AWG Cable Sizes Chart: NEC Ampacity, Derating, and Quick-Jump Reference

The most common AWG cable sizes for standard home branch circuits are 14 AWG (15A), 12 AWG (20A), and 10 AWG (30A). These ratings are dictated by the 60°C column of NEC Table 310.16 for copper conductors, strictly capped by the small-conductor overcurrent rules in NEC 240.4(D). If you are sizing wire for a residential panel today, these three gauges cover 95% of your branch circuit needs. Below is the complete reference data, how to apply derating factors, and the edge cases the standard chart leaves out.

How to Read the NEC Ampacity Table (and Quick-Jump Chart)

Before pulling wire, you must understand how to read the ampacity tables published in the National Electrical Code (NEC). The table below is derived from NEC Table 310.16. It assumes copper conductors, an ambient temperature of 30°C (86°F), and no more than three current-carrying conductors bundled in a single raceway or cable.

Which column applies to your installation? For most residential terminations (breakers, receptacles, switches), you must use the 60°C column because standard residential devices are typically rated for 60°C. You may use the 75°C column only if both the wire insulation and the equipment terminals are explicitly rated for 75°C (common in commercial panels and larger feeders). The 90°C column is almost never used for final ampacity; it exists solely as a starting point for calculating derating adjustments.

NEC Table 310.16 Allowable Ampacities for Copper Conductors (30°C Ambient)

AWG Size	60°C (140°F) - TW, UF	75°C (167°F) - THW, THWN	90°C (194°F) - THHN, XHHW
14	15A	20A	25A
12	20A	25A	30A
10	30A	35A	40A
8	40A	50A	55A
6	55A	65A	75A
4	70A	85A	95A
3	85A	100A	115A
2	95A	115A	130A
1	110A	130A	145A
1/0	125A	150A	170A

Derating Modifiers: When Base Ampacity Drops

The base values in the table above assume ideal conditions: a cool 30°C environment and plenty of physical space for heat dissipation. In the real world, wires heat up. If you bundle multiple circuits in a single conduit or run wire through a blazing hot attic, you must apply derating factors.

How derating modifies the base value: Derating is calculated using the 90°C column, regardless of your termination temperature rating. You multiply the 90°C base ampacity by the derating percentage, then compare that result to your termination column limit. The final allowable ampacity is the lower of the two numbers.

Conductor Bundling Derating Factors (NEC Table 310.15(C)(1))

Number of Current-Carrying Conductors	Adjustment Factor (Percentage of 90°C Base)
1 to 3	100% (No derating)
4 to 6	80%
7 to 9	70%
10 to 20	50%

Worked Numeric Example: You are pulling four 12 AWG THHN current-carrying conductors (two circuits) through a single EMT conduit to a detached garage.

1. Start with the 90°C base for 12 AWG: 30A.
2. Apply the 4-6 conductor derating factor (80%): 30A × 0.80 = 24A.
3. Check the termination limit (60°C column for standard residential breakers): 20A.
4. Compare 24A and 20A. The lower number wins. Your final allowable ampacity is 20A.

In this scenario, the derating didn't force you to upsize the wire because the 240.4(D) small-conductor rule already capped your breaker at 20A. However, if you were pulling four 8 AWG THHN wires, the math changes: 55A (90°C base) × 0.80 = 44A. Since 44A is lower than the 75°C termination limit of 50A, you must drop your breaker size to 40A.

What the AWG Table Cannot Tell You (Edge Cases & Limits)

An ampacity chart is a thermal limit guide, not a complete engineering manual. Relying on it blindly will lead to failed inspections or underperforming circuits. Here is what the table leaves out.

1. Voltage Drop Over Distance

The NEC table assumes you only care about the wire melting, not about the voltage reaching the load. If you run 12 AWG wire 150 feet to a 15A shed subpanel, the wire won't overheat, but the voltage at the receptacle will sag below 114V under load, potentially damaging power tools or tripping compressor motors. As a rule of thumb, keep voltage drop under 3% for branch circuits. If your run exceeds 100 feet at full load, upsize the wire by one or two AWG steps purely for voltage preservation. You can verify your specific run using the Southwire Voltage Drop Calculator before buying wire.

2. The Weakest Link Terminal Rule (NEC 110.14(C))

You might buy premium 90°C rated THHN wire and assume you can push 40A through 10 AWG. You cannot. NEC 110.14(C) dictates that the ampacity of a circuit is limited by the lowest temperature rating of any connected component. If your breaker lug is rated for 75°C and your receptacle is rated for 60°C, the entire circuit is legally bound to the 60°C column. Always verify the terminal temperature ratings stamped on your breakers and devices.

3. Aluminum vs. Copper Confusion

The table above is strictly for copper. Aluminum wire has higher resistance and requires a larger physical cross-section to carry the same current. For example, to carry 50A safely, you need 6 AWG copper, but you must step up to 4 AWG aluminum. Never use the copper column for aluminum feeders, and never terminate aluminum wire on a device that is not explicitly marked 'CO/ALR' or rated for aluminum, as galvanic corrosion and thermal expansion differences will loosen the connection and cause a fire.