I need to add ethernet cables to my business. Above the t-bar ceilling i have all the electrical wires 120 & 240 volts inside several metal pipes. If i run cat7 cables inside one pvc pipes that runs parallel next to the metal pipes. Is it going to cause problems? Interferences? Pipes run 100 feet long. Thanks

  • The metal pipes are EMT conduit. Do I understand you plan to add new PVC conduit going to new junction boxes, and these will have exclusively ethernet and other low-voltage stuff, and not crossing wires inside the boxes with AC lines? (by the way you are allowed to run low voltage in more EMT conduit, lets you use the same fittings and hangers). Jan 31, 2018 at 6:13
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    Yes i would like to add 1 new pvc pipe just for the 7 cat7 cables. No they will not go in the same boxes as the AC wires. They will be completely separate but will run parallel to the metal pipes with AC wiring Jan 31, 2018 at 11:20
  • Well assuming both phases of the 240V loads are equally in use (which should be the case if the motor is working properly) then those signals cancel out (which is why the neutral is rarely used by a 240V device). That said, cat 7 cables are much better at blocking interference IF THE SHIELDING IS PROPERLY GROUNDED. I'm doing something very similar (not 7 cables bundled in one run, but instead running CAT7a adjacent to 120V/240V power lines). No issues with it and since several of my runs are shorter I do achieve the 40Gb speeds.
    – Nick
    Jan 17, 2019 at 15:30

2 Answers 2


Ethernet uses differential signalling. This means that any noise applied to both conductors of a pair will cancel out.

Noise added to differential signal ([Illustration of noise on differential signalling, by Linear77, CC BY 3.0)

The pairs in a twisted pair cable is twisted. This ensures that over some distance the two conductors forming a pair has equal average distance to a parallel noisy cable. The noise induced will be equal in both conductors, and disappears when the signals is subtracted at the receiver end.

The metal pipes will block a lot of interference, as it essentially forms a Faraday cage around the current carrying cables. This reduces the amount of interference that reaches the actual cable.

In addition, Ethernet provides galvanic separation between the internal circuits of the computer, and the cable. This is performed by what's commonly called Ethernet magnetics - usually consisting of a common mode choke, auto transformer and isolation transformer. This transformer is made for signals in the MHz range (10BASE-T has a bandwidth of 10 MHz). To this transformer, 50/60 Hz signals is essentially DC. It's blocked.

In some industrial settings, you may have large frequency converter loads. These will pose more of a problem, as they create more noise on the grid, with higher frequencies, and often the currents are much greater, leading to a stronger EM field. But even in such circumstances, it's possible to use Ethernet - but more care has to be taken.

In short: don't worry. 100ft is not a long stretch, and currents in homes are rather clean, with small or no frequency converter loads, and the currents are rather small (<50A). There is no way you will have any noise in a normal home setting from putting Ethernet cabling close to a power cable.

I work with industrial control systems. We use Ethernet inside switchboards with frequency converters rated in the thousands of kilowatts-range. It works fine.

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    Are you sure you know electrical principles? Noise injected into a conductor pair does not cancel out unless you somehow had 2 phase signals injected and 1 conductor had phase A and the other had phase B. The tightness of the twists of the wire as well as the shielding/ground around the conductors is what protects from interference. Think of it this way. If I yelled really loud into just one of your ears, the other ear would be much less impacted; however, if I put headphones on you and blasted music then your ears did not cancel out the noise by having both ears receiving the signal...
    – Nick
    Jan 17, 2019 at 15:20
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    Yes, I know electric principles. The principle behind a balanced pair is that the signal is the difference between the pairs, and any noise will impact each conductor in the pair more or less equally - so that the difference between the conductors is unchanged by noise. This is explained in the link to differential signalling in my answer. You have clearly not understood differential signalling.
    – vidarlo
    Jan 18, 2019 at 13:13
  • Not “any noise” this is why we space telecom and mains wiring.
    – Ed Beal
    Mar 30, 2020 at 18:44
  • @EdBeal I'm well aware that spacing it is best practice, but Ethernet is rather robust against noise, due to differential signalling. It's extremely unlikely to cause problems.
    – vidarlo
    Mar 30, 2020 at 18:50

Ideally, any copper low voltage wire used for data, when run parallel to line voltage wiring should be kept 18" away and only cross line voltage at 90 degrees to eliminate inductive coupling. However, metallic conduit such as EMT shields the interference from the line voltage, assuming it is properly grounded. You should have no problem.

Why run pvc conduit? Why not just get CADDY datacom bridal rings and T-Bar wire clips? Cheaper, easier, less weight, easier to get into an existing T-bar ceiling, etc. https://www.erico.com/caddy.asp

  • 18" not needed with metal conduit if concerned about noise, the conduit shields the noise. If talking about basic cables running parallel I would agree.
    – Ed Beal
    Jan 31, 2018 at 16:12
  • @EdBeal I did mention the shielding provided by the EMT.
    – C Knight
    Jan 31, 2018 at 19:26
  • Ed you notice I agreed ?
    – Ed Beal
    Mar 30, 2020 at 18:55

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