.
• Metallic containment and careful routing can mitigate EMC issues. Following these guidelines ensures code compliance, operational reliability, and safety when sharing cable trays between fire protection and low-voltage electrical systems.