Smoke alarms on AFCI/GFCI-protected circuits • Tatjana Dinic

Tatjana Dinic
May 26, 2017
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May 26, 2017 - Required by the National Building Code (NBC), smoke alarms must be permanently connected to a lighting circuit, or one that supplies both lighting and receptacles, so as to quickly detect when there’s a problem with the circuit.

Based on current requirements in Rule 32-110 (CE Code 2015), however, smoke alarms are not permitted to be supplied by a branch circuit protected by a ground/arc fault circuit interrupter (GFCI/AFCI) because, during a fire situation, the interrupter may trip and potentially disable the smoke alarm.

In the 24th Ed. of the CE Code (2018), Rule 32-110 will permit a smoke alarm(s)—or a smoke alarm that includes a carbon monoxide alarm—to be connected to a GFCI/AFCI-protected circuit provided it has a battery-powered secondary supply.

This approved code change follows a change in the 2012 NBC, Division B, Clause 9.10.19.4(1), which now requires smoke alarms to be hardwired and have an alternate power source that can power the device for 7 days and still provide 4 minutes of alarm.

Meantime, CAN/ULC-S531 “Standard for smoke alarms” (which includes smoke and combination-type smoke alarms) has also been updated (in 2014). The revised standard now mandates these devices to be connected to a secondary power supply (battery). This secondary supply must be able to power the alarm for no less than 7 days in the standby condition and, thereafter, be able to signal the alarm continuously for at least 4 minutes.

N.B. The permission that will be granted by Rule 32-110 in 2018 only applies to smoke and combo-type smoke alarms. Stand-alone carbon monoxide (CO) alarms are not required by NBC to be permanently connected but, when they are, they are not permitted to be connected to a GFCI/AFCI-protected circuit. Stand-alone CO alarms are certified to a different standard (CSA 6.19), and the optional (not mandatory) secondary power supply provides much less backup power than the one required for smoke alarms.

So, with all of these changes, smoke and combo-type smoke alarms connected to a lighting circuit protected by GFCI/AFCI will continue to operate and alert occupants, even in the event of a trip.
Thankfully, a change in the upcoming CE Code 24th Ed. eliminates this stumbling block that prevents lighting circuits to be included in the group of AFCI-protected circuits, which is the ultimate safety goal in residential installations.

* This article also appears in the May 2017 edition of Electrical Business Magazine. Check out our ARCHIVE page for back issues.


Tatjana Dinic is the acting director for Engineering & Program Development at Electrical Safety Authority (ESA) where, among other things, she is responsible for product safety, code development, improving harmonization and alternative compliance, and aging infrastructure programs. She is Professional Engineer with an M.Eng. from the University of Toronto, and a member of CE Code-Part I, Sections 4, 10 and 30. She can be reached at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

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