ProReact Linear Heat Detection

Linear heat detection is a cable-based type of fire detection. A physical or electronic process occurs within the detection cable and initiates an alarm once the temperature around the cable reaches a certain threshold (i.e. alarm temperature).

Digital linear heat detection cable is often referred to as non-resettable as a physical change takes place in the detection cable once the alarm temperature is reached and the cable must be replaced following a fire or overheat condition. It is constructed of two metal core wires that come into contact at a certain temperature and, in doing so, create a short circuit. This triggers a resulting alarm on the interface unit or fire control panel.

Analogue linear heat detection cable is commonly known as resettable line-type heat detection as the system can be restored following the event of a fire if the detection cable is not exposed to a temperature above 125 ⁰C. Rather than a physical change taking place, the control unit measures for changes in resistance along the entire length of cable. An alarm is triggered once the resistance along the cable falls below a threshold determined by the chosen alarm temperature setting.

A typical system will consist of:

• Detection cable
• An end of line unit (for each zone of detection cable)
• A control unit or interface unit

Other components such as junction boxes, which used for splicing or connecting two lengths of detection cable together, or non-sensing (‘leader’) cable are also available.

One of the main benefits of linear heat detection cable is its versatility. It can be installed in both indoor and outdoor environments and in hazardous areas if required. Please contact Thermocable if you have any installation or design-related questions.

Linear heat detection cable can be installed and used in hazardous areas without ATEX certification as it is regarded as a ‘simple apparatus’ given its low voltage and that it does not contain an ignition source. Intrinsically safe barriers are required when installing linear heat detection cable within hazardous areas. More information can be found in our hazardous area installation guides.

Linear heat detection cable is most commonly installed using fixing clips and tie wraps. It is critical that the operating temperature range of the clips used are suitable for the given environment.

Thermocable’s ProReact Accessories are a comprehensive range of metal clips and supports with suitable maximum ambient operating temperatures for any application thus giving our customers piece of mind.

Plastic clips should be avoided as these are likely to have an unsuitable maximum ambient operating temperature.

Another key advantage of using linear heat detection systems is that the ongoing testing and maintenance is hassle free and cost friendly. Thermocable recommends that a linear heat detection system is tested once a year following installation to ensure it is operating as expected.

There are now sophisticated methods of testing a linear heat detection system whereas previously users tested systems by simply imitating a fire by heating up a section of detection cable. Whilst this still an effective test method, it is a costly exercise as the section of cable must be replaced following a test. Testing is now frequently incorporated into the design and operation of the end of line units and interface modules or control units. Instructions on how to test will be enclosed in the installation manual of a linear heat detection system.

Please get in touch with us if you require further clarification on testing or maintenance.

Simply connect the linear heat detection cable or interface module / control unit into a conventional fire panel or into an addressable loop using an input/output module. Detailed instructions of how to make the connections should be provided within the installation manual of a linear heat detection system.

If digital linear heat detection cable has been exposed to a temperature above its maximum ambient operating temperature or the desired alarm temperature or if analogue linear heat detection cable has been exposed to > 125⁰C, the affected detection cable must be replaced.

We recommend that the affected section of detection cable and 3 metres either side is replaced with new cable and connected to the existing zone using a junction box. Please get in touch if you have any queries on replacing detection cable in an existing system.

Yes this can be common practice in installations where the area requiring protection is a distance away from the main fire control panel. For example, for floating roof tanks where the fire panel is located within a control room a distance away from the tanks.

Non-sensing (or ‘leader’) cable can be installed between the interface module or control unit and the start of the zone of linear heat detection cable. More information on the use of leader cable can be provided by the seller. Please contact Thermocable if you require support.