System Sensor DH500 User Manual

INSTALLATION AND MAINTENANCE INSTRUCTIONS

DH500 Intelligent Air Duct Smoke
Detector Housing

Specifications

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: [phone]

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

H0116-00 H0238-00

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.