Class A fire alarm circuit

[mstrlucky74]

So a class A circuit has a pair of wires going out and a pair coming back. I know there is a minimum distance between these two paths so if the system is to be fully in conduit I would imagine a circuit going to the same device, say smoke detectors, would have to be in separate conduits, correct?

Could an an entire system have ALL class A circuits or it's usually a mixture. Thanks

 

[mstrlucky74]

It's gotta be me.......

 

[Strathead]

So a class A circuit has a pair of wires going out and a pair coming back. I know there is a minimum distance between these two paths so if the system is to be fully in conduit I would imagine a circuit going to the same device, say smoke detectors, would have to be in separate conduits, correct?

Could an an entire system have ALL class A circuits or it's usually a mixture. Thanks

It is actually a lot more complex than that. The code doesn't determine how the installation is accomplished, but more what has to be accomplished. There are classes and styles that make that determination. For example, there are wireless fire alarm devices. Since a failure of one device doesn't affect other devices, that would make it a class A circuit.

That said, when Class A is wired, there are rules about separation, one of them is that the in and out wires to a single device like you describe can be in the same conduit for a certain length. And you can have mixed circuits. It is not uncommon for the initiating circuits to be class A and the NAC circuits to be class B.

 

[mstrlucky74]

Thanks. I just read an article where they said class A has to be in separate conduits....not mention of them able to occupy the same conduit for a certain length.


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[gadfly56]

Thanks. I just read an article where they said class A has to be in separate conduits....not mention of them able to occupy the same conduit for a certain length.


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You are allowed to run the in and out legs in the same conduit under limited circumstances, see NFPA-72 (2007) 6.4.2.2.2. The appendix A note for this article also suggests a minimum separation of 1 foot vertical and 4 feet horizontal for the in and out conduits.

 

[infinity]

Thanks. I just read an article where they said class A has to be in separate conduits....not mention of them able to occupy the same conduit for a certain length.


Sent from my iPad using Tapatalk

I think that the maximum length is 10'.