Length: 14.5 inches (36.7 cm)
Width: 5 inches (12.7 cm)
Depth: 3.5 inches (8.9 cm)
Weight: 2.8 lbs. (1.1 kg)
Operating Temperature Range: 32° to 120°F (0° to 49°C)
Operating Humidity Range: 10% to 93% Relative Humidity
Duct Air Velocity: 500 – 4000 ft./min. (91.4 – 1219.2 m/min.)
Electrical Ratings for DH500
Voltage Range: 14.5 – 32 VDC Peak
Standby Current (nominal): 150uA at 24 VDC
Power-Up Surge at Max.
Rated Voltage: 1.5mA-sec.
LED current (nominal): 6mA at 24 VDC
Before Installing
Please thoroughly read System Sensor’s Guide for Proper
Use of Smoke Detectors in Duct Applications (I56-473-XX),
which provides detailed information on detector spacing, placement, zoning, wiring, and special applications.
Copies of this manual are available from System Sensor.
NFPA Standards 72 and 90A should also be referenced for
detailed information.
NOTICE: This manual should be left with the owner/user
of this equipment.
IMPORTANT: This detector must be tested and maintained
regularly following NFPA 72 requirements. The detector
should be cleaned at least once a year.
General Description
An HVAC system supplies conditioned air to virtually every
area of a building. Smoke introduced into this air duct system will be distributed to the entire building. Smoke detectors designed for use in air duct systems are used to sense
the presence of smoke in the duct.
The DH500 Air Duct Detector Housings are used with
System Sensor’s intelligent model 1551 ionization detector
head and model 2551 photoelectronic detector head. These
two principal smoke detection methods are combined with
an efficient housing design that samples air passing through
a duct and allows early detection of a developing hazardous
condition. When sufficient smoke is sensed, an alarm signal
is initiated at the fire control panel monitoring the detector,
and appropriate action can be taken to shut off fans and
blowers, change over air handling systems, etc. This can
prevent the distribution or isolation of toxic smoke and fire
gases throughout the areas served by the duct system.
Two LEDs on each detector latch ON to provide a local
alarm indication. There is also a remote alarm output
for use with auxiliary devices. The DH500 has remote
test capability with the RTS451/RTS451KEY Remote Test
Station.
Contents of the Duct Detector Housing Kit
The DH500 consists of the following items: (See Figure 1.)
See Note 1 on Page 2 for inlet sampling tube and detector
supply information.
1. Complete housing base and cover assembly.
2. Two #10 sheet metal mounting screws.
3. Two sampling tube filters.
4. One test magnet.
5. Drilling template.
6. Two 5/16-inch O-rings.
7. Two rubber tube bushings seals.
8. Four #6 self-tapping mounting screws for the sampling
tube.
9. One filter adapter.
10. One inlet tube end plug.
11. Four #6x7/10 cover mounting screws.
12. Two #10 speed nuts.
13. One test coil and parts bag.
3825 Ohio Avenue, St. Charles, Illinois 60174
1-800-SENSOR2, FAX: 630-377-6495
www.systemsensor.com
D500-08-00 1 I56-512-07R
SAMPLING TUBE
FILTERS
CONDUIT HOLES
DUCT DETECTOR
HOUSING
TERMINAL STRIP
DUCT DETECTOR
COVER
SAMPLING TUBE
MOUNTING
SCREWS
DETECTOR HEAD
(SUPPLIED SEPARATELY)
EXHAUST
FILTER ADAPTER
DETECTOR BASE
INLET SAMPLING TUBE
(SUPPLIED SEPARATELY)
O-RINGS
FOAM
GASKETS
HOUSING
MOUNTING SCREWS
TEST MAGNET
TUBE
END
PLUG
Figure 1:
CAUTION
NOTE: The inlet sampling tube must be ordered sepa-
rately. It must be the correct length for the width
of the duct where it will be installed. See Table 1 to
determine the inlet tube required for different duct
widths. Smoke detector heads (1551, ionization;
2551, photoelectronic) must be ordered separately.
Installation Sequence Page
Step 1. Verify duct air flow direction and velocity 2
Step 2. Drill the mounting holes 3
Step 3. Secure the housing base to the duct 3
Step 4. Install the inlet sampling tube 3
Step 5. Field wiring 5
Step 6. Install the filters and check pressure differential 5
Step 7. Perform detector check 7
Step 8. Install the cover 8
Step 9. Perform the final system check (Testing) 8
Step 1. Verify Duct Air Flow Direction and Velocity
The DH500 is designed to be used in air handling systems
having air velocities of 500 to 4000 feet per minute. Be sure
to check engineering specifications to ensure that the air
velocity in the duct falls within these parameters. If necessary, an Alnor Model 6000-P velocity meter, Dwyer 460 differential pressure gauge, or their equivalent, may be used
to check the air velocity in the duct.
H0297-00
Step 2. Drill the Mounting Holes
Remove the paper backing from the top and bottom of the
template. Affix the template to the air duct at the desired
mounting location. Make sure the template lies flat and
smooth on the air duct. Center punch hole targets and
remove the template. Drill the holes as indicated on the
template. Slide the two speed nuts over the two small holes
(Hole A) next to the sampling tube bushing holes (Hole B)
previously drilled in the duct. (See Figure 2.)
Step 3. Mount Duct Housing
Remove the duct housing cover. Slide the foam gaskets over
the tube bushings as shown in Figure 2B. Make sure the
two small holes in the gaskets line up with the two base
mounting holes. Put one 5/16-inch O-ring over each of the
two #10 sheet metal screws. Use the two sheet metal screws
to secure the duct housing to the duct.
Do not overtighten the screws.
D500-08-00 2 I56-512-07R
HOLE B
HOLE A
DUCT
WALL
SPEED
NUT
SCREW HOLES FOR AT TACHING
DETECTOR HOUSING TO DUCT
FOAM GASKETS
EXHAUST TUBE
(EXTENSION BUSHING)
DUCT DETECTOR
HOUSING
O-RINGS
MOUNTING
SCREWS
INLET SAMPLING
TUBE BUSHING
Figure 2A. Speed nut mounting location:
INLE
T
TUBE
END
PLUG
AIR HOLES
ARROWS
MUST FACE
INTO AIR FLOW
AIR FLOW DIRECTION
FLANGE
H0116-00H0238-00
Table 1. Sampling (Inlet) Tubes
Tube Outside Duct Width
ST-1.5 1 to 2 ft. (0.3 to 0.6 m)
ST-3 2 to 4 ft. (0.6 to 1.2 m)
ST-5 4 to 8 ft. (1.2 to 2.4 m)
ST-10 8 to 12 ft. (2.4 to 3.7 m)
Step 4. Install the Inlet Tube
The inlet tube (shown in Figure 3) is identified by a series
Figure 3. Air duct detector inlet sampling tube:
Figure 2B. Installation of foam gaskets over sampling tube bushings:
of air inlet holes on the tube. This tube must be purchased
separately. Order the correct length, as specified in Table
1, for the width of the duct where it will be installed. The
exhaust tube is molded into the base of the duct housing.
The inlet tube is always installed in the right house bushing, with the air inlet holes facing into the air flow. To
assure proper installation, the tube mounting flange is
marked with arrows. Mount the inlet tube so that the
arrows point into the air flow. Figure 4 shows the various
combinations of tube mounting configurations with respect
to air flow.
H0108-00
A. Installation for Ducts Less Than 8 Feet Wide
1. If the inlet tube is longer than the width of the air duct,
drill a 3/4-inch hole in the duct directly opposite the
hole already cut for the inlet tube.
If the inlet tube is shorter than the width of the air duct,
install the end cap into the inlet tube (see Figure 3).
2. Slide the inlet tube into the right housing bushing.
Position the tube so that the arrows point into the air
flow.
3. Secure the tube flange to the housing bushing with the
two #6 self-tapping screws.
4. For tubes longer than the width of the air duct, the tube
there are more than 2 holes in the section of the tube
extending out of the duct, select a different tube length
using Table 1. Otherwise, trim the end of the tube protruding through the duct so that 1 to 2 inches of the tube
extends outside the duct. Plug this end with the tube
end plug and tape closed any holes in the protruding
section of the tube. Be sure to seal the duct when the
tube protrudes.
5. Any inlet tube over 3 feet long must be supported on the
opposite side of the duct detector housing.
should extend out of the opposite side of the duct. If
D500-08-00 3 I56-512-07R
WA RNING
AIR FLOW
DIRECTION
DETECTOR
HOUSING
DOTS INDICATE POSITION OF
SAMPLING TUBE HOLES
AIR FLOW
DIRECTION
DETECTOR
HOUSING
INLET
TUBE
EXHAUST
TUBE
AIR FLOW
DIRECTION
EXHAUST
TUBE
INLET
TUBE
INLET
TUBE
EXHAUST
TUBE
DETECTOR
HOUSING
AIR FLOW
DIRECTION
EXHAUST
TUBE
INLET
TUBE
DETECTOR
HOUSING
A.
B.
C.
D.
HORIZONTAL MOUNTING OF HOUSING
VERTICAL MOUNTING OF HOUSING
Figure 4. Tube mounting configurations with varying air flow direction and orientation of detector housing.
Ver tical as well as horizontal mounting is acceptable.
H0109-00
NOTE: An alternate method to using the ST-10 is to use
In no case should more than 2 air inlet holes be cut off the
tube. There must be a minimum of 10 holes in the tube
exposed to the air stream.
B. Installation for Ducts More Than 8 Feet Wide
NOTE: To install inlet tubes in ducts more than 8 feet
wide, work must be performed inside the air duct.
Sampling of air in ducts wider than 8 feet is accom-
NOTE: Air currents inside the duct may cause excessive
plished by using the ST-10 inlet sampling tube.
Install the inlet tube as follows:
1. Drill a 3/4-inch hole in the duct directly opposite the
hole already drilled for the inlet tube.
2. Slide the inlet tube with the flange into the right housing
bushing. Position the tube so that the arrows point into
the air flow. Secure the tube flange to the housing bushing with the two #6 self-tapping screws.
3. From inside the duct, couple the other section of the
inlet tube to the section already installed using the 1/2inch conduit fitting supplied. Make sure the holes on
both of the air inlet tubes are lined up facing the air
flow.
4. Trim the end of the tube protruding through the duct so
that 1 to 2 inches of the tube extends outside the duct.
Plug this end with the tube end cap and tape closed any
holes in the protruding section of the tube. Be sure to
seal the duct when the tube protrudes.
5. Any tube (over 3 feet long) that doesn’t protrude through
the duct (on the side opposite the housing) must be supported by other means.
D500-08-00 4 I56-512-07R
Modification of Inlet Sampling Tubes
There may be applications where duct widths are not what
is specified for the installation. In such cases, it is permissible to modify an inlet sampling tube that is longer than
necessary to span the duct width.
Use a 0.193-inch diameter (#11) drill and add the appropriate number of holes so that the total number of holes
exposed to the air flow in the duct is 10 to 12. Space the
additional holes as evenly as possible over the length of
the tube.
two ST-5 inlet tubes. Remove the flange from one
of the tubes and install as described above. After
the installation, use electrician’s tape to close off
some of the sampling holes so that there are a total
of 12 holes spaced as evenly as possible across the
width of the duct.
vibration. This vibration can slowly open the
seal around the tube and permit air to escape. To
prevent this from occurring, a 3-inch floor flange,
available at most plumbing supply houses, may be
used. This flange/connector mounting technique
makes the initial installation easier because a 1inch to 1-1/4-inch hole may be drilled where the
flange/connector will be used. It is easier to push
the inlet tube through the larger hole.
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