FW2921 | Alarm Bell | Tongfang BMS

Technical Specifications

Model Number	FW2921
Product Name	Alarm Bell
Category	Traditional Audible Signal
Certification	UL Listed (UL464)
Manufacturer	Maple Armor / Tongfang
Warranty	2-Year Standard
Operating Principle	Electromechanical Hammer Action
Sound Level	85 dB(A) minimum at 10 ft (3m)
Frequency	800-1000 Hz (Nominal)
Tone Pattern	Continuous (Code 3 optional)
Operating Voltage	24VDC Nominal (15-32VDC range)
Current Consumption	Standby: 0mA, Active: 50mA typical
Power Rating	1.2W (at 24VDC)
Bell Material	Brass (Weatherproof finish)
Hammer Mechanism	Spring-loaded Solenoid Actuated
Strike Rate	60-80 strikes per minute
Operating Temperature	-10°C to +55°C (14°F to 131°F)
Storage Temperature	-20°C to +70°C (-4°F to 158°F)
Humidity	10% to 93% RH (Non-condensing)
Weatherproof Rating	IP54 (Dust and Water Splash Protected)
Enclosure Material	Polycarbonate (UL94 V-0)
Mounting Type	Surface Mount (Wall or Ceiling)
Dimensions (Diameter x Depth)	6.0" x 4.0" (152mm x 102mm)
Weight	1.8 lbs (0.82 kg)
Wire Gauge	14-22 AWG
Terminal Type	Screw Terminals (Polarity Sensitive)
Color	Red (Standard), Optional colors available
Expected Mechanical Life	500,000 cycles minimum
Audibility Distance	Up to 200 ft (61m) in open areas
Code Compliance	NFPA 72, IBC, ADA Requirements

Sound Level Comparison

60 dB

70 dB

80 dB

85 dB
FW2921

90 dB

100 dB

Normal Conversation: 60 dB | City Traffic: 85 dB | FW2921 Alarm Bell: 85+ dB

Product Overview

The FW2921 Alarm Bell is a traditional electromechanical audible signaling device designed specifically for fire alarm and emergency evacuation systems. Using a time-tested hammer-and-bell mechanism, it provides a distinctive, penetrating sound that is immediately recognizable as a fire alarm signal.

High Audibility

85 dB(A) minimum sound output ensures clear audibility even in noisy environments.

UL Listed Safety

Certified to UL464 standards for fire alarm signaling devices, ensuring code compliance.

Mechanical Reliability

Simple electromechanical design with proven reliability and minimal maintenance.

How It Works

Activation: When 24VDC is applied, the solenoid coil energizes

Hammer Action: Solenoid pulls hammer back against spring tension

Strike: Hammer is released, striking the brass bell

Reset: Spring returns hammer to ready position

Sound Generation: Bell vibration creates audible alarm tone

Repetition: Process repeats at 60-80 strikes per minute

Traditional vs Electronic: Unlike electronic sounders, electromechanical alarm bells provide a distinctive mechanical sound that is less likely to be confused with other building noises. This traditional sound pattern is often preferred in industrial settings and areas with high background noise.

Product Features

Sound & Performance Features

85 dB(A) minimum sound output at 10 ft
800-1000 Hz resonant frequency
Penetrating mechanical bell sound
60-80 strikes per minute rate
Distinctive alarm pattern recognition
Effective in high-noise environments

Construction Features

Brass bell with weather-resistant finish
Polycarbonate enclosure (UL94 V-0)
IP54 weatherproof rating
Heavy-duty solenoid mechanism
Precision spring-loaded hammer
Corrosion-resistant components

Electrical Features

24VDC nominal operation (15-32VDC range)
50mA typical current draw
Polarity sensitive operation
Screw terminal connections
Low standby power (0mA when off)
Compatible with NAC circuits

Reliability Features

500,000 minimum strike cycles
Mechanical simplicity for reliability
Minimal maintenance requirements
Field-serviceable components
Temperature and humidity tested
Vibration and shock resistant

Sound Level Considerations: The FW2921 produces 85 dB(A) minimum at 10 feet. In areas with ambient noise levels exceeding 85 dB(A), additional or alternative signaling methods may be required per NFPA 72 requirements. Always conduct on-site sound level testing during commissioning.

Installation & Configuration

Wall Mount

Standard wall mounting

Ceiling Mount

Overhead ceiling mounting

Outdoor Mount

Weatherproof outdoor locations

Installation Guidelines

Follow NEC and NFPA 72 requirements
Mount 90" (2.3m) minimum above floor
Ensure clear sound propagation path
Avoid mounting near obstructions
Consider ambient noise levels
Verify proper polarity connection

Wiring Requirements

Circuit Requirements

24VDC Notification Appliance Circuit (NAC).

Polarity

Observe positive (+) and negative (-) terminals.

Load Calculation

Include 50mA per bell in NAC calculations.

Outdoor Wiring

Use weatherproof conduit and seals.

Installation Steps

Select mounting location per audibility requirements
Mark and drill mounting holes using template
Install appropriate anchors for mounting surface
Route wiring to bell location in approved conduit
Connect wires to screw terminals (observe polarity)
Secure bell to mounting surface with provided screws
Ensure bell is level and securely mounted
Verify electrical connections are tight
Test bell operation from fire alarm control panel
Measure sound levels at various locations
Document installation and testing results

Sound Coverage Guidelines

Office Spaces

Coverage radius: 50-75 ft (15-23m).

Industrial Areas

Coverage radius: 25-50 ft (8-15m).

High-Noise Areas

Additional bells may be required.

Compatibility & Applications

Compatible Systems

Maple Armor FW2000 Series
Maple Armor FW2100 Series
Maple Armor FW2200 Series
Most 24VDC NAC fire alarm systems
Compatible with conventional and addressable systems

Typical Applications

Industrial manufacturing facilities
Warehouse and storage buildings
Parking garages and structures
School and university buildings
Historical buildings (traditional aesthetic)
Areas requiring distinctive mechanical sound

Application Scenarios

Industrial Plants

Penetrating sound over machinery noise.

Warehouses

Reliable operation in large open spaces.

Historical Buildings

Traditional aesthetic and sound.

Benefits

High Audibility: 85+ dB for clear signaling

Code Compliance: UL Listed for safety

Reliable: Simple mechanical design

Durable: Weatherproof construction

Versatile: Indoor and outdoor use

Serviceable: Easy maintenance access

Audibility Testing: After installation, conduct sound level measurements at various points within the coverage area to ensure compliance with NFPA 72 requirements. The distinctive mechanical sound of the FW2921 is often more effective in waking sleeping occupants than electronic tones.