The baseline 1/0 aluminum wire ampacity is 120 amps when using the 75°C column of NEC Table 310.16, which governs most modern residential and commercial terminations. If your equipment is strictly rated for 60°C, the allowable ampacity drops to 100 amps. At the 90°C column—used exclusively for derating calculations before applying termination limits—the value is 135 amps.

Getting this number right is the difference between a safe, code-compliant subpanel feeder and a melted terminal lug. Below is the complete reference data, the exact rules for selecting your temperature column, and the derating math you need for real-world conduit runs.

The 1/0 Aluminum Wire Ampacity Chart (NEC Table 310.16)

The following table is sourced directly from NEC Table 310.16 (2023/2026 editions) for aluminum conductors with common insulations like THWN-2, XHHW-2, and USE-2.

How to read this table: The columns represent the maximum temperature rating of the wire's insulation. The 60°C column applies to older equipment or specific small-gauge terminations. The 75°C column applies to most modern breakers and lugs. The 90°C column is the wire's absolute thermal limit, used as the starting point for ambient temperature and bundling derating calculations.
AWG Size60°C (140°F) Column75°C (167°F) Column90°C (194°F) ColumnCommon Insulation Types
2 AWG75 A90 A100 ATHWN, XHHW
1 AWG85 A100 A115 ATHWN-2, XHHW-2
1/0 AWG100 A120 A135 ATHWN-2, XHHW-2, USE-2
2/0 AWG115 A135 A150 ATHWN-2, XHHW-2
3/0 AWG130 A155 A170 ATHWN-2, XHHW-2
4/0 AWG150 A180 A205 ATHWN-2, XHHW-2

Which Temperature Column Actually Applies to Your Install?

The most common mistake DIYers and junior electricians make is looking at the 90°C column (135A for 1/0 AL) and assuming they can put it on a 135A breaker. You cannot. NEC Article 110.14(C) dictates that the ampacity of a circuit is limited by the lowest temperature rating of any connected device, terminal, or splice.

  • The 60°C Column (100A): Applies if your breaker or panel lugs are unmarked, or if the equipment is explicitly rated only for 60°C. Historically, the NEC defaulted circuits 100A or less to the 60°C column, but modern equipment listings have largely superseded this for larger wire sizes.
  • The 75°C Column (120A): Applies when your breaker, panelboard lugs, or disconnect switches are clearly marked 'AL/CU 75°C'. Almost all modern 100A and 125A subpanel breakers and main lugs carry this 75°C rating, making 120A the standard usable ampacity for 1/0 aluminum.
  • The 90°C Column (135A): Used only as the baseline for derating. Even if your wire is rated 90°C, the final derated ampacity cannot exceed the termination limit (usually 120A).
Bench Tip: Aluminum oxidizes rapidly when exposed to air, creating a high-resistance layer that generates heat. Always brush the wire strands and apply an anti-oxidant compound (like Noalox or Penetrox) before torquing the lug. Use a calibrated torque screwdriver to hit the exact inch-pound specification printed on the breaker label; aluminum is prone to cold creep and will loosen over-torqued or under-torqued connections.

How Derating Modifies the Base Ampacity

Table 310.16 assumes an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway. If your installation deviates from this, you must derate using the 90°C column as your starting point.

Worked Example: 1/0 Aluminum in a Hot Attic
Suppose you are pulling four current-carrying conductors (two hots, one neutral, one grounded conductor carrying continuous unbalanced load) through an attic where the ambient temperature reaches 110°F (43°C).

  1. Base Value: Start with the 90°C column for 1/0 AL = 135A.
  2. Ambient Correction: Per NEC Table 310.15(B)(1), the correction factor for 90°C insulation at 110°F is 0.87.
  3. Bundling Adjustment: Per NEC Table 310.15(C)(1), 4 to 6 current-carrying conductors require an 80% (0.80) adjustment factor.
  4. The Math: 135A × 0.87 × 0.80 = 93.96A.

Because 93.96A is lower than the 75°C termination limit of 120A, your final usable ampacity is 93.96A. You cannot use a 100A breaker here; you must either upsize to 2/0 aluminum, reduce the ambient heat, or separate the conductors into different raceways.

What the Ampacity Table Cannot Tell You

While NEC Table 310.16 is the law of the land for thermal limits, it does not account for voltage drop or physical installation constraints. Always cross-reference these factors before pulling wire:

  • Voltage Drop: The NEC recommends a maximum 3% voltage drop for feeders. 1/0 aluminum has a higher resistance than copper (roughly 0.20 ohms per 1000 ft vs 0.12 ohms for copper). On a 240V feeder running 150 feet to a detached garage at 100A, 1/0 AL will yield roughly a 2.5% drop. If your run exceeds 180 feet, you must upsize to 2/0 AL to maintain the 3% threshold, regardless of ampacity.
  • Physical Pulling Tension: 1/0 aluminum is stiff. When pulling through conduit with multiple sweeps, use wire pulling lubricant to avoid scoring the insulation or snapping the conductor.
  • Local AHJ Amendments: Some municipalities have banned aluminum branch wiring or have strict rules about aluminum feeders into residential structures. Always verify with your local inspector, as local code overrides general NEC guidance.

Frequently Asked Questions

Can I use 1/0 aluminum wire for a 100-amp subpanel?

Yes, 1/0 aluminum is actually oversized for a standard 100-amp subpanel if you are using the 75°C column (which allows 120A). However, it is highly recommended if your run is longer than 100 feet to mitigate voltage drop, or if you anticipate upgrading to a 125-amp main breaker in the future. For a strict 100A panel at short distances, 2 AWG aluminum (90A at 60°C, 100A at 75°C) is the minimum code-compliant size, provided your terminations are rated 75°C.

What size breaker can I use with 1/0 AWG aluminum?

If your panel lugs and breaker are rated 75°C, you can use a breaker rated up to 120 amps. Standard breaker sizes jump from 100A to 110A to 125A. Since there is no standard 120A breaker in most residential load centers, the NEC 'next size up' rule (Article 240.4(B)) allows you to protect a 120A calculated load with a 125A breaker, provided the load is not continuous. For continuous loads, you must size the breaker at 125% of the load, meaning a 100A continuous load requires a 125A breaker, which perfectly aligns with 1/0 AL wire.

How does 1/0 aluminum compare to copper for the same ampacity?

To achieve the same 120A ampacity in the 75°C column, you would need 1 AWG copper wire. Aluminum is significantly lighter and cheaper—often 40% to 60% less expensive per foot than copper—but it requires a larger physical gauge (1/0 vs 1 AWG) to carry the same current. You also must use larger conduit, as the cross-sectional area of 1/0 AL is greater than 1 AWG copper.

Is 1/0 aluminum wire safe for direct burial?

Yes, but only if the insulation type is rated for wet locations and direct burial. Standard THWN-2 in conduit is fine, but if you are burying the wire without conduit, you must use USE-2 (Underground Service Entrance) or direct-burial rated XHHW-2. The ampacity for direct burial installations is governed by NEC Table 310.104 and specific underground thermal resistivity rules, which generally align with the 75°C column limits for residential applications.