Fire Detection Panel

[eeee]

There is regulation that states a fire detection alarm panel must be upgraded to class A from Class B if major renovation work is being done. Note that Class A is 4 wire (loop architecture with each set of wires in a separate conduit for survivability during an inadvertant cut of fire cable) and Class B is 2 wire (star architecture).

This includes cable, conduit and panel.

I wonder if it is required to upgrade to Class A from Class B if all that is being done is changing pipes and adding heads to the fire suppresssion system. This is major work to the fire suppression system, but not the fire detection system.

It is possible that some additional wiring will be required (for the fire detection alarm panel) for some zone changes.

 

[ron]

Re: Fire Detection Panel

I know of no such national requirement.
Be sure it is a requirement and not an ole wives tale.
If it is a local requirement, then you need to see the actual wording in that code.

 

[peter d]

Re: Fire Detection Panel

This will most definitely be a local requirement if it indeed exists. Check with your fire marshall, AHJ or whoever has jurisdiction over fire alarms in your area.

 

[steve66]

Re: Fire Detection Panel

loop architecture with each set of wires in a separate conduit

That is a new one for me, but I'm not real familiar with fire alarm systems. Are you saying you need (2) conduits ran to and from each device with each conduit carrying 2 of the 4 wires?

I thought different classes had some inherent survivability against one open or short. I also thought any open or short would also set off a trouble signal.

Steve

 

[iwire]

Re: Fire Detection Panel

Steve, class B fire alarms have one pair of conductors tied into the alarm panel and all the devices are installed parallel on that pair, at the end of the circuit a resister is placed that provides a known resistance that the panel expects to read. As long as the panel is reading that resister the panel will not be in trouble.

If the circuit opens the panel will go in trouble and any device between the panel and the break will still function, obviously devices past the break will not work this could be a lot of devices put out of service.

If the system is an old type zone system a short will be an alarm condition, on a new addressable system a short will disable that loop.

Now a Class A fire alarm eliminates the resister and brings that far end of the circuit back around to the panel. The panel has a loop in and a loop out connection.

Now a break will put the panel in trouble but all the devices will still operate, because they have two paths back to the panel.

A dead short will again be an alarm on the old systems, on the addressable systems a short will disable that loop. One addressable loop may have one to many (120 or so) devices so a short can take out a lot of protection.

What can be done with a class A addressable system is to install many isolation modules spread out throughout the loop. If a short happens the isolation modules isolate out the shorted section and the disabled device(s) show up as 'missing' to the panel causing a trouble.

A Class A system for the most part requires each pair in a separate raceway or cable. there are some exceptions for short distances.

The class A system will not help much if you run the 'in and out' in the same raceway or cable.

A properly engineered and installed Class A system can be quite fault proof. At least until a lightning strike and then all bets are off.

 

[steve66]

Re: Fire Detection Panel

Thanks for the education Iwire.

I assume any short that "disables" the loop would also cause a trouble system.

I have seen descriptions of Class A and B in NFPA 72. (Thanks again Iwire, your 4 or 5 short paragraphs are probably about 5 pages of unintelligable code language in NFPA 72). But the big question I have is:

Where does any code require a particular class of Fire Alarm System?

Steve

 

[peter d]

Re: Fire Detection Panel

Originally posted by steve66:
Where does any code require a particular class of Fire Alarm System?

Again, this usually is a local issue. I own the NFPA 72 as well and I agree that it is very difficult to understand. It may be in the 72 but I'll be darned if I can figure it out. So I just refer to my local code which is based on the 72 plus some local "oddballs."

In my area, we are required to use Class A systems for all fire alarms that directly communicate with the fire department via radio transmitter or the old fashioned hardwired Morse Code transmitters. This includes schools, hospitals, apartment buildings with 8 or more units, large office buildings, high occupancy restaurants, all night clubs, places of assembly, etc. High rise buildings also require them but they have a code unique code as well, primarily for the voice evacuation system.

Class B systems are limited to local fire alarms only.

So for me, the issue is very clear. Connected to fire dept = class A, not connected = Class B.

 

[peter d]

Re: Fire Detection Panel

I just wanted to add that our local code also requires us to separate the incoming and outgoing loop of a Class A system in separate raceways, one foot vertically and four feet horizontally. This rule was never followed about 6-7 years ago, and many fire alarms were installed with all the incoming and outgoing conductors installed in one large pipe. Not so any more. This rule is now being vigorously enforced.

We are also required to use metal raceway for the entire system, but an exception allows us to use a specially approved Fire Alarm MC cable.

 

[eeee]

Re: Fire Detection Panel

Steve66,

The class B system is 2 wire to all devices. The class A system is 2wires in one conduit and 2 wires in another conduit but ran architecturally as explained by the previous responder. There are some exceptions depending on the fire alarm notification device. I believe a pull station does not require two conduits in a class A system, just 1 conduit with 2 wires as a special case.