Douglas Krantz - Technical Writer - Describing How It Works

Is it Permissible to Connect Addressable Devices in a Class A System?

When a devcie is removed, the electrical pathway is interrupted, and the panel shows trouble.

Greetings Douglas,

I have a couple of questions.

1. Is addressable (connected in Class A) NAC permissible in NFPA?

2. What is allowable time in NFPA to get the trouble signal if you remove a NAC device?

Thank you, R C

1. Is addressable (connected in Class A) NAC permissible in NFPA?

Yes, the NFPA (National Fire Protection Association) does allow for addressable horns, strobes, and speakers, but there's more to the question.

Notification Appliance Circuits (NAC) whether they're Class A or Class B have to be consistent. All of the horns, strobes, and any speakers on the circuit have to be of the same manufacturer, and work with each other in the circuit; they have to be compatible with each other. If they are of different types, some of the horns or strobes won't sound off at the proper rate, and possibly won't work at all. Some of the speakers will be either too loud or too quiet.

When addressable horns, strobes, and speakers are on the same circuit as conventional horns, strobes, and speakers, some won't work at all, and some will stay on all the time. In other words, mixing conventional devices and addressable devices won't work at all.

All of the horns, strobes, and speakers have to be compatible with (work with) the fire alarm system manufacturer, or the circuit and devices won't work right.

Call the technical support for the manufacturer of the fire alarm system to find out what devices are going to work with their system (be compatible with their system).

2. What is allowable time in NFPA to get the trouble signal if you remove a NAC device?

As such, the NFPA does not allow a fire alarm system to have trouble. It is their opinion that a fire alarm system should always work. If there's trouble with the system, the trouble means that parts of the system aren't working. Possibly the fire alarm system won't detect some or all fires, or the fire alarm system won't warn anyone about the fire. A "Trouble Signal" doesn't show what's wrong; a "Trouble Signal" just shows that something's wrong.

To work on a fire alarm system, though, there will be trouble; that's what "working on the system" does. When you are on site and working on the system, the assumption is that you, personally, are also watching for fires. You are required, personally, to have awareness of the possibility of fire, and should have a plan in the back of your mind of what to do in case of fire.

If you remove a horn or strobe from the circuit, be aware that some or all of the horns or strobes on the circuit won's work (that's what trouble with the NAC circuit means). Make sure that occupants of the building can be warned of a fire before you leave.

The local fire marshal might have further ideas about the trouble signal.

Douglas Krantz

Further Question

Mr. Krantz

By trouble signal, I mean that if I remove any detector, what is the allowable time to get the signal at the panel?

Thank you, R C

I have not found a reference in the NFPA Code to how much time "allowable" to get a trouble signal at the panel if a detector is removed.

The NFPA Code requirements are based on good fire detection practices, and on what, physically, any fire alarm system is capable of doing.

Conventional Fire Alarm System

A conventional fire alarm system (non-addressable) isn't capable of figuring out if a detector is connected, a conventional fire alarm system is only capable of figuring out if the wiring is complete. To remove a detector in a properly installed fire alarm system, the wiring is taken apart. Even when a detector is just unplugged from the ceiling, the wiring is automatically taken apart or disconnected when the detector is removed.

There might be a code somewhere that says what time is an acceptable time to show a trouble on the panel, but from what I've seen, all conventional fire alarm systems (non-addressable) show a trouble in less than a second after the wiring is disconnected.

Addressable Fire Alarm System

An addressable fire alarm system is different. An addressable fire alarm system "polls" each detector to make sure it is connected to the system.

Polling is like taking classroom attendance. When the teacher takes attendance, the teacher askes "Detector 1, are you here?", and detector 1 answers "Here". One at a time, the teacher asks "Detector 2", "Detector 3", "Detector 4", and so on. After asking each detector, the teacher expects the detector to respond with "Here".

If the teacher asks "Detector 27, are you here?", and detector 27 doesn't answer, the teacher marks "absent" - the panel shows a trouble signal.

The NFPA Code says that the fire panel has to take attendance, or poll each detector, once every 20 seconds. In essence, if an addressable detector is removed, then according to the NFPA, a trouble signal will be shown on the panel in 20 seconds or less.

Trouble Signal

The trouble light on the panel is going to stay on until the trouble is repaired. For a conventional panel, the wiring has to be reconnected (usually by reinstalling the detector). For an addressable panel, the detector has to be reinstalled.

Douglas Krantz
Life Safety
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