Douglas Krantz - Technical Writer - Describing How It Works

Can I Trip one NAC Panel Using Another NAC PS?

By Douglas Krantz | Descriptions

Can I Trip one NAC Panel Using Another NAC PS?

Can I Trip one NAC Panel Using Another NAC PS?

Greetings Douglas,

I'm having a hard time finding what the code says regarding the tripping of a Supplemental Notification Appliance Circuit [SNAC] power supply panel. I'm being told to use the output of another SNAC power supply panel for tripping it. That doesn't seem right to me, and I'm trying to justify using an alternate method. What are your thoughts?

Thank You, SD

I'm guessing that you're referring to using a SNAC panel to trigger off of a Class A or Class B Notification Appliance Circuit (NAC) that has horns and strobes on it. In a modern-day fire alarm system, I'm not sure you can.

In order to understand the issue, we have to consider the difference between what is legal, and what is not-expedient. We'll look at the direct legal part first.


No, I have not found anywhere in the NFPA 72 that specifically says that tripping a Supplementary Notification Appliance Circuit (SNAC) panel with another SNAC panel is prohibited. The NFPA seems to be going away from wiring issues, and instead is just saying that the equipment (along with its specific wiring requirements) has to be "Listed For Use".

For equipment to be "Listed For Use", the equipment has to be tested. Testing the equipment, like a SNAC panel, Fire Alarm Control Panel (FACP), heat or smoke detector, horn, strobe, switch, etc., is done by a third-party nationally-known testing laboratory like UL, ULC, FM, CE, CCC, etc. If the equipment passes the test, the equipment is placed on the testing laboratory's list of useable equipment; the equipment has been "Listed For Use".

The installation sheets and installation manuals that come with the equipment and devices are important. They show the exact wiring that was being used for the test.

Using Google or other high ranking search engines, the installation manuals and installation sheets on any specific fire alarm equipment or devices can be easily found on the web.

When checking out the legality of an installation, make sure to use the installation sheets and installation manuals provided by the manufacturer. The word "Installation" will be in the title of the literature. If the literature does not include the word "Installation" in the sheets or manual, it's not the legal "Listed For Use" sheet or manual.

Knowing that the manufacturer's marketing department writers sometimes guess at the specifications, you can take the marketing literature from the manufacturer with a tiny grain of salt. Overall, though, a manufacturer's marketing department is at least trying to get the specifications accurately described.

However, it's not a good idea at all to trust the marketing literature from a third-party wholesaler or distributer. The marketing literature shown on their websites is often obsolete, and it includes ideas of how they think the equipment could be usable. The claims, however, are not backed up by the real "Listed For Use" specifications.

Example: One distributer markets a common SNAC panel and says "These circuits may be activated [by] . . . existing Class A or Class B notification appliance circuits with operating voltages ranging from 12 to 32 VDC." The distributer is saying that this SNAC panel can be triggered by an existing circuit that is already loaded up with horns and strobes.

On the other hand, the manufacturer's official "Listed For Use" installation manual for the same panel does not show any notification devices on the circuit between the Fire Alarm Control Panel and the trip inputs on the SNAC panel. They also show the SNAC panel as the last device on the circuit.

For legal design work, if the wiring isn't shown on the installation sheets or manuals, calling the manufacturer's technical support team is a good start to find out if the equipment or devices can be used in a specific installation.

The technical support team has to be accurate. They are the ones that can tell you accurately if what you want to do is the legal "Listed For Use".


A different way of saying not-expedient is "Legal or not, if it doesn't work, it doesn't work".

Synchronization of the horns and the strobes is becoming very important. Old fashioned systems that are not synchronized have to become synchronized when they are updated. This is an issue when triggering a SNAC panel with a synchronized NAC circuit.

Notification Appliance Circuit (NAC) synchronization is a study onto itself. Any wiring layout that isn't specifically shown in the installation sheets and installation manuals requires great original-design care, great retrofit-design care, and great long-term-maintenance care. This includes triggering a SNAC panel with the output of another SNAC panel.

Synchronization, by itself, is a very specialized concept. But then again, most manufacturers use an upgraded form of synchronization. To turn on old fashioned horns and strobes, they base their NAC circuits on the conventional DC power signal. Then, to synchronize the newer audible and visible devices, they include very short pulses in the DC power signal.

Each manufacturer, though, uses a different set of synchronization signals. I don't have specific technical information on how any manufacturer does the signaling, and no manufacturer will tell you, either.

In the United States, some of the major systems are:
  • Faraday
  • Gentex
  • System Sensor
  • Wheelock
  • EST
  • Johnson Controls

If it's the output of the SNAC panel that is being used to trigger another SNAC panel, the first SNAC panel cannot already send out a synchronized power signal. If it does, the second panel might actually work, the second panel might not work reliably, or the second panel might not work at all.

The manual for the SNAC panel I'm looking at has a warning box that says,


For all synchronization options, input 1 is the strobe input and input 2 is the audible input. The signals to input 1 and input 2 must be DC signals for the synchronization patterns to work properly.

When they say "DC", they mean clean power, without synchronization signals. In other words, for triggering, they want a regular NAC power output from the FACP that is not synchronized. This is another "Listed For Use" issue.

Technically, what you're describing might possibly work, at least right now. If, however, the two SNAC panels are daisy-chained as you described, and there are any changes made to the synchronization later, all I can say is, good luck keeping the system working.

The fire marshal might also require different synchronization. Just making that change could be enough to stop the show. Be careful if you are daisy-chaining the SNAC panels.

Douglas Krantz
Life Safety
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