Fire Alarm Zones/Loops

[Gshell82]

Could someone be kind enough to explain the difference between FA Zones and loops?


Also what determines how many zones you need and what determines how many loops you need?




Thank You

 

[gadfly56]

Could someone be kind enough to explain the difference between FA Zones and loops?


Also what determines how many zones you need and what determines how many loops you need?




Thank You

A zone is usually a geographic area in a building, a floor or part of a floor, which can be defined by construction (fire rated walls) or purpose (architect defined). A loop is usually the term describing the cable connecting fire alarm initiating or notification devices and the devices themselves. A loop may cross from one zone to another, or you may have more than one loop in a zone, or a combination.

In fire alarm design, the magic numbers for zones are 22,500 sq ft and 300 feet. No zone should be more than 22,500 square feet or longer than 300 feet. These restrictions were much more important before the advent of addressable systems which allow you to pinpoint the exact location of an alarm.

 

[Gshell82]

A zone is usually a geographic area in a building, a floor or part of a floor, which can be defined by construction (fire rated walls) or purpose (architect defined). A loop is usually the term describing the cable connecting fire alarm initiating or notification devices and the devices themselves. A loop may cross from one zone to another, or you may have more than one loop in a zone, or a combination.

In fire alarm design, the magic numbers for zones are 22,500 sq ft and 300 feet. No zone should be more than 22,500 square feet or longer than 300 feet. These restrictions were much more important before the advent of addressable systems which allow you to pinpoint the exact location of an alarm.

Thank You. What dictates how many loops I need for my FA system? Is this more of a field routing issue as needed for cabling?

 

[gadfly56]

Thank You. What dictates how many loops I need for my FA system? Is this more of a field routing issue as needed for cabling?

The number of loops required is dictated first by the number of devices you have, and second by the number of zones you need. As an example, suppose that the notification appliance circuit (loop) can handle 20 horn/strobes and you need 4 per floor. That would suggest that you could run 5 floors off a single loop. When you go to NFPA 72, you'll find that each floor is considered a separate fire zone, requiring a separate circuit. Conversely, you have a 30 story building and a Siemens XLS addressable fire alarm control unit. Each floor has 8 addressable devices. Since the XLS is capable of handling 252 devices. Since NFPA 72 only requires that the area be identified separately if over 22,500 square feet, and addressable devices can be tagged with their precise location, you could wire the whole building on a single addressable device loop.

As you surmise, there may be matters of convenience that would suggest using more zones than the minimum in order to make the installer's job easier, or facilitate phased construction.

There is a lot of information on zones and zoning in NFPA 72, particularly Annex A. I would suggest getting a copy of the 2013 or 2016 edition and giving it a read.

 

[lielec11]

gadfly has done a great job explaining different ways to do this and as you can imagine it is an art as much as it science when it comes to FA wiring. In addition to the codes mentioned be mindful of the local AHJ, as some of them are very stubborn and only want jobs wired their way.

 

[Strathead]

The number of loops required is dictated first by the number of devices you have, and second by the number of zones you need. As an example, suppose that the notification appliance circuit (loop) can handle 20 horn/strobes and you need 4 per floor. That would suggest that you could run 5 floors off a single loop. When you go to NFPA 72, you'll find that each floor is considered a separate fire zone, requiring a separate circuit. Conversely, you have a 30 story building and a Siemens XLS addressable fire alarm control unit. Each floor has 8 addressable devices. Since the XLS is capable of handling 252 devices. Since NFPA 72 only requires that the area be identified separately if over 22,500 square feet, and addressable devices can be tagged with their precise location, you could wire the whole building on a single addressable device loop.

As you surmise, there may be matters of convenience that would suggest using more zones than the minimum in order to make the installer's job easier, or facilitate phased construction.

There is a lot of information on zones and zoning in NFPA 72, particularly Annex A. I would suggest getting a copy of the 2013 or 2016 edition and giving it a read.

I wish I had a copy of a more recent NFPA 72 to see your references. In 2011 I did a 105,000 square foot building and it only had one initiating circuit. It was designed by an Engineer and approved by the building department. I understand Fire alarm fairly well, so I don't see any issue of safety in this design as it is an addressable system. So in effect every device is it's own zone and each device can be effectively an "area" identified separately so why would I need more than one initiating loop?. That is why I want to see the wording. If it was an old system and we were putting monitor modules on large conventional smoke detector zones, what would you consider a zone in reference to the 22,500?

Also, are your definitions of zones and loops, official code terms? I ask because I am used to everyone I know referring to a zone as either a single NAC circuit or a conventional initiating circuit, period. As in the FCPS24 power supply feeds a maximum of 4 zones. And i think of a loop as an SLC loop from the FACP.

 

[Gshell82]

are there typically two separate loops for the notification devices and the initiation devices or can they both be in one loop?

 

[lielec11]

are there typically two separate loops for the notification devices and the initiation devices or can they both be in one loop?

Yes these are always on different circuits.

 

[Strathead]

are there typically two separate loops for the notification devices and the initiation devices or can they both be in one loop?

They are completely different kinds of circuits. Their entire operating principle is different. And there are two types of initiating device circuits as well. We usually refer to them and addressable and either conventional or non-addressable.

 

[gadfly56]

Yes these are always on different circuits.

Unless...you have Simplex TrueAlert notification appliances. A TrueAlert speaker strobe will have: strobe power, speaker power, and signal loop circuit (SLC). Hat trick!

 

[Strathead]

Unless...you have Simplex TrueAlert notification appliances. A TrueAlert speaker strobe will have: strobe power, speaker power, and signal loop circuit (SLC). Hat trick!

That isn't really correct. A True Alert speaker strobe has addressable strobe power circuit and a conventional (EOL) speaker circuit. It is still a NAC circuit and it has nothing to do with the initiating SLC (which the cal IDNet)

 

[sameguy]

Class A or B

 

[gadfly56]

Class A or B

Oh, now you're just trying to cause trouble!

 

[lielec11]

Oh, now you're just trying to cause trouble!

trouble.. or supervisory?? Oh hey, a door...:dunce:

 

[sameguy]

Oh, now you're just trying to cause trouble!

Probably just a ground. )