90, Arts College Road, Coimbatore




Fire Fighting & Protection Engineering Division

Linear Heat Detection Cables

The Linear Heat Sensing Cable comprises a warped pair twin core cable. Each core is of passivated steel and has a special heat reactive polymer insulation. The cable has an overall protective jacket Sheath. The primary mechanism of heat (Fire) Detection is that inner core insulating polymer is specially formulated such that is plasticises at a specific temperature. The cable is constructed such that the warped steel cores are in tension, and at the polymer trigger temperature the conductors connect. This provides an alarm signal to any associated monitoring device. However in most fire alarm installations the minimum requirement is that the LHS circuit is monitored for disconnections by means of an End Of Line (EOL) device and an appropriate Fire Alarm Channel or Address Loop Interface Unit.

Linear Heat Sensing Cable is versatile in that it can both provide an alternative to point heat detectors win conventional (space) protection situations and it may also be readily installed in very close proximity to monitor hazards. The detector is particularly suited to applications where harsh environmental conditions preclude the use of other forms of detection in areas that have access restrictions due to either physical difficulties or personnel health risks.


  • Cable Tunnels, Ducts & Mezzanines
  • Escalators & Moving Walkaways
  • Petro-Chemical Storage Tank Rim Seals
  • Paint Shops & Spray Booths
  • Conveyors - Coal, Wood, Sulphur, etc.
  • Ceiling Voids & Attic Spaces
  • Road & Rail Tunnel Carriageaways
  • Nuclear Reactor Plant Areas
  • Refrigerated Stores & Cold Rooms
  • Electrical Control & Switchgear Cabinets
  • Warehouse High Rise Pallet Racking
  • Oil Rigs & Off Shore Platforms
  • Fume Cupboards & Glove Boxes
  • Grain Silos & Agricultural Storage
  • Road | Rail Vehicle Engine Compartments
  • Steam Pipe Leaks & Trace Heating Faults
  • Computer Room Under Floor Cable Voids

Features of Linear Heat detectors:

  • Early detection of hazards at temperatures well below flame point.
  • Rugged construction for use in harsh environments.
  • Ease of installation.
  • Compatible with many existing zone monitors and control equipments.
  • Identifies and displays at the module, the alarm location anywhere along its length when used with digital LHSC Monitor & Locator.
  • Sensitivity is not affected by changes in ambient temperature or length of cable used on the detection area.

Linear Heat Detection Module

The module is designed to Monitor a length of Digital Linear Heat Sensing Cable (LHSC) for both fire condition, and Fault status (open circuit). The unit is designed such that it may be configured to operate in a ‘two wire’ mode that emulates the operation of conventional smoke & heat detectors. The unit may therefore be directly interfaced with Fire Control Panel by connection to fire zone trigger circuits or addressable interface modules. The unit has a 3 Digit LCD which activates on fire conditioned displays the distance into the zone that the alarm has occurred. Digital LHDC may be employed in lengths less than 2Km (1999m). The unit has an adjustment to accommodate interposing cables


Operable from two wire fire panel Trigger Circuits. Line/Low Power. Analog addressable loop interface - Loop Powered. Display of Alarm Location - Distance in meters. Fault monitoring of LHDC for open circuit conditions. LED indication of fire, Fault & supply status. Test & reset push-buttons. Volt free contact outputs for Fire & Fault conditions - Optional.

The unit is operated in conjunction with a length of Digital Linear Heat Sensing Cable (LHSC) and an End OF Line (EOL) terminator. The LHSC is a twisted pair twin core cable. When the trigger temperature of the LHSC is reached these cores connect and a Fire alarm is registered. The unit automatically determines the distance to the point of operation and displays this by means of an LCD.


  • 14-30 Vdc (2 wire mode)
  • > 10 Vdc - Latched Fire
  • Normal < 1.5 mA
  • Current-Fire < 12 mA
  • Current-Fault < 700 μA
  • Four digit LCD: 0 to 1999m
  • Unit Accuracy: +/-1% (+/-1 digit)
  • LHDC Tolerance: +/-3%
  • Lock Time: 3s
Sensor Range

The LHDC can be provided in a variety of constructional configurations that will meet the requirements of both standard and special applications. Two of the most commonly employed types are defined in the following table.

Part Number
Min. Alarm
Max. Alarm
Size - Oval
Min / Max
Core Ident.
700-070 60°C 70°C 45°C 3.5 - 4.5 mm Nylon Black Orange / Blue
700-090 80°C 90°C 70°C 3.5 - 4.5 mm Nylon Nylon Red / White