Inputs
Formula
\[
I_{\text{adj}} = I_{\text{base}} \times C_T \times C_A
\]
NEC 2023 · 310.15(B)(1) temperature correction · 310.15(C)(1) adjustment factor
| Symbol | Meaning | Source |
|---|---|---|
| \(I_{\text{adj}}\) | Adjusted (derated) ampacity — the value to use for load calculations | 310.15 |
| \(I_{\text{base}}\) | Base ampacity from Table 310.16 for the selected size, material, and insulation temperature rating | Table 310.16 |
| \(C_T\) | Ambient temperature correction factor (varies with actual ambient vs. rated ambient of 30 °C) | Table 310.15(B)(1) |
| \(C_A\) | Conduit fill adjustment factor for number of current-carrying conductors | Table 310.15(C)(1) |
Results
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Important Notes & Limitations
Terminal temperature limits (110.14(C)):
Even when using 90 °C–rated insulation, ampacity used for equipment terminations
must not exceed the 60 °C or 75 °C column value unless the termination is listed for the higher temperature.
For conductors 1 AWG and smaller connected to equipment rated 100 A or less, use the 60 °C column.
For conductors larger than 1 AWG or equipment rated over 100 A, use the 75 °C column.
This calculator shows 90 °C column values for 90 °C insulation — apply 110.14(C) separately when sizing for termination purposes.
Neutrals and conduit fill (310.15(E)):
A neutral conductor that carries only the unbalanced current of a balanced circuit (non-linear loads excluded)
is NOT counted as a current-carrying conductor for adjustment purposes.
Equipment grounding conductors are never counted.
Parallel conductors (310.10(H)):
Conductors 1/0 AWG and larger may be installed in parallel.
Each individual conductor must have the same ampacity required for the load divided by the number of parallel sets.
This calculator sizes one conductor.
Table 310.16 scope:
Table 310.16 applies to not more than three current-carrying conductors in a raceway, cable, or direct burial —
at ambient 30 °C — for insulated conductors rated 0–2000 V.
The conduit fill adjustment (310.15(C)(1)) applies when more than three are present.
Study aid only — verify against the adopted code edition and a licensed professional before use in real project or estimate documentation. NEC® is a registered trademark of the National Fire Protection Association.