AWG Cable Rating Chart: NEC Ampacity & Wire Size Guide

For standard residential branch circuits, the baseline AWG cable rating is 15A for 14 AWG, 20A for 12 AWG, and 30A for 10 AWG copper wire. These values are derived from the 60°C column of NEC Table 310.16 (formerly 310.15(B)(16)). However, simply memorizing these three numbers will lead to failed inspections or melted terminations on larger feeds. Ampacity is not a fixed property of the metal; it is a thermal limit dictated by insulation type, termination ratings, and how many wires share a conduit.

This reference guide provides the exact ampacity values you need, explains how to read the temperature columns, and details the derating math that shrinks your wire's capacity in real-world installations.

The Master AWG Cable Rating Chart (NEC Table 310.16)

Before pulling wire, consult the table below. This data is extracted directly from the National Electrical Code (NEC) for copper and aluminum conductors rated up to 2000V.

Bookmark Quick-Jumps: 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 2 AWG | 1/0 AWG

Which Temperature Column Applies to Your Installation?

The most common mistake DIYers and junior apprentices make is looking at a spool of 90°C-rated THHN wire, finding the 90°C column, and assuming they can push that maximum current. In almost all residential and light commercial scenarios, you cannot use the 90°C column for your final ampacity.

Here is the decision framework dictated by NEC 110.14(C):

• The 60°C Column (Circuits 100A or less): For circuits rated 100 amps or less, or for wire sizes 14 AWG through 1 AWG, you must use the 60°C column. This is because standard residential breakers, receptacles, and switches are typically tested and rated for 60°C terminations. Even if your wire insulation can handle 90°C, the plastic housing of a standard 15A duplex receptacle will deform if the termination point exceeds 60°C.
• The 75°C Column (Circuits over 100A): For circuits rated over 100A, or wire sizes larger than 1 AWG, you may use the 75°C column. Most modern main breaker panels, subpanel lugs, and heavy-duty disconnects are rated for 75°C terminations.
• The 90°C Column (Derating only): The 90°C column is almost exclusively used as the starting baseline for derating calculations (explained below) or for specific high-temperature industrial equipment explicitly marked for 90°C terminations.

Real-World Example: You are wiring a 60A subpanel using 6 AWG copper THHN. The 90°C column says 75A. The 75°C column says 65A. The 60°C column says 55A. Because the subpanel lugs are rated 75°C, you use the 75°C column. 65A is greater than your 60A breaker, so 6 AWG is legal and safe. If you used standard NM-B (Romex), which is strictly limited to the 60°C column regardless of breaker size, 6 AWG NM-B is only rated 55A, forcing you to upsize to 4 AWG NM-B for a 60A feed.

Derating Factors: When the Base Value Drops

The ampacity chart above assumes two ideal conditions: an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors bundled together. When you violate either condition, the wire cannot dissipate heat as efficiently, and you must apply a derating multiplier to the 90°C column (for THHN/THWN-2) to find your new allowable ampacity.

1. Bundling (More than 3 Current-Carrying Conductors)

Per NEC 310.15(C)(1), if you pull 4 to 6 current-carrying conductors in a single raceway, you multiply the 90°C base ampacity by 80%. For 7 to 9 conductors, the multiplier drops to 70%.

2. Ambient Temperature

If your conduit runs through an attic in a southern climate where temperatures hit 50°C (122°F), you must apply an ambient temperature correction factor. For 90°C insulation at 50°C ambient, the multiplier is 0.82. You multiply the 90°C base by 0.82, then apply the bundling factor if applicable. Always check the Southwire Ampacity Chart or NEC Table 310.15(B)(1) for exact temperature correction multipliers.

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

While NEC Table 310.16 is the bible for thermal limits, it is blind to three critical physical and electrical realities that can force you to upsize your wire regardless of the ampacity chart.

Voltage Drop on Long Runs

Ampacity only tells you if the wire will melt; it does not tell you if the voltage at the far end will be sufficient to run your equipment. The NEC generally recommends a maximum 3% voltage drop on branch circuits and 5% total from service to outlet. If you are running a 120V, 15A circuit to a detached garage 150 feet away, 14 AWG is thermally legal for 15A, but the voltage drop will exceed 6%. You must calculate voltage drop using the formula VD = (2 × K × I × L) / CM and likely upsize to 10 AWG or 8 AWG to keep the saw running at full power.

Conduit Fill Capacity

You might calculate that 12 AWG is perfectly fine for your derated ampacity, but if you are trying to pull twelve 12 AWG THHN wires through a 1/2-inch EMT conduit, you will violate NEC Chapter 9, Table 1. Conduit fill limits dictate that for 3 or more wires, you cannot exceed 40% of the conduit's internal cross-sectional area. Always check a conduit fill calculator before buying wire; sometimes you are forced to upsize the conduit rather than the wire.

Short-Circuit Withstand Ratings

Ampacity assumes normal operating loads. In a dead short, thousands of amps flow for milliseconds before the breaker trips. Smaller wires (like 14 AWG) can vaporize or suffer severe insulation damage if subjected to high available fault currents (e.g., 42,000A at a main panel) before the magnetic trip clears. While residential services rarely hit these extremes, industrial and commercial installations must verify that the chosen AWG cable rating aligns with the available fault current and the specific let-through current of the protective device.