System Sensor 2WT-B Photoelectric i3 Smoke Detector, 2-Wire, 135F Fixed Thermal Sensor

The System Sensor 2WT-B is a two-wire i3 Series photoelectric smoke and fixed-temperature heat detector designed for compatible conventional fire alarm control panels. It combines photoelectric smoke detection, a 135 F (57.2 C) thermal sensor, and a 41 F (5 C) freeze trouble feature in one low-profile device. Operating at nominal 12/24 VDC, the detector features automatic sensitivity compensation, dual-color LED status indicators, and remote maintenance signaling with compatible equipment. Its included mounting base, replaceable sensing chamber, and built-in test switch simplify installation and servicing in commercial and institutional fire alarm systems.

System Sensor 2WT-B i3 Series 2-Wire Photoelectric Smoke and Heat Detector, 135 F

The System Sensor 2WT-B i3 Series Smoke and Heat Detector provides combined smoke and temperature detection for compatible conventional fire alarm systems. Manufactured by System Sensor, a Honeywell brand, this two-wire photoelectric detector incorporates a restorable 135 F (57.2 C) fixed-temperature thermal sensor and a low-temperature trouble function that detects conditions below 41 F (5 C). Its optical sensing chamber identifies smoke particles associated with developing fires, while the integrated thermal element provides an additional alarm-initiating function when the fixed temperature threshold is reached. The 2WT-B is designed for open-area protection in offices, schools, healthcare facilities, hotels, commercial buildings, and other occupancies requiring supervised smoke and heat detection through compatible initiating device circuits.

The 2WT-B features a nominal smoke sensitivity of 2.5% obscuration per foot and an onboard microprocessor that applies drift compensation and signal-smoothing algorithms to account for gradual contamination of the sensing chamber. This technology helps maintain detector sensitivity and reduce unwanted alarms caused by accumulated dust or environmental changes. Two integrated LEDs provide visual operating information: green flashes indicate normal standby, steady red indicates an alarm, red flashes every five seconds indicate an out-of-sensitivity condition, and red flashes every ten seconds indicate freeze trouble. When connected to a compatible i3-enabled control panel or the System Sensor 2W-MOD2 maintenance module, the detector can communicate maintenance conditions for cleaning, replacement, or low-temperature supervision. The optional EZ Walk loop-testing feature also supports circuit verification without individually activating every detector.

The System Sensor 2WT-B operates at nominal 12/24 VDC using a non-polarized two-wire connection, with an allowable voltage range of 8.5-35 VDC. The detector draws a maximum average standby current of 50 A, with a peak standby current of 100 A and a maximum alarm current of 130 mA, limited by the connected fire alarm control panel. Power and alarm signaling share the same initiating circuit conductors, simplifying field wiring compared with four-wire configurations. The detector must be connected to a compatible UL-listed two-wire fire alarm control panel and cannot be substituted for a four-wire detector without confirming circuit compatibility. The related 2W-B provides photoelectric smoke detection without the thermal sensor, while the 4WT-B incorporates smoke and heat detection using separate four-wire circuit connections.

The 2WT-B measures 5.3 inches (135 mm) in diameter and 2 inches (51 mm) high, including its supplied mounting base, and weighs approximately 6.3 ounces (178 g). Its plug-in Stop-Drop 'N Lock mounting system allows installers to pre-wire the base before attaching the detector head. The base accommodates 3-1/2-inch and 4-inch octagonal electrical boxes, single-gang boxes, 4-inch square boxes with plaster rings, or direct ceiling mounting, with SEMS screw terminals accepting 14-22 AWG conductors. The detector operates from 32 F to 100 F (0 C to 37.8 C) and at 0-95% non-condensing relative humidity. It is UL 268 Listed for fire protection signaling applications and includes a manufacturer-documented three-year limited warranty. The replaceable sensing chamber, built-in test switch, and optional sensitivity reader support routine inspection and maintenance. Detector placement, panel compatibility, sensitivity testing, cleaning, and system commissioning must follow System Sensor installation instructions and applicable NFPA 72 requirements.