I could be wrong on this, but when I was a "pup" in the field I was always told to keep control wires(signal) and supply wires (AC power) seperate to avoid 60hz hum and hamonic distortion from invading the DC lines and distorting the signals...i.e. capacitance, induction, etc., so I've always made a practice of this. Even with shielded cables, such as TV/Cable/Sat, and non-shielded such as phone, solinoid & relay, speakers, etc., the possibility of induction leads me to keep them from crossing paths or feeding through the same conduit.
I've never put the theory to the test completely, but maybe someone here can back me up or shoot me down with some experience with troubleshooting such a matter.
