3 Wire Ampacity & Specifications
NEC ampacity, resistance and typical uses for 3 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
100A
Copper 90°C
110A
Aluminum 75°C
75A
Typical breaker
100A
3 Wire Specifications
| Ampacity — Copper (60 / 75 / 90°C) | 85 / 100 / 110 A |
| Ampacity — Aluminum (60 / 75 / 90°C) | 65 / 75 / 85 A |
| Cross-section | 52,620 circular mils |
| DC resistance — Copper | 0.245 Ω / 1000 ft |
| DC resistance — Aluminum | 0.403 Ω / 1000 ft |
| Typical voltage drop (240V) | 1.0% at 50 ft · 2.0% at 100 ft (at 100A) |
Common Uses for 3 Wire
- 85–100A feeders
- 100A sub-panel feeders (copper)
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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