Layout of fire-fighting heat-sensing cable terminal box

A fire-fighting heat-sensing cable terminal box houses the PCB, provides secure cable entry via glands, and uses a DIN rail or terminal block for proper cable termination.

Terminal Box Structure

The terminal box is designed to interconnect or terminate linear heat detection cables. It typically includes:

• Printed Circuit Board (PCB): Held in place initially by rubber plugs for temporary positioning, then permanently fixed to the mounting surface using screws through the PCB and box ( ).
• Cable Entry Glands: Two or more glands allow incoming and outgoing cables to pass into the box while maintaining environmental protection and correct polarity ( ).
• Terminal Block: A five-way DIN rail mounted terminal block is commonly used for secure cable terminations, ensuring reliable electrical connections ( ).

Mounting and Securing

• The box is mounted to a flat surface using screws appropriate for the material, securing both the PCB and the enclosure ( ).
• The heat-sensing cable should never be kinked or squashed; it is best secured with loose cable ties at intervals to prevent mechanical stress ( ).
• Boxes are often rated IP66, providing protection against dust and powerful water jets, suitable for industrial environments ( ).

Cable Connections

• Incoming and Outgoing Cables: Cables from the Control and Indicating Equipment (CIE) or previous terminal boxes enter through the glands and are connected to the appropriate terminals, ensuring correct polarity ( ).
• End-of-Line (EOL) Device: The terminal box may function as an EOL box for continuity monitoring, ensuring the system can detect cable faults or breaks ( ).
• Leader Cable Junctions: The box can also serve as an in-line junction to join multiple lengths of heat-sensing cable ( ).

Dimensions and Materials

• Typical dimensions for a junction box are 94mm × 94mm × 57mm, constructed from durable polycarbonate and halogen-free for safety ( ).
• The box layout allows for quick installation and maintenance, with clear access to terminals and secure cable routing.

Summary

A properly laid-out terminal box ensures reliable fire detection by securely housing the PCB, providing organized cable entry and termination, and supporting EOL monitoring. Correct installation prevents false alarms, mechanical damage, and ensures the system responds accurately to heat events. Proper cable securing, correct polarity, and adherence to mounting guidelines are essential for optimal performance ( ).