Douglas Krantz - Technical Writer - Describing How It Works

How are Addressable Speaker NACs Supervised?

Each manufacturer uses a different method to supervise the Addressable Notification Circuit (NAC) wiring. A lot of times, they only indirectly supervise the wiring; if signals reach the speakers, the wiring must be good.

How are Addressable Speaker NACs Supervised?

Greetings Douglas,

I know about the DC monitoring method (the speaker NAC wiring uses DC voltage at standby, and switches to audio AC voltage at alarm). I want to know if there is another method used to fire speaker wiring monitoring? And what is the advantage of each method?

Thank you, WC

The National Fire Protection Association, Inc. (NFPA) has a lot to say about how to do supervision correctly; so do the people who design fire alarm systems, the manufactures.

In the beginning, the NFPA was looked to as the primary source of information about "how to supervise fire alarm systems". Over time, though, that has changed.

For the NAC, First You had Conventional Supervision . . .

Before the NFPA, everyone did their own thing. When NFPA came along, they showed everyone how to wire a fire alarm system so it was reliable, and the NFPA showed everyone how to supervise the wiring in a fire alarm system. Manufacturers followed the NFPA's guidelines. The two major classifications of circuits were Class A and Class B.

Of course, though, the methods of supervision were limited by what could be done with the technology that was available.

Then for the NAC, You had Not-Conventional Supervision (AKA Addressable) . . .

Then came the transistor and addressable systems, and more was available. As higher technology ideas started to become miniaturized, the NFPA's guidelines had to be expanded. To keep things simple(?) they called the variations on the different classifications "Style".

If the wiring was not specifically Class A or Class B, but had other means of supervision and redundancy, instead of Class A and Class B, there was Style 1, Style 2, Style 3, Style A, Style B, Style C, etc. for the copper-wire signal-carrying loops.

Then, included with those styles, there was wireless (Radio Frequency or RF), and fiber optics.

The improvements that manufacturers wanted were coming much faster than the NFPA could classify them under the Class or Style systems. Not only that, but because of the different ways of powering devices, many systems and designs were falling through the cracks.

Keeping all the styles current with the life safety considerations was very difficult, especially from the AHJ enforcement end.

Then you had Listing . . .

Testing by third party laboratories like UL, ULC, FM, CE, CCC, etc. have been around for a long time. The laboratories would test devices and systems, and if the device or system was safe and worked, it was put on the testing laboratory's list.

The NFPA looked at the listing, and decided to get out of the method-requirement business.

Instead of a method-requirement, the NFPA came up with a new way of classifying; they came up with a system to show how a fire alarm system handled failures in the fire alarm system.


NFPA's 7 Classes of Fire Alarm Paths

What the NFPA essentially says is "If something is used in a fire alarm system, it has to be listed for use (See above explanation of listing) in a fire alarm system.

What About Addressable Speaker Systems?

Addressable speakers can be turned on and off individually. That means that the audio-power wiring you referred to has to be able to provide audio at all times. Rather than a conventional NAC (Notification Appliance Circuit) the audio power is distributed by other means. The means, though, still has to be on a testing laboratory's "List".

One method to supervise the wiring is to use an "end of line device". There has to be constant or regular intermittent audio sent down the line in order to sense that audio is getting to the end of the line. If not, a trouble is sent to the panel.

Another method to supervise the wiring is to put this same end of line device in every speaker. At all times, there has to be constant or regular intermittent audio getting to every speaker. If the audio doesn't reach a specific speaker, that speaker sends a trouble to the panel.

Every manufacturer has a different way of designing their addressable speaker system, but every way of designing the power distribution system has to be listed by a testing laboratory.

I don't know all of the different ways that all of the different manufacturers use for their audio risers. But the method of designing the audio risers still has to be on a list. Check with the manufacturer of the system to find out what is listed for their system. Remember, it's manufacturer who designed the system, and it's the manufacturer who paid for the testing and listing. They'll know.

Douglas Krantz
Life Safety
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