System Sensor 2WT-B — conventional 2-wire i3 series combination photoelectric smoke and heat detector with a 135°F (57.2°C) fixed thermal sensor, supplied as a plug-in head with its mounting base included.
The 2WT-B adds fixed-temperature heat sensing to the photoelectric chamber, so it responds both to visible smoke from slow smouldering fires and to a rapid temperature rise past 135°F. It also provides a freeze trouble signal at 41°F, which makes it useful in areas where a loss of heat is itself a hazard. The detector powers from a conventional 2-wire initiating device circuit, so alarm current is limited by the control panel. The plug-in design lets the base be pre-wired and mounted during rough-in and the head fitted later with a Stop-Drop ’N Lock action, keeping the optical chamber out of construction dust. Drift compensation and smoothing algorithms hold sensitivity steady as contaminants accumulate. With a 2W-MOD2 loop test/maintenance module or an i3-protocol panel on the loop, the 2WT-B reports a remote maintenance signal and supports the EZ Walk loop test, which verifies initiating-circuit wiring from the LED at each detector. Sensitivity is read in percent-per-foot obscuration with the SENS-RDR. Head and base ship together.
Specifications
| Model |
2WT-B (i3 series) |
| Detection |
Photoelectric smoke with fixed-temperature thermal sensor |
| Wiring |
2-wire |
| Operating voltage |
12/24 V nominal, non-polarized; minimum 8.5 V, maximum 35 V |
| Maximum ripple voltage |
30% peak to peak of applied voltage |
| Standby current |
50 µA maximum average |
| Peak standby current |
100 µA |
| Maximum alarm current |
130 mA, limited by control panel |
| Alarm contacts |
None (2-wire) |
| Sensitivity |
2.5%/ft nominal |
| Thermal sensor |
135°F (57.2°C) fixed |
| Freeze trouble |
41°F (5°C) |
| Operating temperature |
32°F to 100°F (0°C to 37.8°C) |
| Operating humidity |
0 to 95% RH, non-condensing |
| Input terminals |
14 to 22 AWG, SEMS screws |
| Dimensions (including base) |
5.3″ diameter × 2.0″ (51 mm) height |
| Weight |
6.3 oz (178 g) |
| Listing |
UL 268, Fire Protection Signaling Systems |
| LED — power up |
Green and red both blink every 10 seconds, 80 second initial indication |
| LED — normal standby |
Green blinks every 5 seconds, red off |
| LED — out of sensitivity |
Red blinks every 5 seconds, green off |
| LED — freeze trouble |
Red blinks every 10 seconds, green off |
| LED — alarm |
Red solid, green off |
| Mounting |
3½″ octagonal, 4″ octagonal, single-gang or 4″ square back box with plaster ring, or direct to ceiling |
Installation notes
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Temperature ceiling drops to 100°F: adding the thermal sensor narrows the operating range to 32°F–100°F, against 32°F–120°F for the photoelectric-only 2W-B. Do not substitute a 2WT-B into an attic or unconditioned mechanical space where a 2W-B was specified.
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Two red blink rates mean two different things: red every 5 seconds is out-of-sensitivity; red every 10 seconds is freeze trouble at 41°F. Misreading one for the other sends a technician after the wrong fault.
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Alarm current is set by the panel: the 130 mA figure is a maximum limited by the control panel, not the detector’s own draw. Size the initiating circuit from the panel’s published alarm current and confirm the 2WT-B is on the panel’s compatibility list.
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Power-up blink is normal: both LEDs blink every 10 seconds for the first 80 seconds after power is applied. That is the initial status indication, not a trouble.
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Remote maintenance needs a companion device: maintenance signaling and EZ Walk require a 2W-MOD2 module or an i3-protocol panel on the loop. On a plain conventional panel the detector still functions, but those features are inactive.
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No sounder, no relay: the 2WT-B is the plain combination detector. For a built-in 85 dBA sounder on a 2-wire circuit use the 2WTA-B; for a Form C relay use the 2WTR-B.
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Fixed temperature, not rate-of-rise: the thermal element is a 135°F fixed-temperature sensor. It does not provide rate-of-rise detection.
Related models
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2W-B — same 2-wire detector without the thermal sensor or freeze trouble; rated to 120°F
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4WT-B — 4-wire photoelectric/thermal version; 20 mA at 12 V / 23 mA at 24 V alarm current, 0.5 A @ 30 V AC/DC alarm contacts, 10–35 V
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4W-B — 4-wire photoelectric only
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2WTA-B — 2-wire photoelectric/thermal with an 85 dBA sounder
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2W-MOD2 — 2-wire loop test / maintenance module enabling remote maintenance signaling and EZ Walk
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SENS-RDR — wireless sensitivity reader; RT removal/replacement tool; A77-AB2 retrofit adapter bracket, 6.6″ (16.76 cm) diameter
Specifications taken from the System Sensor data sheet “i3 Series Photoelectric Smoke Detectors,” document A05-0318-007 (6/09). Manufacturer specifications are subject to change without notice.
