Network Connections: Are Class N Pathways the Fire Alarms of the Future?

What will fire alarm systems of the future be like? Technology is changing rapidly, and historically, fire alarm systems have not kept up with these modifications. That is starting to change.

In the 2016 NFPA 72, National Fire Alarm and Signaling Code, a new class of pathways was added—Class N (for network). When a contractor wants to connect new equipment to a fire alarm system, the equipment must be allowed by NFPA 72 and, in most cases, be listed for fire alarm usage. Of course, none of this happens quickly. It took three code cycles back in the early 1980s to approve the use of digital alarm communicator transmitters. Now, that technology is obsolete and is being phased out of the codes. They are being replaced with newer technologies such as IP, mesh radio and cellular.

Similarly, Class N has taken a long time to make it into the code. Some view the introduction of Class N as a threat. Some feel this is a way for IT departments to take over fire alarm systems by connecting devices to the computer networks in buildings. As buildings become more automated and demand faster communications to identify and correct problems, fire alarm systems need to keep up or be left behind. If computer networks can be used for handling billions of dollars of commerce, they should be able to monitor fire alarm equipment.

I don’t claim to be an expert on Class N, but I served on the NFPA 72 Protected Premises Committee and the Correlating Committee during the time it was being debated. Like you, I don’t need to know everything about Class N, but I need to have the resources to get info when I need it.

I recommend reading the Annex of NFPA 72 and Dan Horon’s guide, “Class N: Networks for Fire Alarm and Mass Notification Systems.” Horon has been using computer technology to monitor fire alarm systems for about 30 years. He has served on several NFPA committees and was a key player in getting Class N into NFPA 72.

There is a lot of information in the Annex of NFPA 72 that helps explain Class N. It is worth reading if you plan to design or install ethernet fire alarm systems.

Here are some of the key items on Class N. First, instead of wiring multiple fire alarm devices in parallel on a pair of wires throughout the building as we currently do, each device is now an “endpoint” on its own circuit and will be identified with its own IP address. Ethernet cables are not affected by a single ground fault like typical fire alarm circuits since network connectors are galvanically isolated from the cables, meeting IEEE requirements. As a side note, you will see quite a few changes in testing and replacing fire alarm batteries in upcoming editions of NFPA 72 to also meet IEEE requirements.

All fire alarm circuits and pathways must be monitored for integrity. Class N pathways will be monitored similar to signaling line circuits using verification by end-to-end communications. In addition, anytime you have more than one device that could be impacted by a fault, you need redundant pathways. The pathways to single devices will not require the redundancy. NFPA 72 has many diagrams in Annex A to help make this clearer. Redundant pathways must be separately supervised.

You will also need to provide backup power for all network components, unlike a typical computer network. This will be 24 hours in most cases, although NFPA 72 allows 8 hours of backup power for shared pathways, provided that a risk analysis has been performed and it is permitted by the authority having jurisdiction.

Obviously, there are concerns about security. In 23.6.3.2 on Accessibility, it states “Class N pathways shall not be accessible to the general public for any purpose or building occupants for any purpose other than specified in the analysis, maintenance, and deployment plans.”

Chapter 23 also has requirements for a deployment plan, change control plan, management organization, analysis and maintenance plan. All are important for a successful networked fire alarm system.

As more manufacturers use ethernet circuits, you will need to get up to speed on the technology.

About the Author
Tom Hammerberg

Thomas P. Hammerberg

Life Safety Columnist

Thomas P. Hammerberg, SET, CFPS is president of Hammerberg & Associates Inc. Retired from the Automatic Fire Alarm Association (AFAA) after 23 years, he represents the AFAA on the NFPA 72 Technical Correlating Committee and Protected Premises...

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