300 kcmil THHN Aluminum Ampacity
300 kcmil aluminum THHN: 260A base at 90°C, 230A usable after 110.14(C) termination limit.
Base260A
Usable230A
NEC Table310.16
Full derating calculation
Applications
300 kcmil aluminum is commonly used for commercial main feeders (240-285A), hospital and data center power distribution.
Voltage drop by distance
| Distance (ft) | 240V Drop | % Drop | Verdict |
|---|---|---|---|
| 50 ft | 1.6V | 0.7% | OK |
| 75 ft | 2.4V | 1.0% | OK |
| 100 ft | 3.2V | 1.4% | OK |
| 150 ft | 4.9V | 2.0% | OK |
| 200 ft | 6.5V | 2.7% | OK |
| 250 ft | 8.1V | 3.4% | Caution |
| 300 ft | 9.8V | 4.1% | Caution |
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NEC 2023 references verified April 2026