NFPA 72 code sections · Advanced Topics: Addressable, Wireless & IoT
Class N: Ethernet pathways with a dedicated path per device
Class N recognises network (Ethernet-style) pathways in fire alarm systems. Each device or group of devices connects by its own pathway to a switch, so a single open or short affects only that one branch; redundant pathways are required between switches and the control unit where a loss of the pathway would affect more than one device; the whole pathway is monitored for integrity with the trouble requirements of Chapter 12; and the pathway class is documented along with its survivability and shared-pathway level. Class N is not 'the building's LAN' — it is a fire alarm circuit that happens to use Ethernet.
NFPA 72 reference
Chapter 12 — Circuits and Pathways
12.3.5 Class N (12.3.5.1 individual pathways to each device/endpoint, 12.3.5.2 redundant pathways between switches/control unit where required; 12.6 monitoring integrity; 12.5 shared pathway levels)
References use NFPA 72 2019/2022 numbering — section numbers can shift between editions, so confirm in the edition your AHJ has adopted.
On the job
A tech campus runs addressable speaker-strobes on Class N. A contractor unplugs a patch cable to one lecture hall; that hall's appliances show trouble and every other room keeps working — the Class N promise. Six months later IT proposes merging the fire alarm switches into the campus core; the designer points to the documented shared-pathway Level 3 and the proposal dies.
Quick check
1. On a Class N pathway, a single open affects:
2. Class N pathways are:
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