300 kcmil Wire Ampacity & Specifications
NEC ampacity, resistance and typical uses for 300 kcmil copper and aluminum wire.
Calculations are built on the 2023 National Electrical Code (NEC) and cross-checked against the published code tables. How we verify. Last reviewed June 2026.
Copper 75°C
285A
Copper 90°C
320A
Aluminum 75°C
230A
Typical breaker
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. 14, 12 and 10 AWG are limited to 15A, 20A and 30A overcurrent protection (240.4(D)). Terminations rated 60°C or 75°C usually cap the usable ampacity below the 90°C value.
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