System Sensor 4WT-B Photoelectric i3 Smoke Detector, 4-Wire, 135F fixed thermal sensor

The System Sensor 4WT-B is a four-wire i3 Series photoelectric smoke detector with an integrated 135 F (57.2 C) fixed-temperature heat sensor, 12/24 VDC operation, and a Form A alarm relay. Designed for compatible conventional fire alarm and security control panels, it features automatic drift compensation, a built-in test switch, dual-color status LEDs, and freeze trouble indication below 41 F (5 C). Its 5.3-inch-diameter housing includes a removable sensing chamber and plug-in mounting base for simplified installation, testing, and maintenance. The detector is UL 268 listed.

System Sensor 4WT-B i3 Four-Wire Photoelectric Smoke and Heat Detector

The System Sensor 4WT-B is a four-wire combination photoelectric smoke and fixed-temperature heat detector designed for conventional fire alarm and security system installations requiring smoke detection with supplemental thermal sensing. Part of the System Sensor i3 Series, the 4WT-B combines an optical smoke sensing chamber with an integrated 135 F (57.2 C) restorable fixed-temperature thermal sensor, allowing the detector to initiate an alarm in response to smoke or a qualifying high-temperature condition. Its four-wire architecture uses a separate power circuit and alarm relay connections, enabling integration with compatible conventional fire alarm control panels and security control systems that support four-wire smoke detectors. The unit operates from nominal 12 or 24 VDC power and is designed for open-area smoke detection in commercial buildings, offices, institutional facilities, apartment buildings, and other protected indoor environments. Its low-profile white housing and included plug-in mounting base provide a practical solution for new installations and replacement applications.

The 4WT-B incorporates microprocessor-controlled photoelectric smoke detection with automatic drift compensation and signal-smoothing algorithms to help maintain sensitivity as dust and airborne contaminants accumulate in the sensing chamber. Its nominal smoke sensitivity is 2.5% obscuration per foot, and its intelligent processing helps reduce nuisance alarms while identifying conditions that require detector cleaning or maintenance. The detector includes a 135 F fixed-temperature heat sensor and a freeze trouble threshold of 41 F (5 C), providing additional environmental condition monitoring. Dual-color, wide-angle LED indicators communicate operating status: the green LED flashes every five seconds during normal standby, while the red LED flashes every five seconds when detector sensitivity exceeds acceptable limits, flashes every ten seconds during a freeze trouble condition, and remains continuously illuminated during an alarm. A recessed test switch allows technicians to verify detector alarm operation, while the optional System Sensor SENS-RDR infrared sensitivity reader provides a method for measuring the detector's sensitivity without removing the sensing chamber.

The System Sensor 4WT-B operates within an 8.5 to 35 VDC input range, with nominal 12/24 VDC non-polarized power connections. Its electrical requirements include a maximum average standby current of 50 microamps, an alarm current of 20 mA at 12 VDC, and 23 mA at 24 VDC. The detector provides a Form A normally open alarm relay rated at 0.5 amp at 30 VAC/VDC for connection to compatible initiating device circuits. Alarm conditions are latched until the detector receives a momentary power interruption from the control panel or associated reset circuit. The unit is designed for operation at temperatures from 32 F to 100 F (0 C to 37.8 C) and relative humidity levels from 0% to 95%, non-condensing. Measuring 5.3 inches in diameter and 2.0 inches high with its mounting base, the detector weighs approximately 6.3 ounces (178 grams). Its compact construction accommodates standard commercial and residential electrical mounting configurations.

The 4WT-B features a plug-in detector head and pre-wireable mounting base with System Sensor's Stop-Drop 'N Lock attachment mechanism, allowing installers to complete field wiring before attaching the sensing head. The base supports mounting to 3-1/2-inch or 4-inch octagonal electrical boxes, single-gang boxes, and 4-inch square boxes with plaster rings, as well as direct ceiling installation using appropriate fasteners. Large wire entry openings and in-line SEMS screw terminals accommodate 14 to 22 AWG conductors, while an optional tamper-resistant locking feature helps prevent unauthorized detector removal. The removable smoke sensing chamber and protective screen support periodic inspection and cleaning according to the manufacturer's maintenance procedures. The detector is UL 268 listed for fire protection signaling systems and is intended for installation in accordance with NFPA 72, the manufacturer's instructions, and applicable building and fire codes. Unlike the smoke-only System Sensor 4W-B, the 4WT-B incorporates both fixed-temperature thermal detection and freeze trouble indication. Its combination of photoelectric smoke sensing, 135 F thermal detection, automatic drift compensation, relay-based alarm signaling, and simplified maintenance makes it suitable for conventional four-wire smoke detection applications.