underground service (conduit size and spacing)

Old 10-06-04, 10:15 AM
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underground service (conduit size and spacing)


I have a couple of questions about underground conduit for phone (and eventually cable). I live in a house that was built in 1929 (very old by California standards) that has a detached garage. I'm currently in the process of redoing the electrical and was going to go underground. Since I'll have this trench, I thought it might be a good idea to also lay conduit for phone (and cable?). The plan is to drop the service to the garage, go through the garage, and then from there to the house. The power company (Edison) has provided me with the specs to go underground from the pole to the garage, so now I'm trying to figure out the conduit from the garage to the house (it's about a 25' run). I'm currently planning on a 3' deep trench for the electrical (and the electrician is using 1 1/2 conduit for it). I was going to put 12" of dirt on top of that and then lay the conduit for the phone. So now the questions ... what diameter counduit should I run for the phone? If I also (eventually) go underground with the cable, will I be able to run it through the same conduit as the phone? Though it's easy to keep a foot separation between the electrical and the phone lines while they're underground it's more difficult at the endpoints. Just how critical is the foot separation, and is there anything I can use as shielding between the two (assuming I can't keep them a foot apart).



p.s., oops, I forgot to mention that I really prefer to over-engineer things ... it's funny, people find Monk real funny; well, I'm not half the obsessive-compulsive he is, but they don't find me funny at all.

Last edited by perion; 10-06-04 at 05:31 PM.
Old 10-06-04, 02:35 PM
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1st let me say that I know nothing about code or how this might work for you.

I can tell you that my neighbor ran CAT5 (It's twisted so it's naturally shielded) under ground to to my house. He ran it out the same hole in the wall where the electric comes in and it goes into my home where the electric goes in. He just barried the line without any conduit about a foot under ground and it's been fine. We use it to connect the PCs together.

So since we use it to connect data only, I don't know if there has been any static on the line, but I can say it's never been a problem for transferring data.

BTW, I'm having a new home built and the guys who ran the phone lines (They used CAT5) tried to stay a foot away from any electrical wiring. Staying a foot away does not happen everywhere. Before the drywall went up, I could see there were multiple places where the lines either cris-crossed or ran together for a short run. Based on that, I don't think you will have many, if any problems.

Good luck with whatever you end up doing.
Old 10-15-04, 12:32 AM
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conduit size and spacing

I work with data and phones every day. The space is to help avoid AC hum in the lines. Since you are running everything in conduit, that alone should shield from interference. From what you describe in your message, the 12" should be more than enough space.

As for the size of conduit, 1/2" would easily handle up to 8 pair cable (cat5) and a cable for tv. If you want to over do it, go for 3/4.
Old 10-15-04, 06:46 PM
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Go for the 3/4". Your biceps will thank you.

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