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#93255 - 05/09/05 07:30 PM Class A System
George Little Offline
Member
Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
When you install a Class A fire alarm system, how far apart should the out going and return conductors be apart?
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George Little
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#93256 - 05/10/05 03:30 AM Re: Class A System
Ron Offline
Member
Registered: 03/13/02
Posts: 577
Loc: White Plains, NY
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
6.4.2.2.2 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.
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#93257 - 05/10/05 05:01 AM Re: Class A System
George Little Offline
Member
Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
Ron- That's what I came up with and then I had a fire Marshal tell me and an installer that the out going and return conductors had to be 4 feet apart and I don't know where he got that information.
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#93258 - 05/10/05 05:55 AM Re: Class A System
Ryan_J Offline
Moderator
Registered: 08/19/03
Posts: 1355
Loc: West Jordan, Utah, USA
In the state of Nevada I am told there is a state code that regulates this....funny how the MGM Grand fire makes a person change rules. You might check to see if there is a local requirement.
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Salt Lake City
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#93259 - 05/10/05 06:13 AM Re: Class A System
iwire Offline
Moderator
Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
I believe RI has a rule for separation that was just recently added.

Perhaps Peter (CT wireman) will know.
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Bob Badger
Construction & Maintenance Electrician
Massachusetts
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#93260 - 05/10/05 04:51 PM Re: Class A System
Ron Offline
Member
Registered: 03/13/02
Posts: 577
Loc: White Plains, NY
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).]
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#93261 - 05/13/05 07:31 PM Re: Class A System
CTwireman Offline
Member
Registered: 02/07/02
Posts: 839
Loc: Connecticut, USA
You rang, Bob?

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 6.4.2.2.2 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.

Peter

[This message has been edited by CTwireman (edited 05-13-2005).]
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#93262 - 05/14/05 05:46 AM Re: Class A System
George Little Offline
Member
Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
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.
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George Little
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#93263 - 05/14/05 06:28 PM Re: Class A System
tdhorne Offline
Member
Registered: 03/22/01
Posts: 344
Loc: Maryland, USA
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
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Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
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#93264 - 05/14/05 07:55 PM Re: Class A System
George Little Offline
Member
Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
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.
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George Little
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