wired UTP ethernet cables (or especially STP due to possible fire hazard or sparks or ground loops? don't know for sure, just a guess) I don't think should be used in equipment across different branch circuits.
you should make sure all your wired equipment is on the same branch circuit of your house. ethernet is possibly the exception here (but I repeat the former order for STP, though I am no expert, it seems like it might be a problem)
It can cause ground loops which cause noise in signals, etc.
wired ethernet cables I have used at home have not worked properly when I have plugged in my Motorola WiMAX modem on one side of the room and my router on the other side of the room with the rest of the equipment. I figure it was due to 60Hz hum or ground loops or some other electrical noise caused by being on a different branch circuit.
I was concerned for destruction of my equipment when it was acting up (at the request of technical support - I know you are supposed to play stupid!).
It would have been interesting to get out my DMM and actually measure what was going on across those wires.
Whatever it was, it was radical, and it went away when I put it all on the same wall.
Further later notes: I have not had trouble with other networking equipment, only the old router and that particular 1-10Mbps motorola WiMAX modem. there are coming new modems with better speeds like 300Mbps (and hopefully better isolation).
printers up in flames
one guy I know has a printer which went up in flames because he connected it across the room via cable (many years ago). could have been a house wiring issue, but I have had issues with networking across the room (noise). not a good idea.
this could happen with USB cables and devices like printers, since it has a grounded, shielded outside connector.
What about UTP?
UTP ethernet cable for connections is generally is simply fine.
if your equipment is properly isolated from the signal lines like it usually is (unless it's a bad design), you should have no problems with having stuff on different branch circuits.