Douglas Krantz - Technical Writer - Describing How It Works
Get the Book Make It Work - Convetional Fire Alarms
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What Does Listed Mean?

Listed means that something has been put on a list of devices that work by a testing laboratory like UL, ULC, FM, CE, CCC, etc. The NFPA doesn't keep lists, testing companies keep their own lists.

What Does Listed Mean?

What Does Listed Mean?

Greetings Douglas,

If the equipment has to be listed for that use in a fire alarm system, then why does the NFPA 72 specifically mention "All devices and appliances that receive their power from the Initiating Device Circuit (IDC) or Signaling Line Circuit (SLC) of a control unit shall be listed for use with the control unit." (article 10.3.3 Edition 2013)?

Thank you, JM

Before going any further, start by understanding that the NFPA (National Fire Protection Association, a non-profit publisher) does not "List" anything. . . at all.

The word "Listed" can be considered a legal term, with legal definitions. However, to understand what "Listed" really means, we have to look at what "Listed" does.

Grocery List

Think of a Grocery List. When you want to remember to get a potato at the grocery store, you put the words "A Potato" on the grocery list. You "Listed" the words "A Potato". So, if something is "Listed", it has been put on a list.

In this case, the lists are the ones kept by nationally known, third party testing laboratories like UL, ULC, CCC, CE, FM, etc. These laboratories aren't associated with any manufacturer, and to perform their tests, they get paid exactly the same if they say the equipment works, or the equipment doesn't work. If the equipment does work, they put it on their list of equipment that works. That's how the equipment becomes "Listed".

NFPA Required Listing

In your question, the NFPA is emphasizing that any device that uses power from the IDC (Initiating Device Circuit) or SLC (Signaling Line Circuit) has to be Listed to be used with the fire alarm control panel it's connected to. In other words, the devices have to be compatible with the panel.

It's one of those requirements that really mean "If it's not Listed (not compatible), it probably won't work properly. So, skip trying it yourself, just make sure it's Listed (compatible). It's a requirement based on common sense.

Appliances - Smoke Detectors on the Initiating Device Circuit

Conventional smoke detectors are appliances, and they have electronics in them. When they are standing by, they are always using a little power from the IDC (Initiating Device Circuit). When they go into alarm, they draw more power. At all times, they receive power from the IDC, which gets its power from the fire alarm control panel.
  • If the smoke detector is designed to draw too much power when the detector is just standing by, that could be considered by the control panel as an alarm (false alarm). No one wants false alarms.
  • If the smoke detector isn't designed to draw enough power when it's in alarm, the control panel might not see the alarm. No one wants a fire alarm system that doesn't go into alarm when the smoke detector goes into alarm.
  • If the smoke detector is designed to draw too much power when it's in alarm, the smoke detector un-latches and the red light goes off. People really do want to know which smoke detector went into alarm.

The only way to tell that a smoke detector is going to work with a particular panel is to have the testing laboratory test the combination, and if it works, put it on their list; it has been "Listed" as being compatible. If a combination smoke detector and control panel doesn't work, it won't be on anyone's list; the combination won't be "Listed".

Appliances - Devices on the Signaling Line Circuit

Addressable devices are also appliances. All addressable devices get power to operate their electronics from the Signaling Line Circuit (SLC). Some modules and addressable devices have auxiliary power, but the addressing portion still receives it power from the SLC. The devices also use data to send and receive signals on the SLC. The SLC is connected to the fire alarm control panel.

All addressable devices are very specifically designed to be connected to their own particular type of control panel; they have to be compatible. When the manufacturer has the control panel tested and listed with a testing laboratory, all devices that are going to be connected to the SLC are tested to work with the control panel. If the testing laboratory has the module or detector on their list as being compatible, the testing laboratory has completely tested the device with the panel, and the combination works.

Lists are Kept by the Testing Laboratories

With devices that use power from the IDC or the SLC, the NFPA is concerned that the devices themselves work. But they're also concerned that the devices work with the control panel. Assuming that one smoke detector is like any other smoke detector, or that an addressable device made by one manufacturer is just like an addressable device made by another manufacturer will get one into trouble. That is why the device and the control panel have to be listed together. They have to be compatible.

Remember, the NFPA is not a testing laboratory, the NFPA does not have a list of devices that work in a fire alarm system. The manufacturer is not a testing laboratory, the manufacturer does not have a list of devices that work in a fire alarm system.

There is a huge number of devices and equipment that has been tested and put on the laboratory's lists as working. What the NFPA is saying is that anything used in a fire alarm system has to be on a third-party, nationally known testing laboratory's list of equipment and appliances.

The many references to "Listing" that the NFPA uses in all their books of Code are referring to the same set of "Lists".

Douglas Krantz
Life Safety
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