FJ GROUP AFRICA
LINEAR HEAT
DETECTION
SYSTEMS
IN SOUTH AFRICA
Linear heat detection systems use temperature-sensitive cable installed close to a fire risk. Instead of monitoring only one point, the cable detects abnormal heat along its protected route. This suits conveyors, cable trays, tunnels, cold stores, power facilities and demanding industrial environments.
FJ Group Africa designs, supplies, installs, commissions and maintains linear heat detection systems across South Africa. Each solution is selected for the application, ambient temperature, required alarm point, cable length, environmental exposure, fire alarm interface and applicable product approval.
What is linear heat detection?
Linear heat detection, commonly shortened to LHD, is a cable-based fire detection method. The sensing cable and its controller or interface form the detector. When the cable experiences the specified heat condition, the system generates an alarm for the fire alarm panel, control system or other approved interface.
The cable covers routes where point heat detectors may be difficult to install or position close to the risk. Depending on the technology, the system may also supervise faults and provide pre-alarm, temperature or alarm-location information.
How does a linear heat detection system work?
A complete system normally includes sensing cable, approved fixings, junction or end-of-line components, a controller or interface and fire alarm integration.
The cable follows the hazard. On a conveyor it may track idler or bearing risks; on a cable tray it may run above the cables. The controller supervises the sensing circuit, while the main panel monitors alarm and fault outputs.
Performance depends on cable position, heat transfer, ambient conditions and the selected alarm rating. Linear coverage does not remove the need for proper spacing and system design.
Analogue and digital linear heat detection
The two common cable-based approaches are:
- Digital fixed-temperature cable: Conductors are separated by heat-sensitive insulation. At the rated temperature, the insulation softens and permits contact. The activated section is generally non-resettable and must be replaced as instructed.
- Analogue or programmable cable: The cable's electrical characteristics change with temperature. A compatible controller may provide adjustable alarm levels, pre-alarm, rate-of-rise evaluation or ambient compensation. Reset capability and exposure limits are product-specific.
Fibre-optic distributed temperature sensing can provide temperature and location data over long distances, but requires a compatible interrogator and project-specific design.
Not every LHD system provides an exact temperature or precise alarm location. Some identify only the affected zone. The required information must be defined before the product is selected.
Where is linear heat detection used?
LHD is useful where a risk extends along a route, the environment is harsh or detector access is difficult. Applications include:
- Belt conveyors, idlers, bearings and transfer points
- Power, control and communication cable trays
- Road, rail and service tunnels
- Warehouses, high-bay storage and roof voids
- Cold stores, freezers and refrigerated facilities
- Power stations, substations and transformer areas
- Mining, mineral processing and industrial plant
- Escalators, moving walkways and machinery spaces
- Tank rims, loading areas and selected hazardous locations
- Car parks, loading docks and waste-processing facilities
The cable jacket, alarm rating and certification must suit oil, chemicals, ultraviolet exposure, moisture, dust, abrasion and temperature conditions.
Benefits of linear heat detection cable
Continuous sensing coverage. The detector follows the risk rather than relying on isolated sensing points.
Close-proximity detection. Cable can often be positioned near equipment, tray runs or conveyor components where abnormal heat is expected.
Harsh-environment options. Suitable jackets and accessories are available for wet, dusty, corrosive and low-temperature areas.
Flexible integration. Approved interfaces can report alarm and fault conditions to conventional, addressable or specialist control systems.
Practical maintenance access. The controller and termination equipment can be placed where they are accessible, while the cable protects difficult areas.
These advantages depend on correct engineering. LHD is not automatically earlier than smoke detection, maintenance free or suitable for every fire type.
Linear heat detection for conveyors and cable trays
Conveyors present friction, bearing, material build-up and access risks. Cable should follow identified fire points without damage from material, vibration, cleaning or maintenance. Protection may be coordinated with shutdowns or suppression through an approved cause-and-effect strategy.
Cable trays can carry fire over long distances. LHD provides local heat detection where smoke movement may be unpredictable. Position, tray width, layers, covers, airflow and zone separation must be considered.
In both applications, the sensing cable must remain close enough to receive heat while being mechanically protected and accessible for inspection.
EN 54, UL and FM-approved options
Approved products are available for projects specifying EN, UL or FM requirements. EN 54-22 applies to resettable line-type heat detectors, while other products may use another applicable standard. UL 521 covers heat detectors for fire protective signalling systems. FM approval applies to specific configurations.
Approval is never a blanket property of all linear heat detection cable. The exact cable, controller, interface, end-of-line device, accessories and installation limits must match the product documentation and project specification.
For South African projects, the design may also need to consider SANS 10139, SANS 10400-T, the approved fire-safety design, insurer requirements, client standards and local authority conditions.
Hazardous-area applications
LHD may be used in a classified hazardous area when the complete arrangement is suitable. The design must address the zone, gas or dust group, temperature class, ambient range, glands, junction boxes, barriers or isolators and earthing.
An intrinsically safe design may place the controller in a safe area with approved barriers. Cable alone does not make the installation intrinsically safe; certificates and instructions must be followed.
System design and installation
A reliable design considers:
- Normal and maximum ambient temperature
- Required alarm temperature and response objective
- Cable route, spacing and distance from the risk
- Zone length and controller capacity
- Minimum bend radius and maximum pulling tension
- Approved clips, supports and fixing intervals
- Mechanical, chemical, moisture and ultraviolet exposure
- Junctions, end-of-line devices and fault supervision
- Panel compatibility, alarm text and cause-and-effect
Unapproved ties, tight bends, excessive tension and unsupported spans can cause damage. Cable should not be covered by insulation or exposed to routine impact.
Commissioning and handover
Commissioning confirms the route, checks continuity and resistance where applicable, verifies end-of-line supervision and proves panel alarm and fault reporting.
Functional testing should use the manufacturer's approved controlled heat source or simulator, never an open flame. Programmed outputs and interfaces must be proved against the cause-and-effect procedure.
Handover includes drawings, zone descriptions, cable details, settings, certificates, test results and maintenance requirements.
Complete supply, installation and maintenance support
FJ Group Africa can support the linear heat detection system lifecycle:
- Site assessment and technology selection
- Cable routing, zoning and interface design
- Approval and environmental suitability checks
- Supply, installation and panel integration
- Alarm, fault and cause-and-effect configuration
- Testing, commissioning and handover
- Planned maintenance, fault finding and alterations
Inspection and maintenance
Maintenance should inspect for cuts, crushing, corrosion, contamination, loose supports, sag and changes to the risk. Junction boxes, end-of-line components, interfaces and controllers must also be checked.
Alarm and fault functions should be tested using the approved method, with results recorded. An activated non-resettable section must be replaced as specified. Resettable cable must still be inspected after an event because excessive heat or physical damage may require replacement.
Frequently asked questions
What is the difference between linear heat detection and a point heat detector?
A point detector senses heat at one installed location. Linear heat detection uses sensing cable along a route, giving coverage close to an extended risk such as a conveyor or cable tray. The fire strategy determines whether either system, or both, are required.
What is the difference between analogue and digital LHD cable?
Digital cable normally operates at a fixed activation temperature and the affected section is generally replaced after alarm. Analogue cable changes electrically with temperature and a compatible controller may provide programmable thresholds, pre-alarm or reset functions. Exact features depend on the product.
Can linear heat detection show the exact fire location?
Some controllers estimate the distance to an alarm, and fibre-optic systems can provide distributed location data. Other systems report only the alarm zone. Location capability must be confirmed for the selected equipment.
Can linear heat detection be used in hazardous areas?
Yes, when the full system and installation method are certified for the classified area. The cable, barriers or isolators, junction boxes, glands, controller location and wiring must all meet the approved design.
Can FJ Group Africa connect LHD to an existing fire alarm panel?
Yes, subject to a compatibility and site assessment. We verify the supervised interface, power requirements, alarm and fault outputs, zoning, panel programming and cause-and-effect before confirming the solution.
Request a linear heat detection assessment or quotation
If your facility needs dependable heat detection along a conveyor, cable route, tunnel or industrial risk, contact FJ Group Africa. We will review the application, environment, detection objective, certification and existing fire alarm infrastructure before recommending a suitable system.
