Overview
The Allen-Bradley 855T-B24DD4 is a 70mm control tower stack light designed for industrial machinery status indication and alarm signaling. This two-circuit module combines a steady red incandescent lens with an integrated piezo sounder, operated independently via dual control circuits. Rated for 24V AC/DC operation, it delivers reliable visual and audible signals in manufacturing environments, process monitoring, and panel-mount applications.
Key Features
- Two-Circuit Steady Module: Separate circuits for light and sound enable independent control of visual and audible warnings
- Red Incandescent Lens: Bright, immediate visibility for fault and critical alert states
- Piezo Sounder with DIP Switch: Configurable for continuous or pulsing audio output
- 24V AC/DC Rated: Compatible with low-voltage industrial control systems
- 70mm Modular Stack Design: Stacks with up to three light modules; positioned at top of stack assembly
- Industrial Certifications: CE, CUL, KC, and UL approved for safety-critical applications
Technical Specifications
- Voltage Rating: 24V AC/DC
- Lens Color: Red
- Lamp Type: Incandescent
- Operation Type: 2-Circuit Steady
- Sound Module: Piezo (pulsing or continuous, DIP-switch selectable)
- Housing Color: Black
- Module Size: 70mm stack light module
- Weight: 0.33 lb
- Leakage Current Tolerance: Up to 3 mA absorption from solid-state outputs
- Certifications: CE, CUL, KC, UL
- Series: 855T Control Tower Stack Lights
- Compatible Bases: 855T-BSB, 855T-BCB (stackable), 855T-BPM10, 855T-BPM25, 855T-BPM40 (pole mount)
Typical Applications
- Machine status indication on production lines and manufacturing equipment
- Alarm and hazard signaling in industrial control panels
- Process monitoring in pharmaceutical, food, and discrete manufacturing
- Warning and fault notification in packaging and material handling systems
- Safety and traffic control in warehouse and logistics automation
- Multi-state status indication using stacked tower configurations
Compatibility & Replacements
Compatible With
- Allen-Bradley 855T series stack light modules (colors: green, red, amber, blue, clear, yellow)
- 855T-BSB and 855T-BCB modular stack bases
- 855T-BPM10, 855T-BPM25, and 855T-BPM40 pole-mount bases
- 24V DC industrial control systems (PLC outputs, relay circuits, solid-state switches)
- Low-voltage hardwired and programmable automation environments
Replaces / Drop-In Replacement For
The 855T-B24DD4 is a discontinued model (end-of-life as of October 1, 2019). Modern direct replacements in the 855T line include the 855T-B24DN4 (24V AC/DC, red lens, steady light without sound) and other 855T-B24D* variants. Verify compatibility with your system integrator before ordering, as wiring and mounting requirements may differ between generations.
Works With
- 24V DC solid-state PLC outputs (digital I/O modules from CompactLogix, ControlLogix, MicroLogix)
- 24V AC hardwired relay circuits and contactors
- Siemens S7-1200/1500 with 24V safety modules
- Omron and Mitsubishi 24V control systems
- EtherNet/IP and PROFINET-enabled devices with 24V I/O interfaces
- Industrial Ethernet gateways and remote I/O nodes
