Originally Posted by Stubbie
The overcurrent can be 60 amps for #6 nm-b but only because the next size up rule is applied since the ampacity is only 55 amps for #6 nm-b column 1 60C conductors.
There is pretty much NO situation where we can use the 90 deg C column to figure circuit amperage, since there is basically nothing that is rated for 90 deg C other than the conductors themselves. Most breakers and terminals are rated for 75 deg C.
As Stub stated, because of 334.80 we MUST use the 60 deg C column for figuring ampacity of NM circuits.
True, we do use the actual conductor
temperature column for derating purposes.