Suite Fault Isolators: What They Are and Where They Actually Go

Last updated: September 2026

Quick answer

• The problem they solve: a fault inside one apartment silencing the alarm in the apartments next door
• The two arrangements in circulation: Class A wiring, or Class B wiring with suite fault isolators. A third route, a separate signal circuit per suite, sits in the same code clause
• Whether Class A is open to you is jurisdictional. City of Markham treats Class A as acceptable under the Ontario Building Code. City of Vancouver Bulletin 2022-002 does not: Note 4 of that bulletin bars it
• Where the isolator goes: outside the suite it protects
• What the isolator must do: provide wire to wire short circuit protection, and keep the suite isolated in both trouble and alarm conditions
• How it is proven: impose a wire to wire short inside each suite and demonstrate corridor devices are unaffected
• One notable exception: hotel and motel sleeping rooms without kitchens, per the Vancouver bulletin

Correction, September 2026. An earlier version of this page said the Vancouver bulletin offers two compliant options for in suite audible devices. It does not. Note 4 of Bulletin 2022-002 rules Class A out in that city. The two path framing is an Ontario position, not a Vancouver one, and the section below explains why the two documents differ.

Why this requirement exists

Think about what a residential building actually looks like electrically. Dozens of dwelling units, each with an audible device inside it, all hanging off shared circuits running through the corridors.

Now put a fault in one of them. A tenant drives a picture hook through a wall. A renovation nicks a conductor. Water gets into a device.

On an unprotected circuit, that single fault can take out notification for every unit on the circuit, including units whose occupants have no idea anything is wrong, in a building where the whole point of the system is waking people up at 3 a.m.

Suite fault isolators contain the damage. A fault inside suite 402 stops at the boundary of suite 402.

Class A or isolators: a jurisdictional question, not a design preference

The building code states the outcome it wants and leaves the method open. Three methods are in circulation, and only two of them are wiring classes:

1. Class A wiring on the circuit serving the in suite devices
2. Class B wiring with a suite fault isolator at each suite
3. A separate signal circuit for each suite, which sidesteps the question entirely but consumes panel circuits

Which of the first two your authority will accept depends on the wording of the sentence it enforces, and the wording is not the same everywhere.

Ontario. Clause 3.2.4.18.(9)(a) of the 2024 Building Code is written around a single open circuit at one device. City of Markham Builder Tip No. 57 reads that clause as permitting Class A wiring, or Class B wiring with signal circuit isolators, and reads clause (b), a separate circuit per suite, as the third route. (City of Markham Builder Tip No. 57)

City of Vancouver. The equivalent Vancouver Building By-law clause, 3.2.4.18.(8)(a), says open circuit or short circuit. Bulletin 2022-002 works through both halves of that phrase. Where damage produces an open circuit, it accepts Class A wiring. Where damage produces a short circuit, it requires Class B wiring and installation of a suite fault isolator. Then Note 4 closes the door:

Class A signal circuits shall not be used in lieu of suite fault isolators for the audible signal devices within dwelling units or suites of residential or care occupancy.

(City of Vancouver Bulletin 2022-002)

So in the City of Vancouver there is one in suite path, and it is Class B plus an isolator. In Ontario the choice survives, because the Ontario sentence never names the short circuit case.

Two things follow from that. A Vancouver bulletin does not settle the national position, and neither does a Markham builder tip. Both are municipal AHJ documents interpreting different building codes. And Vancouver is not a stand in for British Columbia: the city has its own by-law under the Vancouver Charter, so a job in Surrey or Kelowna works from the provincial code instead. See the British Columbia guide.

The longer treatment of the wording difference, with both sentences side by side, is in the two ways to wire residential audibility.

The placement rule people get wrong

Markham's builder tip is the most useful Canadian document on this, because it addresses the two things a bulletin usually skips: where the hardware goes, and how the inspector will test it.

Isolators shall be installed outside the suite they protect.

Worth noting that even the tip updated to the 2024 Ontario code still attributes that rule to CAN/ULC-S524-06, an edition two revisions back. The placement principle has not moved, but if you are quoting a clause number in a submission, check it against the edition your code actually adopts. That problem is the subject of which edition of the standard applies.

Why outside? The isolator's job is to protect the rest of the circuit from a fault inside the suite. If you mount the isolator inside the suite, it sits on the wrong side of the very fault it exists to contain, and it is now itself inside the volume where the damage happens. Water, renovation, tenant activity: whatever gets the wiring gets the isolator.

Mounting it inside is the convenient choice. It is next to the device, easy to terminate, one less j-box in the corridor. It is also wrong, and it is visible on inspection.

What the isolator has to do

The Vancouver bulletin describes the device as one used for wire to wire short circuit protection for the wiring to an audible signal device located within a dwelling unit. That is the basis on which every device behind it is treated as compliant.

It also has to keep working once the circuit is already in trouble, which is the detail nobody thinks about at ordering time. The bulletin requires that a suite containing a short circuit be isolated from the rest of the wiring in each possible mode, trouble and alarm, and that once the trouble signal is reset and the short is cleared the isolator returns to being operational. Short first, initiating device afterwards: the signal still has to sound.

The hotel and motel exception. Note 2 of the Vancouver bulletin says it is not intended by the requirement to provide a suite fault isolator for audible signal devices located within a sleeping room of a hotel or motel suite that does not have a kitchen. The kitchen is the hinge: a unit with one is somewhere people live, cook and renovate. Treat that as one jurisdiction's bulletin rather than a national exemption and confirm it locally.

How acceptance actually works

Here is the part worth reading twice, because it changes how you install.

For the common floor circuit option, Markham requires:

A wire to wire short circuit fault shall be imposed within each suite

and the corridor devices must be demonstrated to be unaffected.

Within each suite. Not a sample. Not one per floor. Each one.

Two practical consequences:

Access matters. If you cannot get into every unit on verification day, you cannot complete the test. On an occupied retrofit that is a scheduling problem, and it is one that gets discovered late.

Your terminations get tested for real. A short is imposed deliberately, at the device, and the system has to behave. Marginal work shows up here.

Where isolators fit in the bigger picture

The 2019 edition of S524 recognises six isolator types under Section 10.2:

1. Field device data
2. Network data
3. Audio buss
4. Field device power buss
5. Equipment power buss
6. Suite

(BOABC / UL, May 2023, a presentation authored by UL and delivered to BC building officials)

Suite fault isolators are one member of a family. The underlying principle is the same across all six, and it is the fault tolerance rule that shapes the whole 2019 edition:

Where any type of fire alarm circuit serves more than one National Building Code of Canada required fire alarm zone, a single fault, open circuit, short circuit or ground fault, shall not prevent the normal operation of input or output field devices in more than one zone.

Note what changed there. The previous edition defined the boundary with a 2,000 m² area figure. The 2019 edition replaced that with a reference to NBC required zones, so the question is no longer how big is this area but is this a zone the building code requires.

Isolators are simply how you satisfy that rule when a single circuit has to cross zone boundaries.

On the section number: suite fault isolators are commonly associated with Section 49 of the 2019 edition. That attribution comes from a Canadian training provider rather than from a primary source we could read. Section 10.2 and the six isolator types are confirmed from UL's own material. If you are citing a section number in a compliance document, check it against your own copy of the standard.

Testing them, after the building is occupied

Suite fault isolators do not stop mattering once verification is signed off. They become part of the ongoing inspection and testing regime under CAN/ULC-S536.

A Canadian trade source reports that Ontario's 2026 Fire Code changes bring a specific isolator testing protocol:

• Document the location and identification of each isolator
• Map isolator and device interaction across fire separations
• Verify isolated zones operate independently
• Confirm automatic resumption after the fault is cleared and the panel reset
• Record loop performance and control panel response under simulated fault
• Test each isolator individually by temporary fault simulation

(FSS Canada)

That is a single trade source rather than a primary one, so treat the specifics as reported. But the direction is consistent with everything else in the 2019 standards, and the first bullet has an implication worth acting on now:

If you install isolators, document where you put them. A technician arriving in five years to do an annual has to find every one of them. An undocumented isolator buried above a corridor ceiling is a problem you created for someone else, quite possibly for yourself.

What to actually do on site

• Ask the AHJ which method they accept before you buy cable. Do not assume Class A is available: in the City of Vancouver it is expressly not
• Check whether the units are excepted, meaning hotel or motel without kitchens, and confirm that locally
• Install every isolator outside the suite it protects
• Confirm the isolator provides wire to wire short circuit protection
• Confirm the suite stays isolated in both trouble and alarm, and that the isolator recovers once the fault is cleared and the trouble reset
• Record the location and ID of every isolator in the as builts
• Plan verification access to every suite, because you will be imposing a short in each one
• Demonstrate corridor devices are unaffected during each test

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