Fire Alarm Piping and Wiring CLASS A LOOP

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kungfuthug

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Hello.

I understand that a Class A loop is a ring. I am unsure on a few things.

Can the outgoing and return wires reside in the same conduit coming from the panel? If so then how does it get wired. Lets assume I have a 4 wire cable. Red, Black, Blue, Green wires in it.

Lets also assume I have 2 smoke detectors in this addressable system. Can someone explain or draw the wiring through the devices and conduit?

Thanks
 
kungfuthug said:
Hello.

I understand that a Class A loop is a ring. I am unsure on a few things.

Can the outgoing and return wires reside in the same conduit coming from the panel? If so then how does it get wired. Lets assume I have a 4 wire cable. Red, Black, Blue, Green wires in it.

Lets also assume I have 2 smoke detectors in this addressable system. Can someone explain or draw the wiring through the devices and conduit?

Thanks
Click to expand...

The out and return wires can reside in the same conduit for 10 feet where they come to the FACP. After that, they need to be separated by 1 foot for vertical runs and by 4 feet for horizontal runs. There is some additional leeway:

12.3.7* Class A and Class X circuits using physical conductors
(e.g., metallic, optical fiber) shall be installed such that the out-
going and return conductors, exiting from and returning to the
control unit, respectively, are routed separately. The outgoing
and return (redundant) circuit conductors shall be permitted in
the same cable assembly (i.e., multi-conductor cable), enclosure,
or raceway only under the following conditions:

(1) For a distance not to exceed 10 ft (3.0 m) where the out-
going and return conductors enter or exit the initiating
device, notification appliance, or control unit enclosures
(2) For single raceway drops to individual devices or appliances
(3) For single raceway drops to multiple devices or appliances installed within a single room not
exceeding 1000 ft2 (93 m2) in area

A.12.3.7 A goal of 12.3.7 is to provide adequate separation
between the outgoing and return cables. This separation is
required to help ensure protection of the cables from physical
damage. The recommended minimum separation to prevent
physical damage is 12 in. (300 mm) where the cable is installed
vertically and 48 in. (1.22 m) where the cable is installed hori-
zontally.
 
kungfuthug said:
Hello.

I understand that a Class A loop is a ring. I am unsure on a few things.

Can the outgoing and return wires reside in the same conduit coming from the panel? If so then how does it get wired. Lets assume I have a 4 wire cable. Red, Black, Blue, Green wires in it.

Lets also assume I have 2 smoke detectors in this addressable system. Can someone explain or draw the wiring through the devices and conduit?

Thanks
Click to expand...

Class A is more of a performance spec, and not really an exact wiring schematic. I think you will have to refer to the specific manufacturers instructions for exact wiring diagrams.

Class A could also be a 2 wire system.
 
steve66 said:
Class A is more of a performance spec, and not really an exact wiring schematic.
Click to expand...

In my experience it pretty much is, it is a loop where class B is not.

I understand there are times when you can T-tap the class A loop but I don't see that being done around me.

01_Fire%20Wire.jpg
 
Why is there a end of line of some class A loops? I see that at my workplace. The loops are for sure class A how does that work?


Sent from my iPhone using Tapatalk
 
kungfuthug said:
Why is there a end of line of some class A loops? I see that at my workplace. The loops are for sure class A how does that work?


Sent from my iPhone using Tapatalk
Click to expand...

Siemens, for one, in their System 3 product put the EOL devices at the panel for Class A. It's just the way they designed them.
 
kungfuthug said:
Why is there a end of line of some class A loops? I see that at my workplace. The loops are for sure class A how does that work?
Click to expand...

It's not Class A with an EOL. Here we are required to put the EOL inside the panel by state code which by necessity requires bringing the loop back to the panel, so much just opt for a Class A system.
 
kungfuthug said:
Hello.

I understand that a Class A loop is a ring. I am unsure on a few things.

Can the outgoing and return wires reside in the same conduit coming from the panel? If so then how does it get wired. Lets assume I have a 4 wire cable. Red, Black, Blue, Green wires in it.
Click to expand...

Red and black would be your outgoing conductors and blue and green would be your return conductors, unless you have some funky local ordinance that specifies color code. After you leave the panel, you would have to split your raceway system two different directions to meet the separation requirements.
 
peter d said:
It's not Class A with an EOL. Here we are required to put the EOL inside the panel by state code which by necessity requires bringing the loop back to the panel, so much just opt for a Class A system.
Click to expand...

Not true.
 

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gadfly56 said:
Hmmm, title of the figure is "Class A Style D". Wonder what that means...
Click to expand...

I think it means it is a wiring example that could be Class A.

Again, Class A is more of a functional Spec. than a specific wiring diagram. Here is the definition:

Code: 
[URL="http://www.madcad.com/library/170121/468282/#nfc_72_2013_ID000072112109"]12.3.1*[/URL] Class A. A pathway shall be designated as Class A when it performs as follows: (1) It includes a redundant path.

(2) Operational capability continues past a single open, and the single open fault shall result in the annunciation of a trouble signal.

(3) Conditions that affect the intended operation of the path are annunciated as a trouble signal.

(4) Operational capability is maintained during the application of a single ground fault.

(5) A single ground condition shall result in the annunciation of a trouble signal.

Exception:  Requirements in [URL="http://www.madcad.com/library/170121/468009/#nfc_72_2013_ID000072108290"]12.3.1[/URL](4) and (5) shall not apply to nonconductive pathways (e.g., wireless or fiber).

So you have to also consider how the specific devices react to an open or a short circuit.

If there is a ground fault or an open, will the alarm still activate if smoke is detected? Just looking at the diagram, I'm not sure. I think its a case of "not enough info. to determine". So it could be Class A, or it could be Class B. It depends on the hardware.
 
steve66 said:
I think it means it is a wiring example that could be Class A.

Again, Class A is more of a functional Spec. than a specific wiring diagram. Here is the definition:
Click to expand...

That is not true in my state, as I have outlined already.

The moral of the story is that you should always check locals rules and regulations when dealing with fire alarm systems instead of relying on industry standards and best practices.
 
peter d said:
I don't know what it means but I do know how it is defined where I work.
Click to expand...

Fine. I'll tell you what it means. It means that when a circuit is wired Class A on that module, it has an End-Of-Line device installed at the panel.
 
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