Wire Ampacity Chart — NEC Table 310.16
Complete wire ampacity reference based on NEC Table 310.16. Find allowable ampacities for copper and aluminum conductors at 60°C, 75°C, and 90°C insulation ratings.
What Is Wire Ampacity?
Ampacity is the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.The word “ampacity” combines “ampere” and “capacity.”
NEC Table 310.16 is the most referenced table in electrical work. It lists allowable ampacities for insulated conductors rated up to 2000 volts, in raceways, cables, or direct-buried, based on an ambient temperature of 86°F (30°C) with no more than 3 current-carrying conductors in a raceway.
The ampacity depends on four factors: wire gauge (AWG/kcmil), conductor material (copper vs. aluminum), insulation temperature rating (60°C, 75°C, or 90°C), and installation conditions (ambient temperature and number of conductors in a raceway).
Important:Even when using 90°C-rated wire (THHN, XHHW-2), you must use the ampacity from the column matching the lowest temperature-rated component in the circuit — usually the terminals, which are typically rated 60°C or 75°C. See NEC 110.14(C).
Copper Conductor Ampacity — NEC Table 310.16
Based on ambient temperature of 86°F (30°C), ≤3 current-carrying conductors in raceway or cable
| Wire Size | 60°C TW, UF | 75°C THW, THWN, XHHW | 90°C THHN, THWN-2, XHHW-2 | Typical Breaker |
|---|---|---|---|---|
| 14 AWG | 15A | 20A | 25A | 15A |
| 12 AWG | 20A | 25A | 30A | 20A |
| 10 AWG | 30A | 35A | 40A | 30A |
| 8 AWG | 40A | 50A | 55A | 40A |
| 6 AWG | 55A | 65A | 75A | 60A |
| 4 AWG | 70A | 85A | 95A | 70A |
| 3 AWG | 85A | 100A | 115A | 100A |
| 2 AWG | 95A | 115A | 130A | 100A |
| 1 AWG | 110A | 130A | 145A | 110A |
| 1/0 AWG | 125A | 150A | 170A | 150A |
| 2/0 AWG | 145A | 175A | 195A | 175A |
| 3/0 AWG | 165A | 200A | 225A | 200A |
| 4/0 AWG | 195A | 230A | 260A | 200A |
| 250 kcmil | 215A | 255A | 290A | — |
| 300 kcmil | 240A | 285A | 320A | — |
| 350 kcmil | 260A | 310A | 350A | — |
| 400 kcmil | 280A | 335A | 380A | — |
| 500 kcmil | 320A | 380A | 430A | — |
| 600 kcmil | 350A | 420A | 475A | — |
| 750 kcmil | 385A | 460A | 520A | — |
| 1000 kcmil | 445A | 545A | 615A | — |
Aluminum Conductor Ampacity — NEC Table 310.16
Based on ambient temperature of 86°F (30°C), ≤3 current-carrying conductors in raceway or cable
| Wire Size | 60°C TW, UF | 75°C THW, THWN, XHHW | 90°C THHN, THWN-2, XHHW-2 |
|---|---|---|---|
| 12 AWG | 15A | 20A | 25A |
| 10 AWG | 25A | 30A | 35A |
| 8 AWG | 35A | 40A | 45A |
| 6 AWG | 40A | 50A | 55A |
| 4 AWG | 55A | 65A | 75A |
| 3 AWG | 65A | 75A | 85A |
| 2 AWG | 75A | 90A | 100A |
| 1 AWG | 85A | 100A | 115A |
| 1/0 AWG | 100A | 120A | 135A |
| 2/0 AWG | 115A | 135A | 150A |
| 3/0 AWG | 130A | 155A | 175A |
| 4/0 AWG | 150A | 180A | 205A |
| 250 kcmil | 170A | 205A | 230A |
| 300 kcmil | 190A | 230A | 260A |
| 350 kcmil | 210A | 250A | 280A |
| 400 kcmil | 225A | 270A | 305A |
| 500 kcmil | 260A | 310A | 350A |
| 600 kcmil | 285A | 340A | 385A |
| 750 kcmil | 315A | 380A | 425A |
| 1000 kcmil | 375A | 445A | 500A |
Note: Aluminum wire requires special installation practices. Use anti-oxidant compound on all connections, torque terminals to manufacturer specifications, and only use connectors rated for aluminum (marked AL or AL/CU). NEC 14 AWG aluminum is not commonly available and is rarely used.
Temperature Correction Factors — NEC Table 310.15(B)(1)(1)
Multiply the ampacity from Table 310.16 by this factor when ambient temperature exceeds 86°F (30°C)
| Ambient Temperature | 60°C Wire | 75°C Wire | 90°C Wire |
|---|---|---|---|
| 70–77°F (21–25°C) | 1.08 | 1.05 | 1.04 |
| 78–86°F (26–30°C) | 1 | 1 | 1 |
| 87–95°F (31–35°C) | 0.91 | 0.94 | 0.96 |
| 96–104°F (36–40°C) | 0.82 | 0.88 | 0.91 |
| 105–113°F (41–45°C) | 0.71 | 0.82 | 0.87 |
| 114–122°F (46–50°C) | 0.58 | 0.75 | 0.82 |
| 123–131°F (51–55°C) | 0.41 | 0.67 | 0.76 |
| 132–140°F (56–60°C) | — | 0.58 | 0.71 |
| 141–149°F (61–65°C) | — | 0.47 | 0.65 |
| 150–158°F (66–70°C) | — | 0.33 | 0.58 |
Example: 6 AWG THWN copper in a 104°F (40°C) attic. Base ampacity = 65A (75°C column). Temperature factor = 0.88. Derated ampacity = 65 × 0.88 = 57.2A.
Conduit Fill Adjustment Factors — NEC 310.15(C)(1)
Reduce ampacity when more than 3 current-carrying conductors are in the same raceway or cable
| Number of Conductors | Percent of Ampacity | Multiplier |
|---|---|---|
| 1–3 | 100% | 1.00 |
| 4–6 | 80% | 0.80 |
| 7–9 | 70% | 0.70 |
| 10–20 | 50% | 0.50 |
| 21–30 | 45% | 0.45 |
| 31–40 | 40% | 0.40 |
| 41+ | 35% | 0.35 |
Example: Six 12 AWG THHN conductors in one conduit (6 current-carrying conductors). Base ampacity = 30A (90°C column for derating purposes). Conduit fill factor = 0.80. Derated ampacity = 30 × 0.80 = 24A. Since the 75°C column value is 25A, the final ampacity is 24A.
How to Use the Wire Ampacity Chart
Determine the load current
Calculate the full-load amperage of your circuit. Use our amps to watts calculator or Ohm's Law calculator if needed.
Identify the temperature column
Check the temperature rating of your equipment terminals (usually marked on the device). Most residential terminals are 60°C; most commercial are 75°C.
Find the wire size
Look up the ampacity in the correct column. Select a wire with ampacity equal to or greater than your load current. Use our wire sizing calculator for automated results.
Apply derating if needed
If ambient temperature exceeds 86°F or there are more than 3 conductors in a raceway, apply the correction factors above. You may use the 90°C column as the starting point for derating calculations.
Check voltage drop
For long runs, verify that voltage drop stays within NEC recommendations (3% branch, 5% total). You may need to upsize the wire.
Common Wire Sizes: Quick Reference
Residential (Copper)
- 14 AWG — 15A breaker, lighting circuits
- 12 AWG — 20A breaker, general receptacles, kitchen
- 10 AWG — 30A breaker, dryers, water heaters
- 8 AWG — 40A breaker, cooktops, large A/C
- 6 AWG — 60A breaker, sub-panels, large EV chargers
- 4 AWG — 70A breaker, sub-panels
- 2 AWG — 100A sub-panel feeders
- 4/0 AWG — 200A service entrance
Commercial / Aluminum
- 1/0 AL — 100A service (residential)
- 4/0 AL — 200A service (residential)
- 250 kcmil AL — 200A feeders
- 350 kcmil AL — 250A feeders
- 500 kcmil AL — 300A feeders
- 750 kcmil AL — 400A services
- Parallel runs — 2+ sets for >500A
Frequently Asked Questions
What is wire ampacity?
Wire ampacity is the maximum amount of electrical current a conductor can carry continuously without exceeding its temperature rating. Ampacity depends on the wire gauge (size), insulation type, ambient temperature, and the number of current-carrying conductors in a raceway. NEC Table 310.16 lists standard ampacity values.
What is the ampacity of 12 AWG copper wire?
12 AWG copper wire has an ampacity of 20 amps at 60°C (TW), 25 amps at 75°C (THWN), and 30 amps at 90°C (THHN). For most residential wiring with 60°C-rated terminals, the 20-amp rating applies, which is why 12 AWG is used on 20-amp breakers.
What size wire do I need for 100 amps?
For 100 amps, you typically need 1 AWG copper (130A at 75°C) or 1/0 AWG aluminum (120A at 75°C). For a 100-amp service entrance, NEC 230.79 requires a minimum of 1 AWG copper or 1/0 aluminum. Always check local codes and consider voltage drop for long runs.
What is temperature derating?
Temperature derating reduces the ampacity of a wire when the ambient temperature exceeds 86°F (30°C). For example, in a 104°F (40°C) environment, a 75°C-rated conductor's ampacity is multiplied by 0.88, reducing it by 12%. This is required by NEC 310.15(B)(1).
What is conduit fill derating?
When more than 3 current-carrying conductors are installed in a raceway, the ampacity must be reduced per NEC 310.15(C)(1). For 4–6 conductors, ampacity drops to 80%. For 7–9 conductors, 70%. This is because more conductors generate more heat in a confined space.
Can I use the 90°C ampacity column for wire sizing?
Generally no — you must size wire based on the temperature rating of the lowest-rated component (usually the terminal). However, per NEC 310.15(B)(1), you CAN use the 90°C column as a starting point for derating calculations, then verify the final ampacity doesn't exceed the 60°C or 75°C column value.
What is the difference between 60°C, 75°C, and 90°C wire ratings?
These ratings indicate the maximum temperature the wire insulation can handle. 60°C (TW, UF) is basic. 75°C (THW, THWN) is most common for commercial work. 90°C (THHN, THWN-2) allows the highest ampacity but is limited by terminal ratings — most equipment is rated 60°C or 75°C.
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