#12 THHN, 9 conductors in conduit, ambient 45°C. Base @90°C = 30A Bundling (9 wires) = 0.70 Temp (45°C) = 0.82 Final = 30 × 0.70 × 0.82 = 17.22A
| Number of conductors | Derate factor | |----------------------|---------------| | 4–6 | 0.80 | | 7–9 | 0.70 | | 10–20 | 0.50 | | 21–30 | 0.45 | | 31–40 | 0.40 | Does not include ground wires, neutrals that carry only imbalance (in multiwire branch circuits), or control wires not carrying continuous load. Apply both factors to the base ampacity (from the insulation temp column). Do not derate twice from the same table. wire derating
| Ambient Temp (°C) | 60°C wire | 75°C wire | 90°C wire | |------------------|-----------|-----------|-----------| | 21–25 | 1.00 | 1.00 | 1.00 | | 26–30 | 0.91 | 0.94 | 0.96 | | 31–35 | 0.82 | 0.88 | 0.91 | | 36–40 | 0.71 | 0.82 | 0.87 | | 41–45 | 0.58 | 0.75 | 0.82 | | 46–50 | 0.41 | 0.67 | 0.76 | Example: #12 THHN (90°C) rated 30A at 30°C ambient. At 45°C ambient → 30A × 0.82 = . B. Bundling / Raceway Fill (NEC 310.15(C)(1)) For more than 3 current-carrying conductors in a raceway or cable: #12 THHN, 9 conductors in conduit, ambient 45°C