That's just it. Bundling is not really defined, and, as someone pointed out, bundling is equated to running in a conduit. But what about the size of the conduit? Wouldn't 6 #12s in a two inch conduit have enough room to shed heat? At the least much more than the same 6 #12s in a 1/2 inch conduit. It is this lack of differentiation that leads me (and other inspectors) to err on the side of caution and intrepret installing cables in bored holes further than 24 inches as bundling.
Cheer up, as I stated earlier, you can run 4 cables in all your holes. When you do the math, the derated cables meet code. #14s go to 15 amp breakers, #12s go to 20 amp breakers, and #10s go to 30 amp breakers.
Most electricians will use a 7/8 inch drill bit to limit this automatically.(it's tough to force 5 NM cables into the hole) And, when drilling 2 x 4 studs, the hole will be centered 1-1/4 inch back from either edge. (1/8 inch fudge factor)
Earl
