About
Calculators that cite their own authority
A number without the clause behind it is not useful on a job site.
The code is shown
Every result carries the NEC article and table it came from, not just the arithmetic.
Pass or fail
Where the code sets a limit, the tool says whether the selection complies and names the clause it violates if not.
Visible arithmetic
Full-load current, the coefficient applied, the computed value and the standard-size rounding step are all shown.
Which edition
Tools are built against the 2023 edition of NFPA 70. Jurisdictions adopt different editions and coefficients have changed between revisions, so check which edition your Authority Having Jurisdiction enforces before relying on any result here.
What these tools are not
Nothing here is engineering advice or a substitute for the code text. Transformer protection and conductor sizing decisions affect life safety. Verify every result against the NEC itself and with the engineer or inspector responsible for the installation.
Corrections
If a result looks wrong, the NEC text wins over this tool. Report the inputs and the output and it will be checked against the code.
Disclaimer. Based on the 2023 NEC. Not engineering advice and not a substitute for the code text. Verify against the edition adopted in your jurisdiction and with your Authority Having Jurisdiction — protection decisions affect life safety.