For homeowners, do you need to follow the derating rule? Illustration:
The point is conductors can be used that is 83% of the supposed size compared to service conductor.
But in the above example. What if the residential houses have so many guests and the wire amperage reach 190A. Then since the breaker is still 200A, and the wire is only rated at 175A (or 83%). Then the wire can burn before the breaker trips. So isn't the 83% kinda dangerous for those with many guests? The philosophy is the breaker should protect the wire. But in this case. It can't anymore.
For my actual use. I have service entrance breaker of 150A. 38mm^2 is within the 83% rule (according to Harper in related Can I do a 125A subpanel feeder with slightly-larger-than-#3 wire?). But 38mm^2 is only 122A max at 75C. What if my house load is 130A (with many guests), then the 38mm^2 wire can burn before the 150A breaker trips.