Wire Ampacity Reference
Look up NEC Table 310.16 allowable ampacities by wire size, conductor material (copper or aluminum), and temperature rating column. Apply ambient temperature correction per NEC Table 310.15(B)(1).
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- NEC 310.16
- Cu & Al
- Ambient correction
Wire ampacity
NEC Table 310.16 + 310.15(B)(1)
Formula
Ampacity = Base × Ambient factor
- Material
- Cu · Al
- Columns
- 60/75/90°C
- Sizes
- 14 AWG – 500 kcmil
- Correction
- Ambient °C
Lookup parameters
Select wire and conditions
Assumptions: not more than 3 current-carrying conductors in raceway/cable/earth, 30°C (86°F) base ambient per NEC Table 310.16. Ambient correction from NEC Table 310.15(B)(1). This tool does not apply bundling adjustment (NEC 310.15(C)(1)) or NEC 240.4(D) small-conductor OCPD caps. Use the wire size calculator for full sizing with all derating.
Ampacity lookup result
12 AWG copper @ 75°C
Corrected ampacity
25 A
- Wire size
- 12 AWG/kcmil
- Material
- Copper
- Temperature column
- 75°C
- Base ampacity (30°C)
- 25 A
- Ambient temperature
- 30°C
- Correction factor
- 1.00
- Corrected ampacity
- 25 A
Calculation
25 A × 1.00 = 25 A
Source: NEC Table 310.16 (base ampacity), NEC Table 310.15(B)(1) (ambient correction). ≤3 current-carrying conductors in raceway/cable/earth.
Full ampacity table — Copper, 75°C column
| Size (AWG/kcmil) | Base Ampacity (A) | Correction Factor | Corrected (A) |
|---|---|---|---|
| 14 | 20 | 1.00 | 20 |
| 12 | 25 | 1.00 | 25 |
| 10 | 35 | 1.00 | 35 |
| 8 | 50 | 1.00 | 50 |
| 6 | 65 | 1.00 | 65 |
| 4 | 85 | 1.00 | 85 |
| 3 | 100 | 1.00 | 100 |
| 2 | 115 | 1.00 | 115 |
| 1 | 130 | 1.00 | 130 |
| 1/0 | 150 | 1.00 | 150 |
| 2/0 | 175 | 1.00 | 175 |
| 3/0 | 200 | 1.00 | 200 |
| 4/0 | 230 | 1.00 | 230 |
| 250 | 255 | 1.00 | 255 |
| 300 | 285 | 1.00 | 285 |
| 350 | 310 | 1.00 | 310 |
| 400 | 335 | 1.00 | 335 |
| 500 | 380 | 1.00 | 380 |
NEC Table 310.16 — allowable ampacities, ≤3 current-carrying conductors, 30°C base ambient. Ambient correction per NEC Table 310.15(B)(1) at 30°C.
Safety & accuracy notice
This wire ampacity reference is a planning aid only. It is not engineering, a permit, or design approval, and it is not legal or code certification. Table values are reproduced from NEC 2020/2023 Table 310.16.
Always verify against the current adopted NEC (National Electrical Code), equipment listings and manufacturer instructions, and your local AHJ (Authority Having Jurisdiction — the inspector or department that enforces the code). Final conductor sizing should be reviewed and approved by a licensed electrician or professional engineer.
Wire ampacity FAQ
What is NEC Table 310.16?
NEC Table 310.16 lists allowable ampacities of insulated conductors rated 0 through 2000 volts, 60°C through 90°C, with not more than three current-carrying conductors in a raceway, cable, or earth, and an ambient temperature of 30°C (86°F). It is the primary table used for sizing conductors in electrical installations.
How do temperature correction factors work?
When the ambient temperature differs from the 30°C base, NEC Table 310.15(B)(1) provides correction factors. For example, at 40°C ambient with 75°C rated copper THHN, the correction factor is 0.88, so a 2 AWG copper conductor rated at 115 A becomes 115 × 0.88 = 101.2 A. Higher temperatures reduce ampacity; lower temperatures increase it.
What is the difference between 60°C, 75°C, and 90°C columns?
The temperature rating column used depends on the lowest-rated termination in the circuit per NEC 110.14(C). For circuits rated 100 A or less, the 60°C column is typically used. For circuits over 100 A, the 75°C column may be used. The 90°C column is used as the starting point for derating (ambient correction and conductor bundling) but the final ampacity must not exceed the termination temperature rating.
Is this reference a substitute for the NEC?
No. It is a planning aid only — not engineering, a permit, or design approval. Always verify against the current adopted NEC and your local AHJ.
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