Article 760: Fire Alarm Systems

Article 760: Fire Alarm Systems

By Mike Holt for EC&M Magazine

The requirements for fire alarms circuits may vary with the power supply listing or classification.

Article 760 tells us how to install wiring and equipment for fire alarm systems. This includes all circuits the fire alarm system controls and provides power to. Article 760 does not, however, tell us when a fire alarm system is required to be installed. The locally adopted building code or NFPA, 101 Life Safety Code is where you will find this information. It also doesn’t tell us where to place the alarm equipment, such as pull stations or horn/strobe units. Placement of such equipment is the job of NFPA 72, National Fire Alarm Code.

Article 760 does not cover residential smoke alarm systems (including interconnecting wiring), because those are not powered by a fire alarm system as defined in NFPA 72, National Fire Alarm Code. Fire alarm systems include fire detection and alarm notification, voice communications, guard’s tour, sprinkler water flow, and sprinkler supervisory systems [760.1 FPN 1].

Chapter Three in reverse

When applying most Articles in Chapters 5 through 8, Chapter 3 wiring methods apply—except as noted. When applying Article 760, Chapter 3 wiring methods do not apply, except as noted. You’ll find the Chapter 3 references, as well as some other Article references, in 760.3.

One of the requirements is, naturally, that of firestopping. Openings in fire-resistant walls, floors, and ceilings must be sealed to minimize the possible spread of fire or products of combustion [300.21].

This requirement logically leads into the requirement to remove abandoned cable. Doing so limits the accumulation of products of combustion within a building. You must remove the accessible portion of fire alarm cable that isn’t terminated at equipment and not identified for future use with a tag [760.2]. This rule doesn’t require the removal of concealed cables that are abandoned in place. Cables in raceways are concealed cables, per the definition of “concealed” in Article 100.

Some Chapter Three wiring methods apply conditionally. For example, suppose you want to install fire alarm cables in ducts or plenums. If this is necessary for the direct action upon (or sensing of) the contained air, such as for a smoke detector inside of an air duct, you can do it, but only if you install those cables in electrical metallic tubing, intermediate metal conduit, or rigid metal conduit per 300.22(B) (Figure 760-6).

You can install plenum-rated fire alarm cables above a suspended ceiling or below a raised floor used for environmental air movement [760.30(B)(1) and (2), 760.61(A), and 760.82(A)]. You can also install nonplenum-rated fire alarm cables above a suspended ceiling or below a raised floor used for environmental air, but only if you install the cable within electrical metallic tubing or one of the other raceways identified in 300.22(C)(1). Nonplenum-rated fire alarm cables are, of course, allowed above a suspended ceiling that is not used for environmental air.

Fire alarm cables installed beneath a raised floor in an information technology equipment room aren’t required to be plenum rated [300.22(D) and 645.5(D)(5)(c)].

The power source for a fire alarm circuit must not be supplied through a GFCI or an AFCI [760.21] . But this limitation applies only to the circuit that supplies a power-limited fire alarm system (PLFA) or a nonpower-limited fire alarm system (NPLFA). This rule is not intended to apply to the single station smoke alarms commonly found in a dwelling unit. Once again, Article 760 does not cover these types of devices.

Access and execution

As with many other Articles, this one requires you to install equipment and cabling in a neat and workmanlike manner [760.8]. The NEC doesn’t define this, but if you’re qualified to do the work you know the difference between sloppy and neat work.

Article 760 does provide a few hints as to what the AHJ will expect. For example, one aspect of “sloppy” is allowing ceiling-routed cables to accumulate in a way that prevents moving the ceiling panels so a person can get to them [760.7] .

Article 760 also tells us that one aspect of good workmanship is supporting the cables by the structural components of the building so the cable won’t be damaged by normal building use. Secure those cables with the right hardware, and take care not to pinch or damage the cable when you do.

Common sense says you haven’t done quality work unless you have properly labeled the circuits at terminal and junction locations. This labeling is a requirement for fire alarm circuits [760.10] (Figure 760-11). But, contrary to some manufacturers’ statements, Article 760 does not require you to mark raceways and cables [760.42].

Where Article 760 is silent on other aspects of good workmanship, don’t read something that’s not there. To avoid being forced to rewire or reinstall, don’t ignore the generally accepted workmanship practices.

Circuit types

A fire alarm system circuit can be one of two types: nonpower-limited fire alarm (NPLFA) or power-limited fire alarm (PLFA). What’s the difference between the two?

An NPLFA can operate at up to 600V, and the power output isn’t limited [760.21].
A PLFA has the voltage and power limited by a listed power source that complies with 760.41.

This difference means easier installation requirements for PLFA circuits. But, these two types of circuits share all of the requirements detailed in Part I.

NPLFA

To meet NPLFA requirements, you’ll need to refer to Chapter 3 and use those wiring methods where specified. Here are some highlights.

Overcurrent protection. For conductors 14 AWG and larger, this must be limited to the conductor ampacity per Table 310.16 and 240.6(A). Overcurrent protection can’t exceed 7A for 18 AWG conductors, or 10A for 16 AWG conductors [760.23].

Wiring methods. NPLFA circuits must be installed using Chapter 3 wiring methods. 760.25 provides a specific list of requirements that must be complied with [110.3(B), 300.11, 300.15, 300.17]. Contain all splices in enclosures [300.15], except for splices and terminations in fire alarm devices and utilization equipment (e.g., detectors) [760.30(A)(1)]. This rule does not apply to multiconductor NPLFA cables for circuits operating at 150V or less [760.30].

Conductor size. Only copper conductors can be used for fire alarm systems. You can use conductors of sizes 18 AWG and 16 AWG (installed in a raceway, enclosure, or listed cable) if they do not supply a load that exceeds the ampacities given in 402.5. Conductors larger than 16 AWG must not supply loads greater than the ampacities given in 310.15 [760.27(A)].

Conductor insulation. Use conductors with a 600V insulation rating, and comply with Article 310. For conductors 18 AWG and 16 AWG, comply with 760.27(B). Table 402.3 provides application provisions [760.27(B) FPN].

Number of Conductors in a Raceway. Comply with the fill requirements of 300.17 [760.25].

PLFA

PLFA requirements, found in Part III of Article 760, apply to the load side of the circuit. For supply side wiring and equipment, use Part II (NPLFA), as well as the general installation rules in chapters 1 through 4 [760.51].

Wiring methods. You can use NPLFA wiring methods and materials [760.52(A)], if you choose, instead of PLFA. The PLFA wiring requirements are minimal 760.52(B)]. You can sum them up this way: Put cable splices or terminations in listed fittings, boxes, etc., and ensure exposed cables are adequately supported (Figure 760-15).

Separation from power conductors. Provide a minimum of 2 inches of separation between PLFA conductors and conductors of electric light, power, Class 1, or NPLFA circuits, unless you meet the requirements of 760.55(G) (Figure 760-16). Don’t put PLFA conductors in any enclosure, raceway, or cable with conductors of electric light, power, Class 1, or NPLFA circuit conductors, except when you:

Provide barriers.
Meet the requirements outlined in 760.55(D), one of which is these conductors are present solely for connection to the same equipment.

Class 2, Class 3, and communications circuits. Class 3 and communications circuits can be in the same cable, enclosure, or raceway as PLFA circuits [760.56(A)]. Class 2 circuits can be in the same cable, enclosure, or raceway as PLFA circuits—if the Class 2 circuit conductor insulation isn’t less than that required for the PLFA circuits [760.56(B), 760.82(C)].

You can’t install audio system circuits [760.56(D), 640.9(C)] (using Class 2 or Class 3 wiring methods) in the same cable or raceway with PLFA conductors or cables.

Listing

Part IV of Article 760 details the listing requirements. This information is primarily for manufacturers. What this means for you is this: use the cables listed for the application.

The NEC doesn’t require outside or underground cable to be listed, but the cable must be approved by the AHJ as suitable for the application per 90.4, 90.7, and 110.2.

Give special consideration to cables in areas that move or transport environmental air, so as to reduce the hazards that arise from the burning of conductor insulation and cable jackets. Because listed plenum-rated cables have adequate fire-resistance and low smoke-producing characteristics, you can use them in environmental air space. But you can’t use them in ducts or plenums.

Before deciding how to install fire system equipment or wiring, turn to Article 760. Apply the requirements of Part I, regardless of the power level. Apply the requirements of Part II to the supply side and to load side wiring and equipment of NPLFA. Don’t apply Part III requirements unless the power source for the circuit is a Class 3 transformer or power supply, or it’s a listed PLFA power source [760.41].

If you find it more economical to apply Part II requirements in place of Part III requirements, Article 760 allows you to do so. Review a line drawing of the circuits involved, before making this determination.