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In a few days, we will be having a small tower set up so that we can have internet connection in our rural home. We need to trench a cat-5 cable from the tower to our house but we also want to, in the same trench, run a power line out there so we are able to go farther with electrical items such as weed-eaters. What I wish to know is, how far down should the power cable be from the cat-5 as to not interfere with data signals? Both cables will be in separate conduits.

marked as duplicate by keshlam, Tester101 electrical Aug 12 '16 at 12:15

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  • What kind of tower is this? I think there's a limit to the number feet that something like cat5 can be run, regardless of nearby power lines. Are you sure they won't be bringing fiber or cable to the house? – BrownRedHawk Aug 11 '16 at 15:26
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    If it's metallic conduit, that will give you good isolation even if it's right next to the CAT-5, but even without metallic conduit, CAT-5 has built-in noise isolation, so it should be fine laying next to the power cable. But, if this were my house, since you'll have power at the tower anyway, I'd run fiber and use a media converter on each end to convert back to cat-5. That will prevent stray voltages/lightning from making it back to your network equipment. – Johnny Aug 11 '16 at 15:28
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    Just use shielded flavor of cat5 (STP or FTP instead of UTP) - if you can't afford fiber – Agent_L Aug 11 '16 at 15:29
  • @Johnny We don't have a whole lot of money for that. The company is supplying the cat-5. They aren't metal (I think they are just a type of rubber). – Prowler1000 Aug 11 '16 at 15:31
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    @mmathis I saw that but it was for inside walls. I am wanting to trench cables. – Prowler1000 Aug 11 '16 at 15:52
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Possible duplicate of Can I run CAT5/6 cables parallel to electrical cables?, although that was more concerned with in-wall installation rather than buried. The general consensus from that thread seemed to be about 16" spacing (one wall cavity between studs) for typical #12 wire (servicing 20A circuits), though of course more distance is better. Assuming your power cable will be #12 or smaller (i.e., you're just planning to put a couple outlets over there, and no pool equipment or an AC condenser or something), that would be a good guide to use as well. Depending on what the conduit is made of, you could probably go a bit closer together to avoid more digging...but not closer than 12" (as per @Ecnerwal's answer)

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There is, in fact, an applicable standard.

National Electrical Safety Code (NESC), Section 320 (B) (2),

Separations Between Supply and Communication Conduit Systems: Conduit systems to be occupied by communication conductors shall be separated from conduit systems to be used for supply systems by 75 mm (3 in.) of concrete, 100 mm (4 in.) of masonry, or 300 mm (12 in.) of well-tamped earth.

Only one of those is practical and affordable for a project on a budget, so I bolded it. You can be 12" apart at the same level, 12" above (power deeper, communication shallower) or a diagonal that works.

Type of conduit makes no difference - only the material separating the conduits changes the spacing required.

  • Is that spacing for safety only or for interference as well? – mmathis Aug 11 '16 at 19:20
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    @mmathis: The design of CAT5+ cable (plus ethernet wiring standards) is such that it inherently rejects interference. The separation has more to do with lightning and static protection than signal pollution. – wallyk Aug 11 '16 at 19:22
  • @wallyk The design (twisted pairs) does not reject external interference (like that from a nearby power cable). This is why, after all, it's suggested to not run data lines next to power, and if you do need to cross them, they should be crossed at right angles. – mmathis Aug 11 '16 at 19:30
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    @mmathis: Yes, it will inject signals, but in common mode only. The transceivers at the end only look at differential signals across the pair and ignore common mode information. – wallyk Aug 11 '16 at 19:32
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    It is an electrical safety item (first and foremost) and a maintenance item secondarily. If a power cable fails and shorts, burning an arc through its conduit, the intent is that the communications conduit should not be affected. The "side-by-side" orientation is preferred (but not required) such that one of the conduits could be dug up without disturbing the other. – Ecnerwal Aug 11 '16 at 21:38

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