NEC vs CEC: 10 differences that change the answer

We got this wrong ourselves

We shipped a Canadian conduit-fill calculator that used American conductor dimensions. It gave answers about 50% too permissive. We found it, fixed it, and went looking for what else differs. This is what we found.

1. Ampacity: mostly harmonized

CEC Tables 2 and 4 are numerically identical to NEC 310.16 in the 60/75/90°C columns at every shared size. The old “14 AWG copper is 20 A in Canada” difference was real in the 2012 edition. It was harmonized away around 2015–2018. Anyone repeating it is a decade out of date. But the free-air tables still differ. The harmonization is not total.

2. Conductor-count derating: a live difference

At ten current-carrying conductors, the NEC drops to 0.50. The CEC allows 0.70. Same bundle, different answer. This difference is current and easy to miss.

3. Canada gives no credit for a cool room

The NEC lets you increase ampacity below 30°C ambient. The CEC does not. Its single-point rows give no cool-ambient credit below 30°C. Bringing the US habit north silently allows more current than the CEC does.

4. Continuous loads work in opposite directions

NEC: Multiply the load by 125%. CEC: In the Rule 8-104 rated-equipment case, limit the conductor to 80% of its permitted ampacity.

The results land close, but these are not the same operation. Show the operation the local code uses.

5. Voltage drop: a suggestion in one country, a rule in the other

The 3% and 5% figures live in NEC Informational Notes. They are not requirements. In Canada, Rule 8-102 makes voltage drop mandatory. The physics is the same. The legal status is completely different. This is the marquee difference on this list.

6. Conduit fill: the one that caught us

Canadian RW90 is unjacketed cross-linked polyethylene. American THHN has a nylon jacket and is thinner for the same copper. RW90 is roughly 14–43% larger in cross-section, depending on size. Canadian EMT is also slightly smaller inside than its US counterpart. The two differences compound.

In one common case, the permitted count differs by a third. We reported nine conductors where the Canadian tables give six.

T90 nylon, by contrast, lands within about 2% of THHN. It is the Canadian THHN-equivalent. The conductor type matters more than the country.

7. Conductor colour: the phases are not in the same order

Canada, three-phase where colour coding is required: red = A, black = B, blue = C.

The common US convention is black = A, red = B, blue = C. The NEC does not mandate ungrounded conductor colours; it prohibits white, grey, and green. The US pattern is convention and job specification.

A and B are effectively swapped across the border.

8. The high leg is on a different phase

On a 4-wire delta, Canada puts the higher-voltage-to-ground conductor on phase A under Rule 4-032. NEC 408.3(E) puts the high leg on phase B, the centre bus. An electrician looking where their home code taught them finds the wrong conductor.

9. A citation that has been dead for over a decade

Nearly every online source we found cites Canadian colour rules as “Rule 4-038.” In the current 26th edition there is no Rule 4-038. Section 4 ends at Rule 4-036, “Busbar.” The colour rule was Rule 4-038 in the 2012 edition. It is Rule 4-032 now. Sources agreeing with each other is not verification when they are copying each other.

10. What we could not verify

Where a Canadian table has not passed our checks, the page says so. We do not borrow an American number and hide the source. Read how VoltDrop checks its numbers.

Edition checked

Findings checked against CSA C22.1:24, Canadian Electrical Code, Part I, 26th edition (2024), and NEC 2023 (NFPA 70). Adoption is local and local amendments can change the result.

Confirm the edition in force with the local inspection authority, and use a meter before touching any conductor.