Layout of Fire Detection Distribution System

[eeee]

The fire department wants 39 zones for a class A conventional fire detection system in this 50,000 single story square foot building with 25 large and small rooms containing a tall ceiling in the rafters. Fro a Monaco 2 fire control panel, I estimate 4 wires per zone since each device (heat detectors, bells, horns, etc.) requires 4 wires. Since it is class A conventional, two separate conduits and sets of cable will be required. Total required wires is 4 wiresX39 zonesX2 conduits (to make it class A)=312, 22 guage THHN fire cables. The ugly's handbood indicates only 22, 22AWG THHN cables will fit in the 3/4 EMT conduit.

That is far too much conduit to run accross these high rafters and would cost an extra 70,000 compared to wiring this facility for 2 zones, the way it is now.

Can I put in much larger conduit sizes (to save much money on conduit counts) which go from the devices to the main long rectangular junction box located just above the fire control panel, then traversing to the fire control panel? Can I put in, for example, 2 " EMT conduit for a couple of main runs, and then use 3/4 " conduit for branch circuits.

My concern is the 2 " EMT conduit mating with the fire control panel.

I need to call Monaco and will-I know.

 

[peter d]

Re: Layout of Fire Detection Distribution System

This whole installation raises more questions than answers.

Why does the fire department want 39 zones?

Do you have an extremely good reason why you are not using an addressable system. 39 zones?!?! 50,000 square feet!?!?

$70,000 could easily pay for an addressable system.

This sounds like a nightmare in the making.

 

[eeee]

Re: Layout of Fire Detection Distribution System

We must have 39 zones since the fire departement says this will tell then in exactly what room the fire is or what air handler (or duct), what flow switch and what tamper switch. The operations engineers and fire alarm electrician agree.

If we stay conventional, we get a free (donated) fire control panel.

The mechanical engineer said he thinks he could elliminate my whole system and put a sprinkler system in cheaper-problem is that this project is 100% design.

If it is cheaper to put in an addressable fire control panel than pay for all that conduit, I must look at this again. I have two zones of conduit already installed for a conventional class B system which I can reuse now. That should save some money. If I go to an addressable system, which is of course one big loop for the most part, all this existing conduit must be replaced. Looks like I am going to have to replace most of it anyway since we are going from 2 to 39 zones.

 

[steve66]

Re: Layout of Fire Detection Distribution System

According to NFPA 72, a zone should not exceede 22,500 sq feet, or be more than 300' in any direction. Also, each floor should be a separate zone. Add a zone for each air handler, and you probably have more like 10 zones.

There should be a fire rated wall at the border between two zones.

Steve

 

[don_resqcapt19]

Re: Layout of Fire Detection Distribution System

4 wiresX39 zonesX2 conduits (to make it class A)=312, ...

Why do you need 4 wires in both of the conduits? I thought that class A was two wires out, to each device and then two back to the panel.
Don

 

[mhulbert]

Re: Layout of Fire Detection Distribution System

Sounds like getting a free non-addressable panel isn't really free at all.

I'm not sure why you'd have to redo your conduit for an addressable system (we can't see your layout), but there are many small addressable panels that will handle around 250-500 "points", all from one-two loops. I don't know their exact cost, but it is sure less than $70k. Check out some of the manufacturers websites, they will have all of the data sheets you need...silent knight, notifier, etc. There are isolation modules that will isolate a fault in one part of your loop from affecting the rest of the system as well.

 

[eeee]

Re: Layout of Fire Detection Distribution System

Don,

You say that class A is two wires going out to each fire device (heat detectors, bells, strobes, etc.) and two wires back to the fire control panel for a conventional fire control panel. My understanding is that class A is two wires going to each device and two wires back to the fire control panel for one conduit; then you have to do the same procedure for another conduit. That makes a total of 4 wires for each conduit (two comming and two returning) for one zone. Of course more cable can be inserted in each conduit for additional zones.

 

[don_resqcapt19]

Re: Layout of Fire Detection Distribution System

My understanding is that class A is two wires going to each device and two wires back to the fire control panel for one conduit; then you have to do the same procedure for another conduit.

That is not how I understand a Class A system. My understanding is that it is only a 2 wire loop that starts and ends at the fire alarm control panel. Only two wires per zone would be in any section of conduit and the conduits must be physically separated except at the devices.
Don

 

[peter d]

Re: Layout of Fire Detection Distribution System

I said it before, I will say it again: addressable, addressable, addressable!!!!

Don is correct, as usual. You must physically separate the incoming and outgoing conductors. Therefore, you will have only 2 wires per zone in each raceway. It sounds to me like you are planning to run the outgoing and the return in the same pipe, which is a big no-no.

A "true" class A system will be just like a big circle. The loop will start at the panel, go around the building, braching off the the various devices, and then returning to the panel. I repeat, you cannot put the incoming and outgoing conductors in the same raceway! There are a few small exceptions to this rule found in NFPA 72.

 

[eeee]

Re: Layout of Fire Detection Distribution System

You are right. The class A system is a loop for the intitiating devices. The class B system is not a loop, but dead ends to the familiar resistor we all know about. 2 wires per conduit for Class A. The 8 wires I was talking about before was because we had relays connected to the initiating devices for another class A system already installed I was using for comparison; thus 2 wires were required to power the relays.

I have physically seen 18AWG fire cable being used. I think I will spec out 18AWG.

My mechanical engineering friend is going to be in for a big surprise if he thinks he can put in a wet (low maintenance) sprinkler system cheaper. Schedule 40 pipe is expensive.

The alarm notification devices do not loop back to the panel for a class A system and this will need to be accounted for when estimating the amount of cable and conduit.

 

[eeee]

Re: Layout of Fire Detection Distribution System

There is one other thing that has been overlooked and that is the shut down circuits. Each air handler for the HVAC and each ventillation fan will need a shut down circuit wired to it. Some motor disconnects may also need a shut down circuit wired to it. This is an additional compliment of wiring required for the conduits that must interface with the fire control panel.

It would be nice if the addressable system paid for itself in this renovation, since two 18AWG cables for the loop or maybe an additional loop is all that would be required. I am calculating the costs now condidering that I have some existing conventional conduit in place now and have a donated conventional fire control panel.

 

[mhulbert]

Re: Layout of Fire Detection Distribution System

eeee,
if you are using duct-mounted detectors, they will have a CC for air handler shutdown on them. If you only need to shut down the zone that detects smoke, you do not need to run anything back to your panel.

If you need to doa building wide shutdown, there are interface boxes that will give you a CC output off the NAC (the horn circuit), which may save you a lot of wiring.

With most of the addressable panels, you can run a 4-wire serial link out to remote CC boards(for shutdowns), as well as additional loops, and remote annunicators. Do not overlook making it a less centeralized system, with a supervised, serial backbone.

My vote is still addressable- it sounds like you are building a fairly complex and large system, with many zones/points. You could probably do it with an analog setup, but it would not be nearly as configurable and adjustable. Think about moves, Adds, and Changes (MAC's), these are a pain in the butt with an analog system, with an addressable, it's mainly a software change, and the new devices are on their own zones.

mike

 

[don_resqcapt19]

Re: Layout of Fire Detection Distribution System

eeee,
Sprinkler systems and fire alarm systems are not interchangeable. In general sprinkler systems are property protection systems and fire alarms systems are people protection systems.
Don

 

[eeee]

Re: Layout of Fire Detection Distribution System

The sprinkler systems are recommended by the fire department since they fight the fire before the fire department gets there. I know it is common fashion to put in sprinkler systems for protecting equipment.

Our fire chief indicates he perfers sprinkler system for protecting people better since they start fighting the fire before the fire department gets there.

 

[don_resqcapt19]

Re: Layout of Fire Detection Distribution System

eeee,

Our fire chief indicates he perfers sprinkler system for protecting people better since they start fighting the fire before the fire department gets there.

I'm sorry but in my opinion, he is wrong. It is very possible for the people to be dead from the smoke before the first sprinkler head releases any water. Even if that is not true, there are very few fires where a sprinkler head will open before a smoke detector alarms. Again, in general, fire alarms protect people and sprinklers protect property.
Don

 

[eeee]

Re: Layout of Fire Detection Distribution System

Don,

I have a problem here with our fire control panel solution as opposed to a sprinkler system for protecting people. We only have smoke detectors on the air handlers in the ducts. The rest of the facility is planned for heat detectors per the fire departments' wishes.

Please advise?

 

[eeee]

Re: Layout of Fire Detection Distribution System

The mechanical engineer states that people would see the smoke in time to get out before being injured significantly. Therefore you would reap the benefits of the sprinkler system fighting the fire before the fire department gets there and thus saving more lives in the process.

 

[eeee]

Re: Layout of Fire Detection Distribution System

Monaco stated that a sprinkler system is best to put in with smoke detectors at egress hallways, exit signs and above fire control panel if it is decided that smoke detectors are too costly to maintain.

Monaco did say that smoke detectors are the best for life safety if you want to maintain them and put up with all the false alarms.

 

[don_resqcapt19]

Re: Layout of Fire Detection Distribution System

The mechanical engineer states that people would see the smoke in time to get out before being injured significantly.

Maybe. I guess I am really thinking more of residential type occupancies than commercial. If the occupants are not sleeping, then they should be able to see the smoke and the sprinklers should be able to provide enough exit time. This completely changes when there are sleeping occupants.
Don

 

[don_resqcapt19]

Re: Layout of Fire Detection Distribution System

eeee,

Monaco did say that smoke detectors are the best for life safety if you want to maintain them and put up with all the false alarms.

Why would there be false alarms with the smokes. What do they do in this occupancy.
Don