The base ampacity for 1 AWG copper wire is 130A at 60°C, 150A at 75°C, and 170A at 90°C. For 1 AWG aluminum (or copper-clad aluminum), the ratings are 100A at 60°C, 120A at 75°C, and 135A at 90°C. However, these base numbers are only the starting point. The actual allowable current depends entirely on your insulation type, termination temperature ratings, and raceway fill conditions.

How to Read the 1 AWG Ampacity Table (NEC Article 310.16)

Before pulling wire, you must understand how to read the National Electrical Code (NEC) ampacity tables. The table below is derived directly from NFPA 70 (NEC) Table 310.16, which dictates the allowable ampacities of insulated conductors rated up to 2000 volts.

How to read this table: The rows represent the wire gauge (AWG/kcmil) and material. The columns represent the temperature rating of the wire's insulation. To find your base ampacity, locate 1 AWG in the left column, then move right to the column that matches your wire's insulation rating (e.g., THHN is 90°C, THWN is 75°C, older NM-B is 60°C).
Table 1: 1 AWG Base Ampacity (Source: NEC Table 310.16, 30°C Ambient)
Conductor Material 60°C (140°F) Column 75°C (167°F) Column 90°C (194°F) Column
1 AWG Copper 130 Amps 150 Amps 170 Amps
1 AWG Aluminum / Cu-Clad 100 Amps 120 Amps 135 Amps

Which Column Actually Applies to Your Installation?

A common mistake is looking at a spool of 90°C THHN wire, seeing the 170A rating, and assuming you can push 170 amps through it. In almost all residential and commercial applications, the 75°C column is your functional limit.

Under NEC Article 110.14(C), the allowable ampacity is limited by the lowest temperature rating of any connected component. Because standard circuit breakers, panel lugs, and disconnect switches are typically rated for 75°C terminations, your 1 AWG copper wire is legally capped at 150A, regardless of the fact that the wire's insulation can handle 90°C. The 60°C column is generally only used for older NM-B (Romex) cable installations or specific equipment explicitly marked for 60°C.

Applying Derating Factors to 1 AWG Conductors

The base ampacity table assumes two ideal conditions: an ambient temperature of exactly 30°C (86°F) and no more than three current-carrying conductors bundled in a raceway. When real-world conditions deviate, you must apply derating factors. This is where the 90°C column finally earns its keep.

When calculating derating for ambient temperature or conduit fill (bundling), you always start your math using the 90°C column, even if your terminations are rated for 75°C. After applying the derating multiplier, you compare the result to the 75°C terminal limit and use whichever number is lower.

Worked Derating Example

Imagine you are pulling four 1 AWG THHN copper conductors (two hots, one neutral, one ground) through a single conduit to feed a subpanel. Because you have four current-carrying conductors (the ground does not count, but the neutral does in a multi-wire setup with non-linear loads or specific 3-phase configurations; let's assume all 4 are current-carrying for this worst-case scenario), NEC Table 310.15(C)(1) requires an 80% derating factor.

  • Step 1 (Start at 90°C): Base ampacity for 1 AWG Cu at 90°C is 170A.
  • Step 2 (Apply Bundling Factor): 170A × 0.80 = 136A.
  • Step 3 (Check Terminal Limit): The breaker lugs are rated 75°C (150A limit).
  • Final Result: Compare 136A (derated) to 150A (terminal). The lower number wins. Your final allowable ampacity is 136 Amps.
Pro-Tip for Attic Runs: If that same conduit runs through an attic that reaches 110°F (43°C), you must also apply the ambient temperature correction factor from the bottom of Table 310.16 (0.87 for 90°C wire). You multiply the bundling factor and the temperature factor together: 170A × 0.80 × 0.87 = 118.3A. Always calculate the worst-case thermal bottleneck.

What the Ampacity Table Cannot Tell You

Ampacity charts only address the thermal limits of the wire's insulation. They do not guarantee a functional or code-compliant installation on their own. Here is what the table leaves out:

1. Voltage Drop Over Distance

NEC Table 310.16 does not account for voltage drop. If you are running a 1 AWG aluminum feeder 200 feet to a detached garage subpanel drawing 100A at 240V, the wire will not overheat, but your voltage at the destination will drop below the NEC-recommended 3% threshold for feeders. For long runs, you must consult NEC Chapter 9, Table 8 for DC resistance values and upsize the wire (e.g., to 1/0 or 2/0 AWG) to maintain voltage stability, even if 1 AWG satisfies the ampacity requirement.

2. Physical Termination Fit

1 AWG wire is physically thick and stiff. Many standard 100A or 125A residential breakers are designed to accept a maximum of 2 AWG or 3 AWG wire under their lug screws. Forcing a 1 AWG conductor into an undersized lug can damage the breaker, strip the setscrew, or create a high-resistance connection that leads to arcing and thermal failure. Always verify the breaker manufacturer's datasheet for maximum wire sizing before purchasing.

3. Short-Circuit Withstand Ratings

Ampacity defines continuous thermal loading. It does not tell you how the wire will behave during a massive fault current event. The available fault current at your service entrance, combined with the let-through current of your breaker, dictates whether the wire will survive a short circuit without melting its insulation. This requires engineering calculations beyond standard ampacity tables.

1 AWG Ampacity FAQ

Can I use 1 AWG aluminum wire for a 100-amp subpanel feeder?

Yes. 1 AWG aluminum wire has a 75°C ampacity of 120A, which comfortably exceeds the 100A breaker requirement. In fact, 1 AWG aluminum (often sold as 1-1-1-3 AL MH feeder) is the industry standard, cost-effective choice for 100A residential subpanel feeds. Just ensure you use an anti-oxidant compound (like Noalox) on the aluminum strands before torquing the lugs to prevent oxidation and thermal creep over time.

What size breaker can I use with 1 AWG copper wire?

Assuming standard 75°C terminations, 1 AWG copper is rated for 150A. Under NEC 240.4(B), if your calculated continuous and non-continuous load does not exceed 150A, you can protect this wire with a 150A breaker. If your calculated load is slightly higher (e.g., 155A) and the next standard breaker size is 175A, you cannot use the next-size-up rule because the wire's ampacity (150A) does not correspond to a standard breaker size that allows rounding up past its limit. You would need to upsize to 1/0 AWG copper.

Does 1 AWG wire ampacity change if it is buried directly in the earth?

Yes. Table 310.16 applies to conductors in raceways or cable trays. For direct burial, you must use NEC Table 310.16(1) (or the specific cable assembly listing). For example, 1 AWG copper USE-2 (Underground Service Entrance) cable buried directly in the earth has an allowable ampacity of 150A, but this is heavily dependent on the thermal resistivity of the soil and the depth of the trench. Always check the specific cable jacket printing and local AHJ requirements for direct burial installations.