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I'm putting in a trench with electricity + water + phone from the street to a future house site. The trench will be around 150' long. The electricity and phone will each be in their own conduit, probably 2".

A friend suggested I install an extra 4" conduit in the trench now, for future use. If I wanted 400A electrical one day, it would be easy to pull. Or if the water line fails, I could pull a replacement in this conduit. Or I could pump sewage up to the septic system, if I use a macerator and pull a hose through the conduit. Etc.

My contractor says that 4" conduit is very difficult to work with, since it won't bend as easily as the smaller stuff. (The trench meanders through the woods.)

Would 2" conduit be enough for one of those possible future uses?

Any other advice?

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2" is likely overkill for electrical or phone. I generally use 1" or 1.5" The only time I've ever needed larger than the 1" was when my neighbor decided to re-run the cables between our homes, and he pulled two exterior grade coax and two cat5 through the 1". (because he had pulled the electrical to his shed in the 1.5") It fit, but it was damned right. (if you're wondering how the shed works into this ... the full run is my house -> my garage -> his shed -> his house) –  Joe May 24 '11 at 21:50
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@Joe: I ended up pulling 2-2-2-4 Al (it was less than 1/2 the price of the required #8 copper), so I'm really glad I had the extra room of a 2" conduit. –  Jay Bazuzi Jun 23 '11 at 5:05
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2 Answers

up vote 3 down vote accepted

I would want a good separation between the electrical, water, gas, and any other conduits. I doubt you'd be able to push a water line through the conduits anyway unless they are using plastic pipe for the main, and even then it would be a challenge. In terms of what you may need in the future, here we have electrical, water/sewer, gas, phone (copper and fios), and cable all running underground, but this will vary by area. All the low voltage stuff (phone/cable) can be run in the same conduit.

For a real world example, looking at the construction site next to me, the sewer and storm water lines were buried first because they depend on gravity. Next, they ran a load of conduit right by my home with what appears to be electrical on the bottom. I believe the water lines are running on the complete opposite side of the road. The electrical conduit was encased in cement (this is a large site, so I don't think they want to risk anything messing with these lines). For all of the 4" or larger conduit, they mostly use pre-curved corner joints rather than bending a straight piece.

In addition, there are a few things you may want to use from this site. Above every conduit, a few feet higher, they run a plastic ribbon indicating what is buried below that gets pulled up by any trenching equipment before the line is hit. Every 50 yards or so they have access panels where they can splice the lines running through the conduits and make it easier to pull new lines. And access panels are physically separate for each type of utility running below ground. These panels are 5 sided boxes (bottom is open) that are buried to have the removable top flush with the ground, and the conduit makes a 90 degree turn up to the box and the next piece of conduit makes a 90 degree turn going back down and continuing to the next panel. The more curves, the closer you should space these.

Edit: I just noticed that you said 150', for some reason I had it in my head that you were doing 150 yards. Ignore all my concerns about access panels for only 150'. But like shirlock says, conduit is for the wiring, not the plumbing and piping, and I don't think I made that clear enough in my answer. And for only 150', I'll leave it up to you whether you're worried about forgetting where the lines are buried to want to run the indicator tape above the conduit. It's likely overkill, but the utilities aren't responsible for marking stuff after their demarcation.

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Jay, Jay Jay.... you come up with the weirdest questions.!!!! We gotta talk!!! lol. Love your enthusiastic ways, but concerned for your welfare!!! lol. 150 ft is not a long run if you use sweeps, forget the sewer and water, ain't gonna happen, EVER! Maybe a 2 inch line with a few extra pull strings. You better call me so I can set you straight on this one. I'll be on the Podcast next Tuesday, call in!!!!

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In the beginners mind there are many possibilities; in the expert's mind, there are few. :-) –  Jay Bazuzi May 24 '11 at 23:44
    
stick with me buddy, you'll be a pro in no time! lol –  shirlock homes May 25 '11 at 0:36
    
I'm convinced; I'll put an extra 2" as my future-proofing. –  Jay Bazuzi May 25 '11 at 5:29
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what podcast are you referring to? –  mohlsen May 26 '11 at 15:29
    
@mohlsen: The StackOverflow podcast. blog.stackoverflow.com/category/podcasts –  Jay Bazuzi Jun 23 '11 at 5:06
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