Det-Tronics U7698A, B, C, E Unitized Frequency IR Detector/Controller - Manual (Page 8)

Although the infrared detector is less affected by smoke
than other detectors, the U7698B should not be placed
where rising CO2 and particulates can obscure its
vision. For indoor applications, if dense smoke is
expected to accumulate at the onset of a fire, mounting
the detector on a side wall a few feet (1 meter) down
from the ceiling will normally allow enough time for the
unit to respond before it is affected by rising smoke. If
possible, fire tests should be conducted to determine
correct detector positioning and coverage.
WIRING REQUIREMENTS
The system should be wired using a 16 to 22 gauge (1.5
to 0.5 mm2) cable. The use of shielded cable is highly
recommended to protect against interference caused by
extraneous electrical “noise.” In applications where the
wiring cable is installed in conduit, the conduit should
not be used for wiring to other electrical equipment. Foil
type shielded cable is recommended to protect from
electromagnetic and radio frequency interference. The
size and length of cable should be considered when
wiring the system to ensure that a minimum input voltage
of 18 vdc is present at the U7698B. When using cables
with shields, the shield should be cut back and insulated
at each unit.
NOTE
It is important to use cable that is suitable for the
installation environment. In applications involving
high humidity or salt water, use a cable that is
made specifically for harsh, salt water environ-
ments. In all cases, typical cable insulation resis-
tance should be at least 100 megohms. If the
resistance drops below 10 megohms, the cable
could be deteriorating and should be replaced to
avoid shorting out the system. When testing the
insulation resistance, disconnect the leads from the
detector/controller before connecting the megohm-
meter (insulation tester) to the cable.
Since moisture can be detrimental to electronic devices,
it is important that moisture not be allowed to come in
contact with the electrical connections of the system.
Moisture in the air can become trapped within sections
of conduit, therefore the use of conduit seals is required
to prevent damage to electrical connections caused by
condensation within the conduit. These seals must be
water-tight and explosion-proof and are to be installed
even if they are not required by local wiring codes. A
seal must be located as close to the U7698B as possi-
ble. In no case should this seal be located more than 18
inches (46 cm) from the unit. When an explosion-proof
installation is required, an additional seal must also be
installed at any point where the conduit enters a non-
hazardous area.
When pouring a seal, the use of a fiberdam is required to
assure proper formation of the seal. The seals should
never be poured in temperatures that are below freezing,
since the water in the sealing compound will freeze and
the compound will not dry properly. Contamination
problems can then result when temperatures rise above
the freezing point and the compound thaws. The shield-
ing of the cable should be stripped back to permit the
seal to form around the individual leads, rather than
around the outside of the shield. This will prevent any
siphoning action that might occur through the inside of
the shield.
Moisture in the air can be trapped within sections of con-
duit and can condense and accumulate at the base of
vertical conduit runs. To eliminate this condition, explo-
sion-proof drains and breathers should be installed to
automatically bleed off accumulated water.
When using steel wire armored or mineral-insulated cop-
per-sheathed cables, select an approved gland with a
watertight compression stage and an overall gland
shroud for outdoor applications. A sealing washer must
be fitted between the gland and the conduit entry to
ensure IP66 rating.
WIRING PROCEDURE
The following procedure should be used for mounting
and wiring the U7698B.
1. The detectors should be positioned to provide the
best unobstructed view of the area to be protected.
Be sure that the units are easily accessible for clean-
ing and other periodic servicing. Particular attention
should also be paid to potential false alarm sources
within the cone of vision of the detector, such as the
rotating blades of a fan or surface vibration of an IR
source, since these could allow a flickering IR signal
to reach the detector. Dense fog, rain, or ice can
absorb IR radiation, which can reduce the capability
of the detector. For outdoor applications, aim the
detector downward to prevent the cone of vision
from scanning the horizon. This minimizes response
to distant IR sources outside the protected area.
NOTE
The wiring procedures in this manual are intended
to ensure proper functioning of the device under
normal conditions. However, because of the many
variations in wiring codes and regulations, total
compliance to these ordinances cannot be guaran-
teed. Be certain that all wiring complies with appli-
cable regulations that relate to the installation of
electrical equipment in a hazardous area. If in
doubt, consult a qualified official before wiring the
system.
2. Mount the bulkhead and mounting bracket assem-
bly of the detector/controller on the wall or ceiling.
See Figure 6. The mounting surface must be free of
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