500 kcmil THHN Copper Ampacity
500 kcmil copper THHN: 430A base at 90°C, 380A usable after 110.14(C) termination limit.
Base430A
Usable380A
NEC Table310.16
Full derating calculation
Applications
500 kcmil copper is commonly used for large service entrance (320-380A), paralleled feeder sets, and switchgear connections.
Voltage drop by distance
| Distance (ft) | 240V Drop | % Drop | Verdict |
|---|---|---|---|
| 50 ft | 1.0V | 0.4% | OK |
| 75 ft | 1.5V | 0.6% | OK |
| 100 ft | 2.0V | 0.8% | OK |
| 150 ft | 2.9V | 1.2% | OK |
| 200 ft | 3.9V | 1.6% | OK |
| 250 ft | 4.9V | 2.0% | OK |
| 300 ft | 5.9V | 2.5% | OK |
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NEC 2023 references verified April 2026