🏠 Wire Size for a Sub-Panel in Canada (Shed or Detached Garage)
Sized to the Canadian Electrical Code — where voltage drop isn't a suggestion, it's Rule 8-102. 🇺🇸 US version
The short answer
For a 100 amp sub-panel at 45 m (150 ft): #2 copper or 1/0 aluminum. For a 60 amp sub-panel at 30 m (100 ft): #6 copper or #4 aluminum. Full table below — and unlike in the US, staying inside the drop limit is mandatory in Canada: CEC Rule 8-102 caps voltage drop at 3% on a branch circuit, 3% on the feeder, 5% total, as enforceable code. Your exact run: Wire Size calculator.
The two checks (and why Canada makes the second one law)
Sizing a feeder is two stacked checks. First, ampacity — the wire must be rated for the current (CEC Table 2 for copper, Table 4 for aluminum; these are harmonized with the US tables, which is why cross-border answers on ampacity agree). Second, voltage drop — over a long run to a shed or garage, the wire must be fat enough that the far panel still sees healthy voltage. In the US that second check is a recommendation; in Canada, Rule 8-102 makes it a "shall." Past roughly 30 m, it's the drop check — not ampacity — that sets your wire size, and an inspector can hold you to it.
The table: minimum size at 240 V, 3% drop
Sized at the full breaker rating (conservative — the 2024 CEC lets you use the connected load, or 80% of the breaker if unknown, so these sizes have margin built in). One-way distance:
| Feeder | 15 m (50′) | 30 m (100′) | 46 m (150′) | 61 m (200′) | 76 m (250′) | 91 m (300′) |
|---|---|---|---|---|---|---|
| 50 A copper | 8 | 6 | 4 | 4 | 3 | 2 |
| 50 A aluminum | 6 | 4 | 3 | 2 | 1 | 1/0 |
| 60 A copper | 6 | 6 | 4 | 3 | 2 | 2 |
| 60 A aluminum | 4 | 4 | 2 | 1 | 1/0 | 2/0 |
| 100 A copper | 3 | 3 | 2 | 1 | 1/0 | 2/0 |
| 100 A aluminum | 1 | 1 | 1/0 | 2/0 | 3/0 | 4/0 |
AWG sizes (Canada sizes wire in AWG, same as the US), 75°C terminations, computed with our verified engine (K = 12.9 copper / 21.2 aluminum). Aluminum means modern AA-8000 feeder cable — standard and code-recognized in Canada, where aluminum feeders are especially common for cost.
Worked example: 100 A at 46 m
Drop = 2 × K × amps × one-way feet ÷ circular mils. #2 copper (66,360 cmil) at 150 ft: 2 × 12.9 × 100 × 150 ÷ 66,360 = 5.8 V = 2.4% of 240 V — inside the mandatory 3%. One size down (#3) gives 3.1% — over the line, and in Canada that's a code issue, not a judgment call. Check any run in the Voltage Drop calculator.
Canadian specifics people miss
1. It's a 4-wire feeder — two hots, neutral, and a separate bonding conductor, with neutral and bond on separate bars at the sub-panel. 2. The cable will likely be NMD90, TECK90, or direct-burial (NMWU) / conduit — Canadian names for what Americans call Romex, armored cable, and UF; underground runs to outbuildings are commonly NMWU at proper burial depth or conductors in buried conduit. 3. The drop budget is structured: 3% for the feeder, 3% for the branch beyond it, 5% total — drop doesn't "reset" at the sub-panel. 4. Bury copper once — if the garage might someday charge an EV or run a welder, upsizing now is the cheapest it will ever be.
Related
Wire Size calculator · Voltage Drop calculator · Voltage drop & Rule 8-102, explained · CEC ampacity chart