900 kcmil Wire — Ampacity, Conduit Fill & Dimensions
Everything the code tables say about 900 kcmil conductors on one page: ampacity by temperature rating, breaker limits, conduit fill, physical size, resistance and voltage-drop distances.
900 kcmil copper carries 435 A at 60°C, 520 A at 75°C and 585 A at 90°C.
900 kcmil ampacity
| Copper | Aluminum | |||||
|---|---|---|---|---|---|---|
| Installation | 60°C | 75°C | 90°C | 60°C | 75°C | 90°C |
| Raceway, cable or earth — Table 310.16 | 435 | 520 | 585 | 355 | 425 | 480 |
| Single conductor in free air — Table 310.17 | 730 | 870 | 980 | 580 | 700 | 790 |
Typical use: 520 A copper. Rare in practice.
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.
900 kcmil conduit fill
| Conduit | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 4" |
|---|---|---|---|---|---|---|---|---|---|
| EMT | — | — | — | — | — | 1 | 1 | 3 | 4 |
| PVC Schedule 40 | — | — | — | — | — | 1 | 1 | 1 | 4 |
| PVC Schedule 80 | — | — | — | — | — | 1 | 1 | 1 | 3 |
| Rigid Metal Conduit | — | — | — | — | — | 1 | 1 | 1 | 4 |
| IMC | — | — | — | — | — | 1 | 1 | 1 | 4 |
| Flexible Metal Conduit | — | — | — | — | — | 1 | 1 | 1 | 4 |
| Liquidtight Flexible Metal Conduit | — | — | — | — | — | 1 | 1 | 1 | 4 |
| ENT | — | — | — | — | — | 1 | — | — | — |
Mixing sizes or using another insulation? Use the conduit fill calculator.
900 kcmil dimensions
| Insulation | Diameter (in) | Diameter (mm) | Area (in²) | Area (mm²) |
|---|---|---|---|---|
| THHN, THWN, THWN-2 | 1.252 | 31.80 | 1.2311 | 794.3 |
| XHHW, XHHW-2, XHH | 1.254 | 31.85 | 1.2351 | 796.8 |
| TW, THW, THHW, THW-2 | 1.314 | 33.38 | 1.3561 | 874.9 |
| RHH, RHW, RHW-2 (with outer covering) | 1.444 | 36.68 | 1.6377 | 1056.6 |
900 kcmil voltage drop
| Load | 120 V 1-phase | 240 V 1-phase | 208 V 3-phase | 480 V 3-phase |
|---|---|---|---|---|
| 200 A | 629 ft | 1258 ft | 1259 ft | 2906 ft |
| 250 A | 503 ft | 1006 ft | 1007 ft | 2325 ft |
| 300 A | 419 ft | 839 ft | 839 ft | 1937 ft |
| 400 A | 314 ft | 629 ft | 629 ft | 1453 ft |
| 500 A | 251 ft | 503 ft | 503 ft | 1162 ft |
Based on 0.0143 Ω per 1000 ft for stranded copper at 75°C (0.0235 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 900 kcmil wire carry?
900 kcmil copper is rated 435 A at 60°C, 520 A at 75°C and 585 A at 90°C when run in conduit or cable. Aluminum is rated 355, 425 and 480 A. Most terminations are rated 75°C, so the 75°C figure is the one normally used.
What size conduit do I need for 900 kcmil wire?
Three 900 kcmil THHN conductors need at least 3-inch EMT. Add the ground wire’s area and check the chart above for larger bundles.
What is the diameter of 900 kcmil wire?
The bare conductor is 900,000 circular mils (456.03 mm²). With THHN insulation the overall diameter is about 1.252 in (31.80 mm) and the area is 1.2311 in², which is the figure used for conduit fill.
How far can I run 900 kcmil wire?
For a 3% voltage drop on a 240 V single-phase circuit carrying 500 A, about 503 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.