For the full breakdown, see our best 1/0 Aluminum Wire guide.
For most residential and commercial runs, the usable 1/0 aluminum wire ampacity is 120 amps, not the higher 90°C rating. This single number solves the most common wiring headache: matching the wire to the breaker and the load without guessing. But because real-world panels and lugs are almost always rated for 75°C, the 120-amp figure is the one you’ll rely on in the field.
NEC Ampacity Table for 1/0 Aluminum Wire
The exact ampacity is tied to the insulation’s maximum temperature rating, so read the wire’s jacket markings before making a call.
| Insulation Temperature Rating | 1/0 Aluminum Ampacity | Common Insulation Types |
|---|---|---|
| 60°C | 100 A | TW, UF |
| 75°C | 120 A | THW, THWN, SE, USE, XHHW |
| 90°C | 135 A | THHN, THWN-2, XHHW-2, USE-2 |
Why the 90°C Rating Is Not Always Usable
You can legally use the 135-amp 90°C rating for derating calculations, but it rarely applies to a finished circuit. The reason is a code rule built into NEC 110.14(C): the ampacity of the conductor cannot exceed the lowest temperature rating of any connected termination, lug, or equipment terminal. Most breakers, panels, and disconnects are only tested and labeled for 75°C terminations.
When you land 1/0 aluminum on a standard 100-amp or 120-amp panel, the terminal is the weak link. The practical result is that the circuit is limited to 120 amps, never 135. This is the most common mistake among DIYers who buy 90°C-rated wire and assume they can size a 135-amp breaker to it. The breaker still gets sized from the ampacity of the wire, but the terminations cap that ampacity first.
Copper vs. Aluminum and Common Sizing Mistakes
Aluminum isn’t the only material in play, and comparing it to copper makes the difference clear.
Another frequent error is confusing ampacity with a mandatory breaker rating. Ampacity is the wire’s current-carrying capacity, not a rule that says “use exactly 120 amps.” The actual breaker size comes from the calculated load per NEC 220, and the wire ampacity merely sets the maximum boundary. Ambient temperature, conduit fill, and voltage drop all act as derating factors that can pull that boundary lower.
If you’re ready to buy, our roundup of the best 1/0 aluminum wire choices covers top-rated spools and building wire for feeder and service applications.
FAQs
What size breaker do I use with 1/0 aluminum wire?
You can use a 100-amp or 120-amp breaker with 1/0 aluminum wire, since the practical ampacity is 120 amps at the standard 75°C termination rating. Confirm that your panel and lugs are rated for 75°C before installing, then size the breaker to your calculated load, never above the wire’s ampacity.
Can 1/0 aluminum wire handle a 200 amp service?
No. 1/0 aluminum is only rated for 120 amps at the 75°C termination rating that governs most equipment.
Does the insulation type change the ampacity of 1/0 aluminum?
References & Sources
- Cerrowire. “Ampacity Charts.” Confirms 1/0 aluminum at 120 amps for 75°C and 135 amps for 90°C.
