The direct answer for standard residential and light commercial wiring: 1/0 AWG aluminum wire has an ampacity of 100 Amps in the 60°C column, 120 Amps in the 75°C column, and 135 Amps in the 90°C column per NEC Table 310.16. For a standard 100A subpanel feeder, you must use the 60°C column value, making 1/0 aluminum the exact minimum size required.

When searching for the 1 0 aluminum ampacity, most builders get tripped up by the three different temperature columns in the National Electrical Code (NEC). Picking the wrong column leads to either a failed inspection or an undersized feeder that overheats at the breaker lugs. Below is the complete reference data, the physics behind the temperature ratings, and a strict decision path to finalize your breaker and wire sizing.

1 0 Aluminum Ampacity: The Quick Reference Chart (NEC Table 310.16)

This table is extracted directly from NFPA 70 (NEC) Table 310.16, which governs allowable ampacities for insulated conductors rated up to 2000 volts. The values below assume an ambient temperature of 30°C (86°F) and not more than three current-carrying conductors in a raceway or cable.

How to read this table: The columns represent the temperature rating of the weakest link in your circuit—usually the breaker or panel lugs, not the wire insulation itself. Even if your 1/0 aluminum wire has 90°C THHN insulation, you cannot use the 90°C column for your final breaker sizing unless every single termination point in the circuit is explicitly rated for 90°C (which is virtually nonexistent in standard residential gear).
Table 310.16 Allowable Ampacities for 1/0 AWG Aluminum (30°C Ambient)
Conductor Size Material 60°C (140°F) Column 75°C (167°F) Column 90°C (194°F) Column
1/0 AWG Aluminum (XHHW, THHN, USE-2) 100 Amps 120 Amps 135 Amps
1 AWG Aluminum 85 Amps 100 Amps 115 Amps
2/0 AWG Aluminum 115 Amps 135 Amps 150 Amps

Source: Southwire Ampacity Chart / NEC Table 310.16. Always verify with the specific manufacturer datasheet for your wire brand.

Which Temperature Column Actually Applies to Your Installation?

The NEC dictates which column you must use based on the rating of your equipment terminations, governed by NEC 110.14(C). Here is how the rules apply specifically to 1/0 aluminum:

  • The 60°C Column (100A): NEC 110.14(C)(1)(a) states that for circuits rated 100 Amps or less, you must use the 60°C column unless the equipment is specifically marked and listed for 75°C. Because most standard 100A residential breakers and subpanel lugs are conservatively rated, the 60°C column is the default governing rule for a 100A feeder. This yields 100 Amps.
  • The 75°C Column (120A): NEC 110.14(C)(1)(b) allows the use of the 75°C column for circuits rated over 100 Amps, or if the equipment is explicitly marked for 75°C terminations. If you are feeding a 125A subpanel and the main breaker lugs are rated 75°C, you can use the 75°C column, yielding 120 Amps.
  • The 90°C Column (135A): You never use this column for final termination ampacity in standard residential work. This column exists solely as a mathematical starting point for derating calculations (explained below).

Derating 1/0 Aluminum: When Heat and Conduit Fill Reduce Capacity

Ampacity drops when you bundle multiple current-carrying conductors in a single conduit or when the ambient temperature exceeds 30°C (86°F). This is where the 90°C column finally earns its keep. Per NEC 310.15(C)(1), derating calculations always start from the 90°C column, even if your final termination must use the 60°C column.

Worked Numeric Example:
You are pulling two hots, a neutral, and a ground for a 120/240V subpanel through a conduit that passes through an attic where the ambient temperature hits 40°C (104°F). You have 3 current-carrying conductors (the ground does not count).

  1. Start with 90°C base: 135 Amps.
  2. Apply Temperature Correction (Table 310.15(B)(1)): At 40°C ambient, the correction factor for 90°C wire is 0.91. 135A × 0.91 = 122.8 Amps.
  3. Apply Adjustment Factor (Table 310.15(C)(1)): 3 current-carrying conductors means no adjustment (100% factor). If you had 4-6 conductors, you'd multiply by 0.80.
  4. Compare to Termination Limits: Your derated wire capacity is 122.8A. However, your 100A breaker lugs are limited to the 60°C column (100A). The final allowable ampacity is the lower of the two numbers.
Result: The wire is thermally capable of 122.8A in that hot attic, but the breaker lugs tap out at 100A. Your 1/0 aluminum is still perfectly legal and safe for a 100A breaker in this scenario.

Decision Path: Sizing the Breaker and Wire for Your 1/0 Feeder

Use this decision tree to lock in your exact material list. Do not guess; follow the logic to the terminal node.

Condition / Scenario Required Action Final Concrete Pick
IF your calculated continuous and non-continuous load is ≤ 80 Amps, and run is < 100 ft. 1/0 Al is oversized but acceptable. You can downsize to save money. Use #2 AWG Aluminum on a 90A or 100A breaker.
IF your load is exactly 100A (standard subpanel), run is < 100 ft, standard residential lugs. Use the 60°C column. 1/0 Al is the exact minimum required size. Use 1/0 AWG Aluminum on a 100A breaker.
IF your load is 110A–120A, and panel lugs are explicitly rated 75°C. Use the 75°C column. 1/0 Al is sufficient up to 120A. Use 1/0 AWG Aluminum on a 125A breaker (next standard size up per 240.4(B)).
IF your run is > 100 feet regardless of load. Ampacity table is insufficient. Voltage drop will exceed 3% at 240V. Upsize to 2/0 AWG Aluminum to mitigate voltage drop.

Default Recommendation: If you are pulling a standard 100A subpanel feeder for a detached garage or workshop under 100 feet away, buy a 100A breaker and pull three strands of 1/0 AWG aluminum (two hots, one neutral) plus one #2 AWG aluminum ground. Terminate strictly using the 60°C column limits.

What the Ampacity Table Cannot Tell You (Voltage Drop & Physical Limits)

The NEC ampacity tables only address thermal limits—preventing the wire insulation from melting. They do not guarantee your equipment will operate correctly. When working with 1/0 aluminum, you must account for three physical realities that the table ignores:

1. Voltage Drop Over Distance

NEC 310.15(B) contains an informational note recommending a maximum 3% voltage drop for feeders. At 240V, a 3% drop is 7.2 volts. 1/0 aluminum has a resistance of roughly 0.20 ohms per 1,000 feet. If your feeder run is 150 feet and pulling a full 100A load, your voltage drop will be approximately 6 volts (2.5%), which is acceptable. However, if you push 120A over 200 feet, you will drop over 9.6 volts (4%), causing motors to overheat and lights to dim. For runs over 125 feet at full load, upsize to 2/0 aluminum.

2. Aluminum Creep and Termination Torque

Unlike copper, aluminum expands and contracts significantly more under thermal cycling. Over time, this "creep" can cause mechanical lug connections to loosen, increasing resistance and creating a fire hazard. You must use a calibrated torque screwdriver or wrench to tighten the breaker and panel lugs to the manufacturer's exact specification (typically printed on the breaker label, often between 25 and 40 in-lbs for 1/0 wire). Hand-tightening is a code violation and a fire risk.

3. Anti-Oxidant Compound

Raw aluminum oxidizes almost instantly when exposed to air, forming a highly resistive layer. While modern AA-8000 series aluminum alloy wire is more stable than the problematic aluminum wiring of the 1970s, best practice (and often local code) requires applying an anti-oxidant paste (like Noalox or Penetrox) to the stripped wire before inserting it into the lug. This paste displaces moisture and prevents oxide buildup, ensuring a stable, low-resistance connection for decades.