At 55°C ambient, the factor is .
| Ambient Temp | Adjustment Factor for 90°C-rated wire | |--------------|----------------------------------------| | 21–25°C | 1.00 | | 26–30°C | 0.96 | | 31–35°C | 0.91 | | 36–40°C | 0.87 | | 41–45°C | 0.82 | | 46–50°C | 0.76 | | | 0.71 | | 56–60°C | 0.65 | wire derating chart
Use the chart, or rewire the fire later. Find wire’s 90°C column ampacity → multiply by ambient temp factor → multiply by bundling factor (if >3 CCCs) → result must be ≥ load + 125% if continuous. If not, go up one wire gauge. At 55°C ambient, the factor is
At 20°C, that 12 AWG wire’s insulation can shed heat easily. But at 55°C, the wire starts hotter. It heats up more under load. Now the copper and insulation approach — the insulation’s long-term limit. If not, go up one wire gauge