350 kcmil Wire Specs
Ampacity, geometry, resistance, conduit fill and maximum run length for 350 kcmil conductors in copper and aluminium.
Quick answer
350 kcmil copper carries about 319 A at 75 °C (271 A at 60 °C, 360 A at 90 °C). The bare conductor is 0.5916 in (15.03 mm) and 350,000 circular mils, with 0.0296 Ω per 1000 ft. It pairs with a 300 A breaker at 75 °C terminations.
Copper 75 °C
319A
Aluminium 75 °C
249A
Diameter
0.5916in
Circular mils
350,000
Full specification
| Size designation | 350 kcmil |
|---|---|
| AWG gauge number | n/a (kcmil size) |
| Circular mils | 350,000 |
| kcmil | 350.00 |
| Bare diameter (in) | 0.5916 |
| Bare diameter (mm) | 15.027 |
| Cross-section (mm²) | 177.34 |
| THHN/THWN-2 OD (in) | 0.817 |
| Insulated area (sq in) | 0.5242 |
| Copper resistance (Ω/1000 ft) | 0.0296 |
| Aluminium resistance (Ω/1000 ft) | 0.0486 |
| Max standard breaker (Cu, 75 °C) | 300 A |
Published standard — source: Geometry computed from the ASTM B258 AWG formula; resistance from standard resistivityFormula estimate — source: Ampacity from the site model
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 | 360 A | 329 A | 294 A | 255 A |
| 6 | 288 A | 263 A | 235 A | 204 A |
| 9 | 252 A | 230 A | 206 A | 178 A |
| 15 | 180 A | 164 A | 147 A | 127 A |
| 25 | 162 A | 148 A | 132 A | 115 A |
Source & method: The governing value is also capped by the termination rating, commonly 75 °C, which for this size is 319 A. Run your own conditions.
Maximum run length at 3% voltage drop
One-way distance for 350 kcmil copper before drop exceeds 3%.
| Load | 120 V 1Ø | 240 V 1Ø | 208 V 3Ø | 480 V 3Ø |
|---|---|---|---|---|
| 10 A | 4,883 ft | 9,767 ft | 9,774 ft | 22,557 ft |
| 15 A | 3,255 ft | 6,511 ft | 6,516 ft | 15,038 ft |
| 20 A | 2,441 ft | 4,883 ft | 4,887 ft | 11,278 ft |
| 30 A | 1,627 ft | 3,255 ft | 3,258 ft | 7,519 ft |
| 40 A | 1,220 ft | 2,441 ft | 2,443 ft | 5,639 ft |
| 50 A | 976 ft | 1,953 ft | 1,954 ft | 4,511 ft |
How many 350 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 | 4 | 6 | 8 | 11 |
| IMC | — | — | — | 1 | 1 | 2 | 3 | 6 | 8 | 10 |
| RMC | — | — | — | 1 | 1 | 2 | 3 | 5 | 7 | 9 |
| PVC Sch 40 | — | — | — | 1 | 1 | 1 | 3 | 5 | 7 | 9 |
| PVC Sch 80 | — | — | — | 1 | 1 | 1 | 3 | 4 | 6 | 8 |
Neighbouring sizes
Frequently asked
- How many amps can 350 kcmil wire carry?
- 350 kcmil copper is estimated at 271 A at 60 °C, 319 A at 75 °C and 360 A at 90 °C, at 30 °C ambient with no more than three current-carrying conductors. Aluminium of the same size is about 249 A at 75 °C.
- What breaker size goes with 350 kcmil copper?
- The largest standard overcurrent device that 350 kcmil copper supports at 75 °C is 300 A. For a continuous load, the load itself must not exceed 80% of that rating.
- What is the diameter of 350 kcmil wire?
- The bare conductor is 0.5916 inches (15.027 mm) in diameter, which is 350,000 circular mils. With THHN/THWN-2 insulation the nominal outside diameter is about 0.817 inches.
- What is the resistance of 350 kcmil wire?
- About 0.0296 ohms per 1000 feet for copper and 0.0486 ohms per 1000 feet for aluminium, at 75 °C.
- How far can I run 350 kcmil wire?
- Distance depends on load and voltage. At 20 A on a 120 V single-phase circuit, 350 kcmil copper stays under 3% voltage drop for about 2441 feet one-way. Doubling the voltage roughly doubles the allowable distance.
Materials for this size
Materials for this size
Wire, cable and terminations for 350 kcmil.
- THHN/THWN-2 350 kcmil copper350 kcmil copperBuilding wire in the size this page covers (350 kcmil copper).Check price on Amazon →
- NM-B cable 350 kcmil350 kcmilRomex-type cable for dry indoor branch circuits at this size.Check price on Amazon →
- Wire connectors for 350 kcmil350 kcmilPush-in or twist-on connectors rated for this conductor size.Check price on Amazon →
- Terminal lugs & anti-oxidantCopper-rated mechanical lugs for panel and disconnect terminations.Check price on Amazon →
Links go to Amazon search results, not a single listing — confirm ratings, insulation type and listing details before buying, and make sure the part is approved for your application.
Related charts & calculators
- Voltage Drop CalculatorPercent drop, end voltage and minimum conductor for any run length.
- Conduit Fill CalculatorFill percentage and maximum conductor count for EMT, RMC, IMC and PVC.
- 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.