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Code requires holes for NM electrical cable to be at least 1.25 inches back from either face of the stud. If the holes are closer, you must use metal plates on the stud face in order to protect the wiring from drywall screws, siding nails, erstwhile future picture hangers, etc. Holes in the center (widthwise) of the stud cause the least structural weakening of the stud. Any notches or off-center holes should be located towards the top or bottom of the stud for the same reason. (This is only significant for exterior walls subject to wind load.) It is best to avoid running wires in walls that are to be insulated. The wires complicate the installation of insulation (especially fiberglass batts), to the point that the insulation quality inevitably suffers. Code requires receptacles every 12 feet, and also often wall switches in exterior walls, so try to bring the wiring up from the sill or down from the top plate in these circumstances, instead of running a long run laterally through an exterior wall. Keep lateral electrical wiring to the bottom 2 feet of walls. This puts it where it is close to the switches and receptacles, but down below the height where anyone is likely to hang a picture or cabinet in the future. You can then run your Cat5 phone/computer wires near the top of the walls, in order to keep them away from the electrical wiring (and also out of the "danger zone" from future nails/screws/picture hangers). Take some photographs of your wiring before you close up the walls. That way, you'll know where things are at in the future, should you want to extend a circuit, cut a new door, or whatever. You should not bundle more than three NM cables through a set of holes down the length of a wall, due to current de-rating reasons. Some electrical inspectors will limit you to less. A 3/4 inch bit will allow you to pull up to 3 NM cables through each hole, without creating needless structural weakness (or sawdust for that matter.) A 1/2 inch bit is about the minimum useful size.
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