I've already mentioned about my workshop circuits where I ran 10/2 & 12/2 for a 20 amp & 15 amp circuit. At one point, the circuit runs through some studs. When I drilled the holes for the studs, I drilled them to the max size allowed (at the time, I looked it up and I beleieve that was 3/4") because I expect to run another wire through the same hole when I wire the den on the other side of the wall.
But as I understand it, if you have more than 2 cables running through studs together (in this case for a distance of about 6'-8'), you are supposed to derate the cables.
While I don't have the tables to show how to derate the cables, I assume that by having them one size larger than required, I'm already good for the current circuits.
But what about when I add the third? I plan it to be a 20 amp circuit. Am I going to HAVE to use 10/2 for the 20 amp circuit (at least for the part that runs through the wall with these other two cables)?