For standard residential copper branch circuits, the baseline ampacities are: 14 AWG is 15A, 12 AWG is 20A, and 10 AWG is 30A. However, pulling a wire gauge ampacity chart off the internet without understanding the National Electrical Code (NEC) temperature columns and derating factors is how beginners end up with melted lugs or tripped breakers. This guide translates NEC Table 310.16 from a confusing matrix into a direct decision-making tool for your next wiring project.

How to Read the NEC 310.16 Ampacity Table

Before looking at the numbers, you must understand how the table is structured. The NEC separates conductors by material (Copper vs. Aluminum/Copper-Clad) and by insulation temperature rating (60°C, 75°C, and 90°C).

How to read this table: Find your AWG size in the left column. Move right to the Copper section. You will see three temperature columns. The 60°C column is for older equipment and small wires; the 75°C column is for most modern terminations; the 90°C column is strictly a starting point for derating calculations. Always assume copper unless your wire is explicitly marked AL or ALR.
Table 310.16 Allowable Ampacities of Insulated Conductors (Copper, 30°C Ambient, Not More Than Three Current-Carrying Conductors)
AWG / kcmil 60°C (140°F) TW, UF 75°C (167°F) THW, THWN, RHW 90°C (194°F) THHN, XHHW-2
1415A20A25A
1220A25A30A
1030A35A40A
840A50A55A
655A65A75A
470A85A95A
385A100A110A
295A115A130A
1110A130A145A
1/0125A150A170A
2/0145A175A195A
3/0165A200A225A
4/0195A230A260A

Source: NEC 2023/2026 Table 310.16. For aluminum, drop down one or two AWG sizes to find equivalent ampacity.

Quick-Jump: Most Queried Residential Wire Sizes

Bookmark this section for the most common branch circuit and feeder sizing questions. These assume standard 75°C terminations and no more than three current-carrying conductors in a raceway.

  • 14 AWG Copper: 15 Amps. Used for 120V lighting circuits. Restriction: NEC 240.4(D) strictly limits 14 AWG to 15A, even if the insulation is rated 90°C.
  • 12 AWG Copper: 20 Amps. The workhorse for 120V kitchen, bathroom, and general receptacle circuits.
  • 10 AWG Copper: 30 Amps. Standard for 120V/240V electric dryers (if 30A) and heavy 120V window AC units.
  • 8 AWG Copper: 40 Amps (at 60°C) / 50 Amps (at 75°C). Common for 40A EV chargers or 50A electric ranges (when 75°C rated).
  • 6 AWG Copper: 55 Amps (at 60°C) / 65 Amps (at 75°C). The standard choice for 50A hot tubs, subpanels, and 60A EV chargers.
  • 4 AWG Copper / 2 AWG Aluminum: The go-to pairing for 100A residential subpanel feeders.
  • 2 AWG Copper / 1/0 AWG Aluminum: The standard for 125A to 150A main service entrance feeders (verify with local utility).

Which Temperature Column Applies to Your Installation

The most common mistake DIYers make is looking at the 90°C column because THHN wire is cheap and widely available, then assuming they can push 40A through 10 AWG wire. You cannot. The Copper Development Association and NEC 110.14(C) enforce the "weakest link" rule: your circuit ampacity is limited by the lowest temperature rating of any connected device, termination, or conductor in the run.

The 60°C Column: You must use this column if you are using 14, 12, or 10 AWG wire, regardless of the wire's insulation rating. You also use it if you are connecting to older equipment (pre-1980s) that is not explicitly marked with a 75°C rating.

The 75°C Column: This is your default for modern residential wiring. Almost all modern circuit breakers, receptacles, and lugs are rated for 75°C. If you are pulling 8 AWG or larger, and your devices are marked 75°C, use this column.

The 90°C Column: This column is never used to determine the final breaker size or termination ampacity. It exists solely to give you a higher baseline number to apply derating math to (explained below).

Derating Factors: When Base Ampacity Drops

The chart above assumes an ambient temperature of 86°F (30°C) and no more than three current-carrying conductors (CCCs) bundled together. When you stuff more wires into a conduit or run them through a hot attic, the wires cannot dissipate heat, and their ampacity drops.

You calculate the derated ampacity using the 90°C column, but you must then compare that result to the 75°C (or 60°C) termination limit. The final allowable ampacity is the lower of the two numbers.

Derating Decision Path: Adjusting for Bundling and Heat
Installation Condition Math / Adjustment Factor Concrete Result for 12 AWG THHN (Base 90°C = 30A)
Standard: Max 3 CCCs, ambient under 86°F No derating. Use base 75°C termination limit. 25A (Limited by 75°C col). Breaker: 20A.
Bundling: 4 to 6 CCCs in one conduit Multiply 90°C base by 80% (30A x 0.80 = 24A). 24A (24A < 25A limit). Breaker: 20A.
Bundling: 7 to 9 CCCs in one conduit Multiply 90°C base by 70% (30A x 0.70 = 21A). 21A (21A < 25A limit). Breaker: 20A.
High Heat: 110°F (43°C) attic ambient Multiply 90°C base by 0.87 (30A x 0.87 = 26.1A). 25A (Capped by 75°C limit). Breaker: 20A.
Extreme: 7-9 CCCs AND 110°F attic Multiply 90°C base by 0.70, then by 0.87 (18.2A). 18.2A. Must upgrade to 10 AWG for a 20A breaker.
Neutral and Ground Counting: In a standard single-phase 120V/240V circuit, the neutral carries unbalanced current and counts as a CCC. The equipment grounding conductor (EGC) never counts as a CCC for derating purposes. In a multi-wire branch circuit (MWBC) sharing a neutral, the neutral counts as a CCC.

What the Chart Cannot Tell You (And Your Default Pick)

The NEC 310.16 ampacity chart is a thermal limit chart. It tells you the point at which the wire's insulation will melt or degrade. It completely ignores two critical real-world physics problems:

  1. Voltage Drop: The chart doesn't care if your 12 AWG wire is 10 feet long or 300 feet long. At 300 feet, a 15A load on 12 AWG copper will drop nearly 12 volts (10%), causing motors to overheat and lights to dim. For runs over 50 feet, you must calculate voltage drop using NEC Chapter 9, Table 8 resistance values, often requiring you to upsize the wire by one or two AWG sizes regardless of ampacity.
  2. Conduit Fill: The chart assumes you can physically fit the wires in the pipe. If you try to pull four 6 AWG THHN wires and a 10 AWG ground into a 1/2-inch EMT conduit, you will jam the wires, damage the insulation, and violate NEC Chapter 9, Table 1 (which limits conduit fill to 40% for three or more wires).

Your Concrete Default Recommendation: Stop guessing. If you are wiring a standard 20A indoor receptacle circuit and want a single, foolproof baseline that handles minor bundling, standard attic heat, and avoids voltage drop on runs up to 60 feet: Pull 12 AWG copper THHN/THWN-2 in conduit, terminate on 75°C-rated devices, and protect with a 20A breaker. If your run exceeds 60 feet, step up to 10 AWG copper to mitigate voltage drop, but leave the breaker at 20A.