What size wire do I need for different electrical circuits in my home?
What size wire do I need for different electrical circuits in my home?
Wire Gauge Guide for Residential Electrical Circuits in New Brunswick
Using the correct wire gauge (thickness) for each circuit is critical for safety. Undersized wire overheats under load, creating a fire hazard. The Canadian Electrical Code specifies minimum wire sizes based on circuit amperage.
Wire Gauge Basics
Wire gauge in Canada uses AWG (American Wire Gauge) numbers. Lower numbers = thicker wire = more current capacity. The most common residential wire sizes:
| AWG | Diameter | Typical Use |
|-----|----------|-------------|
| 14 AWG | 1.63mm | 15-amp circuits |
| 12 AWG | 2.05mm | 20-amp circuits |
| 10 AWG | 2.59mm | 30-amp circuits |
| 8 AWG | 3.26mm | 40-amp circuits |
| 6 AWG | 4.11mm | 50-amp circuits |
| 4 AWG | 5.19mm | 60-70 amp circuits |
| 3 AWG | 5.83mm | Sub-panels, large loads |
| 1/0–4/0 AWG | 8.25–11.7mm | Service entrance, 100-200A |
Common Residential Circuits
15-amp circuits (14 AWG NMD90)
- Bedroom outlets and lights
- Living room outlets and lights
- Hallway and closet outlets
- General lighting circuits
- Maximum continuous load: 12 amps (1,440 watts)
20-amp circuits (12 AWG NMD90)
- Kitchen countertop receptacles (minimum 2 circuits required)
- Bathroom receptacles
- Laundry room receptacles
- Garage receptacles
- Outdoor receptacles
- Dishwasher
- Microwave (if dedicated circuit)
- Maximum continuous load: 16 amps (1,920 watts)
30-amp circuits (10 AWG NMD90)
- Electric dryer (240V)
- Window/wall AC unit (large)
- Small hot tub (240V)
- Electric water heater (some models)
40-amp circuits (8 AWG NMD90)
- Electric range/stove (smaller models)
- EV charger (40A)
- Large hot tub
50-amp circuits (6 AWG NMD90)
- Electric range/stove (standard)
- EV charger (50A)
- Large hot tub
- Sub-panel feed (50A)
NMD90 Cable Naming
The cable you buy at Kent or Home Hardware in NB is labelled like this: 14/2 NMD90 or 12/3 NMD90
- First number (14, 12, 10, etc.) = wire gauge (AWG)
- Second number (2 or 3) = number of insulated conductors (plus a bare ground wire)
- NMD90 = Non-Metallic Dry, rated for 90°C — the standard residential cable type in Canada
Voltage Drop on Long Runs
This is where many DIYers and even some electricians make mistakes. Over long distances, wire resistance causes voltage drop — the appliance at the end of the run receives less than 120V or 240V.
The CEC limits voltage drop to 5% maximum from the panel to the furthest outlet (3% on the branch circuit is the recommended design target).
Practical impact in NB:
Detached garages, barns, and workshops are often 20–40 metres from the house panel. At these distances, you may need to upsize the wire:
| Circuit | Up to 15m | 15–25m | 25–40m |
|---------|-----------|--------|--------|
| 15A (120V) | 14 AWG | 12 AWG | 10 AWG |
| 20A (120V) | 12 AWG | 10 AWG | 8 AWG |
| 30A (240V) | 10 AWG | 10 AWG | 8 AWG |
| 50A (240V) | 6 AWG | 6 AWG | 4 AWG |
These are copper wire values. Aluminum wire (common for larger feeds due to cost savings) requires upsizing by 1–2 gauge sizes.
Copper vs. Aluminum
For branch circuits (15A, 20A), copper is standard in NB residential work. Aluminum is used for:
- Service entrance cables (100A, 200A feeds)
- Large sub-panel feeds (60A+)
- Long underground runs where copper cost is prohibitive
Aluminum costs about 40–60% less than copper but requires:
- Larger gauge for the same amperage
- Anti-oxidant compound on all connections
- AL/CU-rated devices and connectors
- Proper torque on terminal screws
Never mix aluminum and copper at a connection point without approved AL/CU connectors. This caused house fires in the 1960s–1970s when aluminum branch wiring was connected to copper-only devices.
Cost of Wire in NB (2025–2026)
| Wire | Approximate Cost per Metre |
|------|---------------------------|
| 14/2 NMD90 (copper) | $1.50–$2.50 |
| 12/2 NMD90 (copper) | $2.00–$3.50 |
| 10/3 NMD90 (copper) | $4.00–$6.00 |
| 6/3 NMD90 (copper) | $8.00–$14.00 |
| 4/0 aluminum (service) | $8.00–$12.00 |
Wire prices have been volatile since 2020 due to copper market fluctuations. Get current pricing before budgeting a project.
Key Takeaway
The wire gauge is determined by the breaker size, not the other way around. Never put a larger breaker on existing wire to "stop it from tripping" — this removes the overcurrent protection and can cause the wire to overheat and start a fire. If a breaker trips frequently, the solution is reducing the load or running a new properly sized circuit. A TSANB-licensed electrician in New Brunswick will size everything correctly as part of permitted work.
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