600 kcmil Wire — Amp Rating, Ampacity & Diameter
Ampacity, geometry, resistance, conduit fill and maximum run length for 600 kcmil conductors in copper and aluminium.
Quick answer
Copper 75 °C
454A
Aluminium 75 °C
354A
Diameter
0.7746in
Circular mils
600,000
Full specification
| Size designation | 600 kcmil |
|---|---|
| AWG gauge number | n/a (kcmil size) |
| Circular mils | 600,000 |
| kcmil | 600.00 |
| Bare diameter (in) | 0.7746 |
| Bare diameter (mm) | 19.675 |
| Cross-section (mm²) | 304.03 |
| THHN/THWN-2 OD (in) | 1.051 |
| Insulated area (sq in) | 0.8676 |
| Copper resistance (Ω/1000 ft) | 0.0173 |
| Aluminium resistance (Ω/1000 ft) | 0.0283 |
| Max standard breaker (Cu, 75 °C) | 450 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 | 511 A | 467 A | 417 A | 361 A |
| 6 | 409 A | 373 A | 334 A | 289 A |
| 9 | 358 A | 327 A | 292 A | 253 A |
| 15 | 256 A | 233 A | 208 A | 181 A |
| 25 | 230 A | 210 A | 188 A | 163 A |
Source & method: The governing value is also capped by the termination rating, commonly 75 °C, which for this size is 454 A. Run your own conditions.
Maximum run length at 3% voltage drop
One-way distance for 600 kcmil copper before drop exceeds 3%.
| Load | 120 V 1Ø | 240 V 1Ø | 208 V 3Ø | 480 V 3Ø |
|---|---|---|---|---|
| 10 A | 8,372 ft | 16,744 ft | 16,757 ft | 38,670 ft |
| 15 A | 5,581 ft | 11,162 ft | 11,171 ft | 25,780 ft |
| 20 A | 4,186 ft | 8,372 ft | 8,378 ft | 19,335 ft |
| 30 A | 2,790 ft | 5,581 ft | 5,585 ft | 12,890 ft |
| 40 A | 2,093 ft | 4,186 ft | 4,189 ft | 9,667 ft |
| 50 A | 1,674 ft | 3,348 ft | 3,351 ft | 7,734 ft |
How many 600 kcmil 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 | 2 | 4 | 5 | 6 |
| IMC | — | — | — | 1 | 1 | 1 | 1 | 3 | 4 | 6 |
| RMC | — | — | — | — | 1 | 1 | 1 | 3 | 4 | 5 |
| PVC Sch 40 | — | — | — | — | 1 | 1 | 1 | 3 | 4 | 5 |
| PVC Sch 80 | — | — | — | — | 1 | 1 | 1 | 2 | 4 | 5 |
600 kcmil 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 | 384 A | 454 A | 511 A |
| Aluminium | 300 A | 354 A | 399 A |
The 600 kcmil copper ampacity figure you use on a real circuit is the 75 °C column, 454 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, 511 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 (354 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 600 kcmil with the sizes immediately above and below it before sizing a circuit.
600 kcmil amp rating, diameter and metric equivalent
The amp rating for 600 kcmil wire depends on the insulation temperature rating, not on the conductor alone. Copper ampacity is about 384 A on a 60 °C conductor, 454 A at 75 °C and 511 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, 600 kcmil is 0.7746 in (19.67 mm) in bare diameter, which is 600,000 circular mils. The cross sectional area works out to 304.02 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 600 kcmil actually gets used
600 kcmil, at roughly 420 A copper and 340 A aluminium, is an engineered distribution conductor. It shows up on utility-adjacent work, large service entrances, generator paralleling and substation secondary connections rather than on ordinary building branch and feeder wiring.
It exists mainly where parallel sets are undesirable: a single conductor per phase simplifies terminations at some switchgear, avoids the requirement that parallel conductors be identical in length and material, and reduces the number of raceways or tray runs to install and support.
The trade-off is handling. A 600 kcmil conductor is heavy enough that installation planning covers reel logistics, pulling equipment capacity, support intervals in vertical risers and expansion, and every bend has to respect a large minimum radius that often decides where pull boxes go.
Frequently asked
- How many amps can 600 kcmil wire carry?
- 600 kcmil copper is estimated at 384 A at 60 °C, 454 A at 75 °C and 511 A at 90 °C, at 30 °C ambient with no more than three current-carrying conductors. Aluminium of the same size is about 354 A at 75 °C.
- What is the ampacity of 600 kcmil copper?
- Use 454 A for 600 kcmil copper on equipment with 75 °C terminations, which covers most breakers and panel lugs. Read 384 A instead when the conductor is inside NM-B cable, and treat 511 A as the derating base only. Aluminium of the same size is about 354 A at 75 °C.
- What breaker size goes with 600 kcmil copper?
- The largest standard overcurrent device that 600 kcmil copper supports at 75 °C is 450 A. For a continuous load, the load itself must not exceed 80% of that rating.
- What is the diameter of 600 kcmil wire?
- The bare conductor is 0.7746 inches (19.675 mm) in diameter, which is 600,000 circular mils. With THHN/THWN-2 insulation the nominal outside diameter is about 1.051 inches.
- What is the resistance of 600 kcmil wire?
- About 0.0173 ohms per 1000 feet for copper and 0.0283 ohms per 1000 feet for aluminium, at 75 °C.
- How far can I run 600 kcmil wire?
- Distance depends on load and voltage. At 20 A on a 120 V single-phase circuit, 600 kcmil copper stays under 3% voltage drop for about 4186 feet one-way. Doubling the voltage roughly doubles the allowable distance.
Related charts & calculators
- Breaker Size CalculatorOvercurrent device rating and minimum conductor from load current.
- Wire Ampacity CalculatorDerated ampacity for ambient temperature and bundled conductors.
- Box Fill CalculatorVolume allowances for conductors, clamps, devices and grounds per NEC 314.16.
- Ampacity ChartEstimated allowable ampacity by conductor size, material and insulation rating.
- Wire Gauge ChartAWG diameter, circular mils, resistance and amp capacity in one table.
- Wire Size ChartWhat size wire for each breaker rating and typical circuit.