System Sensor 4WT-B Four-Wire Optical and Heat Detector Head

The System Sensor 4WT-B Four-Wire Optical and Heat Detector Head provides reliable fire detection for compatible conventional fire alarm systems. It combines an advanced optical sensing chamber with a 135°F fixed-temperature thermal sensor. In addition, its automatic sensitivity compensation and dual-color LED indicators support efficient inspection and maintenance.

Part of the System Sensor i³ Series, this detector offers a practical solution for professional fire alarm installations requiring both optical and thermal sensing.

Combination Optical and Heat Detection

The detector uses two complementary sensing technologies to monitor developing fire conditions.

First, its optical sensing chamber detects airborne particles associated with combustion. Meanwhile, the integrated thermal sensor monitors surrounding temperature.

When the sensing chamber identifies an alarm condition, the detector activates its alarm output. The thermal element also provides an alarm response when the temperature reaches its rated threshold.

Therefore, the device provides two detection functions in one compact housing.

135°F Fixed-Temperature Heat Detection

The integrated thermal sensor has a fixed-temperature rating of 135°F (57.2°C).

When the surrounding temperature reaches this threshold, the thermal element initiates an alarm condition.

Unlike mechanical heat detectors with non-restorable fusible elements, this model features a restorable thermal sensor.

As a result, the detector can return to normal operation after the alarm condition clears and the system is properly reset, provided the unit remains serviceable.

41°F Freeze-Trouble Indication

The detector includes a freeze-trouble monitoring function.

When the surrounding temperature falls below approximately 41°F (5°C), the device provides a visual trouble indication.

This feature helps maintenance personnel recognize environmental conditions outside the intended operating range.

However, the freeze indication is a diagnostic feature rather than a substitute for a dedicated low-temperature monitoring system.

Automatic Sensitivity Compensation

The i³ Series uses an onboard microprocessor to monitor changes in the optical sensing chamber.

Over time, dust and airborne contaminants can affect detector sensitivity. Therefore, the device automatically compensates for gradual contamination within its designed operating limits.

In addition, the detector provides an out-of-sensitivity indication when maintenance becomes necessary.

This feature supports dependable operation and simplifies routine inspection.

Dual-Color LED Diagnostics

The detector features green and red LED indicators.

During normal standby operation, the green LED flashes approximately every five seconds.

Meanwhile, a steady red LED identifies an alarm condition.

The red LED can also flash to indicate sensitivity problems or a freeze-trouble condition.

Consequently, technicians can recognize important operating states without removing the detector head.

Four-Wire Conventional Operation

The System Sensor 4WT-B uses a four-wire connection arrangement.

A dedicated power connection supplies the detector. Separate alarm contacts interface with a compatible conventional initiating circuit.

The unit operates from a nominal 12 or 24 VDC supply and supports an operating voltage range of 8.5 to 35 VDC.

In addition, its alarm contacts are rated at 0.5 amp at 30 VAC or VDC.

Therefore, installers must verify the power supply, initiating circuit, and supervision requirements before installation.

Key Features

• System Sensor i³ Series detector
• Four-wire conventional operation
• Combination optical and thermal fire sensing
• 135°F fixed-temperature thermal sensor
• 41°F freeze-trouble indication
• Advanced optical sensing chamber
• Automatic sensitivity drift compensation
• Onboard microprocessor
• Dual-color green and red LED indicators
• Out-of-sensitivity indication
• Plug-in detector head
• Pre-wirable mounting base
• SEMS screw wiring terminals
• Removable sensing chamber components
• Nominal 12/24 VDC operation
• Alarm relay contacts rated 0.5A at 30V
• Compatible conventional fire alarm systems
• UL 268 listing documented by manufacturer
• Professional installation and maintenance applications

Plug-In Design and Mounting Base

The detector features a removable head and a separate pre-wirable mounting base.

Installers can connect the base before attaching the sensing unit. As a result, installation becomes more convenient during construction and maintenance.

The base supports several standard electrical box configurations.

These include 3½-inch and 4-inch octagonal boxes, single-gang boxes, and 4-inch square boxes with an appropriate plaster ring.

Direct ceiling mounting is also supported when the manufacturer’s instructions permit it.

Maintenance and Inspection

The detector includes a removable sensing chamber screen and related serviceable components.

Qualified technicians can inspect and clean the sensing chamber according to the manufacturer instructions.

However, personnel must disconnect power before opening the chamber or performing internal maintenance.

Regular testing and cleaning help maintain dependable operation.

Environmental Requirements

The detector operates in ambient temperatures from 32°F to 100°F (0°C to 37.8°C).

It supports relative humidity from 0% to 95%, non-condensing.

These environmental limits help determine suitable installation locations.

The freeze-trouble feature provides an additional indication when temperatures fall below the specified threshold.

Typical Applications

This four-wire combination detector supports compatible commercial and institutional fire alarm installations.

Typical applications include office buildings, schools, hotels, healthcare facilities, retail properties, warehouses, and other approved indoor environments.

Its combination of optical and thermal sensing makes it useful where the approved fire alarm design requires both detection methods.

Installation and Compatibility

Before installation, verify the fire alarm control panel, power supply, alarm contact configuration, and initiating circuit supervision.

Also, confirm the detector’s mounting arrangement and environmental requirements.

Qualified fire alarm professionals should install, test, and maintain the unit according to System Sensor instructions and applicable fire alarm codes.

Overall, the System Sensor 4WT-B combines optical fire detection, fixed-temperature thermal sensing, automatic sensitivity compensation, and diagnostic LED indication in one conventional four-wire device. Its plug-in construction and serviceable sensing chamber make it a practical choice for professional fire alarm installations and replacement projects.

4WT-B Datasheet