750 kcmil Wire — Amp Rating, Ampacity & Diameter
Ampacity, geometry, resistance, conduit fill and maximum run length for 750 kcmil conductors in copper and aluminium.
Quick answer
Copper 75 °C
524A
Aluminium 75 °C
409A
Diameter
0.8660in
Circular mils
750,000
Full specification
| Size designation | 750 kcmil |
|---|---|
| AWG gauge number | n/a (kcmil size) |
| Circular mils | 750,000 |
| kcmil | 750.00 |
| Bare diameter (in) | 0.8660 |
| Bare diameter (mm) | 21.996 |
| Cross-section (mm²) | 380.01 |
| THHN/THWN-2 OD (in) | 1.158 |
| Insulated area (sq in) | 1.0532 |
| Copper resistance (Ω/1000 ft) | 0.0138 |
| Aluminium resistance (Ω/1000 ft) | 0.0227 |
| Max standard breaker (Cu, 75 °C) | 500 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 | 591 A | 540 A | 482 A | 418 A |
| 6 | 473 A | 432 A | 386 A | 334 A |
| 9 | 414 A | 378 A | 338 A | 292 A |
| 15 | 296 A | 270 A | 241 A | 209 A |
| 25 | 266 A | 243 A | 217 A | 188 A |
Source & method: The governing value is also capped by the termination rating, commonly 75 °C, which for this size is 524 A. Run your own conditions.
Maximum run length at 3% voltage drop
One-way distance for 750 kcmil copper before drop exceeds 3%.
| Load | 120 V 1Ø | 240 V 1Ø | 208 V 3Ø | 480 V 3Ø |
|---|---|---|---|---|
| 10 A | 10,465 ft | 20,930 ft | 20,946 ft | 48,337 ft |
| 15 A | 6,976 ft | 13,953 ft | 13,964 ft | 32,225 ft |
| 20 A | 5,232 ft | 10,465 ft | 10,473 ft | 24,168 ft |
| 30 A | 3,488 ft | 6,976 ft | 6,982 ft | 16,112 ft |
| 40 A | 2,616 ft | 5,232 ft | 5,236 ft | 12,084 ft |
| 50 A | 2,093 ft | 4,186 ft | 4,189 ft | 9,667 ft |
How many 750 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 | 1 | 3 | 4 | 5 |
| IMC | — | — | — | — | 1 | 1 | 1 | 3 | 4 | 5 |
| RMC | — | — | — | — | 1 | 1 | 1 | 2 | 3 | 4 |
| PVC Sch 40 | — | — | — | — | — | 1 | 1 | 2 | 3 | 4 |
| PVC Sch 80 | — | — | — | — | — | 1 | 1 | 1 | 3 | 4 |
750 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 | 444 A | 524 A | 591 A |
| Aluminium | 347 A | 409 A | 461 A |
The 750 kcmil copper ampacity figure you use on a real circuit is the 75 °C column, 524 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, 591 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 (409 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 750 kcmil with the sizes immediately above and below it before sizing a circuit.
750 kcmil amp rating, diameter and metric equivalent
The amp rating for 750 kcmil wire depends on the insulation temperature rating, not on the conductor alone. Copper ampacity is about 444 A on a 60 °C conductor, 524 A at 75 °C and 591 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, 750 kcmil is 0.8660 in (22.00 mm) in bare diameter, which is 750,000 circular mils. The cross sectional area works out to 380.03 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 750 kcmil actually gets used
750 kcmil is near the practical upper end of conductors installed in building raceway, around 475 A copper and 385 A aluminium. Uses are service entrance conductors on large buildings, switchgear and busway terminations, and utility service laterals.
It illustrates the ampacity ceiling better than any other size: 750 kcmil has roughly three times the area of 250 kcmil but nowhere near three times its ampacity, because heat dissipation scales with surface area while resistance losses scale with volume. Skin effect on alternating current adds to the same effect.
For that reason large services are almost never designed around single 750 kcmil conductors when parallel sets are available. Where 750 is used, expect engineered supports, hydraulic compression terminations, dedicated large raceway or tray, and coordination with the utility on lateral and termination details.
Frequently asked
- How many amps can 750 kcmil wire carry?
- 750 kcmil copper is estimated at 444 A at 60 °C, 524 A at 75 °C and 591 A at 90 °C, at 30 °C ambient with no more than three current-carrying conductors. Aluminium of the same size is about 409 A at 75 °C.
- What is the ampacity of 750 kcmil copper?
- Use 524 A for 750 kcmil copper on equipment with 75 °C terminations, which covers most breakers and panel lugs. Read 444 A instead when the conductor is inside NM-B cable, and treat 591 A as the derating base only. Aluminium of the same size is about 409 A at 75 °C.
- What breaker size goes with 750 kcmil copper?
- The largest standard overcurrent device that 750 kcmil copper supports at 75 °C is 500 A. For a continuous load, the load itself must not exceed 80% of that rating.
- What is the diameter of 750 kcmil wire?
- The bare conductor is 0.8660 inches (21.996 mm) in diameter, which is 750,000 circular mils. With THHN/THWN-2 insulation the nominal outside diameter is about 1.158 inches.
- What is the resistance of 750 kcmil wire?
- About 0.0138 ohms per 1000 feet for copper and 0.0227 ohms per 1000 feet for aluminium, at 75 °C.
- How far can I run 750 kcmil wire?
- Distance depends on load and voltage. At 20 A on a 120 V single-phase circuit, 750 kcmil copper stays under 3% voltage drop for about 5232 feet one-way. Doubling the voltage roughly doubles the allowable distance.
Related charts & calculators
- kcmil Wire Size ChartMCM to AWG conversion, circular mils, resistance and ampacity for 250-750 kcmil.
- Conduit Fill ChartMaximum THHN conductors per trade size for every raceway type.
- EMT Conduit Fill ChartConductor counts and internal areas for electrical metallic tubing.
- PVC Conduit Fill ChartSchedule 40 and Schedule 80 conductor counts and usable areas.
- Rigid Conduit Fill ChartRMC and IMC conductor counts per trade size, side by side.
- Sheet Metal Gauge ChartGauge to thickness in inches and millimetres for steel, galvanised and aluminium.