Linear Heat Detection

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Typical Detecting Temperature 68 °C[1] (building) 180 °C (plant)
Maximum Length 3000m[1][2]

Linear Heat Detection (LHD) (also known as Linear Detection Wire or Linear Heat Detection Cable or Linear Heat) is a very commonly used method of fire detection. It can detect a fire anywhere along the length of the cable, and can be of lengths in excess of a kilometer.

Applications can range from building fire alarm systems to mobile plant machinery.


Linear Heat Detection (LHD) cable is essentially a two-core cable terminated by an end-of-line resistor (resistance varies with application). The two cores are separated by a polymer plastic, that is designed to melt at a specific temperature (commonly 68 °C for building applications[1]), and without which causes the two cores to short. This can be seen as a change in resistance in the wire.

There are a limited states the LHD cable can be in:

  1. Open-circuit - Effectively an infinite resistance
  2. Normal Operating Condition - Apparent resistance will be the same as the end-of-line resistor
  3. Fire Detection - Resistance of the Linear Heat Cable to the short circuit

See also[edit]


  1. ^ a b c "Linear Heat Detection cable information" (PDF). Retrieved 26 April 2014.
  2. ^ "Safe Fire Detection, LHD Information". Safe Fire Detection. Retrieved 26 April 2014.