A fire alarm system alerts people when smoke, fire, carbon monoxide, or other fire-related hazards are detected. These alarms may be activated automatically by smoke detectors and heat detectors, or manually by fire alarm activation devices such as manual call points or pull stations. When it comes to something as essential as a fire alarm wire, it’s always a good idea to start with the basics. The fire alarm wire serves as the foundation of every fire alarm system. It transmits signals from room to room, rings the alarm, and is crucial in various fire-related concerns. There is no specific type of fire alarm cable, and there are several variations, including cable design, conductor selections, color, striping options, safety ratings, and environmental ratings.
Common Fire Alarm Systems 
Most fire alarm systems fall into two categories: conventional or addressable.
Conventional fire alarm systems are a simple, common, time-proven technology that protects many commercial buildings today. Their reliability and low cost make them ideal for small to medium size properties. Conventional fire alarm systems are characterized by a fire alarm control panel, which holds the entire system’s intelligence. Connected to this panel via hardwires are several detectors or initiating devices such as smoke, flame, or heat detectors. Additionally, the control panel is wired to notification devices such as alarm bells, strobe lights, and automatic dialers.
Addressable (intelligent) systems assign a unique address to each connected initiating device such as smoke and heat detectors or pull switches. This design makes for easy troubleshooting and servicing the system since a technician can isolate faulty devices. Addressable systems also require less cabling than conventional systems since all devices can be placed on a single loop of cable running through the premises.
What is Fire Alarm Cable? 
While it is a fire alarm cable, it has a wide range of applications, including smoke alarms, smoke detectors, voice communications, microprocessor-controlled systems, pull boxes (fire alarm signals), burglar alarms, and other low voltage applications. When it comes to fire alarm systems in particular, fire alarm circuits control and power applications such as safety functions, elevator capture and shutdown, damper control, and door release. According to NEC Articles 760 and 725, there are two types of fire alarm system circuits: power restricted and non-power limited. Power Limited Fire Alarm Wires typically work at 24 volts DC, whereas non-power limited cables run at 120 volts AC. Non-power limited cables are typically obsolete since low-voltage cable offers greater benefits.
Fire Alarm Cable Standards 
The National Fire Protection Association (NFPA) plays an essential role in standards in the United States since it produces the National Electrical Code (NEC). This guideline governs electrical wiring and equipment installation and should be carefully reviewed before beginning a project. ASTM International and Underwriters Laboratories (UL) also develop testing and standards for a wide range of wires and cables, including those used in fire alarm and security systems. CSA International conducts comparable work in Canada and can assist with ensuring compliance with the Canadian Electrical Code.
Fire Alarm Cable Ratings 
One of the most essential factors to consider when purchasing a fire alarm cable is the fire rating. There are three key fire safety ratings to consider: FPL, FPLR, and FPLP. While NEC Article 760 explains what a power-limited cable is. The fire alarm cable is tested and certified by UL, which specifies its applications and fire safety requirements.
FPL — FPL cable is ideal for general-purpose applications but should not be installed in air ducts, plenum spaces, riser closets, or any other place where environmental airflow occurs. These cables are fire resistant and have passed both the UL 1424 and the vertical flame test 1581.
FPLR — Riser-rated fire alarm wire is suited for vertical runs in elevator shafts as well as floor-to-floor paths. These cables feature fire-resistant properties, such as the capacity to self-extinguish and emit little harmful smoke. They keep the fire from spreading from floor to floor. Riser cables need to pass the UL 1424 and 1666 vertical riser tests.
FPLP – Plenum-rated fire alarm wire is intended for use in plenum spaces, air ducts, and other places with high ambient airflow. When burned, they self-extinguish and produce a minimal amount of hazardous chemicals and smoke. These cables are UL 1424 and Steiner tunnel test 910 compliant.
What’s the difference between Power Limited Cables & Non-Power Limited Cables? 
The key difference between power limited cables and non-power-limited cables is which sections of the NEC they are required to comply with. The non-power limited wire is a fire alarm circuit powered by NEC section 760-21 and 760-23 compliant sources. A power-limited cable is a fire alarm circuit powered by a section 760-41 compliant source. Power-limited options connect to power supplies that limit the voltage and power travel through the cabling. The power supply used with PL fire alarms (PLFA) should be either a power supply or transformer specifically listed for use with PLFA or a class 3 design. Non-power limited fire alarms (NPLFA) do not need limiting from their power source and operate up to 600 volts, and type is less commonly used than power-limited cable.
What gauge size will you need? 
Another factor to consider when purchasing fire alarm components is the size of the cabling and the number of conductors included therein. NEC permits for either stranded or solid copper wires in PLFA circuits, solid conductors are more popular and often available. The number of conductors is another feature that distinguishes different types of fire alarm cables. Fire alarm cables come in two to six conductor configurations, all of which are typically certified for up to 300 VRMS. The number of wires needed is determined by the system type (conventional, addressable, or hybrid) and the device type.
The size of the fire alarm cable ranges from 18 AWG to 12 AWG (American Wire Gauge; the smaller the value, the larger the wire diameter). The amount of the wire needed for the work is determined by whether or not each individual detector or notification device in the circuit receives enough voltage to operate. This is due to the wire’s internal resistance creating a voltage drop. The greater the wire gauge, the lower the resistance and the voltage drop. When considering the uses and the length of the run, choosing a bigger or smaller gauge is critical because resistance rises with the distance of the cable run. So choosing a larger gauge wire will provide less resistance to the current passage.
| Wire Gauge | Conductor Diameter | Resistance | Loop Resistance |
| 18 AWG | 0.0403″ | 6.5 Ω/1,000 ft | 13.0 Ω/1,000 ft loop |
| 16 AWG | 0.0508″ | 4.1 Ω/1,000 ft | 8.2 Ω/1,000 ft loop |
| 14 AWG | 0.0641″ | 2.6 Ω/1,000 ft | 5.2 Ω/1,000 ft loop |
| 12 AWG | 0.0808″ | 1.8 Ω/1,000 ft | 3.6 Ω/1,000 ft loop |
| Typical Fire Cable Solid Core Wire Resistance | |||
When to Use Shielded Fire Alarm Cables? 
A Shielded fire alarm cables include an aluminum polyester foil shield over the conductors to protect against interference. Shielding is the most effective technique to eliminate electromagnetic interference (EMI). Shielded fire alarm wire reflects outside energy and transmits it to the ground. In systems with a lot of cable lines and electronic equipment, the shielded cable will offer you a better signal with no interference. A shielded fire alarm cable may be required in instances of high EMI noise exposure or to avoid cross-talk between wires within the cable.
Syston Cable offers Premium Power Limited Unshielded and Shielded Riser & Plenum Cables in 12 AWG to 22 AWG from 2 to 6 conductors configurations in UV Sunlight Resistant Riser-rated and Premium Plenum-rated cables.
Visit our webpage for all our Fire Alarm Cable options we have to offer: Fire Alarm Cable
References:
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