{"id":2171,"date":"2026-04-29T08:42:13","date_gmt":"2026-04-29T12:42:13","guid":{"rendered":"https:\/\/groupecsx.ca\/?p=2171"},"modified":"2026-05-05T08:45:04","modified_gmt":"2026-05-05T12:45:04","slug":"circuit-classes-between-fire-alarm-and-ground-notification","status":"publish","type":"post","link":"https:\/\/groupecsx.ca\/en\/classes-de-circuits-entre-alarme-incendie-et-notification-de-masse\/","title":{"rendered":"Circuit classes between fire alarm and ground notification"},"content":{"rendered":"<p class=\"wp-block-paragraph\"><a href=\"https:\/\/www.linkedin.com\/company\/groupe-csx-inc\/\"><\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember50\">On an integrated project combining a fire alarm system and a mass notification system (MNS), the drafting of a technical specification may have to simultaneously articulate three frames of reference: <strong>NFPA 72<\/strong>, <strong>CAN\/ULC 524<\/strong> and <strong>CAN\/ULC 576<\/strong>. Three standards of different origins and generations, with circuit classifications that resemble each other on the surface, but do not overlap. The same \u00abClass\u00bb label can designate significantly different architectures, depending on the reference system implicitly invoked. This discrepancy is not theoretical: it becomes tangible during commissioning, when differences of interpretation between designer, integrator and authority having jurisdiction become material.<\/p>\n\n\n\n<h5 class=\"wp-block-heading\" id=\"ember51\">A nomenclature specific to the United States<\/h5>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember52\">The \u00abClass A, B, C, D, E, N, X\u00bb classification system now used in U.S. technical specifications was originally developed by NFPA. Prior to the 2010 edition, NFPA 72 used a hybrid system combining Class A\/B and <em>Styles<\/em> numbered (4, 5, 6, 7, B, C, D, E...) which had been stratified edition after edition to describe the behavior of different circuit types (IDC, NAC and SLC) under different fault conditions. The system had become cumbersome and ill-suited to modern topologies: fiber, Ethernet, wireless.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember53\">The NFPA 72-2010 edition has undergone a structural overhaul. The <em>Styles<\/em> have been deleted and a new chapter 12, \u00ab <em>Circuits and Pathways<\/em> \u00bbwas created. The logic shifted from a wiring description to a performance description: the class no longer says how a circuit is made, but how it behaves in the face of a single fault: open, short-circuit, ground. Class N followed in 2016 to, among other things, formalize redundant Ethernet architectures.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember54\">It's this performancerelated vocabulary that has taken hold in North American technical culture, to the point of becoming shorthand for professional conversation.<\/p>\n\n\n\n<h5 class=\"wp-block-heading\" id=\"ember55\">On the Canadian side, several standards, two nomenclatures<\/h5>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember56\">CAN\/ULC 524, in its 8\u1d49 edition, governs the installation of fire alarm systems in Canada. It also uses, albeit partially, the NFPA class concept, but with a simplification: Class A and Class B for conventional circuits (IDC, NAC), and its own nomenclature (DCLA, DCLB, DCLC, DCLN) for data communication links (<em>Data Communication Link<\/em>). No \u00abClass\u00bb C, D, E or X as presented by NFPA in CAN\/ULC 524.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember57\">CAN\/ULC 576, which covers mass notification equipment, uses another, albeit similar, nomenclature in its 2\u1d49 edition: Class A, Class B, Class C and Class N applied to four types of pathway (<em>pathways<\/em>) distinct : <em>input circuits, signaling circuits, DCL for devices, DCL for networks.<\/em> Four thirds of paths, each to be designated by a class.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember58\">A fourth standard, CAN\/ULC 573 (1\u02b3\u1d49 edition), governs the installation of auxiliary devices connected to the fire alarm system, which explicitly includes the MNS. However, it does not introduce its own class nomenclature: it relies on that of CAN\/ULC 524 for the circuits it governs. Relevant to the drafting of MNS specifications in Quebec, it does not complicate the class table discussed here.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember59\">On an integrated fire alarm and mass notification project in Quebec, the designer is therefore working simultaneously with different reading grids in terms of classes: NFPA 72 Chapter 12 invoked as a de facto reference for the performance of a MNS system via its Chapter 24, CAN\/ULC 524 for the host fire alarm system, CAN\/ULC 576 for the MNS equipment, as well as CAN\/ULC 573 to govern the installation of the latter. The various grids are compatible, but not identical.<\/p>\n\n\n\n<h5 class=\"wp-block-heading\" id=\"ember60\">The \u00abC-Class\u00bb trap\u00bb<\/h5>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember61\">This is probably one of the most misunderstood aspects of the current standards landscape. The notion of Class C does not have the same meaning depending on the applicable standard.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember62\">In <strong>NFPA 72, Chapter 12<\/strong>, Class C corresponds to a path whose operational capability is verified by end-to-end communication, without supervision of the individual integrity of each path.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember63\">In <strong>CAN\/ULC 524<\/strong>, the appropriate term is not \u00abC-Class\u00bb, but <strong>Data Communication Link Style C<\/strong> (DCLC). This is a style of data communication link specific to fire alarm systems, aimed at fault tolerance performance and limiting the effect of a fault to the affected fire alarm zone. Depending on the architecture, this requirement is usually met by fault isolators, or an equivalent method. Functionally, DCLC is more akin to the spirit of NFPA 72 Class X than to its Class C, without constituting a direct normative equivalence.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember64\">In <strong>CAN\/ULC 576<\/strong>, A Class C designates a path comprising a primary path and an alternative path, with operational capability maintained beyond a single open and a single short-circuit, accompanied by the announcement of applicable trouble conditions within prescribed time limits, including 200 s for restoration of operational capability after a fault. This requirement is functionally much more robust than NFPA 72 Class C, and is closer in technical intent to redundant path logic with isolation or short-circuit tolerance.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember65\">The implications are concrete. CAN\/ULC 576 Class C requires an alternative path and maintenance of operational capability beyond a single short circuit, while NFPA 72 Class C can be satisfied by end-to-end communication of the type without local physical redundancy of the cabling.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember66\">Simply specifying \u00abClass C\u00bb in a technical specification, without specifying the reference standard and applicable edition, therefore opens up a significant area of interpretation. The same wording can lead to significantly different architectures depending on whether it is read through NFPA 72, CAN\/ULC 524 or CAN\/ULC 576. Compliance may then depend not on the clarity of the contractual document, but on the interpretation of the designer, integrator, auditor or authority having jurisdiction.<\/p>\n\n\n\n<h5 class=\"wp-block-heading\" id=\"ember67\">Class N and fiber optics: a subject in its own right<\/h5>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember68\">Class N, added to NFPA 72 in 2016, deals specifically with Ethernet network architectures: physical redundancy of primary and secondary paths, verification by end-to-end communication, explicit prohibition of sharing traffic on the same physical segment.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember69\">The massive arrival of fiber optics in modern MNS architectures poses a parallel question: how do you classify a fiber path in a classification system designed around copper faults (open, short, ground)? Standards have begun to answer this question.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember70\">For example, CAN\/ULC 524 explicitly includes fiber conductors in its circuit definition. Several table notes, however, exclude copper faults from fiber and wireless paths. The relationship between Class N, fiber and wireless, however, deserves detailed treatment.<\/p>\n\n\n\n<h5 class=\"wp-block-heading\" id=\"ember71\">Three principles for the design phase<\/h5>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember72\">Three practices emerge from this mapping for the drafting of a robust technical specification.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember73\"><strong>Explicitly declare the reference standard for each subsystem.<\/strong> On an integrated project, CAN\/ULC 524 governs the circuits of the fire alarm system and CAN\/ULC 576 governs those of the MNS. An introductory clause should make this clear. Without such a statement, \u00abClass C\u00bb remains ambiguous between different possible normative definitions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember74\"><strong>Map critical paths before specifying the class.<\/strong> Specifying \u00abClass A\u00bb by default for all paths is rarely justified and always costly. Class is an architectural decision based on an analysis of the consequences of a fault on each segment of the system, not a default option.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember75\"><strong>Distinguish <\/strong><strong><em>DCL for devices<\/em><\/strong><strong> and <\/strong><strong><em>DCL for networks<\/em><\/strong><strong>.<\/strong> This granularity, specific to CAN\/ULC 576, reflects the reality of multi-building distributed MNS. A technical specification that doesn't make this distinction leaves it up to the bidder to resolve it as he sees fit.<\/p>\n\n\n\n<h5 class=\"wp-block-heading\" id=\"ember76\">In conclusion<\/h5>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember77\">Like intelligibility and interoperability, circuit class is an attribute that is conceived upstream and verified downstream, never the other way around. When it's discovered at provisional acceptance of work that what was written \u00abClass C\u00bb doesn't mean the same thing to everyone around the table, the cost of late clarification invariably exceeds the cost of initial precision.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember78\"><strong>CSX Group Inc. <\/strong>| By Jonathan Henri, Senior Director - Design and Compliance<\/p>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember79\"><strong>Any further questions?<\/strong> Please do not hesitate to contact the author. <a href=\"mailto:jonathan.henri@groupecsx.ca\"><strong>jonathan.henri@groupecsx.ca<\/strong><\/a><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember81\"><strong>Linguistic advice : <\/strong>In this article, the use of pronouns in the masculine or feminine, singular or plural, does not imply any bias or exclusion based on gender. The linguistic choice is intended solely to enhance the readability and fluidity of the text.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p class=\"wp-block-paragraph\" id=\"ember82\"><strong>References<\/strong>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>CAN\/ULC-524<\/strong>, <em>Standard for Installation of Fire Alarm Systems<\/em>. Underwriters Laboratories of Canada, Toronto.<\/li>\n\n\n\n<li><strong>CAN\/ULC-573<\/strong>, <em>Standard for the Installation of Ancillary Devices Connected to Fire Alarm Systems<\/em>. Underwriters Laboratories of Canada, Toronto.<\/li>\n\n\n\n<li><strong>CAN\/ULC-576<\/strong>, <em>Standard for Mass Notification System Equipment and Accessories<\/em>. Underwriters Laboratories of Canada, Toronto.<\/li>\n<\/ul>","protected":false},"excerpt":{"rendered":"<p>Sur un projet int\u00e9gr\u00e9 alliant syst\u00e8me d&rsquo;alarme incendie et syst\u00e8me de notification de masse (MNS), la r\u00e9daction d&rsquo;un devis technique peut devoir articuler simultan\u00e9ment trois r\u00e9f\u00e9rentiels : NFPA 72, CAN\/ULC 524 et CAN\/ULC 576. Trois normes d\u2019origine et de g\u00e9n\u00e9rations diff\u00e9rentes, avec des classifications de circuits qui se ressemblent en surface mais qui ne se [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":2172,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10],"tags":[],"class_list":["post-2171","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-actualites"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Classes de circuits entre alarme incendie et notification de masse - Groupe CSX inc.<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/groupecsx.ca\/en\/circuit-classes-between-fire-alarm-and-ground-notification\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Classes de circuits entre alarme incendie et notification de masse - Groupe CSX inc.\" \/>\n<meta property=\"og:description\" content=\"Sur un projet int\u00e9gr\u00e9 alliant syst\u00e8me d&rsquo;alarme incendie et syst\u00e8me de notification de masse (MNS), la r\u00e9daction d&rsquo;un devis technique peut devoir articuler simultan\u00e9ment trois r\u00e9f\u00e9rentiels : NFPA 72, CAN\/ULC 524 et CAN\/ULC 576. 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