ECN Forum Forums Code Related Discussion NEC & other Code issues Smoke Detector Wiring

Ryan- I'm still wrestling with the wording in 760.61(C)(3) and can't get past the Cables specified in Chapter 3 permitted to be installed in nonconsealed spaces (open??) and then talking about exposed. What's the difference between "exposed" and "nonconsealed"?

I sleep on it over the weekend. Maybe someone else will jump in and add their thoughts.

Maybe I have a mental block or something.

I cannot stress more strongly the need to instal the system as instructed by the manufacturer.

Complete systems are tested, and listed, as complete systems. You may be surprised to learn that reliability, and the prevention of false alarms, weigh in much more heavily in the testing than actually detecting a fire does.
Many times, a smaller wire is used because it is more likely to become damaged, and indicate a fault. (This might seem backwards, until you consider that alarms are sometimes subjected to tampering). Another factor is that, for signaling, "bigger" wire isn't always better; a larger wire simply doesn't have the frequency response that a slender one has (notice how phone wires today are a lot thinner than they once were?)

Well Ryan and others- Did some reasearch on the hot topic and here's what I've come up with:

760.61 Applications of Listed PLFA cables

760.61(C) deals with "Other Wiring Within Buildings (obviously used for PLFA) and (3) references cables "specified" in Chapter 3. The only cables I could find in Chapter 3 that are "specified" as suitable for signaling are MC cable- (330.10(A)(2)), MI cable- (332.10(2)) and Tray Cable- (336.10(1)). The only part that seems murky is the limitation of 10 feet. But there is no doubt in my
mind that wiring for a PLFA must be a listed fire alarm cable or one of the three cables I have listed here. I reiterate NO NM cable.

That my story and I'm sticking to it.

George, why would 760.55(G)(1) mention type NM cable if it can't be used for PLFA circuits?

(G) Other Applications For other applications, power-limited fire alarm circuit conductors shall be separated by at least 50 mm (2 in.) from conductors of any electric light, power, Class 1, non–power-limited fire alarm, or medium power network-powered broadband communications circuits unless one of the following conditions is met:

(1) Either (a) all of the electric light, power, Class 1, non–power-limited fire alarm, and medium power network-powered broadband communications circuit conductors or (b) all of the power-limited fire alarm circuit conductors are in a raceway or in metal-sheathed, metal-clad, nonmetallic-sheathed, or Type UF cables.

Curt

George,
So we can't use conduit and any of the normal building wires for a fire alarm system? If so there are a lot of systems that are in violation, because that is the installation for 90% of the fire alarm systems in this area. Fire alarm cables are not normally used.
Don

Re-classify as NPLFA (760.52(A) exc. 3), use the existing NM, the system works just fine, and the codes are met.

I think that I understand what article 760 says regarding this issue now...

thanx for your help...

shortcircuit

I see one problem with the alarm installers approach. The fire alarm standard that governs the single station smoke detectors requires them to sound an alarm at the detector to a specified sound pressure. If the replacement alarm system indicating devices do not provide at least the same level of alerting than the building code that requires the single station smoke detectors would have to include language that allows the builder to substitute a listed automatic fire alarm system.

On the cable issue I have installed fire alarm systems under engineering supervision by licensed professional fire protection engineers as well as licensed electrical engineers without ever once using specialized fire alarm cable. The Corp of Engineers specifically allowed us to use the wiring that had served the interconnected single station smoke detectors in base housing to serve the replacement system detectors. The engineer on that project held licenses in fire protection and electrical engineering. Since I work in the Washington, DC area I have done a lot of work in federal buildings and they are fanatical about code compliance. In over forty years in the craft I have yet to use one of the specialized fire alarm cables in new work. Even the newer digital systems are installed using listed communications cable in raceways. The only time I've ever had a problem was when I let some course stranded number fourteen THHN get into the system as it did not have sufficient strands to meet the electrical code language.
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Tom Horne

After talking to NFPA and a few others, I going to have to yield to the majority on the use of NM cable for PLFA wiring on the secondary side of the power source. Boy it's tough to type these words. I am only hanging on to one thread of victory in that the specs on the FACP and the specs for the system would have the last call. That being said, baring any restrictions, one could use NM or UF cable for the PLFA system.

George, I may say that I really respect you for admitting the answer that you recieved.

In my opinion, it boils down to this: Why would yo ube able to use a 150 volt conductor but not a 600 volt conductor? I am not saying that I am a huge NM cable fan either, but it beats low voltage cable!

Thanks for the info.