Copper vs Aluminum Wire Size Chart: NEC Ampacity Guide

To carry the same current, aluminum wire must typically be sized two AWG steps larger than copper. For example, a 100-amp residential feeder requires 3 AWG copper or 1 AWG aluminum when using the standard 75°C termination column. This copper vs aluminum wire size chart provides the exact ampacity values derived directly from NEC Table 310.16, assuming an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway.

How to Read This Chart

The table below is divided by conductor material (Copper vs. Aluminum) and temperature rating (60°C vs. 75°C). The 90°C column is omitted from this quick-reference because NEC 110.14(C) strictly limits the final ampacity to the temperature rating of the termination lugs, which are almost never rated for 90°C in residential gear. The 90°C column is only used as a starting point for calculating derating factors (like conduit bundling) before applying the termination limit.

Master Copper vs Aluminum Wire Size Chart (NEC Table 310.16)

Bookmark this section for rapid lookups. The values below represent the maximum allowable ampacity for standard THHN/THWN-2 (copper) and XHHW-2 (aluminum) insulation types.

Quick-Jump: Most Queried Residential Feeder Sizes

• 100-Amp Subpanel: 3 AWG Copper or 1 AWG Aluminum (75°C column)
• 125-Amp Feeder: 1 AWG Copper or 1/0 AWG Aluminum (75°C column)
• 150-Amp Feeder: 1/0 AWG Copper or 2/0 AWG Aluminum (75°C column)
• 200-Amp Main Service: 2/0 AWG Copper or 4/0 AWG Aluminum (75°C column)

Source: Adapted from NEC Table 310.16 (2020/2023 editions). For comprehensive industrial sizing, refer to the Southwire Ampacity Chart or the full NEC text.

Which Column Applies to Your Installation?

The most common mistake DIYers and junior apprentices make is reading the 90°C column because the wire jacket says 'THHN-90°C'. The wire insulation can handle 90°C, but the breaker lugs and bus bars usually cannot. NEC 110.14(C) dictates that the lowest temperature rating of any connected component dictates the column you must use.

The 60°C Column: NM-B (Romex) and Older Gear

If you are running standard non-metallic sheathed cable (NM-B, commonly known by the brand name Romex), you are legally bound to the 60°C column, regardless of the fact that modern NM-B wire insulation is technically rated for 90°C. This is because the NEC specifically restricts NM-B ampacity to the 60°C limits for safety margins inside insulated walls. Additionally, if you are connecting to an older breaker or disconnect switch manufactured before 1995, the lugs are likely only rated for 60°C.

The 75°C Column: THHN in Conduit and Modern Panels

When pulling individual THHN/THWN-2 copper or XHHW-2 aluminum conductors through PVC or EMT conduit to a modern subpanel or main breaker, you use the 75°C column. Virtually all modern residential breakers (Square D Homeline/QO, Eaton BR/CH, Siemens) and load centers feature 75°C rated termination lugs. This is why a 200-amp main service can use 4/0 aluminum (rated 180A at 75°C, but allowed for 200A residential services under specific NEC 310.12 dwelling service exceptions) or 2/0 copper (175A at 75°C, similarly allowed for 200A dwelling services).

Derating, Bundling, and What the Table Cannot Tell You

The copper vs aluminum wire size chart above assumes ideal conditions: an ambient temperature of 30°C (86°F) and a maximum of three current-carrying conductors in a single raceway. Real-world jobsite conditions frequently require you to adjust these base numbers.

How Derating Rows Modify the Base Value

When you run more than three current-carrying conductors in a conduit (for example, two hots, a neutral, and a ground for a multi-wire branch circuit, or feeders for multiple subpanels in one pipe), the wires heat each other up. You must apply a derating factor from NEC Table 310.15(C)(1).

Worked Example: You are pulling four current-carrying conductors (two 240V circuits sharing a neutral) through a single EMT conduit. You want to use copper. The derating factor for 4-6 conductors is 80%. You decide to use 8 AWG THHN. The 90°C column for 8 AWG Cu is 55A. Multiply 55A by 0.80 = 44A. Now, check your termination limits. Your breaker lugs are 75°C rated, and the 75°C column for 8 AWG is 50A. Because your derated value (44A) is lower than the termination limit (50A), the wire is legally limited to 44A. You must protect this circuit with a 40A breaker, not a 50A breaker.

Ambient Temperature Corrections

If your conduit runs through an attic in a southern climate where ambient temperatures regularly exceed 86°F (30°C), you must apply temperature correction factors from the bottom of Table 310.16. For instance, in a 110°F (43°C) attic, the correction factor for 90°C wire is 0.87. You multiply the 90°C base ampacity by 0.87 before comparing it to your termination limits.

What the Table Cannot Tell You

Ampacity charts only tell you the thermal limits of the wire insulation and terminations. They do not account for voltage drop. If you are running a 100-amp aluminum feeder to a detached garage 250 feet away, 1 AWG aluminum will safely carry the current without melting, but the voltage drop at the far end under full load will exceed the recommended 3% threshold, causing motors to overheat and lights to dim. For long runs, you must calculate voltage drop using the formula VD = (2 × K × I × D) / CM and typically upsize the wire by one or two additional AWG steps beyond what the ampacity chart demands.

Furthermore, the chart cannot override your local Authority Having Jurisdiction (AHJ). Some municipalities have local amendments that ban aluminum branch wiring entirely or require specific conduit types for aluminum feeders. Always verify your local electrical code before purchasing bulk wire.