How far can you run 12 gauge wire on a 20 amp breaker in Canada?

About 14 metres (46 feet) one-way at 120 V fully loaded, staying inside the CEC's mandatory 3% voltage-drop limit — about 28 m (91 ft) at 240 V. Using the CEC's 80%-of-breaker calculation basis, distances stretch about 25% further.

Do I calculate voltage drop at the breaker rating or the actual load in Canada?

The 2024 CEC answers this directly: use the connected load if known, otherwise 80% of the overcurrent device rating. Calculating at 100% of the breaker is simply more conservative.

Is there a maximum circuit length table in the Canadian code?

Yes — for dwelling lighting and general-use receptacle circuits up to 20 A at 120 V, Rule 8-102(3) with Table 68 gives precomputed maximum lengths. Dedicated circuits like kitchen, fridge, and heating use the standard voltage-drop calculation instead.

📏 How Far Can You Run 12 Gauge Wire in Canada?

Distance limits by gauge, in metres and feet — under a code where the limit is mandatory. 🇺🇸 US version

The short answer

On a fully loaded 20 amp, 120 V circuit, #12 copper stays inside the 3% drop limit for about 14 m (46 ft) one-way; at 240 V, about 28 m (91 ft). And in Canada that 3% is not advice — CEC Rule 8-102 makes it enforceable. The full table is below; your exact case: Max Wire Length calculator.

Distance table (3% drop, copper, fully loaded)

Wire	At amps	Max one-way @120 V	Max one-way @240 V
14 AWG	15 A	12 m (38 ft)	23 m (76 ft)
12 AWG	15 A	19 m (61 ft)	37 m (121 ft)
12 AWG	20 A	14 m (46 ft)	28 m (91 ft)
10 AWG	30 A	15 m (48 ft)	30 m (97 ft)
8 AWG	40 A	18 m (58 ft)	35 m (115 ft)
6 AWG	50 A	22 m (73 ft)	45 m (146 ft)

Computed with our verified engine (K = 12.9 for copper). Distances are one-way; the round trip is accounted for.

Breaker amps or actual load? Canada actually answers this

The eternal calculator argument — do you compute at the breaker's rating or the load's real draw — has an official Canadian answer: the 2024 CEC says use the connected load if you know it, otherwise 80% of the breaker rating. Our table uses 100% of the breaker (extra margin); at the CEC's 80% basis, every distance above stretches 25% further — so a #12/20 A circuit reaches about 18 m (57 ft) at 120 V. Either way you land inside the rule; ours just lands with room to spare. The calculator takes whichever amps you give it.

Special Canadian case: houses get a lookup table

For ordinary lighting and receptacle circuits in dwellings (up to 20 A, 120 V), the CEC even publishes precomputed maximum lengths (Rule 8-102(3) with Table 68) so electricians don't have to calculate at all — with a bonus: if the run from the service to your panel is short (under 20 m), the branch circuit may use the whole 5% budget itself. Dedicated circuits — fridge, kitchen, heating — don't get that shortcut and use the standard calculation, which is exactly what our tools do.

What happens if you run too far?

Physics doesn't care about borders: motors start hard and run hot, LEDs flicker, chargers crawl, and energy turns into heat in the wall. The Canadian difference is bureaucratic — an over-limit run can also fail inspection, since 8-102 is enforceable.

Worked example

#12 copper, 20 A, 24 m (80 ft) one-way, 120 V: drop = 2 × 12.9 × 20 × 80 ÷ 6,530 = 6.3 V = 5.3% — over the mandatory limit. Fixes: #10 wire (3.3%), a 240 V configuration if the load allows, or a shorter route. The Voltage Drop calculator shows the options instantly.

Max Wire Length calculator · Voltage drop & Rule 8-102 · CEC ampacity chart