1/0 AWG Wire — Amp Rating, Ampacity & Diameter
Ampacity, geometry, resistance, conduit fill and maximum run length for 1/0 AWG conductors in copper and aluminium.
Quick answer
Copper 75 °C
146A
Aluminium 75 °C
114A
Diameter
0.3249in
Circular mils
105,535
Full specification
| Size designation | 1/0 AWG |
|---|---|
| AWG gauge number | 1/0 |
| Circular mils | 105,535 |
| kcmil | 105.53 |
| Bare diameter (in) | 0.3249 |
| Bare diameter (mm) | 8.252 |
| Cross-section (mm²) | 53.49 |
| THHN/THWN-2 OD (in) | 0.486 |
| Insulated area (sq in) | 0.1855 |
| Copper resistance (Ω/1000 ft) | 0.0983 |
| Aluminium resistance (Ω/1000 ft) | 0.1611 |
| Max standard breaker (Cu, 75 °C) | 125 A |
Ampacity with derating
Estimated ampacity from the 90 °C column at various ambient temperatures and conductor counts.
| Conductors in raceway | 30 °C ambient | 40 °C ambient | 50 °C ambient | 60 °C ambient |
|---|---|---|---|---|
| 3 | 165 A | 151 A | 135 A | 117 A |
| 6 | 132 A | 121 A | 108 A | 93 A |
| 9 | 115 A | 105 A | 94 A | 82 A |
| 15 | 83 A | 75 A | 67 A | 58 A |
| 25 | 74 A | 68 A | 61 A | 52 A |
Source & method: The governing value is also capped by the termination rating, commonly 75 °C, which for this size is 146 A. Run your own conditions.
Maximum run length at 3% voltage drop
One-way distance for 1/0 AWG copper before drop exceeds 3%.
| Load | 120 V 1Ø | 240 V 1Ø | 208 V 3Ø | 480 V 3Ø |
|---|---|---|---|---|
| 10 A | 1,472 ft | 2,945 ft | 2,947 ft | 6,801 ft |
| 15 A | 981 ft | 1,963 ft | 1,964 ft | 4,534 ft |
| 20 A | 736 ft | 1,472 ft | 1,473 ft | 3,400 ft |
| 30 A | 490 ft | 981 ft | 982 ft | 2,267 ft |
| 40 A | 368 ft | 736 ft | 736 ft | 1,700 ft |
| 50 A | 294 ft | 589 ft | 589 ft | 1,360 ft |
How many 1/0 AWG conductors fit in conduit
Maximum count of this size alone, at the fill percentage matching the resulting count.
| Conduit | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 3-1/2" | 4" |
|---|---|---|---|---|---|---|---|---|---|---|
| EMT | — | 1 | 1 | 3 | 4 | 7 | 12 | 19 | 24 | 31 |
| IMC | — | 1 | 1 | 3 | 4 | 7 | 11 | 17 | 22 | 29 |
| RMC | — | 1 | 1 | 3 | 4 | 7 | 10 | 16 | 21 | 27 |
| PVC Sch 40 | — | 1 | 1 | 3 | 4 | 7 | 10 | 15 | 20 | 27 |
| PVC Sch 80 | — | 1 | 1 | 2 | 3 | 6 | 8 | 13 | 18 | 24 |
1/0 AWG copper ampacity vs aluminium ampacity
Ampacity by conductor material and insulation temperature rating, at 30 °C ambient with no more than three current-carrying conductors.
| Material | 60 °C (TW, NM-B) | 75 °C (THW, THWN, XHHW) | 90 °C (THHN, THWN-2, XHHW-2) |
|---|---|---|---|
| Copper | 124 A | 146 A | 165 A |
| Aluminium | 97 A | 114 A | 129 A |
The 1/0 AWG copper ampacity figure you use on a real circuit is the 75 °C column, 146 A, because breakers and lugs on most equipment are listed for 75 °C even when the conductor insulation is rated 90 °C. The 90 °C value, 165 A, is the starting point for ambient and conductor-count derating only — you derate from 90 °C, then cap the answer at the termination rating.
Aluminium of the same size carries roughly 78% of the copper value (114 A at 75 °C), so an aluminium feeder is normally stepped up one to two sizes to match a copper circuit. NM-B cable is always read from the 60 °C column regardless of the temperature stamped on the conductor insulation.
Source & method: Values are model estimates from conductor geometry and resistivity — see methodology and verify against the NEC edition enforced locally.
Neighbouring sizes
Compare 1/0 AWG with the sizes immediately above and below it before sizing a circuit.
1/0 AWG amp rating, diameter and metric equivalent
The amp rating for 1/0 AWG wire depends on the insulation temperature rating, not on the conductor alone. Copper ampacity is about 124 A on a 60 °C conductor, 146 A at 75 °C and 165 A at 90 °C, all at 30 °C ambient with no more than three current-carrying conductors in the raceway. The carrying capacity drops from there in hot spaces or crowded conduit, and terminations rated 75 °C cap what you can actually use.
Geometrically, 1/0 AWG is 0.3249 in (8.25 mm) in bare diameter, which is 105,535 circular mils. The cross sectional area works out to 53.47 mm², so the nearest IEC 60228 metric conductor is the next standard size at or above that figure — AWG sizes and mm² sizes never line up exactly, so round up rather than to the closest value.
American Wire Gauge (AWG) is a standard specification for the sizes of solid round wires used as electrical conductors, and the AWG number counts the drawing operations used to reach the diameter. That is why larger gauges are thinner wire and why standardized wire steps follow a fixed ratio: one AWG step changes diameter by about 12.2% and area by about 26%. Above 1 AWG the American standard continues 1/0 to 4/0, then switches to kcmil for anything larger.
Where 1/0 actually gets used
1/0 begins the aught series and the genuinely heavy end of ordinary construction wiring. Copper 1/0 serves 150 A feeders; aluminium 1/0 is a routine 125 A feeder and a common 150 A service conductor. It shows up on apartment house feeders, commercial panelboard feeds and larger shop subpanels.
At 1/0 the conductor is always stranded, always terminated with a lug rated for the range, and often supplied as a parallel or quadruplex service cable assembly rather than as individual THHN. Handling changes character: reels are heavy, sidewall pressure on bends becomes a design check, and a pull lubricant and rope are standard rather than optional.
The 75 degree Celsius termination limit is fully dominant from this size upward. Insulation rated 90 degrees Celsius on 1/0 THHN never yields extra capacity at a panelboard whose lugs are listed at 75, so the 90 degree column is only ever a derating starting point for ambient and conductor-count corrections.
Frequently asked
- How many amps can 1/0 AWG wire carry?
- 1/0 AWG copper is estimated at 124 A at 60 °C, 146 A at 75 °C and 165 A at 90 °C, at 30 °C ambient with no more than three current-carrying conductors. Aluminium of the same size is about 114 A at 75 °C.
- What is the amp rating for 1/0 gauge wire?
- Use 146 A for 1/0 AWG copper on equipment with 75 °C terminations, which covers most breakers and panel lugs. Read 124 A instead when the conductor is inside NM-B cable, and treat 165 A as the derating base only. Aluminium of the same size is about 114 A at 75 °C.
- What breaker size goes with 1/0 AWG copper?
- The largest standard overcurrent device that 1/0 AWG copper supports at 75 °C is 125 A. For a continuous load, the load itself must not exceed 80% of that rating.
- What is the diameter of 1/0 AWG wire?
- The bare conductor is 0.3249 inches (8.252 mm) in diameter, which is 105,535 circular mils. With THHN/THWN-2 insulation the nominal outside diameter is about 0.486 inches.
- What is the resistance of 1/0 AWG wire?
- About 0.0983 ohms per 1000 feet for copper and 0.1611 ohms per 1000 feet for aluminium, at 75 °C.
- How far can I run 1/0 AWG wire?
- Distance depends on load and voltage. At 20 A on a 120 V single-phase circuit, 1/0 AWG copper stays under 3% voltage drop for about 736 feet one-way. Doubling the voltage roughly doubles the allowable distance.
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