About NECTables

What it is

NECTables is a free reference for the tables and calculations electricians use daily: conduit fill, ampacity, derating, box fill, grounding conductor sizes, motor full-load currents and voltage drop. It is built to load fast and read well on a phone.

Where the numbers come from

• Conduit fill counts are calculated, not copied. We start from each raceway’s internal diameter and each conductor’s overall diameter — physical dimensions set by UL and ASTM product standards — and apply the fill percentages and rounding rule of Chapter 9. The arithmetic is shown on the conduit fill page so you can check it.
• Ampacity, grounding and motor values are the widely published figures found on wire manufacturers’ charts, motor data sheets and in the 2023 edition of NFPA 70. Most have not changed in decades.
• Voltage drop uses conductor DC resistance at 75°C. For large conductors on AC, real impedance is somewhat higher; the calculator says so where it matters.

What it is not

This site does not reproduce the National Electrical Code and is no substitute for owning it. Code text, exceptions, informational notes and local amendments all matter, and none of them fit in a table. Jurisdictions adopt different editions; check which one applies to your job. NFPA provides free read-only access to the current code at nfpa.org.

Corrections

If you find a value that disagrees with your code book, please tell us: info@nectables.com. Include the page and the figure and we will check it.