3/0 AWG Wire — Amp Rating, Ampacity & Diameter
Ampacity, geometry, resistance, conduit fill and maximum run length for 3/0 AWG conductors in copper and aluminium.
Quick answer
Copper 75 °C
198A
Aluminium 75 °C
154A
Diameter
0.4096in
Circular mils
167,806
Full specification
| Size designation | 3/0 AWG |
|---|---|
| AWG gauge number | 3/0 |
| Circular mils | 167,806 |
| kcmil | 167.81 |
| Bare diameter (in) | 0.4096 |
| Bare diameter (mm) | 10.404 |
| Cross-section (mm²) | 85.01 |
| THHN/THWN-2 OD (in) | 0.581 |
| Insulated area (sq in) | 0.2651 |
| Copper resistance (Ω/1000 ft) | 0.0618 |
| Aluminium resistance (Ω/1000 ft) | 0.1013 |
| Max standard breaker (Cu, 75 °C) | 175 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 | 223 A | 204 A | 182 A | 158 A |
| 6 | 178 A | 163 A | 146 A | 126 A |
| 9 | 156 A | 143 A | 127 A | 110 A |
| 15 | 112 A | 102 A | 91 A | 79 A |
| 25 | 100 A | 92 A | 82 A | 71 A |
Source & method: The governing value is also capped by the termination rating, commonly 75 °C, which for this size is 198 A. Run your own conditions.
Maximum run length at 3% voltage drop
One-way distance for 3/0 AWG copper before drop exceeds 3%.
| Load | 120 V 1Ø | 240 V 1Ø | 208 V 3Ø | 480 V 3Ø |
|---|---|---|---|---|
| 10 A | 2,341 ft | 4,682 ft | 4,686 ft | 10,815 ft |
| 15 A | 1,560 ft | 3,121 ft | 3,124 ft | 7,210 ft |
| 20 A | 1,170 ft | 2,341 ft | 2,343 ft | 5,407 ft |
| 30 A | 780 ft | 1,560 ft | 1,562 ft | 3,605 ft |
| 40 A | 585 ft | 1,170 ft | 1,171 ft | 2,703 ft |
| 50 A | 468 ft | 936 ft | 937 ft | 2,163 ft |
How many 3/0 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 | 1 | 3 | 5 | 8 | 13 | 17 | 22 |
| IMC | — | 1 | 1 | 1 | 3 | 5 | 7 | 11 | 15 | 20 |
| RMC | — | 1 | 1 | 1 | 3 | 5 | 7 | 11 | 15 | 19 |
| PVC Sch 40 | — | 1 | 1 | 1 | 2 | 4 | 7 | 10 | 14 | 18 |
| PVC Sch 80 | — | — | 1 | 1 | 2 | 4 | 6 | 9 | 13 | 16 |
3/0 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 | 168 A | 198 A | 223 A |
| Aluminium | 131 A | 154 A | 174 A |
The 3/0 AWG copper ampacity figure you use on a real circuit is the 75 °C column, 198 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, 223 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 (154 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 3/0 AWG with the sizes immediately above and below it before sizing a circuit.
Circuits that use 3/0 AWG
Breaker ratings whose smallest copper conductor at 75 °C terminations is 3/0 AWG.
3/0 AWG amp rating, diameter and metric equivalent
The amp rating for 3/0 AWG wire depends on the insulation temperature rating, not on the conductor alone. Copper ampacity is about 168 A on a 60 °C conductor, 198 A at 75 °C and 223 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, 3/0 AWG is 0.4096 in (10.40 mm) in bare diameter, which is 167,806 circular mils. The cross sectional area works out to 85.03 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 3/0 actually gets used
3/0 is a commercial and industrial feeder size: copper 3/0 supports roughly 200 A feeders, and aluminium 3/0 lands around 175 A. It appears in panelboard feeds, transformer secondary conductors and large equipment feeders far more often than in dwellings.
The reason 3/0 is less common than 4/0 in residential work is the service allowance: a dwelling service or main power feeder may be sized against a reduced percentage of the rating, which puts 4/0 aluminium at 200 A and leaves 3/0 without an obvious residential home. Non-dwelling feeders get no such allowance, which is exactly where 3/0 earns its place.
Parallel conductor sets start to be considered near this size. Two smaller conductors per phase can be easier to pull, easier to terminate and cheaper in raceway than one very large conductor, but parallel sets must be the same length, material, size and insulation, and each set needs its own termination provision.
Frequently asked
- How many amps can 3/0 AWG wire carry?
- 3/0 AWG copper is estimated at 168 A at 60 °C, 198 A at 75 °C and 223 A at 90 °C, at 30 °C ambient with no more than three current-carrying conductors. Aluminium of the same size is about 154 A at 75 °C.
- What is the amp rating for 3/0 gauge wire?
- Use 198 A for 3/0 AWG copper on equipment with 75 °C terminations, which covers most breakers and panel lugs. Read 168 A instead when the conductor is inside NM-B cable, and treat 223 A as the derating base only. Aluminium of the same size is about 154 A at 75 °C.
- What breaker size goes with 3/0 AWG copper?
- The largest standard overcurrent device that 3/0 AWG copper supports at 75 °C is 175 A. For a continuous load, the load itself must not exceed 80% of that rating.
- What is the diameter of 3/0 AWG wire?
- The bare conductor is 0.4096 inches (10.404 mm) in diameter, which is 167,806 circular mils. With THHN/THWN-2 insulation the nominal outside diameter is about 0.581 inches.
- What is the resistance of 3/0 AWG wire?
- About 0.0618 ohms per 1000 feet for copper and 0.1013 ohms per 1000 feet for aluminium, at 75 °C.
- How far can I run 3/0 AWG wire?
- Distance depends on load and voltage. At 20 A on a 120 V single-phase circuit, 3/0 AWG copper stays under 3% voltage drop for about 1170 feet one-way. Doubling the voltage roughly doubles the allowable distance.
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