Arc-fault breaker: where the Code requires it

What it detects

If you read that an arc-fault breaker is only required in bedrooms, that was true before 2018. It isn’t anymore. Here is what the Québec Construction Code requires today, with the sections.

An electrical arc is current jumping through the air between two points, in the wiring or in an appliance. The arc-fault breaker is designed to recognize this kind of fault and cut the circuit.

The Code requires the combination type, which detects two kinds of arcs: series arcs and parallel arcs. The older type, which only saw parallel arcs, is no longer permitted in a new installation.

How it works

Not every arc is dangerous: opening a light switch or running a motor produces arcs normally. The arc-fault breaker constantly monitors the current and tells normal arcs apart from dangerous ones. According to a technical report by the U.S. Consumer Product Safety Commission, normal arcs repeat with every 60 Hz cycle, while dangerous arcs are irregular; the device looks at certain frequencies, discontinuities and irregularities in the current waveform.

A series arc happens when the current’s path is accidentally broken, in series with the appliance: a loose connection at an outlet or a splice, a wire worn from bending, a pinched cable. Its current is limited by the appliance plugged in: an ordinary breaker would never trip.

A parallel arc runs between two conductors of opposite polarity; it carries more energy and is generally considered more dangerous. The instantaneous trip of a 15 or 20 A residential breaker is usually set between 140 and 225 A, and ordinary fuses and breakers don’t respond to the first arcs and sparks.

The combination type protects against both kinds of arcs, over the whole branch circuit, including the cords of the appliances plugged in. According to the same report, an arc-fault breaker also usually has a 30 mA ground current sensor that picks up insulation breaking down before an arc. An arc-fault outlet, on the other hand, gives little protection to the wiring ahead of it, according to Ontario’s Electrical Safety Authority: that explains the protection required for the wiring between the breaker and that outlet.

Its limit: it reduces the effects of an arc without eliminating them, and the first arc can sometimes start a fire before the power is cut.

Where it’s required

In the 2026 Code, in force since March 26, 2026, the rule is Section 26-658. Work started before October 17, 2027 can still follow the 2018 Code, where the section has another number; the requirement to protect almost every outlet dates from the 2018 Code. In a dwelling, every branch circuit supplying 125 V outlets of 20 A or less must have combination-type arc-fault protection. The Corporation des maîtres électriciens du Québec (CMEQ) summed it up this way in 2019, at the time of the change:

“From now on, it will be everywhere there is a 120 V 15 A or 20 A outlet. Yes, you read that right, everywhere!” (translated from French)

CMEQ, Informel, January 2019

In practice, the CMEQ names, among others, the outlets in the living room and for the microwave, central vacuum, washer, dishwasher and attached garage. Outdoor outlets on the house become both GFCI and arc-fault protected. A lighting-only circuit isn’t covered.

Since when? The CMEQ says the 2018 Code is mandatory for work started after April 1, 2019. Before that, the requirement covered bedrooms.

The exceptions

In 2019, the CMEQ listed the outlets that don’t need arc-fault protection:

• kitchen counter outlets, including the island and the peninsula;
• bathroom outlets, if the branch circuit doesn’t supply other outlets;
• the refrigerator outlet;
• the single outlet for a sump pump.

Québec broadens this last exception: a single outlet for a sump pump, a sewage pump or an electro-medical device is exempt, if the outlet is permanently marked and the circuit supplies no other outlet. Outlets in a detached building (detached garage, shed) are also exempt, as are EV charging outlets.

Québec’s rules

Québec’s Code amends Section 26-658 on four points. Three are summarized here; the fourth, adding outlets to an existing circuit, is explained in the Renovations section.

“the number of outlets that may be installed on a branch circuit with arc-fault protection must not exceed 10” (translated from French)

Québec Construction Code, Chapter V (Electricity), Section 26-658 4)

Renovations

A point of caution raised by the City of Winnipeg: a hardwired smoke or carbon monoxide alarm shouldn’t be on a circuit that is being modified, unless it has a backup battery. Mention it to your electrician. For how a replacement goes, see replacing an electrical panel: how it works.

When it trips for no obvious reason

The manufacturer Siemens names the causes to check:

• a neutral shared between two circuits;
• a neutral badly connected, at the breaker or on the appliance side;
• a neutral in contact with ground somewhere along the circuit;
• an overload, or a short circuit in an appliance;
• an actual arc, in the wiring or inside an appliance.

According to the City of Winnipeg, older non-combination models can be prone to nuisance tripping. Before calling, press the TEST button: it should trip. Then have the circuit checked. Replacing an arc-fault breaker with an ordinary breaker isn’t a solution: it removes a protection the Code has required on outlet circuits since the 2018 Code. For the full steps, see our guide breaker keeps tripping.

Arc-fault, GFCI or both

The two protections don’t do the same job. A GFCI cuts the power on a current leak to ground, to protect people. An arc-fault breaker cuts the power on an arc, to prevent fire. There are dual-function breakers that do both: Siemens, the panel brand we install most often, makes them.

To know where a GFCI is required, see our guide GFCI: what it protects, and where you need one.

Frequently asked questions