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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). – Harper Jan 31 '18 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 – Ronald Walter Filho Jan 31 '18 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 at 15:30
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Ethernet uses differential signalling. This means that any noise applied to both conductors of a pair will cancel out. In addition the metal pipes will block a lot of interference, as it essentially forms a Faraday cage around the current carrying cables.

In addition, ethernet provides galvanic separation between the internal circuits of the computer, and the cable.

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).

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

  • 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 at 15:20
  • 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 at 13:13
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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 '18 at 16:12
  • @EdBeal I did mention the shielding provided by the EMT. – C Knight Jan 31 '18 at 19:26

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