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Fire Alarm System Cables

Fire Alarm (FA) systems can be put into two system designs: conventional (analog) and addressable (digital). The primary difference between both is scale. Conventional systems are ideal for small buildings or retail shops. Addressable FAs are a necessity for large buildings with many occupants.

West Penn Wire has many cable options for low-voltage conventional and addressable systems, including Aquaseal Water Resistant Cable -- the industry’s original and most recognized name in water resistant, water blocking low voltage cable.

Conventional FA Design (Analog)

In a conventional FA system the “system I.Q.” resides solely within the FA control panel. The panel receives a trigger signal from a conventional detector or initiating device circuit (smoke, heat, flame detectors) which, in turn, signals the condition to the notification (indicating) device circuit such as alarm sounders, horns, strobes, and other remote signaling equipment.

The designer must be sure that the last device on the circuit has sufficient voltage to operate the device within its rated voltage. When calculating the voltage available to the last device, it is necessary to con-sider the voltage drop due to the resistance of the wire. The larger the wire, the less the voltage drop. Generally, for purposes of determining the wire size necessary for the system, it is best to consider all of the devices as “lumped on” the end of the supply circuit; this simulates the worst case scenario.

Conventional FA cables are either power limited or non-power limited with power limited being the dominant system in the marketplace. All conventional FA cables are fire resistant and UL tested.

Type FPL (NPLF) cable – suitable for general purpose FA use

Type FPLR cable – riser cable for vertical runs/floor to floor

Type FPLP (NPLFP) for use in ducts, plenums and all environmental air spaces

Addressable FA Design (Digital)

Addressable FA Systems add more flexibility, intelligence, speed of identification and scope of control than conventional systems, making them the ideal choice for medium-sized larger buildings with more complex system requirements.

In an addressable system, detectors are wired in one or more loops around the building with each detector having its own unique address. The fire alarm control panel is then able to communicate with each address or a group of addresses and display the precise location of the device in question, which obviously helps speed the location of an incident with or without zoning.

The communication is often multiplexed over a common cable or signaling line circuit (SLC). This allows the panel to simultaneously control and communicate the addresses. Addressable detectors are intelligent devices that are capable of reporting not only fire or fault conditions but also predictive maintenance.

The designer must be aware of not only the DC resistance of the cable, but the capacitance and the velocity of propagation of the cable. The designer must assure that the overall loop capacitance is not compromised, and error rates are kept to a minimum.

Nominal Capacitance for wire sizes:

18 AWG solid unshielded: 16pf/ft

18 AWG solid shielded: 25pf/ft t45pf/ft **

16 AWG solid unshielded: 17pf/ft

16 AWG solid shielded: 30pf/ft 54pf/ft **

14 AWG solid shielded: 30pf/ft. 54pf/ft **

12 AWG solid shielded: 35pf/ft. 63pf/ft **

Capacitance between one conductor and the other connected to the shield.

Aquaseal power-limited water-resistant cables are designed for indoor/outdoor FA systems. The Aquaseal products are manufactured using a premium-grade jacket compound and are flame retardant, sunlight and water resistant, and abrasion and crush resistant – making them ideal for direct burial.

Aquaseal is UL listed and NEC type FPL or PLTC rated. Using 18 AWG to 12 AWG makes this cable an excellent choice for low-voltage conventional and addressable systems.

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