Secondary wiring of fire fan distribution box

Secondary wiring of a fire fan distribution box requires fire-resistant power cables, segregated control circuits, protective devices, and compliance with fire and electrical codes to ensure reliable operation during emergencies.

Power Wiring

The secondary power wiring from the fire fan distribution box should use fire-resistant cables such as NH-YJV (cross-linked polyethylene insulated, PVC sheathed) to maintain power supply during a fire . Cable sizing must account for the fan's rated current with a margin for overloads. Wiring can be exposed in metal conduits with fireproof coatings or concealed in rigid conduits within non-combustible structures, ensuring at least 30mm protective layer . The distribution box should include short-circuit, overload, and grounding protection, and its enclosure must be fireproof and moisture-proof .

Control Wiring

Control circuits for fire fans should be separated from power lines to prevent interference . Typical control modes include manual on-site operation, remote control from the fire control room, and automatic activation via fire detectors . Power-limited circuits must be clearly labeled and segregated from non-power-limited circuits, with barriers or dedicated terminal blocks to comply with UL 864 UUKL smoke control requirements . Transient protection devices like MOVs or transzorbs may be required if wiring leaves the controller room .

Layout and Routing

The distribution box should be located close to the fan for easy operation and maintenance . Power should be supplied from a dedicated fire power supply circuit, independent from non-fire circuits, to ensure priority during emergencies . Wiring pathways should minimize exposure to fire hazards, using two-hour rated enclosures or concrete encasement where required for critical circuits . Control panels should be positioned in a fire command center or adjacent to the fire alarm panel, with clear graphical representation of fan and damper status for monitoring and manual override .

Summary

• Use fire-resistant cables for power circuits.
• Segregate power-limited and non-power-limited control wiring.
• Include protective devices in the distribution box.
• Ensure dedicated fire power supply and proper routing through fire-rated enclosures.
• Provide manual, remote, and automatic control with clear labeling and monitoring. Following these practices ensures that the fire fan distribution system remains operational during emergencies, complies with NFPA and NEC standards, and provides safe, reliable smoke control in buildings .