System Sensor 4WT-B — conventional 4-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 4WT-B pairs photoelectric smoke sensing with fixed-temperature heat sensing, so it responds to visible smoke from slow smouldering fires and to a temperature rise past 135°F, and it reports a freeze trouble condition at 41°F where a loss of heat is itself a hazard. As a 4-wire device it draws operating power from a separate supervised power circuit and signals alarm through dry contacts, so the panel sees a contact closure rather than a change in loop current. Alarm draw is 20 mA at 12 V or 23 mA at 24 V, with 50 µA standby. The plug-in design lets the base be pre-wired and mounted at rough-in and the head fitted later with a Stop-Drop ’N Lock action. Drift compensation and smoothing algorithms hold sensitivity steady as contaminants accumulate, and wide-angle dual-color LEDs show power up, standby, out-of-sensitivity, freeze trouble and alarm. Sensitivity is read with the SENS-RDR. Head and base ship together.
Specifications
| Model |
4WT-B (i3 series) |
| Detection |
Photoelectric smoke with fixed-temperature thermal sensor |
| Wiring |
4-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 |
| Maximum alarm current |
20 mA at 12 V; 23 mA at 24 V |
| Alarm contact ratings |
0.5 A @ 30 V AC/DC |
| 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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Supervise the power circuit: as with any 4-wire detector, loss of detector power must be annunciated as a trouble at the panel, normally through an end-of-line relay at the far end of the power run.
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Alarm current is voltage dependent: 20 mA at 12 V and 23 mA at 24 V. Size the power supply and standby battery for the system voltage in use, allowing for every head that could be in alarm simultaneously plus 50 µA standby each.
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Temperature ceiling drops to 100°F: the thermal sensor narrows the range to 32°F–100°F, against 120°F for the photoelectric-only 4W-B. Do not substitute a 4WT-B into an attic or unconditioned mechanical space where a 4W-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. Confusing them sends a technician after the wrong fault.
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Fixed temperature, not rate-of-rise: the thermal element is a 135°F fixed-temperature sensor and provides no rate-of-rise function.
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Contacts are rated 0.5 A @ 30 V AC/DC: do not switch heavier auxiliary loads directly. Where a higher-rated Form C contact is required, use the 4WTAR-B or an external relay.
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Power-up blink is normal: both LEDs blink every 10 seconds for the first 80 seconds after power is applied — the initial status indication, not a fault.
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EZ Walk and remote maintenance are 2-wire features: the 2W-MOD2 module serves 2-wire i3 detectors. Use the SENS-RDR to read this detector’s sensitivity in percent-per-foot obscuration.
Related models
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4W-B — same 4-wire detector without the thermal sensor or freeze trouble; rated to 120°F
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2WT-B — 2-wire photoelectric/thermal version; alarm current limited by the control panel
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2W-B — 2-wire photoelectric only
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4WTA-B — 4-wire photoelectric/thermal with an 85 dBA sounder; 35 mA alarm current
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4WTAR-B — 4-wire photoelectric/thermal with sounder and Form C relay (2 A @ 30 V AC/DC); 50 mA alarm current
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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.
