Fire Alarm Installations

[dragonfly54]

In the nec Article 760 talks about the conductors used in fire alarm installations, but I have run into some question about the proper size allowed. My question is what is the smallest conductor that can be used and does it matter whether it's residential or commercial.

 

[ron]

Re: Fire Alarm Installations

The size for fire alarm circuits is essentially determine by the manufacturer, which must take into account current and voltage drop.
When providing power to the device in a line voltage application, like a residential smoke detector, follow the same sizing as you would for any branch circuit. Generally #14 for 15A circuit and #12 for 20A circuit.

[ December 24, 2005, 11:55 AM: Message edited by: ron ]

 

[iwire]

Re: Fire Alarm Installations

Most of the commercial fire alarm systems I have installed will require us to use 16 minimum.

However it is likely that we will use 14 or 12 for voltage drop reasons.

 

[jbwhite]

Re: Fire Alarm Installations

An actual "fire alarm system" is something that I have never seen in a residential application. I am sure that they do exisit, but I would say they are rare. Instead interconnected stand alone smoke detectors are used.

A fire alarm system has a fire alarm control panel. I too have not seen any wire smaller than #16 used. for these systems. #12 is the largest I have seen used, for larger buildings node panels are installed (similar to a sub panel) to amplify the necessary signals.

 

[iwire]

Re: Fire Alarm Installations

Originally posted by jbwhite:
Instead interconnected stand alone smoke detectors are used.

To be precise UL calls those line voltage interconnected noise making devices "Smoke Alarms"

Smoke detectors are what UL calls what is to be used with a fire alarm system.

 

[thinfool]

Re: Fire Alarm Installations

Originally posted by dragonfly54:
My question is what is the smallest conductor that can be used and does it matter whether it's residential or commercial.

We don't do residential, but my gut feeling is that if you are feeding interconnected smokes from a 15a circuit, you will need #14 minimum.

As for systems with a FA panel, A/V's, smoke and heat detectors, etc, review 760.81 (A) and 760.82 (B).

Oh yeah....dont forget to check mfr's recommendations, too.

 

[dragonfly54]

Re: Fire Alarm Installations

Thank you all for your replies, However I still don't know what to tell these person about the wiring requirements. He has been using 22/4 solid fire wire for residential installs the way I understand the code you can't use anything smaller than 18 solid. I'm I correct?

 

[jbwhite]

Re: Fire Alarm Installations

Originally posted by dragonfly54:
Thank you all for your replies, However I still don't know what to tell these person about the wiring requirements. He has been using 22/4 solid fire wire for residential installs the way I understand the code you can't use anything smaller than 18 solid. I'm I correct?

Is this a FACP system, or a 120V interconnected individual smoke alarms?

 

[celtic]

Re: Fire Alarm Installations

Originally posted by dragonfly54:
In the nec Article 760 talks about the conductors used in fire alarm installations, but I have run into some question about the proper size allowed. My question is what is the smallest conductor that can be used and does it matter whether it's residential or commercial.

Originally posted by dragonfly54:
Thank you all for your replies, However I still don't know what to tell these person about the wiring requirements. He has been using 22/4 solid fire wire for residential installs the way I understand the code you can't use anything smaller than 18 solid. I'm I correct?

I just happened to have a copy of the NJATC's Fire Alarm Systems book lying on my desk...in it, it is noted that:

The NEC is not a design manual. In fact, the NEC will allow wiring that may not permit the fire alarm system to properly operate. An example is the use of power wiring (e.g., THHN)where the manufacturer requires twisted, sheilded pairs

If anyone has this book, check pg. 71.

What this notation is telling ME, is that you MUST consult the manufacturers instructions for the install as the NEC is not a design guide.
Probably not the answer you want to hear...but points in the right direction...you will need to calculate the voltage drop/total resistance/current etc.

Whether the install is commercial or residential *probably* doesn't make all that much of a difference - as long as the proper wiring methods are used. This is again answered by the manufacturers specifications and job specs(THHN, twisted pairs, etc; number of devices, length of run, etc).

Where/how are you arriving at your limitation of #18?(760.27(A)/T402.5)

 

[jbwhite]

Re: Fire Alarm Installations

Originally posted by celtic:
Whether the install is commercial or residential *probably* doesn't make all that much of a difference

The only difference that I say this would make is that if these are not FACP devices, and instead are the more standard residential alarms, then they are wired based on the branch circuit ampacity. #12 for 20 amps #14 for 15 amps.

 

[dragonfly54]

Re: Fire Alarm Installations

I'm reading Article 760-71(b), which states "the size of conductors in a multiconductor cable shall not be smaller han No.26. Single conductors shall not be smaller than No.18.

 

[celtic]

Re: Fire Alarm Installations

Originally posted by celtic:


Whether the install is commercial or residential *probably* doesn't make all that much of a difference - as long as the proper wiring methods are used. This is again answered by the manufacturers specifications and job specs(THHN, twisted pairs, etc; number of devices, length of run, etc).

Let's use the quotes as they are intended - not slice them up to be argumentative.

 

[thinfool]

Re: Fire Alarm Installations

We need more details.

The thought occurred to me that this may be a combination fire/security panel. If so it is likely a 'power-limited'system and would therefore fall under 760.82(B). This way, his 22/4 cable would be in compliance.

'Course, this is all a guess without more facts.

 

[gndrod]

Re: Fire Alarm Installations

Hi dfly54, When installing a residential alarm system, there is a choice of three installation configurations I can site quickly. First and most common is the 3-wire 14-3, 12-3 cable interconnected 120vac suppled through AFCI circuit outlets because of the bedroom NEC [210.12(B)] requirement, a second would be an approved custom alarm system (usually security/fire monitored low voltage) with detector power less than 120 vac not requiring AFCI connection wiring,[760.21] and third is power limited fire alarm (PLFA) circuits that are common commercial systems that must not be wired using GFCI or AFCI power circuits. [760.41]
Keep in mind mixing brands in a common system is not recommended by manufacturers.
rbj, Seattle