500 kcmil Wire — Ampacity, Conduit Fill & Dimensions
Everything the code tables say about 500 kcmil conductors on one page: ampacity by temperature rating, breaker limits, conduit fill, physical size, resistance and voltage-drop distances.
500 kcmil copper carries 320 A at 60°C, 380 A at 75°C and 430 A at 90°C.
500 kcmil ampacity
| Copper | Aluminum | |||||
|---|---|---|---|---|---|---|
| Installation | 60°C | 75°C | 90°C | 60°C | 75°C | 90°C |
| Raceway, cable or earth — Table 310.16 | 320 | 380 | 430 | 260 | 310 | 350 |
| Single conductor in free air — Table 310.17 | 515 | 620 | 700 | 405 | 485 | 545 |
Typical use: 380 A copper. The workhorse of large feeders; parallel 500s build 800–2000 A services.
Use the column that matches the lowest temperature rating in the circuit — usually the 75°C terminations on breakers and lugs. The 90°C column is a starting point for derating, not a rating you can load the wire to. NM-B (Romex) cable is always limited to the 60°C column.
As a copper equipment grounding conductor, 500 kcmil is the minimum for circuits protected at up to 4000 A. See the grounding conductor table.
500 kcmil conduit fill
| Conduit | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 4" |
|---|---|---|---|---|---|---|---|---|---|
| EMT | — | — | — | 1 | 1 | 1 | 3 | 5 | 8 |
| PVC Schedule 40 | — | — | — | 1 | 1 | 1 | 2 | 4 | 7 |
| PVC Schedule 80 | — | — | — | — | 1 | 1 | 1 | 3 | 6 |
| Rigid Metal Conduit | — | — | — | 1 | 1 | 1 | 2 | 4 | 7 |
| IMC | — | — | — | 1 | 1 | 1 | 3 | 4 | 7 |
| Flexible Metal Conduit | — | — | — | — | 1 | 1 | 2 | 4 | 7 |
| Liquidtight Flexible Metal Conduit | — | — | — | 1 | 1 | 1 | 2 | 4 | 7 |
| ENT | — | — | — | 1 | 1 | 1 | — | — | — |
Mixing sizes or using another insulation? Use the conduit fill calculator.
500 kcmil dimensions
| Insulation | Diameter (in) | Diameter (mm) | Area (in²) | Area (mm²) |
|---|---|---|---|---|
| THHN, THWN, THWN-2 | 0.949 | 24.10 | 0.7073 | 456.3 |
| XHHW, XHHW-2, XHH | 0.943 | 23.95 | 0.6984 | 450.6 |
| TW, THW, THHW, THW-2 | 1.003 | 25.48 | 0.7901 | 509.7 |
| RHH, RHW, RHW-2 (with outer covering) | 1.133 | 28.78 | 1.0082 | 650.5 |
500 kcmil voltage drop
| Load | 120 V 1-phase | 240 V 1-phase | 208 V 3-phase | 480 V 3-phase |
|---|---|---|---|---|
| 125 A | 558 ft | 1116 ft | 1117 ft | 2577 ft |
| 150 A | 465 ft | 930 ft | 930 ft | 2148 ft |
| 200 A | 348 ft | 697 ft | 698 ft | 1611 ft |
| 250 A | 279 ft | 558 ft | 558 ft | 1288 ft |
| 300 A | 232 ft | 465 ft | 465 ft | 1074 ft |
Based on 0.0258 Ω per 1000 ft for stranded copper at 75°C (0.0424 Ω for aluminum). For other loads and lengths use the voltage drop calculator.
All wire sizes
- 14 AWG
- 12 AWG
- 10 AWG
- 8 AWG
- 6 AWG
- 4 AWG
- 3 AWG
- 2 AWG
- 1 AWG
- 1/0 AWG
- 2/0 AWG
- 3/0 AWG
- 4/0 AWG
- 250 kcmil
- 300 kcmil
- 350 kcmil
- 400 kcmil
- 500 kcmil
- 600 kcmil
- 700 kcmil
- 750 kcmil
- 800 kcmil
- 900 kcmil
- 1000 kcmil
Frequently asked questions
How many amps can 500 kcmil wire carry?
500 kcmil copper is rated 320 A at 60°C, 380 A at 75°C and 430 A at 90°C when run in conduit or cable. Aluminum is rated 260, 310 and 350 A. Most terminations are rated 75°C, so the 75°C figure is the one normally used.
What size conduit do I need for 500 kcmil wire?
Three 500 kcmil THHN conductors need at least 2-1/2-inch EMT. Add the ground wire’s area and check the chart above for larger bundles.
What is the diameter of 500 kcmil wire?
The bare conductor is 500,000 circular mils (253.35 mm²). With THHN insulation the overall diameter is about 0.949 in (24.10 mm) and the area is 0.7073 in², which is the figure used for conduit fill.
How far can I run 500 kcmil wire?
For a 3% voltage drop on a 240 V single-phase circuit carrying 300 A, about 465 feet one way in copper. Halve that at 120 V. Lighter loads go proportionally farther.
NECTables.com is an independent reference and is not affiliated with, endorsed by, or a substitute for the National Fire Protection Association (NFPA). NEC® and National Electrical Code® are registered trademarks of the NFPA. Values shown are commonly published engineering data and independent calculations based on the methods of NFPA 70; they are not a reproduction of the Code. Always confirm against the edition adopted in your jurisdiction, including local amendments, and consult a licensed electrician or engineer before doing electrical work.