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Running Network Cable Outside of a Building
Last updated: 9/29/2000

This is a collection of questions and answers posted in our Forums about running network cable outside of a building.  I consolidated them here as a one-stop reference for others in search of material on this subject.  If anyone else has additional information/advise, I would appreciate a post in our Network and Internet Sharing Forum or an E-Mail.   Larry

Q.  I was reading the guide to making your own CAT 5 cable, and saw the warning not to run it outside of a building.  I currently live in an apartment, and am setting up DSL, the way the rooms are set up, they all have windows on one side of the apartment building, and are fairly close together, so I had planned to just set up the DSL router and hub in one room, and run the CAT 5 from the other rooms to the hub out through the windows along the outside wall.  The distances the cable would be run is pretty short, 10-15' probably, if I was forced to run them through the apartment, it would at least quadruple the amount of cable I would need, due to the nature of the apartment layout.

Now, the question. I know the warning in that guide is in huge red letters, but is it really that huge of a deal, especially with such short lengths of cable, and in a relatively lightning free city like Seattle?  I really don't want to have to run it through the apartment.

Another Question.  I am trying to network 2 PC's.   One on the forth floor and one on the first floor of my building.  I understand that I should not lay cable from the outside of the building.  Do I have an alternative?  Can I use something to insulate it?

A. I would fish it through the walls or use wire mold on the inside of the building. I suppose you could use a metal conduit on the outside of the building if it is correctly grounded, but it still might present a lightning danger. Until you have actually seen a couple of PC's fried by lightning striking a network wire and the potential danger it presents to the users of those PC’s, it is hard, I presume, to be as serious about it as I am. You might be able to use a phoneline connection (e.g., http://duxcw.com/digest/Reviews/Network/dlink/dhn910/dhn910.htm) or a wireless product. Move one of the PC’s, people?

Q.  Installing a metal Conduit on the outside of the building? Can the CAT5 be installed in some kind of of Rubber coated tubing or pipe. I feel anything metal will be a hazard.

A.  I don't believe you can insulate it against lightning. The voltages are extremely high. If it can be done safely at all, and I doubt it, the cable should be shielded with metal conduit, which is properly grounded (a rod in the ground several feet deep). Theoretically, if lightning strikes, it should be conducted to ground through the conduit instead of to computers via the network cable. However, in my experience lightning can be quite unpredictable and I would not trust this scheme to protect computer users.

cat5j's input... If you MUST run your cable outside, then why don't you use a outdoor type cable, preferably gel-filled. you can also ground it. not only do you need to protect it from lightning, but also the weather elements.

Q.  I have read the article on making your own cables, and saw the admonition against running UTP cables outside. I also saw several messages in the archive about this subject. My question is, why is running UTP outside any different than running telephone wires or TV cable? Are these types of cable somehow inherently safe against lightning, or are they grounded differently? If they are grounded differently, couldn't UTP be grounded the same way?

I have a house that was built in 1917, and need to run network cable from the basement to the 2nd floor. Running it outside would be much easier than trying to run cable through the walls, but I don't want to do it if it isn't going to be safe. However, in the place I would run it up the side of the house, there are already a telephone line and a TV cable. I noticed that the TV cable bracket has a bare wire running from it to where the electrical service enters the house. I assume that this is grounding it in case of lightning.

Would doing the same thing with UTP be just as safe?

A.  Wire is wire... There are lightning arrestors for telephone lines and TV cable. I know of no such device for twisted-pair network cables (I found later; see below).

Q.  I noticed that the TV cable bracket has a bare wire running from it to where the electrical service enters the house. I assume that this is grounding it in case of lightning.  Is this the lightning arrestor you are talking about, or is there some sort of filter in-line?

A.  The lightning arrestor on the TV cable going to my house was installed last week and looks somewhat like a bracket. The cable segments on either side of it have connectors on them. It has a grounding screw on it for a wire to a pipe that goes well into the ground. Theoretically, a lightning arrestor redirects/shunts a very high lightning voltage/current pulse(s) to the ground connection (or up from the ground) before it (or most of it) can get into the house. They don't always work 100%. Even running the wire on the inside of a building is no absolute guarantee that a lightning strike won't find it or that a close strike won't induce a very large and dangerous pulse into it.

You only have to see one lightning strike on a network cable to become a believer. I’ve seen a couple: one outside on a cable running between buildings and one inside where lightning struck a microwave tower immediately outside of the building. The first one totally destroyed two computers and, little doubt, could have killed someone. The second one appeared less lethal but damaged every piece of networked equipment in the building.

Q.  I wonder if there is some sort of filter or weak link within the TV cable lightning arrestor between the in and out connectors. On the one on my house, it doesn't appear that there is room for a filter. Perhaps a weak link, like a fuse, that blows our under high current? Or is it just a straight through connection, in which case the arrestor relies on the grounding wire to have much less resistance and thus carry the brunt of the current?

Okay, so now what about the idea of running the UTP within conduit, and then connecting the conduit to the same grounding source as the lightning arrestor. It would seem that the conduit and grounding wire would carry the brunt of the current. Any reason why this isn't a viable solution?

A.  It has been a long time since I have looked at a lightning arrester, but essentially they shunt large pulses to ground. The surge protectors I have dismantled after a strike have component that looks like a ceramic capacitor. I believe the old antenna arresters used for long wire radio antennas, which I made when I was young (about 45 years ago) for short wave receivers, had a gap, which lightning would hopefully jump, between the circuit to be protected and the ground lead. Obviously, cable TV wire is shielded. After thinking about it some more, I think the clamp used for cable TV lightning protection, simply connects the shield to the wire running to the grounding rod.

If it were me, I would stubbornly find a way to run the network cable (and telephone wire) inside, and that can be done… with some to a lot of difficulty, I’m sure. I have snaked a lot of wires in very old buildings. If I had to run it outside, I would probably put it in a grounded, metal conduit. But don’t assume that I am an expert on lightning, that I endorse this procedure, or that it is guaranteed protection for people, computers, buildings, etc. against lightning.

I would also run a second CAT 5 cable in the conduit for the telephone wiring. This would provide additional pairs for growth. I just installed a CAT 5E cable running about 130 ft though my house, from a small punch-down block near where the phone lines come into the house to a wall plate with four RJ-11 jacks screwed to the (wooden) wall, in my new office/shop, for the three phone lines we presently have installed. I also ran the lines from the Telco termination outside of the house to the punch-down block just inside with a single CAT 5E cable. I have been using the lines for almost two weeks. The data line I use for various MODEMS, etc. works exceptionally well. The voice lines are absolutely clean. I plan to run two more lines like this one to the other two offices in our house, except one of the jacks will be a CAT 5E jack for still additional network lines. Yes, we have three people living here and each of us is setting-up a home office.

You may also want to consider putting a lightning rod on your house. I understand that a properly installed lightning rod system will work to protect a house 90% of the time. I guess you get fried the other 10% of the time.

Today, I found a device for protecting networks, but it doesn’t appear to be designed for outdoor use. See http://www.elect-spec-transformer.com/netwrk_z.htm.

Other relevant links:


Maybe someone, an expert, in academia, etc. will pick-up on this thread after the search engines find it and contribute some knowledge. That would certainly be appreciated. As far as I am concerned, this horse has pretty much been beaten to death by quite a few Forum postings. Good luck!

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