Published April 5, 2026

Wire Size Guide for Canada

Choosing the right wire size in Canada is not a single lookup. You start with CE Code ampacity tables, apply installation corrections, then check whether voltage drop or conduit fill forces an upsize. This guide walks through that sequence and links to our free conductor sizing calculator.

Start with Rule 4-004

Rule 4-004 requires conductors to have ampacity not less than the load they carry, after corrections. Read our Rule 4-004 explainer for the full context, then use Tables 1, 2, or 4 for base values.

Apply derating before comparing to load

Temperature correction (Rule 4-006) and bundling derating (Rule 4-008) reduce table ampacity. See the ampacity and derating guide for worked examples. Raceway fill can increase the number of conductors that count toward bundling—see the conduit fill guide.

Check voltage drop on every long run

Ampacity alone does not guarantee acceptable performance at the load. Rule 8-102 addresses branch and feeder drop. Our voltage drop guide explains planning limits and how to combine drop with ampacity in one workflow using the unified conductor sizing tool.

Copper vs aluminum

Aluminum conductors are permitted when sized to Table 4 and terminated correctly. A 40A circuit might use 8 AWG copper or 6 AWG aluminum at 75°C—but only after derating and drop checks confirm both are adequate for the actual installation.

When to upsize

Upsize when corrected ampacity is below load current, when voltage drop exceeds limits, or when conduit fill and bundling derating stack together on crowded raceways. Professional practice documents the governing factor—thermal, drop, or fill—on the calculation sheet.