Determine conductor size and ampacity per the CEC, including Quebec amendments and free-air derating. Enter your load to find the correctly sized wire.
Ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. Sizing a wire means finding the smallest conductor whose corrected ampacity still meets or exceeds the load, after all derating.
You start from the base ampacity for the conductor size, material, and insulation temperature rating, then apply corrections for ambient temperature and for the number of current-carrying conductors bundled together. Continuous loads are sized so the conductor carries no more than 80 percent of its rating, which is the same as multiplying the load by 125 percent.
A 24 A continuous load at 75 degrees C termination needs a conductor rated for at least 24 times 1.25, or 30 A. A #10 copper conductor at 75 degrees C is rated 30 A, so it just meets the requirement. If that run is also in a hot ceiling space or bundled with other circuits, the derating could push you to #8.
The CEC sets ampacity in Section 4, with allowable values in the Table 2 and Table 4 series and correction factors in Table 5A and Table 5C. Quebec amends some of these, which the calculator reflects. The NEC uses Article 310 and Table 310.16 for the same purpose. The rule that continuous loads run at 80 percent appears in CEC Rule 8-104 and NEC Article 210.19. Verify the current edition and provincial amendments.
Wire size is the physical gauge of the conductor. Ampacity is how much current that conductor can safely carry given its material, insulation rating, and installation conditions. Sizing a wire means picking a gauge whose ampacity covers the load after derating.
A continuous load runs for three hours or more, so the code requires the conductor and overcurrent device to be sized at 125 percent of the load. This keeps the conductor at no more than 80 percent of its rating during sustained operation.
Yes. Higher ambient temperature reduces a conductor’s ampacity, so runs in hot spaces need a correction factor that can require a larger wire than the base table suggests.
Yes. The calculator applies the Quebec-amended CEC values and free-air derating where they differ from the base national code.