FIRE ALARM DEVICE WIRE SIZE

[Alwayslearningelec]

Does the class or style of a system matter as to whether a strobe or pull station etc. gets #14,#16 #18 etc.?

What determines whether whether you use 2p #14 or 2p #16 or 2p #18 for certain devices? Thanks

Does every initiating/annunciating device get a pair of wires?

 

[infinity]

Typically we would use #14 for the strobes and #16 for the speaker and initiation circuits. I have been on jobs (huge post office) where the runs were so long that we used #12 for strobes and #14 for speakers/initiation. It's really up to the F/A company to specify how they want their system built. If you have a separate pair of conductors for each initiation device your system is ancient. hmy:

 

[iwire]

I agree with infinity 100%.

I will add if you are sizing boxes for fire alarm devices go big, pushing horn strobes into place that could have eight 14 or 12 AWG solid conductors connected to it is no joy if the box is tight. It also makes a ground fault more likely


Solid is a standard job spec in this area for fire alarm conductors, I don't know why.

 

[infinity]

I agree with infinity 100%.

I will add if you are sizing boxes for fire alarm devices go big, pushing horn strobes into place that could have eight 14 or 12 AWG solid conductors connected to it is no joy if the box is tight. It also makes a ground fault more likely


Solid is a standard job spec in this area for fire alarm conductors, I don't know why.

I often wondered why too. Pushing all of those solid conductors with a device (8 on a SPK/STRB) can be a nightmare.

 

[del91574]

Solid is typically spec'd around here because on a NAC circuit, a bunch of broken strands from twisting or how a terminal block tends to "cut" them reduces the ampactity they can carry vs. still having the supervision voltage go through the circuit.

 

[Alwayslearningelec]

So with a Class A system(A/B loop) if you have several strobes and speaker or speaker/strobes on the same loop/circuit can't you just run one 2 pair cable instead of 2 separate cables and hit one device then run other pair to the next device and alternate like that? Does that make sense?:? Thanks.

Ah but I just thought then you would be running the same gauge wire for all devices when a speaker and strobe would use (2) different gauges.

 

[infinity]

You can use a two pair cable if you so choose. One advantage of running different size conductors is that no labelling is required, meaning less chance of wiring errors.

 

[nhfire77]

What determines whether whether you use 2p #14 or 2p #16 or 2p #18 for certain devices? Thanks

You must caclulate voltage drop, that's critical for long speaker circuits and heavily loaded NACS

 

[Alwayslearningelec]

So does the spec/drawings usually determine wire size for fa devices?

 

[nhfire77]

So does the spec/drawings usually determine wire size for fa devices?

Usually.

 

[Alwayslearningelec]

Usually.

Thanks!

 

[gadfly56]

So with a Class A system(A/B loop) if you have several strobes and speaker or speaker/strobes on the same loop/circuit can't you just run one 2 pair cable instead of 2 separate cables and hit one device then run other pair to the next device and alternate like that? Does that make sense?:? Thanks.

Ah but I just thought then you would be running the same gauge wire for all devices when a speaker and strobe would use (2) different gauges.

Short answer, no. That does not meet the criteria for Class A, in and of itself. Class A starts at the panel and ends at the panel. There may or may not be an EOL device, but if there is it will be at the panel. The layout you describe is sometimes specified as additional insurance that if one notification circuit fails, you'll still have at least partial coverage in the protected space. The down side is twice the circuits and twice the wire, but if the customer is up for it, so much the better.

 

[Alwayslearningelec]

Short answer, no. That does not meet the criteria for Class A, in and of itself. Class A starts at the panel and ends at the panel. There may or may not be an EOL device, but if there is it will be at the panel. The layout you describe is sometimes specified as additional insurance that if one notification circuit fails, you'll still have at least partial coverage in the protected space. The down side is twice the circuits and twice the wire, but if the customer is up for it, so much the better.

Thanks Gad..so I assume MOST fa device would get a single pair of wires, correct? When would 2 pair be used? THanks.

 

[gadfly56]

Thanks Gad..so I assume MOST fa device would get a single pair of wires, correct? When would 2 pair be used? THanks.

I wish you hadn't used the word "device". So many devices, so little time...

Strobe-only, speaker-only, and audible-only devices get a single pair in and single pair out, unless they are the last device in a Class B circuit.

Combination horn/strobe, chime/strobe, bell/strobe, etc may be single OR double pairs, they frequently come in both styles from Wheelock, System Sensor, and others.

Speaker/strobes will always get at least 2 pairs. Don't screw up the wiring, or " bad things" may befall your fire alarm system, especially if you're using a 70.7 volt speaker setup.

Finally, Mass Notification. I can't recall who, but someone is providing a back box arrangement that lets you tuck a speaker/strobe(fire) and separate strobe(mass notification) in the same back box. The two strobes are usually a different color. Now you have 3 pairs!

The only difference between Class A and Class B with these devices is whether or not you run a pair from the last device back to the panel, or use and end-of-line (EOL) device.

 

[Alwayslearningelec]

I wish you hadn't used the word "device". So many devices, so little time...

Strobe-only, speaker-only, and audible-only devices get a single pair in and single pair out, unless they are the last device in a Class B circuit.

Combination horn/strobe, chime/strobe, bell/strobe, etc may be single OR double pairs, they frequently come in both styles from Wheelock, System Sensor, and others.

Speaker/strobes will always get at least 2 pairs. Don't screw up the wiring, or " bad things" may befall your fire alarm system, especially if you're using a 70.7 volt speaker setup.

Finally, Mass Notification. I can't recall who, but someone is providing a back box arrangement that lets you tuck a speaker/strobe(fire) and separate strobe(mass notification) in the same back box. The two strobes are usually a different color. Now you have 3 pairs!

The only difference between Class A and Class B with these devices is whether or not you run a pair from the last device back to the panel, or use and end-of-line (EOL) device.

Thanks Gad.. You really know our fire alarm. Can a speaker strobe be on the same loop as a device that get a single pair wiring? How would that work?

 

[gadfly56]

Thanks Gad.. You really know our fire alarm. Can a speaker strobe be on the same loop as a device that get a single pair wiring? How would that work?

No, speaker/strobes are never, to my knowledge, single pair (2-wire) devices. Audio doesn't "play well" with the simple "on/off" of the horn, strobe, or horn/strobe devices. You'd have to multiplex the audio with the bang-bang 24VDC for the strobe somehow, and then pull the audio out at the speaker, remove the DC pulse, and also make sure the audio waveform didn't screw up the strobe. I'm sure it could be done, but I'd hate to pay for one of those units!

 

[Alwayslearningelec]

No, speaker/strobes are never, to my knowledge, single pair (2-wire) devices. Audio doesn't "play well" with the simple "on/off" of the horn, strobe, or horn/strobe devices. You'd have to multiplex the audio with the bang-bang 24VDC for the strobe somehow, and then pull the audio out at the speaker, remove the DC pulse, and also make sure the audio waveform didn't screw up the strobe. I'm sure it could be done, but I'd hate to pay for one of those units!

Sorry to be a PIA but what devices would be on the same loop as speaker/strobes? Thanks

 

[gadfly56]

Sorry to be a PIA but what devices would be on the same loop as speaker/strobes? Thanks

Think of the speaker/strobes as the union of two otherwise incompatible devices, sorta like some marriages I know of (not mine!:lol, living in the same house but never talking to each other. The speaker gets one pair and the strobe gets another. Now, downstream (or upstream, for that matter) on the strobe pair only, you might find the strobe for another speaker/strobe, a stand-alone strobe, a 2-wire horn/strobe, a horn, a chime, a 2-wire chime/strobe or any other 2-wire non-speaker device. On the pair landed on the speaker, only speakers up or downstream as far as the eye can see.