300 kcmil Wire Ampacity & Specifications
300 kcmil copper wire carries 285A at 75°C (NEC Table 310.16), or 230A for aluminum; copper is typically protected by a 250A breaker.
Calculations are built on the 2023 National Electrical Code (NEC) and cross-checked against the published code tables. How we verify. Last updated June 2026.
300 kcmil wire has an ampacity of 285A at 75°C for copper and 230A for aluminum (NEC Table 310.16). Its 60°C and 90°C copper ratings are 240A and 320A. Copper 300 kcmil is commonly protected by a 250A breaker.
Copper 75°C
285A
Copper 90°C
320A
Aluminum 75°C
230A
Copper breaker (75°C)
250A
300 kcmil Wire Specifications
| Ampacity — Copper (60 / 75 / 90°C) | 240 / 285 / 320 A |
| Ampacity — Aluminum (60 / 75 / 90°C) | 195 / 230 / 260 A |
| Cross-section | 300,000 circular mils |
| DC resistance — Copper | 0.0429 Ω / 1000 ft |
| DC resistance — Aluminum | 0.0707 Ω / 1000 ft |
| Typical voltage drop (240V) | 0.4% at 50 ft · 0.9% at 100 ft (at 250A) |
Common Uses for 300 kcmil Wire
- 285A copper feeders
- Industrial and commercial feeders
Ampacities are from NEC Table 310.16. Copper 14, 12 and 10 AWG are limited to 15A, 20A and 30A overcurrent protection, aluminum 12 and 10 AWG to 15A and 25A (240.4(D)). Terminations rated 60°C or 75°C usually cap the usable ampacity below the 90°C value.
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