I’ve done a lot of searching, I think I’m understanding this correctly…
House has a main panel, which feeds subpanel A, which then feeds subpanel B.
The wire from the main panel to subpanel A is labelled THWN-2 AWG 6. It runs for about 25 feet in conduit. These are three individual wires and the ground. This wire is rated to 90 degrees, so that column of table 310-16 would allow a 75 amp breaker. But since the breaker and connections on the boxes are only rated for 75 degrees, I use the middle column of the table, which states 65 amps. At the main panel, the wire is attached to a 60 amp breaker, so that’s fine.
Same type of wire, in condut, from subpanel A to subpanel B, except it’s AWG 8. Middle column of the table show 50 amps, and that’s the size of the breaker that the wire is attached to in subpanel A. So that’s OK, too.
Is that correct?