I understand table 250-.122 may be confusing to read but it says
Rating or Setting of
Device in Circuit Ahead
of Equipment, Conduit, etc.,
20 12ga copper
60 10ga copper
I read that to say if you exceed 20a and do not exceed 60a you are in a #10.
Just as a sanity check, what size is the ground in a 10ga or 8 ga cable ... 10ga