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I'd like to run some Category 6 cabling underground, for a distance of about 120 ft, between a main home and a 2nd unit, for ethernet connectivity between the two homes. I've run Category 5 indoors before, but running Category 6 and underground is a new ballgame for me.

  • Is there a specific kind of Category 6 cabling I should use? I see a variety of specifications available here, but to be honest I'm not sure what specifications matter.
  • Can I simply run the cable through PVC pipe for most of the way?
  • I read that Category 6 needs special grounding?
  • Is there any major benefit to running more than one cable through the same ditch or pipe?
  • Are there any pitfalls I may not be aware of?
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Is the conduit already in the ground? Is there other wiring int the same trench? Are you sure you absolutely need Cat6's 10G speeds? –  Jay Bazuzi Aug 8 '11 at 1:12
    
Construction for the 2nd unit is ongoing, and the trench is open at the moment. Electricity is also to be run through this trench. –  DuckMaestro Aug 8 '11 at 3:23
    
Found this related, adding for linkage: diy.stackexchange.com/questions/6192/…. –  DuckMaestro Aug 8 '11 at 4:10
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make sure the earth of the cat6 is not the same as the earth for electrical or you'll get interference that will cripple the network (cat6 earthed to the switch, 110/220v earthed to DB) In some rare cases only do you need to use a ground loop isolator on one side - but that is only if the power sources are different. –  ppumkin Aug 8 '11 at 8:28
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5 Answers

up vote 16 down vote accepted

Cat6 is capable of very high speeds (by today's standards; hi 2021!), but only within a bunch of additional constraints over lower-speed cable.

Especially difficult is terminating the cable. When you untwist enough to terminate, it's easy to expose yourself to interference. Some people buy long, pre-terminated Cat6 and pull that, instead of pulling bulk cable, for this very reason. You'll need larger conduit if you take this approach.

Another difficulty is strains during the pull. If you tug hard to get around a corner, you can damage the cable enough to stop top speeds from working. Limiting the number of elbows, wide sweeps, conduit bodies, larger conduit, and having someone push while you pull all help.

You may decide that you don't need 10G speeds. In that case, save the money and pull Cat5e. Since you're running conduit, it's easy to upgrade later if you change your mind. It's a good idea to leave a pull string, but if you forget, just suck a new one through with a shop vac.

If there is any EMF in the same trench, a shielded cable will help. Ground the shielding at both ends.

If you are sure you need maximum speed, consider using fiber. You'd put a fiber-to-ethernet converter on each end. Very long runs and EMF are non-issues. Cost scales well with distance.

To make sure I've covered your questions:

  • Is there a specific kind of Category 6 cabling I should use?

Solid conductors, since these cables will be immobile. (Stranded is for wires that move often, like from your laptop to the wall.

Shielded is good for protecting against EMF, especially for long runs or if there is a power cable in the same trench.

Gel-filled cable protects against water intrusion that could cause corrosion.

Direct Burial cable has a tough jacket that can tolerate abrasion underground. If you're in conduit this matters less, but you might choose it anyway.

UV-resistant jacket is important if your wire comes out of the PVC where sunlight can get.

  • Can I simply run the cable through PVC pipe for most of the way?

Yes, and this is a good idea. Schedule 40 gray is the normal choice around here.

  • I read that Category 6 needs special grounding?

I dunno about that.

  • Is there any major benefit to running more than one cable through the same ditch or pipe?

You can run multiple low-voltage cables through the same conduit if you want, but don't put power cable in the same conduit as low-voltage. Use a large enough conduit that you can pull additional cables later.

  • Are there any pitfalls I may not be aware of?

Many, but I can't think of any more.

EDIT: Since power will be in the same trench, I recommend staking the conduits to their respective sides before filling, to make sure they keep a good foot space between them. I wish I had known to do that!

For future-proofing, consider installing an additional conduit. A contractor friend likes to install an extra 4" conduit, which can be used for a lot of stuff. Other people think he's nuts. I think they're both right. :-)

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Thanks for your answer, it is very helpful. My only motivation for Cat 6 is to be future proof; but if rerunning new cable through the conduit is as easy as it sounds, then Cat 5e sounds like a better way to go for the time being. –  DuckMaestro Aug 8 '11 at 3:29
    
great point on the pull sting for later use. –  mohlsen Apr 26 '12 at 16:49
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Gel filled or direct burial cable should be used. The conduit provides physical protection, but it will eventually get wet. Run a pull string along with the cable.

Seriously consider putting in ethernet surge protectors at each end. You can get a pretty big difference in ground potential between the two buildings. Surge protectors are available from vendors that sell outdoor wireless (WISP) gear.

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I haven't researched this recently, but another option might be to look into using a fibre optic connection.

When I needed to connect two buildings a few years ago, I found that a (lightly) armoured four fibre cable and cheap 100baseFX transceivers were cheaper and much faster than outdoors rated 10base5 plus lightning arrestors.

I bought a 305ft reel with pre terminated ends, so didn't need to worry about splicing or buying needing special equipment. Even though I only needed two fibres for the connection, I went for a four fibre cable, which meant that three fibres had to fail before the cable would need replacing. In fact, all four were still working several years later.

In addition to removing any risk of ground loops/mismatch between ends of the cable, some of my route was not buried so I had to contend with the possibility of a lightning strike (hence worrying about lightning arrestors).

Some might say that a fibre solution was overkill, but after all the research I did, it was the safest, fastest, cheapest solution overall. It's also flexible, I suspect that if the cable were still in use today, it would be happily running 10Gbase-SR.

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You only need to worry about grounding if you use a shielded cable with the proper jackets on both ends. And your equipment is rated to ground that shield via the jackets. In most cases I would not worry about that, as most pros can't install that properly. Personally, for a 120 ft run, I would use unshielded but solid core wire. You can run it in PVC as long as the PVC will mostly be buried, otherwise you need to use something with better UV resistance. You can run multiple wires. Your max run length is 330 feet. Just be careful not to untwist the wires as you're pulling.

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Also consider using flexible PVC conduit - that way you have no joints underground. I was in the same situation this summer and ended up going that route. The only difficulty with this approach is that you end up pulling the whole cable through the entire run instead of in 10 - 20ft section so fiction becomes a concern if you're pulling through a smaller conduit.

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Use lots of cable lubricant. As long as you don't have too many bends it should pull pretty easily - it is the bends that add all the resistance. –  Steven Jan 11 '12 at 18:09
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