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#97490 - 02/23/06 12:45 PM Fire Alarm System
George Little Offline

Registered: 01/18/04
Posts: 1492
Loc: 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

2014 / 2011 NEC & Related Books and Study Guides
#97491 - 02/23/06 02:47 PM Re: Fire Alarm System
earlydean Offline

Registered: 12/22/03
Posts: 749
Loc: Griswold, CT, USA
I see class 1, 2 & 3 circuits in the NEC, but no class A circuits. What are they?

#97492 - 02/23/06 03:49 PM Re: Fire Alarm System
trekkie76 Offline

Registered: 06/19/04
Posts: 219
Loc: 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.

#97493 - 02/23/06 06:33 PM Re: Fire Alarm System
Yoopersup Offline

Registered: 03/04/03
Posts: 826
Loc: Michigan
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

#97494 - 02/25/06 07:26 PM Re: Fire Alarm System
Ron Offline

Registered: 03/13/02
Posts: 577
Loc: 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"

#97495 - 02/25/06 10:26 PM Re: Fire Alarm System
JoeTestingEngr Offline

Registered: 11/04/05
Posts: 786
Loc: 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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