SS-400-000
1
I56-3065-000R
Before Installing
Please thoroughly read System Sensor’s
Guide for Proper Use of
Smoke Detectors in Duct Applications
(I56-473-XX), which pro-
vides detailed information on detector spacing, placement, zon-
ing, wiring, and special applications. Copies of this manual are
available from System Sensor. NFPA Standards 72, 76, and 90A
should also be referenced for detailed information.
NOTICE:
This manual should be left with the owner/user of
this equipment.
All sensors must be tested after installation and periodically there-
after. Testing methods must satisfy the Authority Having Jurisdic-
tion (AHJ). Sensors offer maximum performance when tested and
maintained in compliance with NFPA 72.
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. In facilities with large air changes per hour, airflow
can carry smoke particles directly to the HVAC system. Per NFPA
76 Very Early Warning Fire Detection (VEWFD) sensors shall be
installed to monitor return air from the space. The 7251DH can be
installed to monitor the return air from the space in order to meet
NFPA 76 requirements.
The 7251DH Air Duct Smoke Detector uses a 7251 laser smoke
sensor. This smoke detection method combined with an efficient
housing design that samples air passing through a duct provides
early detection of a developing hazardous condition. When suf-
ficient 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 as well as provide an alert of a developing hazardous
condition in a facility.
Two LEDs on each detector latch ON to provide a local alarm
indication. There is also a remote alarm output for use with aux-
iliary devices. The 7251DH has remote test capability with the
RTS451/RTS451KEY Remote Test Station.
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 100°F (0° to 38°C)
Operating Humidity Range:
10% to 93% Relative Humidity
Duct Air Velocity:
300 – 4000 ft./min.
Voltage Range:
15 – 32 VDC Peak
Standby Current (nominal):
230uA at 24 VDC (no communication)
330uA at 24 VDC (one communication every 5 sec. with LED enabled)
LED current (nominal):
6.5mA at 24 VDC
Contents of the Duct Detector Housing Kit
The 7251DH consists of the following items: (See Figure 1).
See Table 1 on Page 2 for inlet sampling tube and detector sup-
ply information.
1. Complete laser duct assembly.
2. Two #10 sheet metal mounting screws.
3. Two sampling tube filters.
4. One test magnet.
5. Drilling template.
6. Two
5
/
16
˝ 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 #6x
7
/
10
cover mounting screws.
12. Two #10 speed nuts.
13. One test coil and parts bag.
NOTE:
The inlet sampling tube must be ordered separately. 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.
Installation Sequence
Page
Step 1. Determine duct mounting application . . . . . . . . . . . . 2
Step 2. Verify duct air flow direction and velocity . . . . . . . . . 2
Step 3. Drill the mounting holes . . . . . . . . . . . . . . . . . . . . . . 2
Step 4. Secure the housing base to the duct . . . . . . . . . . . . . 2
Step 5. Install the inlet sampling tube . . . . . . . . . . . . . . . . . . 2
Step 6. Field wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Step 7. Install the filters and check pressure differential . . . . 4
Step 8. Perform detector check . . . . . . . . . . . . . . . . . . . . . . . 4
Step 9. Install the cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Step 10. Perform the final system check (Testing) . . . . . . . . . . 7
Step 1. Verify Duct Air Flow Direction and Velocity
For “Very Early Warning Fire Protection” (VEWFP) NFPA 76 calls
for sensors to be mounted at the return air location for a space
(section 8.5.3.1.2.3). (A) “Where stand-alone packed HVAC units
are installed, sensors or ports shall be installed where return air is
brought back to the unit.” (B) “Sensors or ports shall be installed
such that each covers no greater than 0.4sq.m (4sq.ft.) of the
return air opening.” The System Sensor duct smoke detector is
designed to satisfy NFPA 76 for VEWFD.
I56-3
065-000R
7251DH Intelligent
Air Duct Smoke Detector
INSTALLATION AND MAINTENANCE INSTRUCTIONS
3825 Ohio Avenue, St. Charles, Illinois 60174
1-800-SENSOR2, FAX: 630-377-6495
www.systemsensor.com
firealarmresources.com
