# Fire Alarm Controller Size



## Big John (May 23, 2010)

I have to add 4 smokes onto an existing 4 zone Class B fire alarm system.

It's been a long time since I've done any FA and everything I've worked with was Class A, so I'm trying to get all my ducks in a row with this one:

The existing panel is a Mircon Series 200. The maximum load the initiating circuit can draw is 50mA. However, the Class B loop already has a load of 7 smokes which say they draw 23mA each when in alarm. 

It seems like my initiating device circuit is already overloaded before I even connect my smokes. I understand that the panel should only need one device to initiate to sound an alarm, but what would happen if three devices were to initiate? Would it simply not matter? :confused1:

I've been looking through NFPA72 and the NEC, but haven't seen anything on how you determine the current necessary for the initiation circuit.

I appreciate the help.

-John


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## Big John (May 23, 2010)

Man, no takers on this, huh?

Alright, I'll make it a little easier: I found literature from the smoke detector manufacturer that says I can put 30 detectors on the initiation loop. 

So, I am definitely comfortable adding more smokes, but anyone have any insights on why multiple alarms don't mess up the system?

-John


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## cdnelectrician (Mar 14, 2008)

I am not too familiar with NFPA but...I am going to assume from your original post that these are 2 wire smokes not 4 wire with an EOL relay? Who makes the smoke detectors? You would have to go by Mircoms literature to see the max device load on the circuit and not necessarily the manufacturer of the smokes themselves...Of course there may be something in NFPA which dictates how many current drawing initiating devices may be connected to the circuit.


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## NacBooster29 (Oct 25, 2010)

The short and simple answer is on a conventional zone, you'll never actually have more than one alarm. Once the zone is alarmed its done, other zones can still alarm. You can however have multiple field devices say 2 smoke in the same corridor , have red led's . also if you are adding them to a true class "b" make sure to place the eol res at the actual end of the line


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## bduerler (Oct 2, 2009)

NacBooster29 said:


> The short and simple answer is on a conventional zone, you'll never actually have more than one alarm. Once the zone is alarmed its done, other zones can still alarm. You can however have multiple field devices say 2 smoke in the same corridor , have red led's . also if you are adding them to a true class "b" make sure to place the eol res at the actual end of the line


he is 100% correct.


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