Voltage Drop CalculatorVoltage drop calculator for Canada
Wire size and voltage drop in AWG and metres, checked against the Canadian Electrical Code limits: 3% in a feeder or branch circuit, 5% in total.
Result
Copper, 75 °C basis| Wire size | 12 AWG |
| Area | 3.31 mm² |
| Voltage drop | 3.11 V |
| Percent drop | 2.59 % |
| At the load | 116.89 V |
Within 3% target
12 AWG. Drop 3.11 volts, 2.59 percent. Within 3% target.
How this is worked out
V = 2 × K × I × L ÷ CM
2 × 12.9 × 16 A × 49.21 ft ÷ 6,530 CM = 3.11 V
3.11 V ÷ 120 V × 100 = 2.59 %. At the load: 120 V − 3.11 V = 116.89 V.
- L is the one-way length; the 2 counts the return conductor.
- K is 12.9 for copper and 21.2 for aluminum, in ohm·CM per foot on a 75 °C basis.
- Not checked here: temperature derating, conduit fill, power factor and code compliance.
What the CEC requires: Rule 8-102
- 3% in any one feeder or branch circuit, and 5% in total from the supply side of the service to the point of use.
- It is a rule, not advice. In the US NEC the same figures sit in informational notes; in the CEC they are mandatory.
- The load to use is the connected load if you know it. If you don’t, use 80% of the breaker or fuse rating: 16 A on a 20 A breaker.
Worked example: a 20 A branch circuit, 15 m
A 120 V branch circuit on a 20 A breaker, load not known, so 16 A. The run is 15 m one way in copper, and the limit is 3%.
| Wire | Drop | Against 3% |
|---|---|---|
| 14 AWG | 4.95 V (4.12 %) | Over |
| 12 AWG | 3.11 V (2.59 %) | Within |
So 12 AWG is the smallest copper size within the limit. The calculator above starts with these numbers.
Feeder and branch circuit together
Each part may drop up to 3%, but the two together may not pass 5%. So the branch circuit gets 3% or whatever the feeder leaves, whichever is less:
| Feeder drop | Left for the branch circuit |
|---|---|
| 1% | 3% |
| 2% | 3% |
| 2.5% | 2.5% |
| 3% | 2% |
Enter the branch circuit’s share as a custom target in the calculator.
Table D3 and this calculator
Appendix D, Table D3, gives the distance at which a 120 V two-wire copper circuit drops 1%. Electricians multiply that distance by the allowed percentage, a conductor temperature correction factor, and the circuit voltage divided by 120. The 2024 edition updated the Table D3 calculations and added mm² conductor sizes.
This calculator gets the same kind of answer from conductor resistance (the formula and constants are on the method page), so you don’t need the table. Its temperature basis may differ slightly from Table D3, so if your inspector expects the table method, show the working that way.
Exceptions to know
- Dwelling units: general-use 120 V circuits of 20 A or less may meet the maximum lengths in the code’s Table 68 instead. This does not cover appliance, kitchen counter, heating or cooking circuits.
- Ontario only: ESA lets you ignore service and feeder conductors shorter than 20 m to a combination service panel and use the full 5% on the branch circuit (ESA bulletin, May 2025).
Canadian voltages
- 120/240 V single-phase: houses. Use 120 V or 240 V above.
- 120/208 V three-phase: apartments and commercial buildings. A two-wire 208 V circuit is single-phase: use 208 V.
- 347/600 V three-phase: commercial and industrial, with 347 V lighting circuits: use 347 V.
- 600 V three-phase three-wire: three-phase only, not covered by this calculator yet.
Which edition applies
As of November 2026, the 2024 (26th) edition is in force in British Columbia (from March 4, 2025), Alberta (April 1, 2025), Ontario as the 29th Ontario Electrical Safety Code (May 1, 2025) and Manitoba (April 1, 2026). Quebec moved to the 2021 edition with Québec amendments on March 26, 2026. Check the edition and any local changes with your inspection authority.
Frequently asked questions
Is voltage drop a rule in Canada?
Yes. The Canadian Electrical Code (CSA C22.1), Rule 8-102, limits voltage drop to 3% in any one feeder or branch circuit and 5% in total from the supply side of the service to the point of use. In the US the same figures are only informational notes in the NEC.
What current do I enter?
The connected load if you know it. If you do not, the code says to use 80% of the breaker or fuse rating: 16 A on a 20 A breaker, 12 A on a 15 A breaker.
Can I work in feet or mm²?
Yes. Choose feet or metres, and AWG or mm², under Inputs. This page starts in AWG and metres; the calculator remembers your choice.
Does this cover three-phase circuits?
Not yet. The calculator covers single-phase AC and DC. Three-phase feeders on 120/208 V or 347/600 V systems need a different multiplier.
Do I still need Table D3?
Not to get the answer. Table D3 is a shortcut for the same calculation; this calculator works from conductor resistance directly. If your inspector expects the Table D3 method, show the working that way.
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