Frequently Asked Questions

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.

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.

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.

Analogue linear heat detection systems identify fires or overheat conditions by continuously measuring changes in electrical resistance along the detection cable. An alarm is triggered once the resistance along the cable falls below a set threshold.

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.

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.

Please find the range of settings below:

ProReact EN Analogue = Class A1I / A2I (VdS approved), Class BI (VdS approved), 54⁰C, 64⁰C, 72⁰C, 79⁰C, 86⁰C, 100⁰C

(Other Pre-Alarm temperatures also available).

Yes, this is possible. Please note that two lengths of digital linear heat detection cable should be connected using a junction box.

Yes. For Class A1I / A2I, 54⁰C and 64⁰C alarm settings, the rate-of-rise alarm is activated when 2 to 5% of the sensor cable is heated at more than 15⁰C per minute for more than 3 minutes.

Thermocable recommends against installing its ProReact Analogue linear heat detection cable across varying ambient environments as this can interfere with the operation of the system. We recommend that multiple ProReact Analogue LHD systems are used in this instance (one for each different environment) or a digital linear heat detection system is installed as it would not be affected by varying ambient temperatures.
We also insist that the detection cable or end of line unit do not come into contact with any material that acts as a heat sink. A silicone sleeve (C1283) should be used to support the detection cable to a fixing clip to avoid heat transfer and end of line units should not be installed directly onto metal objects.
System designers and/or installers should ensure that the detection cable is spaced at less than or equal to the maximum approved spacing in the relevant or local building regulations or fire safety standards.

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.

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.

Both the ProReact EN Analogue sensor cable and the ProReact EN Analogue Composite Control (PACC) unit can be tested independently. Please refer to the installation manual and the sensor cable testing instruction manual for more information.

Functional testing of digital linear heat detection by heating a section of cable up until an alarm is initiated is an effective method but can be costly as the section of cable must be replaced following the test.

Alternatively, it is possible to undertake a test using Thermocable’s ProReact Digital EOL unit with Test Facility (SKU: A1385). This unit allowed a functional test to be carried out on the zone of digital LHD cable to verify normal, trouble and alarm functions of the system by simulating a break in the cable or a overheat condition.

Please get in touch with us if you require further clarification on testing a digital 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.

This European Standard applies to non-resettable line-type heat detectors consisting of a sensing element using an electrical sensor cable which can be connected to a sensor control unit or either directly or through an interface module to a control and indicating equipment intended for use in fire detection and fire alarm systems installed in and around buildings and civil engineering works.

The ProReact EN Digital LHD cable (various alarm temperatures available), the ProReact Digital Sensor Control Unit (DSCU) and the ProReact Digital End of Line Unit (EOLU) are all listed as components on the system approval certificate.

Please find below the list of components certified according to UL521:

• ProReact Analogue LHD cable – PVC
• ProReact Analogue LHD Cable – Nylon
• ProReact Analogue Control Unit – Self-Programmable inc. EOL unit
• ProReact Analogue Control Unit – Laptop-Programmable inc. EOL unit

Yes, to our knowledge we were the first manufacturer to have a full system (consisting of detection cable, an interface unit and end of line unit) certified according to EN54-28.

They provide a technical basis to assess the performance of construction products and they enable manufacturers to draw up declarations of performance and affix CE and UKCA marking. Products that are resistant to fire or react to fire fall under the definition of construction products in the European Union.

Low smoke zero halogen cables are being increasingly specified and used in environments where smoke and harmful emissions released in the event of a fire could endanger human life. ProReact Plus Digital LHD cable is a low smoke zero halogen, UV stable and hydrocarbon resistant alternative to traditional digital linear heat detection cable.

Thermocable’s analogue linear heat detection cable and end of line units can continuously operate in temperatures as low as -40⁰C. The control or interface units typically have a minimum ambient operating temperature of 0⁰C.

There are no restrictions in place for the minimum amount of detection cable installed per zone or system.

Each zone of ProReact Digital Linear Heat Detection cable can contain up to 3,000 metres. Two zones of detection cable can be connected into a ProReact Digital Interface Monitor Module allowing the maximum length of detection cable per system to be up to 6,000 metres.

Up to 500 metres of Thermocable’s ProReact EN Analogue sensor cable can be connected to a ProReact EN Analogue Composite Control (PACC) unit.
For nearly all installations, the mandatory minimum zone length is 30 metres. However, the minimum zone length is increased to 50 metres for the Class AI1 / AI2 alarm setting.

Cable zone lengths can vary from 30 metres to 500 metres in length.

Yes. In certain applications it may be desirable or necessary to use non-sensing leader cable between a ProReact EN Analogue control unit and the detection cable. This may be required if the expected ambient temperature range, or other environmental conditions, where the Analogue LHD cable is to be used is greater than the maximum ambient temperature range for the control unit.

The maximum length of leader cable that can be used per ProReact EN Analogue LHD system is 250 metres. Thermocable can manufacture and supply leader cable that is compatible with its ProReact EN Analogue LHD cable. Please contact us or refer to the installation manual if you require further information.

Cable zone lengths can vary from 30 metres to 500 metres in length.

Thermocable recommends that the cable is fixed in place using a clip every 0.5 metres – 1 metre (ideally 0.5 metres to avoid any sagging).

All ProReact EN Analogue sensor cable is manufactured on-site at Thermocable’s factory in Bradford, West Yorkshire. The standard reel lengths available are 100 metres, 250 metres and 500 metres. Non-standard reels can be supplied at a surcharge if required.

This detection cable is available in 100 metre, 200 metre or 500 metre reel lengths as standard. Non-standard lengths can be supplied but will incur a small surcharge. Please note that the maximum available reel length is 500 metres per spool.

Yes, all Thermocable’s control or interface units require a 24V power supply.

UL approval has been granted for two versions of control unit. One is a self-contained unit or, for finer control, a version requiring a laptop prevents uninvited system access via a software programme.

Independent – This is when the interface unit is used as a two zone system. When a fault or overheat condition occurs on a Digital LHD zone, the corresponding fault or alarm output respectively is triggered. The two zones operate independently and both sets of outputs should be connected to a fire alarm control panel. If the zone is not required leave the 3.6kohm resistor in the zone input terminals as supplied. In this mode, the two zones can either contain identical rated temperature Digital LHD cables or two different rated temperature Digital LHD cables.

Interlock – this mode is for applications which require a fail-safe guarantee that an alarm is only triggered when an overheat condition has been detected. This mode may also be known as coincidence detection. In this case, the same rated temperature Digital LHD cable should be attached to both zones of the interface unit. The alarm output is only activated when both Digital LHD cables trigger an alarm due to an overheat condition. If one Digital LHD cable zone input registers an alarm but the second does not, the alarm output will not be activated. This is to prevent an alarm if a mechanical or other issue has triggered one Digital LHD cable and not an overheat condition.

ProReact EN Analogue sensor cable is comprised of four inner core wires.

The installation manual and data sheet are available in English, German, Polish and French. Further languages may be available on request.