🔌 What Size Wire for a 40 Amp Breaker in Canada?
The short answer
Use 8 AWG copper NMD90 for an ordinary 40 A circuit under the conservative 60°C termination method our Canadian tables use. Check the equipment markings in the Canadian Ampacity Check tool before relying on another column.
NMD90 has 90°C insulation, but CEC Rule 4-006 still makes the termination rating part of the answer. The verified 60°C column gives #8 copper exactly 40 A under ordinary conditions. Ampacity Check tool.
NMD90 and the termination rule
NMD90 insulation does not by itself choose the termination column. The verified 60°C column rates #8 copper at exactly 40 A, so the conservative method our Canadian tables use has no extra ampacity headroom; check the equipment markings in the Canadian Ampacity Check tool.
Distance changes the answer — and Rule 8-102 is mandatory
Minimum size at 240 V, sized at the full 40 A with 60°C terminations and kept at or under the mandatory 3% voltage-drop limit (one-way distance):
40 A at 240 V
| Material | 15 m (50′) | 30 m (100′) | 46 m (150′) | 61 m (200′) | 76 m (250′) | 91 m (300′) |
|---|---|---|---|---|---|---|
| Copper | 8 | 8 | 6 | 4 | 4 | 3 |
| Aluminum | 6 | 6 | 4 | 3 | 2 | 1 |
Common Canadian 40-amp jobs
A range is the classic 40 A circuit. In the CEC Rule 8-104 rated-equipment case, a 40 A conductor limit supports 32 A continuous because 40 A × 80% = 32 A; confirm the EV charger's setting and instructions.
Worked example: 40 A at 240 V over 46 m (150 ft)
Our verified calculator selects #6 copper (26,240 circular mils): 2 × 12.9 × 40 × 150 ÷ 26,240 = 5.90 V, or 2.46% of 240 V. #8 passes ampacity but does not meet the mandatory 3% drop limit at this distance.
Related
40-amp wire size FAQ
- What size wire for a 40 amp range in Canada?
- Start with 8 AWG copper NMD90 for an ordinary 40 A range circuit, then follow the appliance instructions and check Rule 8-102 voltage drop for a long run.
- Can I run an EV charger on a 40 amp circuit in Canada?
- In the CEC Rule 8-104 rated-equipment case, a 40 A conductor limit supports 32 A continuous: 40 A × 80% = 32 A. Confirm the charger's permitted setting and the installation's ampacity checks.
- Is 8 gauge wire enough for 40 amps in Canada?
- Yes. The verified 60°C column gives #8 copper 40 A under ordinary conditions. Heat, countable conductors, equipment markings, and long distance can require a larger conductor.