| Ambient Temperature (°C) | 1-3 Conductors | 4-6 Conductors | 7-9 Conductors | | --- | --- | --- | --- | | 30 | 100% | 95% | 90% | | 40 | 93% | 88% | 83% | | 50 | 86% | 81% | 76% | | 60 | 79% | 74% | 69% |
That’s the new maximum before insulation damage. But the breaker is 20A, so the circuit is limited to 20A anyway. wire derating chart
You are running 6 current-carrying wires in one conduit. | Ambient Temperature (°C) | 1-3 Conductors |
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. Find wire’s 90°C column ampacity → multiply by
Use the chart, or rewire the fire later.
Even though the box says the wire is rated for 40 amps, in this specific installation, it can only safely carry 26.24 amps . If you put a 40-amp breaker on this circuit, you are creating a fire hazard. You must size the breaker at 25 amps (standard size) or use a larger wire.