What are the NEC rules for holes in a wooden top plate?
Don't make it larger than half the top plate's width
Since the size of holes in a top plate is a structural concern, not an electrical concern, you need to be looking in the IRC (or other building code) for these details, not the NEC.  In particular, IRC R602.6.1 states that a metal top plate tie strap is needed for a notch or hole in a load-bearing top plate that extends through over half of the top plate's width; unless you're running fat conduit or SE cable, you won't come close to this, though.