SK-Duct Air Duct Smoke Detector

[1] Limitations of Duct Smoke Detectors

WARNING: DUCT DETECTORS MUST NOT BE USED AS A SUBSTITUTE FOR OPEN AREA DETECTOR PROTECTION for life safety, nor as a substitute for early warning in a building’s regular fire detection system. System Sensor recommends users read NFPA Standards 90A, 72, and 101. The SK-Duct Air Duct Smoke Detectors are listed per UL 268A.

This device requires electrical power to operate. Fire situations may interrupt power; discuss system safeguards with your fire protection specialist. The device will not sense smoke unless the ventilation system is operating and the cover is installed. Proper installation according to this manual and adherence to all electrical and environmental specifications are critical for the detector to function correctly and activate when smoke is present.

[2] General Description

Smoke introduced into an air duct system distributes throughout the entire building. Duct smoke detectors are used to sense smoke within the duct.

The SK-Duct Air Duct Smoke Detector uses photoelectric technology for smoke detection. This, combined with its housing design, samples duct air to detect developing hazardous conditions. When sufficient smoke is sensed, an alarm signal is sent to the fire control panel, initiating actions like shutting off fans or changing air handling systems to manage toxic smoke and fire gases.

The SK-Duct features a sensor cover tamper feature that signals a trouble condition if the cover is removed or improperly installed. Proper installation resolves the trouble condition.

If programmed with the system control panel, two LEDs on the detector provide local visible indication. The SK-Duct also offers a remote alarm output for auxiliary devices like the RA400Z/RA100Z remote LED annunciator, and remote test capability with RTS451/RTS151 or RTS451KEY/RTS151KEY Remote Test Stations.

[2.1] Detector Feature Set

• Utilizes plug-in head, part number SK-PHOTOR.
• Sampling tubes install from front and rear.
• Compatible with existing accessories.
• Detector address set via code switches on the sensor head.

[3] Contents of the Duct Smoke Detector Kit

1. Sensor/power board assembly with factory-installed sensor head.
2. Three #10 sheet metal screws for mounting.
3. Drilling template.
4. One sampling tube end cap.
5. One plastic exhaust tube.

Note: A sampling tube must be ordered separately. Ensure it is the correct length for the duct width. Refer to Table 1 on page 3 for required inlet tube lengths.

[4] Detector Installation

[4.1] Verify Duct Air Flow Direction and Velocity

The SK-Duct detectors are designed for air handling systems with air velocities from 100 to 4000 feet per minute and duct widths from 6 inches to 12 feet. Verify that the duct air velocity falls within these parameters using a velocity meter (anemometer).

[4.2] Determine Mounting Location and Configuration

On ducts wider than 18 inches, mount the detector downstream of a bend, obstruction, or supply/return air inlet. Installation is permitted on or within commercial packaged rooftop heating/air-conditioning systems, fire/smoke dampers, and economizers, as determined by local code.

Select a mounting configuration: side-by-side "rectangular" or top-over-bottom "square" (refer to Figure 2). For the square configuration, remove the rear attachment screw, pivot the unit at the hinge, and replace the screw in the new attachment hole. Do not remove the hinge screw. Final installation approval depends on passing differential pressure and smoke entry tests.

[4.3] Drill the Mounting Holes

Use the supplied mounting template. Affix it to the duct at the desired location, ensuring it lies flat and smooth.

[4.3.1] For Rectangular Side-by-Side Mounting Configuration:

Center punch at four target centers: two "A" for sampling tubes and two "B" for mounting tabs. Drill pilot holes at "A" centers and cut two 1.375-inch diameter holes using a 13/8-inch hole saw or punch. Drill .156-inch diameter holes using a 5/32-inch drill at "B" centers.

Figure 2 Illustration: Shows removing a screw, pivoting the detector, and replacing the screw to secure it in place for the square configuration.

[4.3.2] For Square Top-Over-Bottom Mounting Configuration:

Center punch at four target centers: two "A" for sampling tubes and two "C" for mounting tabs. Drill pilot holes at "A" centers and cut two 1.375-inch diameter holes using a 13/8-inch hole saw or punch. Drill .156-inch diameter holes using a 5/32-inch drill at "C" centers. An additional .156-inch hole can be drilled at one of the lower housing mounting tabs if desired.

[4.4] Secure the Duct Detector to the Duct

Use two screws for the rectangular configuration or three screws for the square configuration to attach the detector to the duct. Do not overtighten.

[5] Sampling Tube Installation

[5.1] Sampling Tube Selection

Order the correct length sampling tube, as specified in Table 1, to extend at least 2/3 across the duct width for optimal performance.

*Must extend a minimum of 2/3 the duct width.

Install the sampling tube with the air inlet holes facing into the air flow. The tube connector is marked with an arrow indicating airflow direction (refer to Figure 3). Mounting the detector housing vertically is acceptable if air flows directly into the sampling tube holes. The sampling tube and exhaust tube can be mounted in either housing connection, provided the exhaust tube is downstream from the sampling tube.

Figure 3 Illustration: Shows the sampling tube with end cap and an arrow indicating "ARROW MUST FACE INTO AIR FLOW".

Caution: The sampling tube end cap is critical for proper operation, creating the necessary airflow to the sensor. Ensure it is installed after any length adjustments.

A plastic exhaust tube is included. Install it into the housing connection downstream from the sampling tube connection. A longer 1-foot exhaust tube (model ETX) is available if the molded tube does not extend at least 2 inches into the duct.

[5.2] Sampling Tube Installation

1. For tubes shorter than the duct width, slide the sampling tube (with end cap) into the housing connection facing the airflow first. Ensure the arrow points into the airflow. For tubes over 3 feet long, support the end opposite the detector. In ducts wider than 8 feet, use the 2-inch conduit fitting to couple sections inside the duct. Ensure air inlet holes on both sections are aligned and face into the airflow.
2. For tubes longer than the duct width, extend the tube out the opposite side. Drill a 3/4-inch hole in the duct opposite the sampling tube hole. Angle the sampling tube downward at least 1/4 inch per 12 inches of duct width for moisture drainage (refer to Figure 4). There should be 10 to 12 holes spaced evenly across the duct width. If more than 2 holes extend outside the duct, select a shorter tube. Trim the tube to leave 1 to 2 inches extending outside, plug with the end cap, and tape closed any holes on the protruding section. Seal the duct where the tube protrudes.

Figure 4 Illustration: Shows a diagram with dimensions (12", 2", 3/4" hole, 1/4" angle) illustrating sampling tube installation for moisture drainage.

[5.3] Modifications of Sampling Tubes

If duct widths differ from specifications, sampling tubes can be modified. Use a 0.193-inch diameter (#10) drill to add holes, bringing the total exposed holes to 10-12, spaced evenly. This is a temporary fix and not a substitute for ordering the correct length tubes.

[5.4] Remote Sampling Tube Installation

The detector can incorporate remote sampling and/or exhaust tube mounting. Mount the detector, sampling tube, and exhaust tube rigidly to withstand air velocity pressure and vibrations. Position the detector's sampling tube for uniform airflow in the cross-section area.

Verify the pressure differential across the sampling and exhaust ports is between 0.01 and 1.11 inches of water using a manometer.

[6] Measurement Tests

[6.1] Air Flow

The SK-Duct operates at air speeds of 100 to 4000 FPM. To verify sufficient sampling, turn on the air handler and measure the differential pressure between the two sampling tubes using a manometer. The differential pressure should be between 0.01 and 1.11 inches of water.

For applications with less than 500 FPM, a current-sourcing pressure transmitter (Dwyer Series 607) or aerosol smoke may be required.

Figure 5 Illustration: A wiring diagram for verifying airflow using a differential pressure transmitter (Dwyer Model #607-01), voltmeter, and power supply, showing connections to sampling and exhaust tubes.

[6.2] Low Flow Air Flow Test Using Dwyer Series 607 Differential Pressure Transmitter

Verify air speed is at least 100 FPM using an anemometer. Wire the Dwyer transmitter as shown in Figure 5. Measure voltage drop across the 1000Ω resistor (measurement 1, typically 4.00V) with ports open to ambient air. Connect the transmitter's HIGH side to the detector's sampling tube and the LOW side to the exhaust tube. Measure voltage drop across the resistor again (measurement 2). Subtract measurement 1 from measurement 2. A difference greater than 0.15 volts indicates sufficient airflow.

[7] Field Wiring; Installation Guidelines

All wiring must comply with the National Electrical Code and local codes. Use proper wire gauges and color-coding to prevent errors. Improper connections can hinder system response during a fire.

For signal wiring, use single conductor wire no smaller than 18 gauge. Duct smoke detector terminals accommodate wire sizes up to 12 gauge. Flexible conduit is recommended for the last foot of conduit; solid conduit may be used.

Consult control panel manufacturer specifications for Signaling Line Circuit (SLC) wiring requirements.

[7.1] Wiring Instructions

Disconnect power from the communication line before installing the SK-Duct. The housing provides a terminal strip with clamping plates for easy wiring. Slide the bare wire end under the plate and tighten the screw. Refer to Figure 6 for system wiring.

Figure 6 Illustration: System wiring diagram for SK-Duct, showing connections from a UL/FM listed control panel to detectors in a loop, labeled COMM. LINE, COMM. LINE (+), and COMM. LINE (-).

[7.2] Set the Address

Set the desired address using the code wheel switches on the back of the sensor head. Refer to Figure 7.

Figure 7 Illustration: Shows rotary address switches numbered 0 through 9.

[8] Verification of Operation

[8.1] Install the Cover

Install the cover, ensuring it fits into the base groove. Tighten the seven captured screws. The cover must be properly installed for sensor operation.

[8.2] Power the Unit

Activate the communication line on terminals COM + and COM -.

[8.3] Detector Check

Standby: If programmed by the control panel, observe flashing LEDs through the cover. LEDs flash with each communication.

Trouble: If LEDs do not flash, check for power issues (wiring, cover, programming, supply), a missing sensor head, or a defective unit.

[8.4] Duct Smoke Detector Test & Maintenance Procedures

Test and maintain duct smoke detectors as recommended in NFPA 72. These tests assist maintenance personnel in verifying proper detector operation.

Before testing, notify authorities that the system will be temporarily out of service. Disable the zone or system under test to prevent false alarms.

[8.4.1] Test the Unit

1. Magnet Test (not included): A test magnet simulates smoke in the sensing chamber, testing sensor electronics and panel connections.
2. Remote Test Accessory: Recommended for visible indication of power and alarm.

Verify system control panel alarm status and execution of auxiliary functions (fan shutdown, damper control). Two LEDs on the sensor indicate status, controlled by the panel (blink, latch on/off). Refer to the control panel documentation for LED operation details.

[8.4.2] Resetting the Detector

The detector must be reset by the system control panel.

[8.4.3] Smoke Entry Test Using Aerosol Smoke

This test is for low-flow systems (100-500 FPM). For speeds over 500 FPM, use a manometer as described in Section [6.1].

Drill a 1/4-inch hole 3 feet upstream from the detector. With the air handler on, measure air velocity (must be at least 100 FPM). Spray aerosol smoke into the duct through the hole for five seconds. Wait two minutes for the detector to alarm. If it alarms, air is flowing. Remove the cover, blow out residual smoke, and reset the detector at the panel. Seal the entry hole with duct tape. Replace the cover for proper operation.

*Aerosol smoke testers are available from Home Safeguard Industries (model 25S) or SDi (models CHEK02, CHEK06). Follow manufacturer instructions.

Caution: Canned aerosol smoke formulas vary. Misuse or overuse can adversely affect the smoke detector. Consult manufacturer instructions for warnings.

[9] Detector Cleaning Procedures

Notify authorities that the system will be temporarily out of service. Disable the zone or system to prevent false alarms.

[9.1] Detector Sensor Cleaning

1. Remove the sensor from the system.
2. Press the four removal tabs to remove the sensor cover.
3. Carefully vacuum the screen without removing it. If further cleaning is needed, proceed to step 4; otherwise, skip to step 7.
4. Pull the chamber cover/screen assembly straight out.
5. Use a vacuum cleaner or compressed air to remove dust and debris from the sensing chamber.
6. Reinstall the chamber cover/screen assembly by sliding its edge over the sensing chamber and turning until firmly in place.
7. Replace the cover, aligning it using the LEDs, and gently push until it locks.
8. Reinstall the detector.

[9.2] Reinstallation

1. Reinstall the detector in its housing.
2. Restore system power.
3. Perform Detector Check.
4. Notify authorities that testing is complete and the system is operational.

[10] Sensor Replacement

1. Rotate the sensor head counterclockwise to remove it.
2. Pull gently to remove.
3. Align the mounting features of the new sensor head and rotate clockwise into place.

[11] Optional Accessories

Optional accessories include RA400Z/RA100Z, RTS451/RTS151, and RTS451KEY/RTS151KEY.

Note: Ensure the blue wire remains connected to RA+ on the field connector side of the terminal block.

[11.1] Option 1: Remote Test Using Sensor with Remote Test Capability (Without a Test Coil)

A sensor with suffix "R" (Remote Test Capability) can be used. This eliminates the need for a test coil when wired to a RTS451/RTS151/RTS451KEY/RTS151KEY Remote Test Station.

Wire the device as shown in Figure 9. Wire runs must be limited to 25 Ω or less per interconnecting wire.

Note: The resistor assembly must be in place between RA+ and OUT+ inside the SK-Duct for Remote Test function.

Figure 9 Illustration: Wiring diagram showing connections from SK-Duct to RTS451/RTS451KEY/RTS151/RTS151KEY using a sensor with remote test capability. Terminals labeled TEST COIL +, TEST COIL -, COMM +, OUT (CONV ONLY) +, COMM -, RA/RTS -, RA +, RTS +.

[11.2] Option 2: Remote Test Using a Test Coil

A remote test station requires an accessory coil, part number DCOIL, sold separately.

1. Install DCOIL in the housing pocket, ensuring the arrow points toward the detector.
2. Install the DCOIL mounting screw.
3. Connect each DCOIL lead to a Test Coil Terminal. Refer to Figure 10.

Figure 10 Illustration: Shows the SK-Duct using a test coil, with terminals labeled DCOIL, TEST COIL SCREW, and TEST COIL TERMINALS.

Figure 11 Illustration: Wiring diagram from SK-Duct to RTS451/RTS151/RTS451KEY/RTS151KEY using a test coil. Shows connections to TEST COIL +, TEST COIL -, COMM +, OUT (CONV ONLY) +, COMM -, RA/RTS -, RA +, RTS +. Also shows external power supply connections for the RTS unit.

Note: If using a RA400Z, the tab should be broken for use with the intelligent duct smoke detector. If using RA100Z, ensure the jumper is removed.

The RTS451/RTS151/RTS451KEY/RTS151KEY Remote Test Station tests the alarm capability of the duct smoke detector by providing the stimulus to initiate an alarm. The SK-Duct must be reset by the system control panel.

Note: The RTS451/151, RTS451/151KEY test coil circuit requires an external 24 VDC power supply which must be UL listed.

[11.3] Additional Module Option

The SK-Duct can accommodate a relay or control module (sold separately) within the power board side of the housing. The module must be listed as compatible with the fire alarm control panel.

Physical Module Mounting Illustration: Shows removing breakaway tabs, locating the module at the rightmost corner of the power board, aligning the mounting hole with a screw boss, and installing a screw.

Note: Refer to the corresponding module Installation Instructions for general description, control panel compatibility, wiring, and ratings.

Warranty

Three-Year Limited Warranty

System Sensor warrants its product to be free from defects in materials and workmanship under normal use for three years from the date of manufacture. System Sensor makes no other express warranty. No agent, representative, dealer, or employee can alter this warranty. The Company's obligation is limited to replacing defective parts. To obtain warranty service, call System Sensor's toll-free number 800-SENSOR2 (736-7672) for a Return Authorization number, then send defective units postage prepaid to: Honeywell, 12220 Rojas Drive, Suite 700, El Paso, TX 79936, USA. Include a note describing the malfunction and suspected cause of failure.

The Company is not obligated to replace units damaged by misuse, modifications, or alterations occurring after manufacture. The Company is not liable for consequential or incidental damages, even if caused by negligence. Some states may not allow these limitations, so they may not apply to you. This warranty grants specific legal rights, and you may have other rights that vary by state.

Silent Knight®, System Sensor®, and Honeywell® are registered trademarks of Honeywell International, Inc.