Polk Audio 255c-RT DIY In-Ceiling and In-Wall Installation Guide - Page 8

Standard cross section of a modern 2 x 4 Codes usually recognize walls in two categories: "load bearing" and "non-load bearing". Running speaker cable with alternating current or AC lines: The national code restricts the use of common holes for both. Also for performance reasons try to separate your speaker cabling from the AC lines with as much distance as practical: National Electric Code does not allow low voltage cable to be installed in the same holes or boxes as AC. In load bearing walls be sure to keep your drilled holes to less then 40% the width of the stud speaker cables WRONG! speaker cables AC wiring Studs in load bearing walls have these restrictions: Holes must be LESS then 40% the width of the stud Notches must NOT exceed 25% the width of the stud When unsure if the wall you're planning on using is a load bearing wall or not then just treat it as if it were "Load Bearing". The above photos show the wrong way to run your speaker cables and the photo to the right show the correct way. DIY CI Tutorial 8