Fenwal Detect-A-Fire Switches
Heat and Fire Detection that works.
DETECT-A-FIRE units by Kidde-Fenwal are the "heart" of many Fire Protection
Systems. These highly reliable devices have been a standard of the industry for
over 45 years. Many thousands of these units are now in use controlling the
release of extinguishants such as clean agents, C02, water, or dry chemicals. In
some systems the device is used as an ALARM device, to sense overheat or fire,
and alert personnel. In other systems, it is used as a RELEASE device, to sense
fire and actuate fire attack systems.
DETECT-A-FIRE units by Fenwal Controls have met with wide acceptance because
they are designed with RATE COMPENSATION. This provides a unique advantage over
both fixed temperature and rate-of-rise types of detectors because only the
DETECT-A-FIRE unit accurately senses the surrounding air temperature regardless
of the fire growth rate. At precisely the predetermined danger point, the system
is activated. Fixed temperature detectors must be completely heated to alarm
temperature and therefore a disastrous lag in time may occur with a fast rate
fire. Rate-of-rise devices, on the other hand, are triggered by the rate of
increase in ambient temperature and are subject to false alarms caused by
harmless, transient thermal gradients such as the rush of warm air from process
The secret of the unit's sensitivity is in the design (Figure 1). The outer
shell is made of a rapidly expanding alloy which closely follows changes in
surrounding air temperature. The inner struts are made of a lower expanding
alloy. Designed to resist thermal energy absorption and sealed inside the shell,
the struts follow temperature changes more slowly. A slow rate fire (Figure 2)
will heat the shell and struts together. At the "set point," the unit will
trigger, actuating the alarm or releasing the extinguishant. A transient rush of
warm air up to 40�F/min. may expand the shell, but not enough to trigger the
unit. By ignoring transient warm air excursions, the DETECT-A-FIRE unit
virtually eliminates false alarms prevalent with rate-of-rise devices. If a fast
rate fire (Figure 3) starts, the shell will expand rapidly. The struts will
close, actuating the alarm or releasing the agent. The faster the fire rate of
growth, the sooner the DETECT-A-FIRE unit will react.
Horizontal detectors are designed for locations where appearance is a factor.
The attractive, functional design lends physical protection of the unit while
making it suitable for commercial, industrial, mercantile and public
buildings,institutions and ships in non-hazardous locations (those classified as
"ordinary" under the National Electric Code). Flush mounted units are designed
to fit standard 4" octagonal electrical boxes and surface mounting units are
designed to mount directly on ceilings or on 4" electrical junction boxes.
Canadian Electrical Codes requires mounting only to an electrical junction box.
Fenwal part numbers include: 27020 27021
Temperature Settings (degrees F): 140 160 190 210 225 275 325
Vertical detectors are designed for use in both "ordinary" or "hazardous"
locations. For "ordinary" use, they may be mounted to any approved junction box
with 7/8" diameter opening by using 1/2-14 NPT mounting nuts. The device may be
wired in or out of conduit, depending on local preference and codes. Four lead
wires are provided on normally open vertical units (that close on temperature
rise), per UL requirement, to facilitate supervision of system wiring.
Instruments are Underwriters Laboratory and Underwriters Laboratory of Canada
listed and Factory Mutual approved for hazardous locations, when mounted in a
Fenwal Part Numbers include : 27120 28020 27121 28021
Temperature Settings (degrees F): 140 160 190 210 225 275 325 360 450 500 600
Fenwal DETECT-A-FIRE units are UL and ULC listed and FM approved as fire
detection thermostats (close on temperature rise) and as releasing devices (open
on temperature rise).
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