1.0 Linear Heat Detection
1.1 The linear heat detection system to be installed at site is to be of the
“digital” operating concept – whereby at a pre-selected temperature , an
alarm signal is generated by the two conductors which form the basis of
the temperature / heat sensitive cable move into contact with each other.
In the event of mechanical damage to the sensor cable, a fault signal will
be generated by loss of conductor continuity – monitored by “remote
end” line resistor .
No site calibration should be necessary- with the alarm temperature rating
pre-specified from the range 68C/ 155F, 88C/190F , 105C /220F.
Maximum acceptable alarm temperature tolerances are +/- 4 C ( +/-7F) .
The sensor cable should have been F.M. tested to verify capability of withstanding
continuous exposure to ambient temperatures to minus 40 C. ( -40F).
1.2 Unless otherwise specified in writing by the local authority having
jurisdiction , a minimum +11C ( 20F ) differential must exist between maximum
normal operating ambient temperature of the area/s in which the sensor
cable is to be installed, and the minimum alarm temperature rating of the
sensor cable. This conforms with UL521 section 53.7 and is to ensure
the avoidance of potential false alarm signals resulting from normal
local ambient temperature variations.
1.3 The specified alarm temperature of the heat sensor cable , is not to be
dependant upon the total length of sensor cable installed or upon any
manufacturer specified minimum length being exposed to any overheat / fire
condition .
1.4 For "area" protection applications, the maximum spacing between sensor cable runs
should be up to 10.6m/30 feet .
1.5 Sensor cable construction is to consist of a twisted pair of 0.912 mm (0.036 in)
tinplated copper coated steel conductors - each extruded with 0.294 mm (0.011 in)
temperature sensitive polymer –with an outer extrusion of colour coded
class 43 PVC based polymer ( meeting UL 1581 1090.1 /1090 .2 propogation
and self extinguishing requirements ) .
1.6 The overall sensor cable external diameter is to be 3.5 mm (0.138 in).
1.7 The outer extrusion is to be colour coded for ease of alarm temperature
rating identification . Colour specification is to be in strict accordance with
Industrial Standards , including U.L. 521 Table 53.1 “ Heat Detectors for Fire
Protective Signalling Systems” .
1.8 Sensor cable conductor Resistance should not be greater than 100 ohms / km
( 3 ohms / 100 ft ),increasing the potential for Integration with existing fire system
control panels , in the event no dedicated interface unit is required by the end user .
1.9 The sensor cable is to be suitable – as a minimum - for installation within
external local weather conditions , unless more severe environmental
conditions are specified in detail prior to supply and installation .
1.10 As a minimum , the linear heat sensor cable specified and installed
is to be Factory Mutual (FM) approved AND Underwriters Laboratories ( U.L.) Listed .
1.11The digital linear heat detection system selected should also include the
option for the provision a dedicated interface unit (2000metres sensor cable per interface)
supplied complete with – alarm point location facility , to aid identification on applications
where detection and alarm signal may precede visible flame .
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