The ampacity of 1/0 AWG wire depends entirely on the conductor material and the insulation temperature rating. For copper, the allowable ampacity is 150A at 75°C and 170A at 90°C. For aluminum (or copper-clad aluminum), it is 120A at 75°C and 135A at 90°C. These values assume an ambient temperature of 30°C (86°F) and no more than three current-carrying conductors in a raceway.
While those base numbers are useful for quick mental math, real-world electrical installations require you to navigate termination limits, bundling derations, and ambient heat. Below is the complete reference data and the practical rules for applying it to your panel, subpanel, or feeder run.
The 1/0 AWG Ampacity Quick-Reference Table
How to read this table: This data is extracted directly from NEC Table 310.16 (2020/2023 editions). The columns represent the temperature rating of the wire insulation (60°C, 75°C, 90°C). The rows are grouped by conductor material. To find your value, locate the material on the left, then move across to the column that matches your installation's termination rating (usually 75°C for modern residential/commercial gear). We have included 1 AWG through 3/0 AWG to provide the immediate sizing context above and below your target gauge.
| AWG Size | Copper (60°C) | Copper (75°C) | Copper (90°C) | Aluminum (60°C) | Aluminum (75°C) | Aluminum (90°C) |
|---|---|---|---|---|---|---|
| 1 AWG | 110A | 130A | 145A | 85A | 100A | 115A |
| 1/0 AWG | 125A | 150A | 170A | 100A | 120A | 135A |
| 2/0 AWG | 145A | 175A | 195A | 115A | 135A | 150A |
| 3/0 AWG | 165A | 200A | 225A | 130A | 155A | 170A |
Source: NFPA 70 National Electrical Code (NEC). For dynamic calculations and specific insulation types, refer to the Southwire Ampacity Chart tool.
Which Temperature Column Applies to Your Installation?
The most common mistake DIYers and junior apprentices make is looking at a spool of THHN wire, seeing the '90°C' printed on the jacket, and immediately using the 90°C column to size their breaker. This is a code violation waiting to happen.
Under NEC 110.14(C), the allowable ampacity of a circuit is limited by the lowest temperature rating of any connected component, termination, or conductor. Almost all standard residential and light-commercial circuit breakers, panel lugs, and disconnect switches are tested and rated for 75°C terminations.
Therefore, even if your 1/0 AWG wire has 90°C THHN insulation, the 75°C column (150A for copper, 120A for aluminum) dictates your maximum continuous load and overcurrent protection size.
What the table cannot tell you: Table 310.16 assumes perfect conditions. It does not account for voltage drop over long distances, ambient temperatures in hot attics, or the heat generated by bundling multiple circuits in a single conduit. For those variables, you must apply correction factors.
Derating 1/0 AWG: When Base Ampacity Drops
Derating reduces the base ampacity to prevent the wire insulation from melting when heat cannot dissipate properly. You must apply derating in two scenarios:
1. Ambient Temperature Correction (NEC 310.15(B)(1))
Table 310.16 assumes an ambient temperature of 30°C (86°F). If you are pulling 1/0 AWG feeders through an attic in a southern climate where ambient temperatures hit 46-50°C (115-122°F), you must multiply the base ampacity by a correction factor. For 90°C THHN wire at 50°C ambient, the factor is 0.82.
- Calculation: 170A (Base 90°C Copper) × 0.82 = 139.4A.
- Result: Your 1/0 copper wire is now only good for 139A in that hot attic, meaning it can no longer safely terminate on a 150A breaker.
2. Bundling / More Than 3 Current-Carrying Conductors (NEC 310.15(C)(1))
If you pull four or more current-carrying conductors in a single raceway (conduit), they heat each other up. For 4 to 6 conductors, you must apply an 80% derating factor to the 90°C column.
- Calculation: 170A (Base 90°C Copper) × 0.80 = 136A.
Frequently Asked Questions About 1/0 AWG Sizing
What size breaker can I use with 1/0 AWG copper wire?
Based on the 75°C termination rule, 1/0 AWG copper is rated for 150A. According to NEC 240.6 standard breaker sizes, 150A is a standard trip rating. Therefore, the maximum standard breaker you can use to protect 1/0 AWG copper is 150 amps. If your calculated continuous load exceeds 120A (which requires a 150A breaker due to the 125% continuous load rule), you must step up to 2/0 AWG.
Can 1/0 AWG aluminum wire be used for a 100-amp subpanel feeder?
Yes, and it is a highly cost-effective choice. 1/0 AWG aluminum (often sold as 1/0-1/0-1/0-2 SER cable) has a 75°C ampacity of 120A. Because 120A exceeds the 100A breaker requirement, it is perfectly code-compliant for a 100A subpanel feeder. Just ensure you use an anti-oxidant compound (like Noalox) on the aluminum terminations and torque the lugs to the manufacturer's exact inch-pound specifications to prevent arcing.
How does voltage drop affect 1/0 AWG wire sizing?
The NEC ampacity tables assume zero voltage drop, but physics dictates that long runs will lose voltage. For a 1/0 AWG copper wire carrying 150A on a 240V circuit, you will hit a 3% voltage drop at approximately 185 feet. If your run from the main panel to a detached garage is 250 feet, 1/0 AWG will result in a ~4% drop. While NEC 210.19(A) Informational Note suggests keeping drops under 3% for branch circuits and 5% total, you should upsize to 2/0 AWG or 3/0 AWG for runs exceeding 200 feet at maximum load to prevent motor burnout and dimming lights.
What is the physical diameter of 1/0 AWG wire?
The bare conductor diameter of 1/0 AWG wire is approximately 0.365 inches (9.26 mm). When calculating conduit fill (NEC Chapter 9, Table 1), you must use the outside diameter including the insulation. For 1/0 AWG THHN, the overall diameter is roughly 0.46 inches, meaning you can comfortably fit three 1/0 THHN conductors plus a ground in a 1.25-inch Schedule 80 PVC conduit without exceeding the 40% fill limit.
