We’ve all been there: you plug in the kettle while the toaster is going and the breaker trips, then you become frustrated that the breaker can’t accommodate all your appliances.
The catch is that the breaker isn’t there to protect your toaster – it’s there to protect the wiring inside your walls from carrying more current than it was designed for.
Running a lot of power through a thin strand of metal is exactly how electric heaters work, and it goes without saying that you don’t want to turn your house or business’ wiring into a heating element. Hot wire inside a wall cavity is how electrical fires start, and circuit breakers are there so that they can trip before that happens. That’s why swapping in a bigger breaker to stop the tripping is such a bad idea – there is no longer anything to prevent your wiring from overheating.
The 80% rule
The Canadian Electrical Code limits how much of a circuit’s capacity you can plan on using. Under Rule 8-104, the continuous calculated load on a circuit can’t exceed 80% of the rating of the breaker protecting it. Continuous means a load that runs for an hour or longer at a stretch, so a four minute toaster cycle technically falls outside that definition, but 80% is still the number you want to design around. It leaves headroom for everything else that’s sharing the circuit. For example, this means that a 15 amp breaker gives you 12 usable amps and a 20 amp breaker gives you 16.
Appliances are almost always labelled in watts, so you need one formula to connect the two:
Watts = Volts x Amps
Standard household outlets in Canada run at 120 volts, so to get the number of watts you simply multiply the amperage by 120:
| Circuit | Breaker | Usable amps (80%) | Usable watts |
|---|---|---|---|
| Standard | 15 A | 12 A | 1,440 W |
| Kitchen counter / heavy duty | 20 A | 16 A | 1,920 W |
The 20 amp circuits typically show up on kitchen counters, where the code requires either split receptacles or 20 amp T-slot outlets. If you look at your counter outlets and see one slot turned sideways into a T shape, that’s a 20 amp circuit. Kitchens built or renovated in the past couple of decades often use these instead of the older split-receptacle arrangement.
Determining an appliance’s wattage
Flip the appliance over, or look on the back or the bottom. There’s a nameplate or a sticker with the electrical ratings on it. You’ll see one of three things:
- Watts: Easy – use it directly.
- Amps: Multiply by 120 to get watts. A 12.5 A appliance draws 1,500 W.
- Both: Use the watts.
Here’s what’s typical around the house. Check your own labels, since these vary quite a bit by model:
| Appliance | Typical draw |
|---|---|
| Portable space heater | 1,500 W |
| Hair dryer | 1,200 to 1,875 W |
| Electric kettle | 1,200 to 1,500 W |
| Toaster | 800 to 1,500 W |
| Microwave | 1,000 to 1,700 W |
| Coffee maker | 900 to 1,500 W |
| Vacuum cleaner | 1,000 to 1,400 W |
| Window air conditioner | 500 to 1,500 W |
| Fridge (running) | 100 to 800 W |
| Laptop charger | 45 to 100 W |
| LED bulb | 8 to 15 W |
Look at that list against a 1,440 W budget and the tripping breakers start to make sense. A kettle and a toaster together will exceed a 15 amp circuit on their own. Two space heaters on the same circuit is not going to work, no matter which outlets you use.
Signs a circuit is overloaded
- Breakers that trip regularly, especially at predictable times
- Lights that dim when an appliance kicks on
- Outlets, plugs, or cover plates that feel warm
- A buzzing sound from the outlet or the panel
- Extension cords or power bars feeding high-wattage appliances
Remember that circuits serve more than one outlet
A single 15 amp circuit in an older home might feed every outlet and light in two bedrooms and a hallway. When you add up your load, you’re adding up everything on that circuit, not just the appliance in front of you.
If you want to know what’s connected to what, flip one breaker off and walk around with a lamp or a phone charger testing outlets. It’s tedious, but a labelled panel is genuinely useful information to have. It also tells you which outlets in a room are on separate circuits, which matters if you’re trying to split a load.
Also keep in mind that anything with a motor or a compressor draws considerably more current for the first second or two when it starts. A fridge that runs at 500 W might briefly pull three or four times that on start-up. That’s part of why you want headroom rather than running right at the limit. It’s also why standby generators need more power than the regular draw of your appliances (LINK TO OTHER POST).
What not to do
Do not put a larger breaker in to stop the tripping. Standard 15 amp circuits are wired with 14 gauge copper, and 20 amp circuits with 12 gauge. Putting a 20 amp breaker on 14 gauge wire lets that wire carry more current than it can safely handle, and the safety device that would have caught the problem (the breaker) now enables the problem. If you’re consistently over budget on a circuit, the answer is a new circuit, not a workaround. That’s often the right call for:
- A home office with a heater, monitors, and equipment on one bedroom circuit
- A basement or garage workshop
- A hot tub, EV charger, or heat pump, all of which need dedicated 240 V circuits
- A kitchen renovation, where counter circuits, dishwashers, and microwaves each have their own requirements
- Any older home where the whole main floor seems to be on one or two breakers
Whether your panel has capacity for more circuits is a separate question that needs answering before you plan a renovation around it.
Adding circuits is also permit work in New Brunswick. Licenced contractors are required to pull a wiring permit from Technical Inspection Services for electrical construction involving more than ten outlets or five kilowatts of load, and the permit has to be in place before the work starts.
If you’re tired of resetting the same breaker over and over, give us a call. We can trace out what’s on the circuit, tell you what your panel can support, and add a dedicated circuit where it makes sense.
