Wire Ampacity
Ampacity by gauge, conductor material, insulation rating, ambient.
Example
You enter
- AWG 12
- Material copper
- Insulation rating 75
- Ambient temperature (°C) 30
- Conductor bundle count 1
You get
- Ampacity (physics estimate) 24.4 A
Checked against published worked examples from: NFPA.
Details, formula, and sources
Scopea heat-balance estimate that tracks NEC Table 310.16 through about 8 AWG and reads progressively HIGH above it (about 20% at 2 AWG, 40% at 4/0); size conductors from Table 310.16.
Formula or tableA steady-state thermal balance (I^2 R heating against convective and radiative surface loss) with the coefficient calibrated to a 75 C THWN #12 in 30 C ambient, times the NEC 310.15(C)(1) adjustment for more than 3 current-carrying conductors. NOT a Table 310.16 lookup; it reads high above about 8 AWG.
Source and editionNEC 2023 (NFPA 70).
Free accessFree read-only access at nfpa.org/freeaccess.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesawg, material, insulation_rating_C, ambient_C, bundle_count, ampacity_A
- Termination temperature 75°CNEC 110.14(C) default for the typical residential / light-commercial install
- Ambient temperature 30°C unless user suppliesNEC 310.15(B)(1) base table
- Current-carrying conductors per raceway ≤ 3 unless user suppliesNEC 310.15(C)(1) base case