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Fire Alarm System #97490
02/23/06 04:45 PM
02/23/06 04:45 PM
George Little  Offline OP
Joined: Jan 2004
Posts: 1,489
Michigan USA
Is there anything in NFPA72 that would require an installer or a design professional to install or design an installation of a fire alarm system to meet the requirements of a Class A circuit?

Secondly- what percent of the systems being installed are Class A?

George Little
2017 / 2014 NEC & Related Books and Study Guides
Re: Fire Alarm System #97491
02/23/06 06:47 PM
02/23/06 06:47 PM
earlydean  Offline
Joined: Dec 2003
Posts: 751
Griswold, CT, USA
I see class 1, 2 & 3 circuits in the NEC, but no class A circuits. What are they?

Re: Fire Alarm System #97492
02/23/06 07:49 PM
02/23/06 07:49 PM
trekkie76  Offline
Joined: Jun 2004
Posts: 220
baileyville, maine, usa
A class A FA system uses return conductors for supervision. A class B uses EOLs for the supervision of the circuits.

I have seen more Class B lately. Last Class A I put in was at the Maine State Prison.

Re: Fire Alarm System #97493
02/23/06 10:33 PM
02/23/06 10:33 PM
Yoopersup  Offline
Joined: Mar 2003
Posts: 840
Your answers on Page 72-41 Chaper 3 (3-4)
1999 NFPA 72.
Most nowadays are Class B Class A requires the outgoing and return conductors to be routed separately and shall Not be run in the same cable assembly. Page 72-41 (3-*(Note exceptions) on page 74-42

Re: Fire Alarm System #97494
02/25/06 11:26 PM
02/25/06 11:26 PM
Ron  Offline
Joined: Mar 2002
Posts: 582
White Plains, NY
Depends on the type of buildings you work in. More than 50% of the building I work in are Class A due to reliability requirements and occasional slow repair cycles.
Many are not familiar with Class A circuits and they are not specified due to "that's the way I always did it, and it worked that time"

Re: Fire Alarm System #97495
02/26/06 02:26 AM
02/26/06 02:26 AM
JoeTestingEngr  Offline
Joined: Nov 2005
Posts: 791
Chicago, Il.
Most of our systems use class B, where you see 2 jumpers in the panel per zone and 2 wires going out. Class A is safer because it can be cut in the middle of the loop and still cause an alarm on either end. A class B intelligent system may not use EOLs because each device is polled so you don't need a resistor, capacitor, or diode at the end to know that you're getting to the last device.


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