I'm remodeling my home and I wanted to hardwire some extensions of my ethernet near my 220v outlet, by near at least a foot away from it. I was wondering, would I be able block the interference if I layer the patch extensions with copper tubes and PVC tubes to prevent EMI from the 220v line? If not, what do I do?

  • What wiring method is used for the existing 220V wiring? – ThreePhaseEel Jun 5 '20 at 23:00
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    Does this answer your question? Can I run CAT5/6 cables parallel to electrical cables? – Jim Lewis Jun 5 '20 at 23:16
  • @JimLewis No, unfortunately. I wanted to know if shielding it would work especially if it's even closer than a foot – mdparagon Jun 5 '20 at 23:28
  • @ThreePhaseEel I don't even know what wiring it was so I'd assume it's the most normal one? I apologize – mdparagon Jun 5 '20 at 23:29

You're hunting a snark.

People are constantly forgetting (or never learning) that network signals on Cat5e or Cat6 are differential twisted pair signals, which means that they are composed of a difference in voltage applied to one end of a pair of wires that are twisted together and received by looking at ONLY the difference in voltage on the receiving end. If an interfering voltage couples to the wires, it couples to both of them, resulting in a "common mode voltage" and has very little effect on the voltage difference between them. The twists also tend to make outside voltages nullify themselves when they try to couple. It actually works, quite well.

As such, while it is good practice to maintain separation, it is very rare to have any significant impact from 50 or 60 Hz powerlines on 100+ MHz network signals. I say that as a person who had miles of network cable (in 100 meter or less chunks) attached to switches that reported error rates. Many of those cables were, due to the realities of installing new-fangled network into old buildings without ripping the old buildings to shreds, parallel to power wiring for long distances. Short of actual damage to a cable, the error counts were typically zero.

Given the opportunity in new construction, sure, put it in the next stud bay, (i.e. 16-24" separation) but foolishness like running it in copper pipe is foolishness (you can get foil-shielded cable instead of unshielded cable [FTP .vs. UTP cables,] or just run plain steel EMT conduit if you want to go there at all, and you don't NEED to, at least for "interference from powerlines") - I'm a big fan of EMT to prevent "interference from rodents" but that's a different issue.

  • "Rodent interference" -- that's a good one :D – ThreePhaseEel Jun 6 '20 at 1:59
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    A real life problem when they decide to chew cables. – Ecnerwal Jun 6 '20 at 2:23
  • Oh wow that's elaborate, thank you! – mdparagon Jun 6 '20 at 4:18
  • Yeah, this is like worrying about ocean tides interfering with AM radio... the frequencies are just too far apart to matter. I also like EMT for maintainability. – Harper - Reinstate Monica Jun 6 '20 at 6:09

Assuming you're talking 220V at typical household currents - e.g., 20A to 50A - a foot away is plenty. Don't worry about it. Both the electric and Ethernet cables are designed in a number of ways that generally minimize interference. A far bigger problem would be large motors. But just the power lines themselves? A foot is plenty.

  • How about an inch? Would it still matter? I've already carved the pathway for my 220v on my floors and it would be a ton of work to carve another one just for the ethernet – mdparagon Jun 5 '20 at 23:27
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    There is some distance that is too close. I saw a reference in an answer linked in another comment that has a code recommendation (not sure if it is an absolute requirement) of two inches. That seems reasonable to me. Occasional crossing of wires is fine - the issue is extended (e.g., at least a few inches) closely parallel. Interference is (in general) related to the square of the distance - so 2" (the code recommendation) is 4x as good as 1". And if you already have a defined path, the reality is that the wires would end up literally side-by-side - probably not even 1" apart. – manassehkatz-Moving 2 Codidact Jun 5 '20 at 23:31
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    I thought the 2" minimum separation was an NEC requirement. It has nothing to do with interference, but rather a safety thing by requiring physical separation between voltages that are lethal (110/220 VAC) and those that are not (ethernet, low voltage lighting, etc). – SteveSh Jun 6 '20 at 1:37

My general rule of thumb is 12" separation in parallel runs and to only do parallel runs if absolutely necessary for low voltage cables running next to line voltage. And if low-voltage and line-voltage need to cross, keep them as far apart as possible and do the crossing at a 90 degree angle.

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