| AWG / kcmil | Copper (in conduit) | Aluminum (in conduit) | ||||
|---|---|---|---|---|---|---|
| 60°C | 75°C | 90°C | 60°C | 75°C | 90°C | |
Source: NFPA 70 (NEC) Table 310.15(B)(16) — values shown for conductors in conduit, cable, or raceway at not more than 3 current-carrying conductors, 86°F (30°C) ambient. Not all AWG sizes are available in aluminum. Verify against the current NEC edition and local amendments before installation.
How to Read This NEC Ampacity Chart
Find the AWG size or kcmil size in the left column. Then move right to the temperature column that matches the conductor's insulation rating and, crucially, the temperature rating of the equipment terminals. Per NEC 110.14(C), even if you install 90°C-rated THHN wire, you can only use the 90°C ampacity column if every terminal in the circuit is rated 90°C — which is uncommon. Most residential and commercial equipment is rated to 60°C or 75°C.
The 75°C column is the most frequently used for circuits protected by 100A or larger breakers with 75°C-rated terminals. For circuits protected by 100A or smaller breakers, check the terminal label — many residential panels are rated to 60°C for smaller breakers, requiring the 60°C column.
What Ampacity Means
Ampacity is the maximum current a conductor can carry continuously under specified conditions without exceeding its insulation temperature rating. Heat is the enemy: too much current means too much heat, which degrades insulation and can cause a fire. The NEC ampacity table quantifies this limit per conductor size and material so that installations are both code-compliant and safe.
The table values assume standard installation conditions. Any deviation — higher ambient temperature, more conductors bundled together, or installation in a conduit exposed to solar radiation — requires derating. Use the Ampacity Calculator to apply the correct NEC derating factors automatically.
Copper vs. Aluminum Ampacity
Copper conductors carry more current than the same AWG size in aluminum because copper has lower electrical resistance. As a rough rule: you generally need one to two AWG sizes larger in aluminum to match a copper conductor's ampacity. For example, #2 AWG copper is rated 115A at 75°C while #1/0 AWG aluminum is rated 120A at 75°C — the aluminum conductor is two AWG steps larger to carry the same current.
Aluminum is widely used for feeders, service entrance conductors, and large branch circuits where cost and weight matter. Copper remains standard for branch circuit wiring inside walls where flexibility is more important.
Common Wire Sizing Reference Scenarios
- #14 AWG copper: 15A at 60°C — common for 15A lighting and general-purpose circuits
- #12 AWG copper: 20A at 60°C, 25A at 75°C — standard for 20A kitchen and bathroom circuits
- #10 AWG copper: 30A at 60°C, 35A at 75°C — common for 30A dryer, A/C, and range circuits
- #6 AWG copper: 55A at 60°C, 65A at 75°C — 50A range, EV charger, or hot tub circuit
- #2/0 AWG copper: 145A at 60°C, 175A at 75°C — 150A or 200A service entrance copper
- #4/0 AWG aluminum: 150A at 60°C, 180A at 75°C — 200A service entrance aluminum
- 350 kcmil aluminum: 210A at 60°C, 250A at 75°C — common for 200A+ aluminum service feeders
Frequently Asked Questions
An ampacity chart lists the maximum continuous current a conductor can carry under specific conditions. NEC Table 310.15(B)(16) is the standard reference for conductors in conduit at 86°F ambient with up to 3 current-carrying conductors.
Use the 75°C column unless equipment is limited to 60°C at its terminals (NEC 110.14(C)). For equipment rated 100A or less, check the terminal marking — many require the 60°C column. Only use the 90°C column if all conductors and terminals in the circuit are rated 90°C.
No. Aluminum has lower ampacity per AWG size. You typically need one to two AWG sizes larger in aluminum to match the same ampacity as copper at the same temperature column.
Derating is required when ambient temperature exceeds 86°F (30°C) per NEC 310.15(B)(1), or when more than 3 current-carrying conductors share a raceway per NEC 310.15(C)(1). Use the Ampacity Calculator to apply derating automatically.
kcmil (thousand circular mils) is a unit of cross-sectional area used for conductors larger than #4/0 AWG. 250 kcmil copper has 255A ampacity at 75°C per NEC Table 310.15(B)(16).
Only if all equipment terminals in the circuit are rated for 90°C. In practice, most equipment terminals are limited to 75°C or 60°C, so even 90°C-rated THHN wire must be sized using the 75°C or 60°C column per NEC 110.14(C).
Per NEC Table 310.15(B)(16): #12 AWG copper is rated 20A at 60°C, 25A at 75°C, and 30A at 90°C in conduit with up to 3 current-carrying conductors at 86°F ambient.