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#160411 - 02/13/06 05:49 PM Fire Alarms  
NJ Wireman  Offline
Joined: Aug 2004
Posts: 186
New Jersey (South Jersey)
I am looking to find out if anyone out there can help me out with finding some basic onfo out on fire/ burg. alarm wiring. I work for a company that does such and im now being asked to learn such. For those of you who do not know of me i have been on this site for sometime on the general electrical area. Any and all help would be great where i can locate books etc.

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#160412 - 07/18/06 07:34 PM Re: Fire Alarms  
FrankC  Offline
Joined: Mar 2004
Posts: 16
San Luis Obispo,CA has books on the subject. If you are a member of IBEW, you should be able to find someone in the hall who could help. would be another place to look.

#160413 - 07/20/06 05:01 AM Re: Fire Alarms  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
NJ Wireman,
I may help a bit with some very basic stuff, at least enough to get you headed in some directions as to what types of systems are out there.
Once you are briefed to the system types, it's time to do some major web searching, to find additional information.

Additional information is available from the Manufacturers &/or Vendors of the Systems you will be dealing with.

One great resource site for Electronics and anything related is:


Check out ePanorama's many areas, and you may find almost everything you need.

***Basic Types Of Fire & Security Systems***

Two basic types of Fire Detection / Alarm, and Intrusion Alarm Systems are:

* Addressable,
* Non-Addressable.

Let's look at the basics of the
"Non-Addressable" Systems first.

These systems normally consist of "Appliances" (detectors, indicators, etc.) and Contacts, which are connected to a "Main Panel", in distinct circuits - referred to as "Zones".
Activation of an alarm status comes from a change of state within a certain zone.
For example, we will use a basic Intrusion Detection System, and describe a single "Loop" which carries appliances and contacts for a single zone.

Let's say the Loop has 2 Passive Infrared Motion Detectors on it, and a single "Door Strike".
("Loop" is the communication, or alarm circuit)
Each Loop is a 2 pair cable - one pair is the comm. circuit's loop, and the other pair is the 24 Volt Power circuit for the Motion Detectors.

The PiR Motion Detectors have both; a set of N.O. contacts, and a set of N.C. contacts.
The N.O. contacts are closed when motion is observed (from received infrared light, produced by a living creature's heat).
The N.C. contacts will open if someone tampers with the device.

The Door Strike will have both N.O. and N.C. as one "switch", which allows the installer 2 options for use; along with a N.C. Tamper Switch for its enclosure.

At the "End" of the loop, we place a Resistor - formally known as the "End Of Loop Resistor" - or simply the "EOLR" or "EOL Resistor" (some refer to it as "End Of Line Resistor").
The value of the EOL Resistor is what will be required to "Load" the Loop up with a steady current value.
This type of System has it's Loops

This Loop will have the following connections:
  • Each Motion Detectors' N.O. contacts wired in Parallel across the 2 Wire Comm. Circuit,
  • Each Motion Detectors' N.C. Tamper Switch is in Series with the 2 wire Comm. Circuit,
  • The Door Strike's N.O. contact is wired in Parallel across the 2 Wire Comm. Circuit,
  • The Door Strike's N.C. Tamper Switch is in Series with the 2 wire Comm. Circuit.

During a normal condition - where no motion is detected, and the Door is in its closed position, the Loop draws a "Steady" Current (something like 25 milliamps), and the System observes this as a Normal Condition.

If there is an Intrusion detected - either by one of the motion detectors, or the Door Strike, the effected detector closes the Normally Open contact - which effectively shorts out the EOLR, and causes an increased load current on the Loop.
This is observed as an Alarm State by the Security Panel, and latches in whatever Alarm Annunciation appliances necessary. (sounding off alarm loudspeakers, flashing lights, etc.).

If the Normally Closed Tamper Switch on any device is Opened - due to someone trying to disturb the device, the Loop becomes an Open Circuit - and therefore the "Loading Current" no longer flows as should be.
This is determined to be a fault by the control panel, and initiates a "Trouble" Alarm.

Cutting the Loop's Conductors will also initiate a Trouble condition.

Although this is a VERY SIMPLE DESCRIPTION of a Non-Addressable System, it does convey the basics of its operation.
There are a lot more parameters involved, along with connection schemes and methods of detection.

p.s. Also of interest are the Logic Gates and Op-Amps used for the detection devices, along with inside of the control panels + keypads.

Now a look at the "Addressable" Systems' Basics.

Found at each Appliance or Contact, is a set of "DIP" Switches. The Switch "Options" are either "0" or "1".
These Switches are used to give each device a unique "Address" on the Communications Loop.

The Comm. Loop (refer to it as the "Comm. Bus") is a 2 Wire Serial Communications Bus, typically done with a shielded twisted pair.

Additionally, a 2 Wire Appliance Power Circuit is run for devices such as Strobes, Horns, Detectors (Heat, Motion, Sound, etc.).
These Circuits are typically made of #14 or #12 THHN Copper Wire.

The Devices in a single Loop may be distinguished from each other, by the ability of "Addressing" each item; therefore, several zones may be monitored using a single 2 Wire Comm. Loop.

If any condition takes place - be it an alarm condition or a trouble condition, the affected device will alert the control panel, and the control panel will display the information received from that certain appliance / switch / device, along with take the necessary actions (like display alarms).

This type of System works like a LAN does - more to the point, it functions similar to larger scale "BAS" (Building Automation Systems) do, with the "LON Topology Concepts".

Be sure to ask me about this, if you need a little more basic information.

As you can see, the Addressable System is much more detailed (and expensive), than it's Non-Addressable counterparts.
The need to be very competent exists on both types of Systems - each one having their own specialty of knowledge base.

Good luck on this Endeavor!


[This message has been edited by Scott35 (edited 07-20-2006).]

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#160414 - 07/22/06 07:46 AM Re: Fire Alarms  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA

Bumping zee Thread up again for discussion-ary purposes!


[Linked Image]

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#160415 - 07/22/06 08:07 PM Re: Fire Alarms  
Trumpy  Offline

Joined: Jul 2002
Posts: 8,211
SI,New Zealand
Crikey Scott!,
Thanks for that explanation there, it made really good reading!. [Linked Image]

Let's face it, these days if you're not young, you're old - Red Green grin

#160416 - 07/23/06 02:59 PM Re: Fire Alarms  
JoeTestingEngr  Offline
Joined: Nov 2005
Posts: 782
Chicago, Il.
NJ, I take it you will be involved with the wiring and not the repair and maintenance of these systems. You will usually find the cable requirements on the first or second page of the contract documents. There will be a table that might say that A is 16# twisted pair with an overall shield and B is 14# twisted pair. You might see a section of conduit with 2A,2B going to an addressible pull station and a horn/strobe assembly.

The 2, 14 gauge pairs might be used where they wish to silence an audible alarm, yet keep the strobe flashing until the alarm is cleared. 2 jumpers are removed from the horn/strobe and the unit is fed from separate signal zones, each programmed differently. If the design calls for the "Silence" button to stop both the horn and strobing, the jumpers are left in and the unit is driven from one zone. An EOL resistor is used to sense the integrity of the signal zone. A small, supervisory current flows in one direction. Reversing the polarity allows a greater alarm current to flow in the other direction. Alarm currents are limited to around 3 amps so you shouldn't see more than 5 or 6 devices on a zone.

The addressible pull station below is a different animal completely. 60 or more devices could be placed on a single zone. The ones I deal with most require a portable programmer to tell them which system they are installed on and their address. The system is programmed to display proper verbage should it go into trouble or alarm. These devices are EXTREMELY SENSITIVE to moisture and never get better once they fail. Ones that fail gracefully, cause a single trouble and a "Device Not Responding" message. Others take out the whole addressible loop, causing 100's of trouble messages to roll up at the FACP. This unfortunately, has lead to persons unknown seeking revenge on the FACP. For this reason, weatherproofing is very important in a non-office environment.

T-tapping and wire nuts with pigtails are not generally approved for the loops. They want the loop to go down if a device is removed. Line protectors should be used on any loops that leave a building, detection or signal.
Addressibles put power and bi-directional data over one shielded pair using a combo of time division and pulse position modulation. (my description, not theirs) Proper shielding will make a huge difference in noisy environments.

I have had to correct problems created by those who should've known better. By this, I mean that the name on the truck was the same as the name on the FACP. I was called in to check one system a couple of days after the alarm company was there. They had replaced a horn/strobe without pulling the jumpers from the new one, putting 2 signal zones into trouble. Amazing that they would walk away with the system like that. I set off the alarm at another location and found a large area where no A/Vs were going off. Yet the FACP was perfectly normal. It turns out that the installer had wired the feed and devices on a PAD panel backwards. This caused devices that should have been alarming to be fed a minimum supervisory current. One might wonder why this wouldn't be detected and corrected on an initial system test.

If you're going to be doing this kind of work, you need to start talking to tech reps of the FACP vendors and the AHJ. Cables that would work with the system, might not be flame test rated as required in some locations. Your company should be willing to send you for training or have someone show up on site. At least send you out with someone who knows this stuff.
Hope this has helped out.

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