Sizing Conductors: Ampacity and Derating in Canada

A Canadian ampacity calculator has to do more than read a table in Section 4.

Real installations involve conditions that change the usable ampacity, and the CE Code requires you to apply those adjustments before comparing conductor ampacity to load current.

Factors like ambient temperature such as in hot attics, bundling or grouping of cables, parallel conductor arrangements, and the conductor insulation rating all affect the final ampacity. A proper calculator must carry these adjustments through the entire process, not just display the base value from Table 2.

From base ampacity to installed ampacity

Tables give a starting point. Corrections reduce that value when ambient temperature rises or when conductors run in groups that heat each other. The installed ampacity is what must exceed continuous and non-continuous loads per the rules that apply to your circuit.

When voltage drop becomes the deciding factor

Sometimes the wire that satisfies ampacity still violates drop limits on a long run. Use the conductor ampacity calculator for thermal limits and the combined ampacity and voltage drop tool when both constraints apply.