There is no specific distance required by the NFPA, but established by the project specification. I generally specify riser circuitry to be in raceway and separated by a 2 hour wall (or CI type cable); normal SLC's to be in raceway. NFPA 72-2002 126.96.36.199.2 All styles of Class A circuits using physical conductors (e.g., metallic, optical fiber) shall be installed such that the outgoing and return conductors, exiting from and returning to the control unit, respectively, are routed separately. The outgoing and return (redundant) circuit conductors shall not be run in the same cable assembly (i.e., multi-conductor cable), enclosure, or raceway.
Exception: The outgoing and return (redundant) circuit conductors shall be permitted to be run in the same cable assembly, enclosure, or raceway under any of the following conditions: (1) For a distance not to exceed 3 m (10 ft) where the outgoing and return conductors enter or exit the initiating device, notification appliance, or control unit enclosures. (2) Single conduit/raceway drops to individual devices or appliances. (3) Single conduit/raceway drops to multiple devices or appliances installed within a single room not exceeding 92.9 m2 (1000 ft^2) in area.
Re: Class A System#93257 05/10/0508:01 AM05/10/0508:01 AM
There is no national code requirement to install a system as Class A. If by design/specification Class A is required, it may be a project specific requirement. If not required by project specs, then install Class B system and don't worry about it.
[This message has been edited by Ron (edited 05-10-2005).]
Re: Class A System#93261 05/13/0510:31 PM05/13/0510:31 PM
Yes, there is indeed a separation requirement that is now being enforced in RI, and it is taken from NFPA 72. The RI codemakers took the recommended distances in the Annex of 72 for section 188.8.131.52.2 and put them into the code. Actually, it has been in place here for quite some time (since the adoption of the much stricter 1997 code and subsequent codes), but until the Station fire and the new focus on fire codes, it was never enforced. Now the games are over and every detail of the code is being enforced.
The incoming and outgoing circuits of all FA systems, no matter what type, must be 1 foot apart vertically and 4 feet apart horizontally. (RI code)
There are a few exceptions of course but the new rule being enforced here makes fire alarm jobs quite challenging.
[This message has been edited by CTwireman (edited 05-13-2005).]
Re: Class A System#93262 05/14/0508:46 AM05/14/0508:46 AM
My conclusion on this matter is that a Class A system is optional and that the out going conductors and the return wires are not permitted in the same cable or conduit (with some exceptions). The spacings mentioned in NFPA 72 in the appendix are recommendations. The appendix is not part of the code and I can't enforce "recommendations". I also see only minor advantage of a Class A system over a Class B with addressable devices.
Re: Class A System#93263 05/14/0509:28 PM05/14/0509:28 PM
The obvious advantage to a true Class A fire Alarm system is that it will take more than one fault to take any initiating or indicating device out of service. That makes them a much better choice for public assemblies, residential facilities, custodial care facilities, and extreme high value risks. I have had class A systems were the main riser was sheered off by accident and the system still continued to function completely until we could repair it. -- Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
Re: Class A System#93264 05/14/0510:55 PM05/14/0510:55 PM
Tom- I agree with that feature being a plus. But if the conductors are shorted together we are no different than a Class B system. Since the use of addressable devices is the most common way to go, we see most systems going in as Class B.