What to Know About Fire Alarm Systems and the Cables that are used in them.

What to Know About Fire Alarm Systems and the Cables that are used in them.

Fire alarm systems are critical for ensuring the safety of people and property. They detect smoke, fire, carbon monoxide, or other hazards, then signal occupants to take action. Fire alarm systems may trigger automatically (via smoke or heat detectors) or manually (through pull stations or call points). At the heart of these systems is the fire alarm cable, which transmits signals throughout a building, enabling timely detection and notification.

Types of Fire Alarm Systems

1. Conventional Fire Alarm Systems
2. Addressable (Intelligent) Fire Alarm Systems

What Is Fire Alarm Cable?

The term “fire alarm cable” refers to wiring used not only in fire alarms but also in many other low-voltage applications such as smoke detectors, voice communications, microprocessor-controlled systems, pull boxes, and burglar alarms. Within a fire alarm system, these cables facilitate crucial safety functions—like elevator capture, damper control, and door release—by transmitting power and control signals.

According to the National Electrical Code (NEC) Articles 760 and 725, fire alarm system circuits can be classified as power-limited or non-power limited:

• Power-Limited Fire Alarm (PLFA): Operate at around 24 volts DC and are more common in modern systems.
• Non-Power Limited (NPLFA): Can operate at higher voltages (up to 120 volts AC), but are less common due to the efficiency and safety benefits of power-limited cables.

Fire Alarm Cable Standards

Several organizations regulate the design and performance of fire alarm cables:

• National Fire Protection Association (NFPA): Publishes the National Electrical Code (NEC), outlining electrical wiring and equipment installation requirements.
• Underwriters Laboratories (UL) and ASTM International: Develop testing procedures and standards for wires and cables, including those used in fire alarm systems.
• CSA International: Provides comparable guidance in Canada through the Canadian Electrical Code.

Consulting these standards helps ensure that cables are installed correctly and safely. Non UL Rated Cable should be avoided. Always look for the UL Label.

Fire Alarm Cable Ratings

There are three major fire safety ratings for fire alarm cable—FPL, FPLR, and FPLP—described in NEC Article 760 and tested by UL:

• FPL (General-Purpose)
• FPLR (Riser-Rated)
• FPLP (Plenum-Rated)

Power-Limited vs. Non-Power Limited Cables

The main distinction lies in the NEC requirements they must satisfy:

• Power-Limited Fire Alarm (PLFA) Cables
• Non-Power Limited (NPLFA) Cables

Determining Wire Gauge and Number of Conductors

Proper fire alarm cable selection involves considering both the wire gauge and number of conductors:

• Wire Gauge (AWG)
• Number of Conductors

Example Resistance Values (per 1,000 ft of cable; loop resistance is double):

• 18 AWG: ~6.5 Ω (13.0 Ω loop)
• 16 AWG: ~4.1 Ω (8.2 Ω loop)
• 14 AWG: ~2.6 Ω (5.2 Ω loop)
• 12 AWG: ~1.8 Ω (3.6 Ω loop)

Shielded vs. Unshielded Fire Alarm Cables

• Shielded Cables
• Unshielded Cables

Key Takeaways

1. Fire Alarm Systems Conventional vs. addressable systems determine wiring complexity and troubleshooting methods.
2. Cable Types Choose FPL, FPLR, or FPLP based on the environment (standard, riser, or plenum).
3. Power-Limited Circuits Most common in modern installations for enhanced safety and compliance.
4. Wire Gauge and Conductors Correct gauge and conductor count ensure reliable signal transmission with minimal voltage drop.
5. Shielding Essential in high EMI areas or complex installations.

By understanding these factors, you’ll be better equipped to select the right fire alarm cable for your project, whether it involves new installations or system upgrades.