Allowable Ampacities
High-speed reference for common Copper and Aluminum wire sizes (60°C to 90°C).
Professional Usage Disclaimer
This data is provided for informational purposes only. Always verify with the latest edition of the National Electrical Code (NFPA 70) and consult with a licensed electrical professional or AHJ (Authority Having Jurisdiction) before performing any electrical work. Zing² is a reference tool, not a substitute for qualified engineering.
Professional Field Notes & Gotchas
- ▸The 75°C Terminal Rule: Per NEC 110.14(C), even if you use 90°C wire (THHN/XHHW-2), you must size based on the 75°C column because most equipment terminals are not rated for 90°C.
- ▸Derating Base: You ARE allowed to use the 90°C column as the starting point for ambient temperature or bundling adjustments, as long as the final result doesn't exceed the 75°C rating.
- ▸Rooftop Heat: For wires on roofs, add the 'standard' ambient temperature correction PLUS any specific sun-loading factors required by local AHJs.
- ▸Aluminum vs. Copper: Aluminum wire requires significantly larger gauge (roughly 2 sizes up) to match the ampacity of Copper due to its lower conductivity.
NEC 2023 vs 2026: What changed?
NEC 2023 vs 2026: The 2026 code has maintained the primary ampacity values but simplified the notes regarding 'Adjustment' vs 'Correction' factors to ensure more intuitive math for complex multi-raceway installations.
Technical FAQs
What is the ampacity of 6 AWG THHN?
At 75°C (most terminal ratings), 6 AWG Copper is rated for 65 Amps. At 90°C (for derating base only), it is rated for 75 Amps.
Can I use 2/0 Aluminum for a 200A service?
In most residential single-phase cases using the 83% rule (Table 310.12), yes. However, for a standard industrial feeder per Table 310.16, 2/0 Al is only rated for 135 Amps at 75°C.
Why is 14 AWG limited to 15 Amps?
While the table shows higher values, NEC 240.4(D) 'Small Conductor Rule' generally limits 14 AWG to 15A, 12 AWG to 20A, and 10 AWG to 30A overcurrent protection.