I want to run coax (for a cable modem) and cat6 (for a phone connection) from the garage (where my cable and phone boxes are located) to my basement. The garage wall is not drywalled, so I can run both cables along the wall and then drill a hole at the bottom to run through to the basement. The problem is that the main power trunk runs in to the basement at this same point. I can probably keep the coax and cat 6 a maximum of 4 inches away from the power trunk at this point. Is that too close?

Away from this point I'd separate the coax and cat6 a lot more from the power. Is there anything I could put in the new hole to shield the coax/cat6 from the power?

My alternative is an ugly run in the garage on the outside of a drywalled wall before drilling through to the basement in another spot.

I know this question has been asked before, but I thought this is a slightly different version. I'm not trying to run low voltage in parallel with power over a long run. I just have 1 pinch point in the run and it's a doozy with the giant main power trunk running to the service panel.

  • 1
    It doesn’t matter if it passes thru a wall somewhat near power, but in general 4” is too close for a parallel run, double that is better (8”) or even greater than a foot. What creates the problem is running closely in parallel... cross a power line fine just don’t run in parallel. I had 2 pvc conduits buried in parallel, I don’t get full bandwidth in the out building, it woks tho even with a couple cameras.
    – Tyson
    Apr 3, 2018 at 17:48
  • BTW the coax can take whatever route, the above comment applies to cat6
    – Tyson
    Apr 3, 2018 at 17:49
  • Is this main service trunk in conduit, or some sort of cable? Is the conduit, cable jacket, or cable armor metal or plastic? Apr 3, 2018 at 22:46
  • The main service trunk is in some kind of grey plastic jacket. I'll try to get a good photo when I get home tonight.
    – Ben Mills
    Apr 4, 2018 at 11:15

2 Answers 2


I know there isn't a black and white answer on this one, but I'm going to post the decision I made as the answer (based on everyone's feedback).

It just felt too close to run the coax/cat6 4" from the main power lines. My handyman was able to cut out a small section of the drywall on the adjacent wall, run the coax/cat6 behind it and feed in to the basement in the next joist bay. I feel much better about this solution. Nagging internet issues can be tough to diagnose, so I want to get the best wiring I can up front.


4" doesn't qualify as close, as far as mains electrical is concerned.

Unnecessary long paralleling is to be avoided, but I am skeptical that 60Hz EMF really effects twisted pair that much. The EMF in conductors largely cancels each other out.

Don't hang anything from the power cable.

  • Twisted pair and differential signalling is designed to mitigate this exact concern. Twisting signal pairs minimizes inductive coupling, and differential signalling ensures that interference that creates common mode spikes on signal pairs is eliminated, as the signal is only the difference between two wires.
    – Tristan
    Apr 5, 2018 at 17:36

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