Proper deployment of the System Sensor SS-LD-68-155 digital linear heat detection (LHD) cable ensures rapid, reliable fire alerting across industrial environments such as cable trays, cable tunnels, conveyor belts, escalators, vehicular roads, tunnels, and warehouse racking. The sensor cable features a protective red polypropylene outer jacket tested to 1 kV over a twisted pair of sprung, low-resistance tri-metallic conductors insulated with a heat-sensitive polymer that activates at 68°C (155°F).
Bend Radius and Mechanical Routing
During installation and routing, field personnel must strictly maintain a minimum bend radius of 50 mm. Bending or kinking the cable tighter than the 50 mm limit exerts mechanical stress on the inner tri-metallic conductors and may crush the inner heat-sensitive polymer insulation. Such mechanical deformation can cause conductors to short prematurely, resulting in false fire alarms or trouble faults on the initiating circuit. Ensure the cable is secured along the detection run without pinching or crimping the outer red polypropylene jacket.
Zone Architecture and Module Interface
The SS-LD-68-155 cable supports a maximum zone length of up to 3,000 meters (10,000 feet). The linear heat detection circuit operates at rated voltages up to 30 V AC and 42 V DC. To integrate into a fire alarm system, the detection loop must interface with an addressable intelligent monitor module (such as a Notifier or System Sensor monitor module) for addressable fire alarm control panels (FACPs), or directly into a compatible conventional zone supporting normally-open dry contact detection.
End-of-Line (EOL) Box and Supervision
Continuous line integrity monitoring requires terminating the cable run into an End-of-Line (EOL) box fitted with the designated termination resistor matching the panel or monitor module requirements. This closed supervisory loop allows the system to differentiate between an open-circuit fault (cut or severed line), a short-circuit fault, and a true thermal alarm state triggered when ambient heat melts the polymer core at 68°C.
Critical Installation Specifications
| Parameter | Installation Specification |
|---|---|
| Alarm Activation Temperature | 68°C (155°F) |
| Minimum Bend Radius | 50 mm |
| Maximum Detection Zone Length | 3,000 m (10,000 ft) |
| Conductor Loop Resistance | ~0.05 Ohm/ft of twisted pair |
| Maximum Capacitance | 88 to 150 pF/m (26 to 45 pF/ft) |
| Inductance Range | 540 to 1050 nH/m |
| Maximum Operating Voltage | 30 V AC / 42 V DC |
| Operating Temperature Limits | -40°C to +121°C |
| Operating Humidity | 90% to 98% RH (non-condensing) |
| Outer Sheath Material & Colour | Polypropylene, Red (1 kV tested) |
Post-Activation Splicing Protocol
Digital linear heat detection cable is non-restorable at the specific point of thermal activation. Once the ambient temperature reaches 68°C, the inner polymer insulation melts permanently, allowing the twisted tri-metallic cores to contact each other. After an incident, the affected section must be identified, cut out, and replaced. Installers must splice replacement lengths of SS-LD-68-155 using approved junction boxes to restore electrical continuity and system supervision in accordance with UL 521, FM, and CE standards.
