310.15 Ampacity tables
What changed in 310.15
The ampacity tables went back to their old numbers, Table 310.16 through 310.21. Sizes not in the tables can now be interpolated under engineering supervision, and new notes point to conductor properties and cords.
Point by point
- Table 310.15(B)(16) through Table 310.15(B)(21) were renumbered as Tables 310.16 to 310.21, the numbers used in 2008 and earlier.
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- 4 more points on exactly what changed
- The 2017 rule next to the 2020 rule, side by side
- Why it changed
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This section across NEC® editions
2020 NEC®RevisedYou're here
The ampacity tables went back to their old numbers, Table 310.16 through 310.21. Sizes not in the tables can now be interpolated under engineering supervision, and new notes point to conductor properties and cords.
2023 NEC®Revised
The rooftop distance that triggers the 60°F temperature adder dropped from 7/8 inch to 3/4 inch.
Open the 2023 page →2026 NEC®Revised
The rules on when a neutral counts as current-carrying were put into a clear list. The requirements themselves didn't change.
Open the 2026 page →More 2020 changes in Article 310
This is a plain-English summary, not the NEC®'s exact wording. Always check the full section in the NEC® edition your area has adopted, plus any local amendments.
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