Suite fault isolator

A suite fault isolator is the isolator type that keeps a fault inside one dwelling unit from silencing the audible devices serving the other suites, and it is installed outside the suite it protects. Whether you may use one instead of Class A wiring, or must use one, is a jurisdictional question rather than a design preference: Ontario Building Code Sentence 3.2.4.18.(9)(a) is written around a single open circuit and City of Markham reads it as allowing either method, while the Vancouver Building By-law version says open circuit or short circuit and Note 4 of City of Vancouver Bulletin 2022-002 states that Class A signal circuits shall not be used in lieu of suite fault isolators. Acceptance is proven by imposing a wire to wire short circuit inside each suite and demonstrating that the corridor devices are unaffected.

What it is and what it contains

Picture a residential building with a sounder inside every unit, all hanging off shared notification circuits running through the corridors. A tenant drives a picture hook through a wall, a renovation nicks a conductor, water gets into a device. On an unprotected circuit that one fault can silence every unit on the circuit, in a building whose whole purpose is waking people at 3 a.m.

A suite fault isolator stops the damage at the boundary of the suite it protects. It is one of the six isolator types recognised at Section 10.2 of the 2019 installation standard, and the only one placed per dwelling unit. The general behaviour is covered under isolator.

Why it is a jurisdictional question, not a preference

The building code states an outcome and leaves the method open. Three methods circulate, and only two of them are wiring classes: Class A wiring, Class B wiring with a suite fault isolator, and a separate signal circuit per suite.

Which of the first two your authority accepts turns on the wording of the sentence it enforces.

	Ontario Building Code, 2024	Vancouver Building By-law
Sentence	3.2.4.18.(9)	3.2.4.18.(8)
Fault named in clause (a)	a single open circuit	a single open circuit or short circuit
What the local AHJ accepts	Class A wiring, or Class B with isolators outside the suite	Class B with a suite fault isolator; Class A expressly not accepted in lieu

Bulletin 2022-002 works through both halves of the Vancouver phrase. Where damage produces an open circuit it accepts Class A. Where damage produces a short circuit it requires Class B plus an isolator. Note 4 then closes the door, stating that Class A signal circuits shall not be used in lieu of suite fault isolators for audible signal devices within dwelling units or suites of residential or care occupancy.

So in the City of Vancouver there is one in suite path, not two. In Ontario the choice survives, because the Ontario sentence never names the short circuit case. If you have read elsewhere that the Vancouver bulletin offers two options, read Note 4 yourself. The two documents side by side are in the two ways to wire residential audibility.

Outside the suite, and why

City of Markham's Builder Tip No. 57 states that signal circuit fault isolators shall be installed outside the suite protected. Mount one inside and it sits on the wrong side of the fault it exists to contain, inside the same volume where the tenant, the renovation and the water damage all happen. Mounting it inside is the convenient choice, next to the device and one less box in the corridor. It is also visible on inspection.

Worth knowing that even the Markham tip updated to the 2024 Ontario code still attributes the placement rule to CAN/ULC-S524-06, an edition two revisions back. The principle has not moved, but check the number against your adopted edition before it goes in a submission.

What it has to do, and how it is proven

The Vancouver bulletin describes the device as providing wire to wire short circuit protection for the wiring to an audible signal device inside a dwelling unit. It must also keep the suite isolated in both trouble and alarm, and return to operational once the short is cleared and the trouble reset. Ordering a device that will not pass an alarm arriving after a short is a real failure mode, and the bulletin says so.

Acceptance is a physical test, not a paperwork exercise. A wire to wire short circuit fault is imposed within each suite, in normal and in alarm conditions, and the corridor devices are demonstrated unaffected. Each suite, not a sample. That means access to every unit on verification day, which on an occupied retrofit is a scheduling problem people discover late. It also means your terminations get tested for real.

The longer field treatment, including documenting isolator locations for the next technician, is in the suite fault isolators guide.

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