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Updated June 2026What is a circuit breaker?
A circuit breaker is an automatic safety switch that disconnects a circuit when the current exceeds a safe level. Unlike a fuse, a breaker can be reset after it trips. Every circuit in a Canadian home must be protected by a breaker (or fuse in older installations) sized to match the wire gauge — not the appliance.
This last point is critical: the breaker protects the wire, not the load. An oversized breaker allows the wire to overheat before tripping. A 20A breaker on 14 AWG wire is a code violation for this exact reason — 14 AWG is only rated to 15A, so a 20A breaker will allow dangerous overcurrent before acting.
Breakers come in standard sizes: 15, 20, 25, 30, 35, 40, 50, 60, 70, 100, 125, 150, 175, 200A. When a calculation produces a non-standard number, always round up to the next available size.
CEC Rule 14-104 — the 125% rule
CEC Rule 14-104 governs overcurrent protection sizing. The core formula depends on whether a load is continuous or non-continuous:
- Non-continuous load (runs less than 3 hours): breaker size ≥ load current
- Continuous load (runs 3+ hours): breaker size ≥ load current × 1.25
Most household appliances are non-continuous — they cycle on and off. Lighting circuits, EV chargers charging overnight, and commercial refrigeration are examples of continuous loads. When in doubt, apply the 125% rule — it is conservative and always compliant.
For mixed loads, add 125% of all continuous loads to 100% of all non-continuous loads, then select the next standard breaker size up.
Single pole vs. double pole breakers
Single pole breakers protect 120V circuits and occupy one slot in the panel. They interrupt one hot conductor. Typical applications: lighting, outlets, small appliances, dishwashers, microwaves.
Double pole breakers protect 240V circuits, occupy two adjacent slots, and interrupt both hot conductors simultaneously. This ensures that when the breaker trips, the full 240V circuit is de-energized — critical for safety. Typical applications: electric dryers, ranges, water heaters, EV chargers, air conditioners, subpanels.
A tandem (slim) breaker fits two 120V circuits into one slot — useful when a panel is full. Not all panels accept tandems, and there are restrictions on where they can be installed. Check your panel's labelling or consult a licensed electrician.
Worked examples
Example 1 — Level 2 EV charger (Ontario): 32A continuous load, 240V.
- Continuous load: 32A × 1.25 = 40A
- Next standard breaker: 40A ✓ (40A is a standard size)
- Required wire: 8 AWG copper (45A ampacity)
- Result: 40A double-pole breaker, 8 AWG copper
Example 2 — Electric range (BC): 50A nameplate rating, 240V, non-continuous.
- Non-continuous load: breaker ≥ 50A
- Next standard breaker: 50A ✓
- Required wire: 6 AWG copper (65A ampacity — wire must exceed breaker size)
- Result: 50A double-pole breaker, 6 AWG copper
Example 3 — Workshop subpanel (Alberta): 60A subpanel feed, 240V.
- Feeder breaker: 60A double-pole at main panel
- Required feeder wire: 4 AWG copper or 2 AWG aluminum
- Result: 60A double-pole breaker, 4 AWG copper feeder
Common appliance breaker sizes in Canada
| Appliance | Breaker Size | Type | Wire Size |
|---|---|---|---|
| Electric dryer | 30A | Double pole 240V | 10 AWG copper |
| Electric range | 50A | Double pole 240V | 6 AWG copper |
| EV charger (32A) | 40A | Double pole 240V | 8 AWG copper |
| EV charger (48A) | 60A | Double pole 240V | 6 AWG copper |
| Hot tub | 50A GFCI | Double pole 240V | 6 AWG copper |
| Electric water heater | 30A | Double pole 240V | 10 AWG copper |
| Central air conditioner | 40–60A | Double pole 240V | 8–6 AWG copper |
| Dishwasher | 20A | Single pole 120V | 12 AWG copper |
| Microwave (dedicated) | 20A | Single pole 120V | 12 AWG copper |
| Bathroom outlets | 20A GFCI | Single pole 120V | 12 AWG copper |
Frequently asked questions
What size breaker do I need for a dryer in Canada?
A standard electric dryer requires a 30-amp double-pole breaker on a dedicated 240V circuit, wired with 10 AWG copper. Modern dryers use a 4-prong plug (NEMA 14-30) — two hots, a neutral, and a ground. Gas dryers only need a 15A single-pole circuit for the igniter and controls.
What size breaker for a Level 2 EV charger in Canada?
A Level 2 EV charger running at 32A requires a 40A double-pole breaker (125% of 32A = 40A). A 48A charger needs a 60A breaker. The circuit must be dedicated with no other loads. Wire with 8 AWG copper for 40A, or 6 AWG for 60A.
Do I need a GFCI breaker for a hot tub in Canada?
Yes. The CEC requires GFCI protection for all hot tub and pool circuits. A 50A or 60A double-pole GFCI breaker is standard. The disconnect must be within sight of the hot tub but at least 3 metres away and not within 1.5 metres of the water's edge.
What is the difference between single pole and double pole breakers?
Single pole breakers control 120V circuits and occupy one slot in the panel. Double pole breakers control 240V circuits, take two adjacent slots, and interrupt both legs simultaneously. Large appliances like ranges, dryers, and EV chargers all require double pole breakers.
Can I put a 30-amp breaker on 12 AWG wire?
No. 12 AWG copper wire is rated for 20A maximum per CEC Table 2. A 30A breaker on 12 AWG wire is a serious fire hazard — the breaker won't trip until the wire is already dangerously overloaded. The breaker must be sized to protect the wire, not just the load.
What size breaker for an electric range in Canada?
Electric ranges require a 50A double-pole breaker on a 240V dedicated circuit, wired with 6 AWG copper. The range must be on its own circuit — no dishwashers or other loads sharing it. Use a 4-prong NEMA 14-50 outlet for newer installations.
What is the 125% rule for continuous loads?
Under CEC Rule 14-104, any load that runs continuously for 3 hours or more must be treated as a continuous load. The breaker must be sized at 125% of the continuous load. For example, a 20A continuous load requires a 25A breaker (20 × 1.25 = 25A) — rounded up to the next standard size of 30A.
How many circuits can I add to a 200A panel?
A 200A panel typically has 40–42 spaces. Whether you can add circuits depends on your calculated load, not just empty slots. Use the Electrical Load Calculator to check your existing demand against your 200A service capacity before adding large loads like EV chargers or electric heat.
Code reference
This calculator is based on CEC Rule 14-104 (overcurrent protection sizing), Rule 14-102 (continuous loads), and Rule 26-700 (GFCI requirements). Standard breaker sizes follow CSA C22.2 No. 5. Always verify with a licensed electrician and your local Authority Having Jurisdiction (AHJ).