Are You Cable Able?

It’s important to know what type of cable to use in a fire alarm system no matter what the situation. Not only is it important from a functionality standpoint, but it’s also important because your clients must be code compliant in order to satisfy a number of concerns, such as an insurance company or a government agency.

NFPA 70, National Electrical Code (NEC) is the codebook that fire alarm installers turn to when they install new fire alarm systems. Conscientious workmen have one close at hand while those who don’t understand the importance of code or simply don’t care are not as likely to buy one.

One of the most difficult areas fire alarm technicians deal with is cable, and this is where NEC comes into play. As one reads about the alphabet selection of fire-oriented cables available within the pages of NEC, it’s not always easy to understand the ins and outs of the fire alarm cable maze.

This month, we’ll explore the basics as it pertains to metallic fire wire in fire alarm systems. We’ll also review why possession of a NEC codebook is nine-tenths of the law (see sidebar).

Cable Markings

Almost everything you need to know about installing fire alarm cable is contained in Article 760 of NEC. Sometimes you’re simply going to have to dig in to find what you’re looking for, but I can assure you it’s all there — from A to Z.

One of the great things about fire code is that once it’s in place and it’s been institutionalized, fire alarm equipment and cable manufacturers are obligated to follow it, and thank heavens this applies to cable marking practices.

Without a doubt there’s an alphabet listing of cable types and you’ll find that NEC is knee deep in them. A quick examination of Tables 760.81(G) and 760.82(I), as well as a number of subsections, will show you exactly what I mean. It’s the fire alarm technician’s job to know what each of them is, as well as where each one is used.

A close examination of the fire wire in the photograph within this article should reveal several facts about this particular cable. First, it contains 18 AWG metallic conductors. Second, it bares the UL listing of FPL (fire power-limited) cable. In this case the cable shown is shielded and, therefore, is suitable for transporting data in a signaling line circuit (SLC). Applications where this might be used include addressable fire alarm devices, such as manual fire pulls and initiating device modules.

In many cases you will also find a printed number along with identification of the cable type. In the aforementioned photo the cable footage is not indicated, but in typically either the number of feet at a specific spot or the number of feet left on a roll is included for the installer’s benefit. 

PLFA, NPFA Circuit Classifications

There are a slew of acronyms used in Article 760 that pertain to the type of wire and circuit types. The FPL listing in the previous example is one of several that fire alarm installers use. Some other examples include FPLP, FPLR, NPLF, NPLFP and NPLFR. In addition,  a CI designation can be added to any of the above markings when a cable is designed for circuit integrity, which we’ll talk about in a moment.

The meaning of all these cable designations can be found in Article 760.82(A) through 760.82(H). For example, FPL is used when an application involves PLFA (power-limited fire alarm) circuits. By code FPL cable must be resistant to the spread of fire. The conductors used within it must also be made of solid or stranded copper conductors sized between 26 AWG and 18 AWG with a voltage rating of not less than 300V.  FPLR (fire power-limited riser) and NPLR (nonpower-limited riser) cable types can be used for vertical runs between floors. FPLR cable is used in conjunction with PLFA (power-limited fire alarm) circuits and NPLR-type cable is used with NPLFA (nonpower-limited fire alarm) circuits.

Types FPLP (fire power-limited plenum) and NPLP (nonpower-limited plenum) can be installed in spaces used for environmental airflow, such as above suspended ceilings and inside air ducts.

No fire alarm circuits are to be installed in air spaces that carry dust or a flammable vapor of any kind. Article 300.22(A), NEC, 2008 Edition, says, “No wiring systems of any type shall be installed in ducts used to transport dust, loose stock, or flammable vapors. No wiring system of any type shall be installed in any duct, or shaft containing only such ducts, used for vapor removal or for ventilation of commercial-type cooking equipment.”

The CI designation mentioned earlier is indicated when a cable is designed for two-hour survival as specified in NFPA 72, Section, 2007 Edition. This pertains to notification circuits that run through areas that are not within the same zone of protection as the notification appliance devices themselves.

Cable Types and Their Use

PLFA circuits, which involve voltages of less than 30VDC, are the most commonly used in fire alarm systems. NPLFA circuits are used but they usually involve 120VAC. It’s important for fire alarm installers to mark PLFA wiring as “fire alarm” so other technicians as well as other trades do not mistake them for anything else.  According to Article 760.42, entitled Circuit Marking, “The equipment supplying PLFA circuits shall be clearly marked where plainly visible to indicate each circuit that is a power-limited fire alarm circuit.”

The exception to this rule is where a PLFA circuit is reclassified as a NPLFA circuit, as covered in Article 760.52(A), Exception 3, NEC: “Power-limited circuits shall be permitted to be reclassified and installed as nonpower-limited circuits if the power-limited fire alarm circuit markings required by 760.42 are eliminated and the entire circuit is installed using the wiring methods and materials in accordance with Part II, Non-Power-Limited Fire Alarm Circuits.”

Most of the time it’s the listing on a piece of equipment that determines whether you use NPLFA or PLFA cable, not specifically voltage or application. It’s the third-party listing that largely determines which cable type you use, so be especially aware of the listing with regard to power supplies and other equipment.

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