The American Wire Gauge (AWG) amp chart dictates the maximum continuous current a conductor can carry before its insulation degrades. For standard residential branch circuits using copper THHN/THWN-2 in a raceway at 30°C ambient, 14 AWG is rated 20A, 12 AWG is 25A, and 10 AWG is 35A in the 90°C column. However, NEC 240.4(D) strictly limits small conductors to 15A, 20A, and 30A overcurrent protection devices, respectively. This guide provides the complete reference based on NFPA 70 (National Electrical Code) Table 310.16, explaining exactly how to apply these numbers on the jobsite.
How to Read the American Wire Gauge Amp Chart
The most common mistake DIYers and junior electricians make is blindly pulling numbers from the highest temperature column. The ampacity chart is divided into three temperature ratings: 60°C (140°F), 75°C (167°F), and 90°C (194°F). These columns correspond to the thermal rating of the wire insulation and the equipment terminations.
Your allowable ampacity is limited by the lowest temperature rating of any connected component, splice, or termination in the circuit. If you run 90°C THHN wire but terminate it on a standard residential breaker rated for 75°C, you must use the 75°C column. If you use NM-B (Romex) cable, its internal insulation is rated for 60°C, meaning you are permanently locked into the 60°C column, regardless of how heat-resistant the breaker lugs are.
Which column applies to your installation?
- 60°C Column: Use this for NM-B (Romex), UF-B, and older wiring methods like TW or UF. This is the default for most interior residential branch circuits.
- 75°C Column: Use this for THHN/THWN-2 wires in conduit terminating on standard 75°C rated breakers and lugs, as well as SER cable and THW.
- 90°C Column: Use this only as the starting baseline for derating calculations (ambient temperature or bundling). You almost never use the 90°C column for final ampacity because standard breakers and panel lugs are not rated for 90°C terminations.
The Complete NEC 310.16 Ampacity Reference
Below is the complete data table for common building wire sizes. Values are based on an ambient temperature of 30°C (86°F) with not more than three current-carrying conductors in a raceway.
Bookmark Quick-Jumps: 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 2 AWG
| AWG / kcmil | Cu 60°C | Cu 75°C | Cu 90°C | Al 60°C | Al 75°C | Al 90°C |
|---|---|---|---|---|---|---|
| 14 | 15 | 20 | 25 | - | - | - |
| 12 | 20 | 25 | 30 | 15 | 20 | 25 |
| 10 | 30 | 35 | 40 | 30 | 35 | 40 |
| 8 | 40 | 50 | 55 | 40 | 45 | 50 |
| 6 | 55 | 65 | 75 | 40 | 50 | 60 |
| 4 | 70 | 85 | 95 | 55 | 65 | 75 |
| 3 | 85 | 100 | 115 | 65 | 75 | 85 |
| 2 | 95 | 115 | 130 | 75 | 90 | 100 |
| 1 | 110 | 130 | 145 | 85 | 100 | 115 |
| 1/0 | 125 | 150 | 170 | 100 | 120 | 135 |
| 2/0 | 145 | 175 | 195 | 115 | 135 | 150 |
| 3/0 | 165 | 200 | 225 | 130 | 155 | 170 |
| 4/0 | 195 | 230 | 260 | 150 | 180 | 205 |
Derating Factors and Chart Limitations
The baseline numbers in the table above assume ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When real-world conditions deviate, you must apply derating factors.
How derating rows modify the base value:
Derating is applied to the 90°C column for THHN/THWN-2 wire, even if your final termination limits you to the 75°C column. For example, if you pull four current-carrying 10 AWG THHN conductors through a single conduit, NEC Table 310.15(C)(1) requires an 80% adjustment factor. You start with the 90°C baseline of 40A. Multiplying 40A by 0.80 yields a derated ampacity of 32A. Because 32A is still higher than the 75°C termination limit of 35A (wait, 10 AWG 75°C is 35A, so 32A is lower), your final allowable ampacity becomes 32A. You can still safely protect this circuit with a standard 30A breaker.
The American Wire Gauge amp chart only addresses thermal limits. It does not account for voltage drop, short-circuit withstand ratings, or physical conduit fill. A 12 AWG wire might be thermally rated for 20A, but if you run it 150 feet to a 120V outlet pulling 15A, you will experience a voltage drop exceeding 5%, causing poor tool performance and overheating motors. Always calculate voltage drop using NEC Chapter 9, Table 8 resistance values for runs exceeding 50 feet on 120V circuits.
Frequently Asked Questions
What size breaker do I use for my AWG wire?
While the chart shows 14 AWG copper can handle 25A in the 90°C column, NEC 240.4(D) imposes strict overcurrent protection limits for small conductors to prevent fire hazards in residential settings. You must use a maximum 15A breaker for 14 AWG, a 20A breaker for 12 AWG, and a 30A breaker for 10 AWG. For 8 AWG and larger, you size the breaker based on the 60°C or 75°C column ampacity, rounding down to the nearest standard breaker size (e.g., 6 AWG copper at 65A in the 75°C column requires a 60A breaker).
Can I use the 90°C column for my THHN wire ampacity?
Almost never for the final circuit rating. According to copper wiring standards and NEC 110.14(C), the 90°C column is primarily a mathematical tool used as the starting point for derating calculations (like ambient temperature adjustments or bundling). Once you calculate the derated 90°C value, you must compare it to the 75°C (or 60°C) termination limit of your breaker or lug. The final circuit ampacity is the lower of the two numbers.
Does the ground wire count towards bundling derating?
No. When counting current-carrying conductors for bundling derating under NEC 310.15(C)(1), equipment grounding conductors (bare copper or green) do not count. Furthermore, a neutral wire that only carries the unbalanced current from other conductors in the same raceway (like in a standard single-phase multi-wire branch circuit) also does not count. Only the "hot" wires and neutrals that carry harmonic currents or operate as independent current paths count toward the total.
How does aluminum wire change the chart and installation?
Aluminum has a higher electrical resistance than copper, meaning you must use a thicker wire to carry the same current. As a general rule, aluminum wire needs to be two AWG sizes larger than copper for the same ampacity (e.g., use 4 AWG aluminum where you would use 6 AWG copper for a 55A/60A load). Additionally, aluminum expands and contracts more than copper under thermal cycling, which can loosen terminations over time. You must use lugs explicitly marked "AL" or "CU/AL" and apply an anti-oxidant compound (like Noalox) to prevent galvanic corrosion and high-resistance heating at the connection points.
