2023 NEC · free to read

The reasoning behind the number.

The tables tell you what a conductor carries. These guides tell you which column you are allowed to read it in, what the installation conditions take away from it, and when the run length rather than the heat decides the answer. Every figure links back to the table that publishes it.

Guides published

440

Reference pages they link into

2023 NEC

Edition every figure is transcribed from

NEC 2023Every figure the guides below cite is transcribed from the 2023 NEC (NFPA 70, 2023). The code is republished on a three-year cycle and adoption varies by jurisdiction - confirm against your locally adopted edition and your authority having jurisdiction (AHJ) before you build.

Read

All guides

What wire size for a 50 amp circuit?How a 50 A circuit is sized: the termination rating that picks the column, the copper and aluminum minimums, and the run length where voltage drop wins.7 min read Which ampacity column applies - 60°C, 75°C or 90°C?Why the 90°C column is almost never the one that sizes a conductor, what terminations have to do with it, and where the hot column is legitimately used.7 min read Derating for ambient temperature and conductor countThe published ampacity assumes 30°C and three conductors. What to do when your install is hotter or fuller, in the order the two corrections are applied.7 min read What is voltage drop, and when does it matter?Voltage drop explained: what the 3% and 5% figures are, how the circular-mil estimate works, and the run lengths where drop, not heat, picks the wire.7 min read

Look it up instead

Straight to the numbers

Wire size calculator Ampacity lookup Voltage drop Conduit fill Reference tables Wire size by load and distance

Every figure on this page comes from the 2023 NEC (NFPA 70, 2023). The code is republished on a three-year cycle and adoption varies by jurisdiction - confirm against your locally adopted edition and your authority having jurisdiction (AHJ) before you build.

Reference estimate - verify before you build. AmpSizer reports reference estimates transcribed from published tables in the 2023 NEC (NFPA 70, 2023), and from no other edition. It is not a substitute for the code adopted in your jurisdiction. The code is republished on a three-year cycle and adoption varies by jurisdiction - confirm against your locally adopted edition and your authority having jurisdiction (AHJ) before you build. Final conductor sizing, overcurrent protection, and installation must be determined by a licensed electrician and approved by your AHJ.

These guides explain how the published tables are read. They are not an electrical design and they do not replace the code document, which carries the exceptions and conditions the tables refer to.

Jurisdictions adopt editions on their own schedule and frequently amend them, so the edition enforced where you work may not be the one cited here. Confirm which edition and which local amendments apply to your job before relying on any value on this page.