14/2 vs 12/2 Wire — Which Gauge Do You Need? (Ontario Code Guide)
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14/2 vs 12/2 Wire — Which Gauge Do You Need? (Ontario Code Guide)
Using the wrong wire gauge is one of those mistakes that can get someone killed. The Canadian Electrical Code is specific about which gauge goes with which circuit — and there's no wiggle room. Here's the clear answer.
The Short Answer
| Wire | Gauge | Max Circuit Breaker | Use For |
|---|---|---|---|
| 14/2 NMD90 | 14 AWG | 15A | Standard lighting, bedroom/living room outlets |
| 12/2 NMD90 | 12 AWG | 20A | Kitchen counters, bathrooms, garages, outdoor |
You cannot use 14 AWG wire on a 20A circuit. This is a code violation and fire hazard.
You CAN use 12 AWG on a 15A circuit (it's overkill but allowed), but you cannot use 14 AWG on a 20A circuit.
Understanding the Numbers
14/2 NMD90 means:
- 14 = 14 AWG (American Wire Gauge) conductor size
- 2 = 2 conductors (black/hot + white/neutral) plus bare ground
- NMD90 = Non-Metallic Dry, 90°C rated
12/2 NMD90 is the same but with thicker 12 AWG conductors that handle more current.
The third wire (green or bare copper) is always the ground — it's not counted in the "2."
What the Canadian Electrical Code Says
CEC Rule 14-104 specifies minimum conductor sizes:
| Circuit Rating | Minimum Wire Gauge | Max Continuous Load |
|---|---|---|
| 15A | 14 AWG | 12A (80% rule) |
| 20A | 12 AWG | 16A (80% rule) |
| 30A | 10 AWG | 24A (80% rule) |
| 40A | 8 AWG | 32A (80% rule) |
The 80% rule means you should only load a circuit to 80% of its rating for continuous loads (running more than 3 hours).
Where Each Gauge Is Required in Ontario Homes
14/2 NMD90 (15A Circuits)
| Circuit | Code Requirement |
|---|---|
| Bedroom receptacles | 14/2 on 15A |
| Living room receptacles | 14/2 on 15A |
| Hallway lighting | 14/2 on 15A |
| Bedroom lighting | 14/2 on 15A |
| Dining room | 14/2 on 15A |
| General lighting throughout | 14/2 on 15A |
12/2 NMD90 (20A Circuits)
| Circuit | Code Requirement |
|---|---|
| Kitchen counter receptacles | 12/2 on 20A (minimum 2 circuits) |
| Kitchen island receptacles | 12/2 on 20A (dedicated) |
| Bathroom receptacles | 12/2 on 20A |
| Garage receptacles | 12/2 on 20A |
| Outdoor receptacles | 12/2 on 20A |
| Laundry room receptacle | 12/2 on 20A |
| Dishwasher | 12/2 on 20A (dedicated) |
| Microwave (built-in) | 12/2 on 20A (dedicated) |
Specialty Circuits
| Circuit | Wire Required |
|---|---|
| Electric dryer | 10/3 NMD90 on 30A |
| Electric range | 6/3 NMD90 on 40A or 50A |
| Central A/C | Per nameplate, typically 12/2 on 20A |
| Hot tub | Per nameplate, typically 6/3 on 50A + GFCI |
When to Use 14/3 and 12/3
The "/3" versions have three conductors plus ground:
- 14/3 = black, white, red + ground (15A)
- 12/3 = black, white, red + ground (20A)
Use 3-conductor wire for:
- 3-way switch circuits (controlling a light from two switches)
- Multi-wire branch circuits (two circuits sharing a neutral)
- Smoke detector interconnection (red wire carries the interconnect signal)
Our 14/3 NMD90 Wire - 75M is in stock for 3-way switch wiring.
Physical Differences
| Property | 14 AWG | 12 AWG |
|---|---|---|
| Conductor diameter | 1.63mm | 2.05mm |
| Resistance (per 100m) | 8.28 Ω | 5.21 Ω |
| Weight (75M box) | ~4.5 kg | ~6.5 kg |
| Flexibility | More flexible | Stiffer |
| Ease of pulling | Easier | Harder in conduit |
| Price (75M box) | ~$70 | ~$100 |
Common Mistakes
- Using 14/2 for kitchen countertop circuits — CEC requires 20A circuits (12/2) for all kitchen counter receptacles
- Mixing gauges on the same circuit — If the breaker is 20A, ALL wire on that circuit must be 12 AWG
- Using indoor wire outdoors — NMD90 is for dry indoor locations only. Out door or underground requires NMWU or TECK cable
- Undersizing for long runs — On runs over 30 metres, voltage drop may require upsizing the wire gauge
What to Buy
| Product | Circuit | Price |
|---|---|---|
| NMD90 14/2 - 75M | 15A lighting/receptacles | $69.99 |
| NMD90 14/3 - 75M | 15A 3-way switches | $99.99 |
| NMD90 12/2 - 75M | 20A kitchen/bath/garage | $99.99 |
| TECK90 12/3 - 30M | Commercial/industrial | $149.99 |
All ETL or UL certified copper building wire, available at our Brampton showroom or online.
Need wiring done right? Safer Electric (ESA Licence #7008996) handles residential and commercial wiring across the GTA. ESA permit and inspection included. Call (647) 383-9500.
FAQ
Can I use 12/2 everywhere instead of 14/2? Yes. 12 AWG is rated for both 15A and 20A circuits. Some electricians run 12/2 everywhere for consistency, though it costs more and is harder to work with.
How do I know what gauge is in my walls? Check the breaker rating. If it's 15A, it should be 14 AWG. If it's 20A, it must be 12 AWG. You can also check the cable markings printed on the outer jacket.
Can I extend existing wiring with a different gauge? No. All wire on a circuit must match the breaker rating. You cannot splice 14 AWG onto a 20A circuit, even for a short extension.
Is aluminum wire still used in Ontario? Aluminum branch circuit wiring (from the 1960s-70s) is a known fire hazard. It's no longer permitted for branch circuits. If your home has aluminum wiring, consult a licensed electrician about remediation options.