What gauge wire do I need for a 20 amp circuit?

For a 20-amp circuit in Ontario, you need 12 AWG copper wire minimum. This is required by the Ontario Electrical Safety Code (OESC) and is non-negotiable for safety and code compliance.

The wire gauge must match the circuit breaker amperage to prevent overheating and fire hazards. 12 AWG copper wire is rated for 20 amps maximum, while the smaller 14 AWG wire is only rated for 15 amps. Using undersized wire on a 20-amp breaker would create a dangerous situation where the wire could overheat before the breaker trips.

For most residential 20-amp circuits, you'll use 12-2 Romex cable (12 AWG with hot, neutral, and ground wires). If you're running a circuit that requires a neutral and ground to be separate at the panel, you might need 12-3 cable for specific applications like split receptacle circuits or three-way switch configurations.

Distance and voltage drop considerations also matter for longer runs. If you're running wire more than 100 feet from the panel, you may need to upsize to 10 AWG to compensate for voltage drop, though this is less common in typical residential applications.

Important safety reminder: Installing new circuits requires an ESA permit in Ontario and must be done by a licensed electrician. The wire sizing, connections, and circuit protection all need to meet OESC requirements and pass ESA inspection. DIY electrical work beyond simple outlet/switch replacements is illegal in Ontario and will void your home insurance if something goes wrong.

If you're planning to add a 20-amp circuit for appliances like microwaves, bathroom outlets, or workshop equipment, contact a licensed electrician to ensure proper installation and code compliance. Electrical Ottawa's ESA-licensed electricians can handle new circuit installation with proper permits and inspection for your Ottawa-area home.

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