Fire alarm zone wired with resistor in series

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bgelectric

Senior Member
Hey everyone,
I ran across a fire alarm panel today that had zones with a resistor wired in series with the loop...? is this for zones that have devices wired across the NC contacts vs a NO contact which would receive a resistor in parallel...?
If that is the case which type of devices typically have resistors wired in series?
Thanks in advance!
 
S

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
bgelectric said:
Hey everyone,
I ran across a fire alarm panel today that had zones with a resistor wired in series with the loop...? is this for zones that have devices wired across the NC contacts vs a NO contact which would receive a resistor in parallel...?
If that is the case which type of devices typically have resistors wired in series?
Thanks in advance!
Click to expand...

The first thing that jumped in to my mind was a system I once worked on at a school. The Fire alarm and the PA shared the same speakers and wiring. The devices had a resistor wired in series with part of the circuit internal to each classroom, which had a speaker and a call button. It was a long time ago, so I can't even remember how it was wired. Once I traced out the circuits, I was able to figure it out, but...

BTW, what do you mean by wired in series? If the devices themselves are wired in parallel, then are you saying that somewhere between two devices, a resistor was wired in to only the positive or only the negative wire in relation to the device?
 
gadfly56

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
bgelectric said:
Hey everyone,
I ran across a fire alarm panel today that had zones with a resistor wired in series with the loop...? is this for zones that have devices wired across the NC contacts vs a NO contact which would receive a resistor in parallel...?
If that is the case which type of devices typically have resistors wired in series?
Thanks in advance!
Click to expand...

Is this a fire/burg panel or straight fire? Resi or commercial?
 
B

bgelectric

Senior Member
Strathead said:
The first thing that jumped in to my mind was a system I once worked on at a school. The Fire alarm and the PA shared the same speakers and wiring. The devices had a resistor wired in series with part of the circuit internal to each classroom, which had a speaker and a call button. It was a long time ago, so I can't even remember how it was wired. Once I traced out the circuits, I was able to figure it out, but...

BTW, what do you mean by wired in series? If the devices themselves are wired in parallel, then are you saying that somewhere between two devices, a resistor was wired in to only the positive or only the negative wire in relation to the device?
Click to expand...

There was a resistor wired at the panel in series with the positive wire.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I have seen that when NC contacts were used on the initiating devices. A short is normal operation, an open is a trouble alarm, and current through a resistor is the alarm condition. The initiating devices are wired in series with this system.
 
J

jrdsg

Senior Member
Location
Vancouver, Canada
as you say, typically found on NC zone type

as you say, typically found on NC zone type

Dialers attached to the output relays of fire alarm control panels often use a NC zone configuration with a resistor in series to monitor the trouble output relay of the FACP. When the FA goes into a trouble condition [low batt, zone trouble, etc.] its trouble relay will open and cause the connected zone on the dialer [programmed as an FA zone type] to go into zone trouble and send the appropriate signal to the monitoring station. This configuration is required due to the limited programmable zone types available on most dialers.
 
R

ronaldrc

Senior Member
Location
Tennessee
don_resqcapt19 said:
I have seen that when NC contacts were used on the initiating devices. A short is normal operation, an open is a trouble alarm, and current through a resistor is the alarm condition. The initiating devices are wired in series with this system.
Click to expand...

Don I am not replying to your post. There is a problem with the forum and it would not let me post after the last post any thing above that I could post.

But here is my two cents worth I wanted to add.

A few decades back when I was in the Electrical trade they placed a
resistor in the very end of the alarm circuit. This was a way of supervising
the alarm part of the circuit to make sure there was continuity to the very
end of the circuit and all the way back to the alarm panel.

It worked with a resistor bridge circuit, with no smoke detectors in the alarm
state or no contacts closed if the circuit did not show the resistance of this
resistor the main panel would show trouble.Which meant that there was a
break some where in the alarm circuit.

From this break on to the end of the circuit the smoke detectors would not
be functional.

Ronald :)
 
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