The Direct Answer: 1 AWG Aluminum Wire Ampacity
According to NEC Table 310.16, the base ampacity for 1 AWG aluminum wire is 100 amps at 60°C, 120 amps at 75°C, and 135 amps at 90°C.
For 95% of modern residential and commercial installations, your termination points (breakers and lugs) are rated for 75°C. Therefore, the standard, legally usable ampacity for 1 AWG aluminum is 120 amps. You can safely protect this wire with a 120A breaker, or use it for a 100A subpanel feeder with plenty of thermal headroom. If you are working with older equipment rated only for 60°C, you must downgrade your usable ampacity to 100A, regardless of the wire's insulation rating.
• 60°C Column: 100A (Use for older panels, NM-B cable transitions, or unknown equipment ratings)
• 75°C Column: 120A (The default for modern THWN-2/XHHW feeders and standard subpanels)
• 90°C Column: 135A (Used ONLY as a starting point for derating calculations, never for final breaker sizing)
How to Read the NEC 310.16 Ampacity Table
The National Electrical Code (NEC) organizes ampacity tables by conductor material (Copper vs. Aluminum/Copper-Clad Aluminum) and insulation temperature rating. When looking up 1 AWG aluminum, you must navigate to the right-hand section of Table 310.16.
The table is divided into three primary temperature columns: 60°C (140°F), 75°C (167°F), and 90°C (194°F). The most common mistake DIYers and junior apprentices make is looking at the 90°C column because modern wire insulations like THHN and XHHW-2 are physically rated for 90°C. However, you cannot use the 90°C ampacity for final overcurrent protection sizing unless the entire circuit—including every breaker, lug, and splice—is explicitly rated and marked for 90°C. In the real world, almost all standard breakers and panel lugs max out at 75°C.
The 90°C column is not useless, however. It serves as the mathematical baseline for derating. If your wire runs through a hot attic or shares a conduit with multiple other current-carrying conductors, you apply your derating multiplier to the 90°C base value (135A), not the 75°C value. As long as the final derated number remains at or above your breaker size, the installation is code-compliant.
Complete 1 AWG Aluminum Ampacity & Derating Table
The following spec-sheet-table provides the exact ampacity values for 1 AWG aluminum across common insulation types, including how ambient heat and conduit crowding modify the base numbers. Source Standard: NEC 2023/2026 Table 310.16 and Table 310.15(B)(1)(1).
| Insulation Type | Temp Rating | Base Ampacity (30°C Ambient) | Ampacity at 110°F (43°C) Ambient | Ampacity with 4-6 Conductors in Raceway |
|---|---|---|---|---|
| THWN / THW | 75°C | 120A | 99A (x 0.82 correction) | 96A (x 0.80 adjustment) |
| THHN / THWN-2 | 90°C | 135A | 117A (x 0.87 correction) | 108A (x 0.80 adjustment) |
| XHHW-2 | 90°C | 135A | 117A (x 0.87 correction) | 108A (x 0.80 adjustment) |
| USE-2 (Underground) | 90°C | 135A | 117A (x 0.87 correction) | 108A (x 0.80 adjustment) |
Decision Path: Which Temperature Column Applies to You?
Use this decision-tree-table to terminate your sizing process with one concrete pick. Do not guess; follow the path based on your physical hardware.
| Installation Scenario | Condition / Hardware Rating | Final Ampacity Pick | Max Breaker Size |
|---|---|---|---|
| Residential Subpanel Feeder | Modern panel lugs and breakers (marked 75°C) | 120A (75°C Column) | 120A |
| Older Panel / Unknown Lugs | Equipment installed pre-1990 or unmarked | 100A (60°C Column) | 100A |
| Transition to NM-B Cable | Splicing aluminum feeder to Romex inside a junction box | 100A (60°C Column limit for NM-B) | 100A |
| High Heat / Crowded Conduit | Attic run >104°F or >3 current-carrying conductors | Derate from 135A (90°C). If final result ≥ 100A, use 100A. | Result of derating (round down to standard breaker size) |
The Default Pick: If you are pulling a new feeder to a standard subpanel using XHHW-2 or THWN-2 wire in a normal basement or crawlspace, use the 75°C column (120A). It is the most universally accepted, code-compliant baseline for modern aluminum feeders.
What the Ampacity Table Cannot Tell You
While NEC Table 310.16 dictates thermal limits (how much current the wire can carry before the insulation melts), it completely ignores voltage drop and physical installation constraints. Relying solely on the ampacity chart will lead to failed inspections or poorly performing circuits in three specific scenarios:
1. Voltage Drop on Long Runs
Ampacity tables assume the wire is infinitely short. In reality, 1 AWG aluminum has a resistance of approximately 0.201 ohms per 1,000 feet at 75°C. If you are running a 100A subpanel feeder 150 feet away from the main panel, the voltage drop calculation looks like this:
Voltage Drop = (2 × Length × Current × Resistance) / 1000
Voltage Drop = (2 × 150 × 100 × 0.201) / 1000 = 6.03 Volts.
On a 240V system, a 6.03V drop is exactly 2.51%. This is well under the NEC's recommended 3% maximum for feeders, meaning 1 AWG aluminum is perfectly sized for a 150-foot, 100A run. However, if that same run was 250 feet, the drop would hit 4.1%, and you would need to upsize to 1/0 AWG aluminum despite the ampacity table saying 1 AWG is fine.
2. Termination Temperature Limits (NEC 110.14(C))
As noted by the Copper Development Association and NEC 110.14(C), the weakest link in your circuit dictates the temperature column. You might buy premium 90°C XHHW-2 aluminum wire, but if the breaker you are terminating it into is only rated for 60°C (common in older residential panels or specific HVAC disconnects), the entire circuit is legally bound to the 60°C ampacity limit (100A). Always check the stamped markings on the breaker and panel bus lugs before finalizing your wire size.
3. Conduit Fill and Physical Pulling Limits
1 AWG aluminum is thick and stiff. While the ampacity table tells you the wire won't catch fire, it doesn't tell you if it will physically fit in your conduit. Per NEC Chapter 9, Table 1, conduit fill is limited to 40% for three or more wires. Three 1 AWG XHHW-2 aluminum conductors require a minimum of 1-inch PVC or EMT conduit. If you try to pull them through 3/4-inch conduit, you will likely damage the insulation or fail to pull the wire entirely, creating a dangerous high-resistance fault point. Always run a conduit fill calculation alongside your ampacity lookup.
