DCL Style N

DCL Style N is a data communication link style that the 2019 edition of CAN/ULC-S524 introduced alongside Ethernet wiring for fire alarm systems. UL's own briefing to Canadian building officials lists "data communication link style N (DCLN) circuits and ethernet wiring" among the nine changes that edition made, and that single line is the whole of what is publicly attested. What Style N actually requires, including whether an Ethernet segment used this way must carry fire alarm traffic and nothing else, sits inside a paywalled standard we have not read, and we will not guess at it. It matters now rather than later because Ontario designates the 2019 edition in both codes.

Last updated: September 2026

What is actually on the record

One line, from the standards developer. In a May 2023 presentation to the Building Officials Association of British Columbia, UL listed nine updates in CAN/ULC-S524:2019. The fourth reads, in full: data communication link style N (DCLN) circuits and ethernet wiring. The presentation carries no specification, no diagram and no explanatory text beyond that item.

Two things follow from that wording, and only two.

Style N is a style of data communication link. It belongs to the same lettered series as Style A, which the University of Toronto's published fire alarm design standard names as a Data Communication Link Style A, or DCLA, as defined by CAN/ULC-S524. So the letters are real, they are the standard's own designations, and Canadian specifications already write to them.

UL pairs Style N with Ethernet wiring in one breath. That pairing is why the trade associates Style N with Ethernet carrying fire alarm traffic, and it is a reasonable reading of the line. It is still a reading of one line.

What we could not confirm

Said plainly rather than filled in:

The S524 definition of Style N, and how it differs from the other styles
Whether the standard requires an Ethernet segment used as a data communication link to be dedicated to fire alarm traffic and to carry nothing else. This is what the trade commonly says. We found no free Canadian source that states it, and we did not read the standard.
The supervision and fault tolerance requirements that attach to a Style N link
Permitted media, distance limits, and whether intervening network equipment such as a switch is allowed
Which Canadian listed control units are certified for it

None of that appears in any free Canadian document we could locate. If your work turns on it you need the standard itself, plus the listing and installation instructions for the panel actually going in.

Why the edition matters more than usual here

Style N arrived in the 2019 edition, and 2019 is the edition Ontario designates. Building Code Division B Table 1.3.1.2 designates S524:2019, and Fire Code Division B Table 1.2.1.A designates S524-2019. So this is not a future provision to file away. It sits in the edition your permit is assessed against and your repairs and alterations are judged against.

A newer edition has since been published, and we have not found a Canadian code that designates it. That distance between what is on sale and what is enforceable is the adoption gap, and it is tracked by standard and by province in the CAN/ULC edition tracker.

What to do on a job

If a specification calls for a Style N link, do not reconstruct the requirement from American networking practice or from a manufacturer's marketing sheet. Take the style requirement from S524, take the pathway and equipment from the panel manufacturer's listing, and get the authority having jurisdiction's position in writing before the pathway goes in.

One thing you can rely on without the standard: an Ethernet run installed as ordinary structured cabling, patched through a communications room or shared with the building network pathway, fails Section 32 of the electrical code regardless of what the data does. Fire alarm conductors must be kept entirely independent of all other wiring.

Neighbouring terms

The parent term is DCL. What else the 2019 edition changed, from fault isolators to wireless devices to carbon monoxide detection, is summarised in CAN/ULC-S524, and which edition binds you on a given job is a separate question again, covered in which edition of the standard actually applies.

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