System Sensor 2WTA-B — conventional 2-wire i3 series photoelectric smoke detector with a 135°F fixed thermal sensor and a built-in 85 dBA sounder, supplied as a plug-in head with its mounting base included.
The 2WTA-B gives local audible notification at the detector on a conventional 2-wire initiating device circuit, without the separate power circuit a 4-wire detector needs. Combination photoelectric and thermal sensing responds to visible smoke and to a fixed 135°F heat threshold, and a 41°F freeze trouble signal warns of falling temperatures in unheated areas. Drift compensation and smoothing algorithms hold sensitivity steady as dust accumulates and reject short-term interference. Dual-color LEDs indicate power up, standby, out-of-sensitivity, freeze trouble and alarm at a glance. With a 2W-MOD2 loop test/maintenance module or an i3-protocol panel on the loop, the detector reports a remote maintenance signal when it drifts out of sensitivity or enters freeze trouble. Head and mounting base ship together.
Specifications
| Model |
2WTA-B (i3 series, sounder option) |
| Detection |
Photoelectric smoke with thermal sensor |
| Wiring |
2-wire |
| Operating voltage |
12/24 V nominal, non-polarized; 2-wire range 8.5 V to 35 V |
| Maximum ripple voltage |
30% of applied voltage (peak to peak) |
| Standby current |
50 µA maximum average |
| Peak standby current |
100 µA |
| Maximum alarm current, direct power |
130 mA, limited by control panel (non-reverse polarity) |
| Alarm current, reverse polarity power |
30 mA for the 2WTA-B in alarm; 12 mA for all other 2WTA-B units on the loop |
| RRS-MOD allowance |
Add 25 mA for the RRS-MOD reversing relay alarm current |
| Alarm contacts |
None (2-wire) |
| Sound pressure output |
85 dBA temporal tone |
| 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 |
14–22 AWG, SEMS screws |
| Dimensions (including base) |
5.3″ (134 mm) diameter × 2.0″ (51 mm) height |
| Weight |
7.1 oz (200 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 |
| LED — out of sensitivity |
Red blinks every 5 seconds |
| LED — freeze trouble |
Red blinks every 10 seconds |
| LED — alarm |
Red solid |
| Mounting |
3½″ octagonal, 4″ octagonal, single-gang or 4″ square back box with plaster ring, or direct to ceiling |
Installation notes
-
Two different alarm current figures — use the right one: on direct (non-reverse-polarity) power the alarm current is 130 mA limited by the panel. On reverse polarity power it is 30 mA for the detector in alarm plus 12 mA for every other 2WTA-B on the loop. Sizing a reverse-polarity loop from the 130 mA figure, or a direct-power loop from the 30 mA figure, will both give the wrong answer.
-
Add 25 mA for the RRS-MOD: if a reversing relay/synchronization module is on the circuit, its own 25 mA alarm current must be added to the loop calculation.
-
Sounder synchronization: with the RRS-MOD fitted, all i3 sounders on the loop activate when any one detector alarms, their tones are synchronized, and they can be silenced from the panel. Without it, only the detector in alarm sounds.
-
2-wire minimum is 8.5 V: the 2WTA-B operates from 8.5 V to 35 V; the 10 V minimum published for 4-wire i3 models does not apply. Confirm the detector is on the panel’s compatibility list.
-
100°F ceiling: the thermal sensor limits the operating range to 32°F–100°F, below the 120°F rating of the photoelectric-only 2W-B. Keep it out of attics and unconditioned mechanical rooms.
-
Freeze trouble is a distinct LED pattern: red blinking every 10 seconds is freeze trouble at 41°F, while red blinking every 5 seconds is out-of-sensitivity. They are easy to confuse in the field.
-
No Form C relay: the 2WTA-B is the sounder model. The 2-wire model with a Form C relay is the 2WTR-B.
Related models
-
2WTR-B — 2-wire photoelectric/thermal with a Form C relay instead of the sounder; alarm current 130 mA limited by the control panel
-
2WT-B — 2-wire photoelectric/thermal with neither sounder nor relay
-
2W-B — 2-wire photoelectric only, no thermal sensor, rated to 120°F
-
4WTA-B — 4-wire equivalent with sounder; 35 mA alarm current, 10–35 V
-
4WTAR-B — 4-wire with both sounder and Form C relay; 50 mA alarm current
-
RRS-MOD — reversing relay/synchronization module; 2W-MOD2 2-wire loop test/maintenance module; SENS-RDR sensitivity reader; RT removal tool; A77-AB2 retrofit adapter bracket
Specifications taken from the System Sensor data sheet “Smoke Detectors with Sounder and Relay Option,” document A05-0348-004 (6/09). Manufacturer specifications are subject to change without notice.
