Sources and scope for this page: NFPA 70 National Electrical Code, Table 310.16 (NEC 2023 (NFPA 70-2023)), covering all ampacity values on this page, for copper conductors at 30 °C ambient. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. Full sources, values and limits on this page.
Page last changed 2026-11-08 · based on NEC 2023 (NFPA 70-2023)
Quick Answer
Copper Conductor Ampacity (NEC 310.16)
| Size[1] | 60 °C A[1] | 75 °C A[1] | 90 °C A[1] |
|---|---|---|---|
| 14 # | 15 | 20 | 25 |
| 12 # | 20 | 25 | 30 |
| 10 # | 30 | 35 | 40 |
| 8 # | 40 | 50 | 55 |
| 6 # | 55 | 65 | 75 |
| 4 # | 70 | 85 | 95 |
| 3 # | 85 | 100 | 115 |
| 2 # | 95 | 115 | 130 |
| 1 # | 110 | 130 | 145 |
| 1/0 # | 125 | 150 | 170 |
| 2/0 # | 145 | 175 | 195 |
| 3/0 # | 165 | 200 | 225 |
| 4/0 # | 195 | 230 | 260 |
| 250 kcmil # | 215 | 255 | 290 |
| 300 kcmil # | 240 | 285 | 320 |
| 350 kcmil # | 260 | 310 | 350 |
| 400 kcmil # | 280 | 335 | 380 |
| 500 kcmil # | 320 | 380 | 430 |
| 600 kcmil # | 350 | 420 | 475 |
| 700 kcmil # | 385 | 460 | 520 |
| 750 kcmil # | 400 | 475 | 535 |
| 1000 kcmil # | 455 | 545 | 615 |
Values are for copper conductors, not more than three current-carrying conductors in a raceway or cable, in an ambient temperature of 30 °C. Correction factors apply for higher ambient temperature and for more conductors. Terminations are typically rated lower than the conductor — the lower of the two governs.
Why Three Columns
Ampacity is limited by how hot the insulation is allowed to get. The same copper conductor carries more current with 90 °C insulation than with 60 °C insulation, because more heat can be tolerated before the insulation degrades.
But the conductor is rarely the weakest link. Common circuit breakers, receptacles and other terminations are usually rated 60 °C or 75 °C, and the code requires the lowest rating in the circuit to be used for the ampacity calculation. A 90 °C conductor on a 75 °C breaker is a 75 °C circuit.
The 90 °C column is used mainly for derating calculations, where the higher starting value leaves more margin after correction factors are applied — not as the circuit's actual ampacity.
What Changes the Number
Ampacity from the table is a starting point. Several adjustments apply:
- Ambient temperature — above 30 °C the conductor runs hotter, so capacity is reduced by an ambient correction factor.
- Number of conductors — more than three current-carrying conductors bundled together means less heat can escape, so an adjustment factor applies.
- Continuous loads — a load expected to run three hours or more must be sized at 125% of its rating.
- Voltage drop — on long runs the allowable drop of a few percent often forces a larger conductor before ampacity becomes the limit.
Frequently Asked Questions
- What is the ampacity of 12 AWG wire?
- 20 A at 60 °C insulation, 25 A at 75 °C and 30 A at 90 °C, for copper with not more than three current-carrying conductors in a raceway at 30 °C ambient. A 20 A circuit on 12 AWG is the common residential case, using the 60 °C column because the terminations are rated 60 °C.
- What is the ampacity of 10 AWG wire?
- 30 A at 60 °C, 35 A at 75 °C and 40 A at 90 °C for copper, under the same conditions as the table. A 30 A circuit is the common residential use for 10 AWG — dryers, ranges and some air conditioners.
- Does 60 °C or 75 °C apply to my circuit?
- Use the lowest temperature rating of any component in the circuit — conductor, termination, breaker or device. Because most common breakers and receptacles are rated 60 °C or 75 °C, the 90 °C column is normally used only as the starting point for derating calculations, not as the circuit ampacity.
- Is ampacity the same for aluminium wire?
- No. Aluminium conductors carry less current than copper at the same size and require their own column. Aluminium is also more prone to termination problems, so it is usually installed one or two sizes larger than the copper equivalent.
- What is the ampacity of 4/0 copper?
- 195 A at 60 °C, 230 A at 75 °C and 260 A at 90 °C. This is a common service-entrance size for a 200 A residential service.
- Why does the table stop at 1000 kcmil?
- Above 1000 kcmil parallel conductors become the practical choice, so the table continues in kcmil sizes up to that point and larger services are built from sets of smaller conductors run in parallel.
Related
Value Sources
References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.
| # | Source | Type | Revision / method |
|---|---|---|---|
| [1] | NFPA 70 National Electrical Code, Table 310.16 — Ampacities of Insulated Conductors | reference | NEC 2023 (NFPA 70-2023) — source |
Data Sources
| Standard | Revision | What it covers on this page |
|---|---|---|
| NFPA 70 National Electrical Code, Table 310.16 | NEC 2023 (NFPA 70-2023) | all ampacity values on this page, for copper conductors at 30 °C ambient |
Verification scope
No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.
These are base ampacities for the stated conditions. Ambient temperature, conductor count, continuous loading and voltage drop all modify the allowable current, and the governing requirement is the adopted code in the jurisdiction of installation.
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