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Old 03-01-18, 10:23 PM   #1
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Default trenching for phone and power

We've got overhead wiring for phone and power. We also have big trees and winter storms with strong winds. Not a great combo. So... proactively I thought I'd install underground conduits for the foreseeable upgrade to below grade service wiring. So if a storm hits and the wiring is trashed we can upgrade to underground wiring at that point.

I bought 3" pvc sewer pipe for the mains wire figuring it'd be an easy pull for direct burial cable and 1 1/4" sch 40 for the phone line. How much separation is needed/recommended between the two? I had envisioned two trenches a couple of feet apart but having dug for 6 hrs to make 5 m (I need to go 40) progress at 30" depth today I'm wondering if I can put both conduits in the same trench. I'm no stranger to trenching having dug more than my share but this ground is hellacious - rocks, roots, hardpan. If two trenches are better I'll suck it up and dig but if there's no advantage I'd be happy to save some work. Anyone?

Thanks, Greg

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Old 03-02-18, 02:02 PM   #2
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I'm digging a bit deeper so I can still get 12" of separation and have sufficient cover over the works.
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Old 03-06-18, 11:23 AM   #3
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My Mains trench had to be 36” minimum & used 3” grey schedule 80.
IRC code

As nobody sells schedule 80 fittings, schedule 40 fittings were used & passed inspection.

Seems dumb

I don’t know if there is a code for the phone lines, but if I had phone lines, I think that I would use the same trench for sure & place 1/2 way to surface.
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Old 03-06-18, 11:58 AM   #4
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I found this on web search:

“I'm not a pro, but rather a long-time audio guy and electronics hobbyist. So some of the pros may disagree, but I base this recommendation on my own practical experience.

While code doesn't mandate any separation, IMO good practice calls for keeping electrical wiring and signal or data wiring at least several inches apart where they run parallel.

The problem is the possibility of induced noise in the signal or data cable. The electrical wiring will not be affected in any way.

There is little concern if the wiring is in a grounded metallic raceway, or if the data/signal cable is well shielded. Using thinwall conduit or AC cable instead of NM would take care of the problem easily.

I still wouldn't zip tie an unshielded data or signal cable to conduit, but otherwise you should be fine.

If you're using NM cable, in addition to the separation, I recommend a twist or two per foot in the electrical wires, to help cancel out EM radiation from them.”
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Old 03-06-18, 07:29 PM   #5
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Nowadays, if a phone line fails, the ISP is likely to replace it with fiber. (Maybe ask your ISP, explaining the situation and that you would like to be prepared.) There would be no technical problems putting fiber in the same conduit as power lines but I'm not sure if code has recognized that. If you're putting in a separate conduit anyways, 1 foot separation should be OK.
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Old 03-06-18, 09:54 PM   #6
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Quote:
Originally Posted by NiHaoMike View Post
Nowadays, if a phone line fails, the ISP is likely to replace it with fiber.
Except where I live!! I wish I could get fiber in my neighborhood. This antique (1959) copper is complete garbage. When it rains, I get static, or crackles. I have fiber to my farm in a rural town (823 people) in Northern Maine. (500Mbps down, 700Mbps up, 15ms ping times) I can't get fiber to my suburban residence in South Florida, but my village can get fiber to the public works building where they park the garbage trucks.

My 100' of phone in conduit (3/4") right on top of 100' of 240Vac in conduit has no discernible issues with hum or pickup. I'd pull fiber through my phone line conduit in a heartbeat, if they'd pull it down my block.

Hardened underground utilities in my neighborhood is a pipe dream. The money the utility makes on decades of storm surcharges for repairs after a hurricane basically ensure the utilities will never bury their lines.
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Old 03-08-18, 08:53 AM   #7
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I ran my mains in 3" PVC and the internet cable two feet above that in 1.25 PVC. The power company had a 150 foot limit for underground service. Mine is about 149 feet. We haven't had any problems with the coax.

You need to consider the sweep elbows at each end of the 3" conduit. The 4-0 mains cable went into the first elbow fine but was extremely difficult to pull through the second elbow. They had to separate the second elbow from the pipe to get the wire out.
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Old 03-09-18, 10:20 AM   #8
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Good point Cranky, the end hangs up when pushing, I had to remove the 90’s also.

White PVC or black ABS would work, but don’t meet code.

U can do anything that u want if you own the place & don't need an inspection.

But if u ever sell and then have to pass that new buyers home inspection, white PVC coming out of the ground will be visible & might sour the sale. Also insurance companies might object.
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Old 03-09-18, 05:27 PM   #9
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Thank you all for the very informative contributions to this thread. I've learned a great deal.

I assumed I'd be using direct burial armoured cable for the mains install so figured a conduit would be unnecessary. I just wanted to put a raceway in now so I could have an electrician run the wire later. According to "bcsa_handout_-low_voltage_service_-part_1_2" there is a 600 mm (24") minimum for cover over a raceway that will be subject to vehicular traffic unless there is extra protection afforded by solid planking, poured concrete, or concrete slabs in which case cover can be as little as 450 mm (18"). I read somewhere that Sh 80 PVC conduit is required for the 24" of vertical cable at the ends of the trench but can't find the reference now. In any case that seems like reasonable protection so I plan to switch to the sch 80 at the ends. I do want to be code compliant. For the small extra cost I'll do the same for the 1 1/4" phone line conduit.
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Old 06-10-18, 09:02 AM   #10
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For your pipe out of the ground I prefer steel pipe when its in an area that is subject to damage from cars mowers etc.

I like my conduit buried at least 3' but on a commercial site I like it deeper as it puts it further out of reach of GCs that like to play with the mini excavator... Had quite a few light pole conduits dug into and he even hit a 2" copper water line twice the same day...

Residential can be done with aluminum wire if you want but since you are using heavier wire its more of a hassle and you should go up a conduit size for it as well.

But anything is easier than running 4 600mcm(3/4"ish stranded copper) through 4" conduit... Its not fun and involves a mini ex pulling on the rope and a skytrak holding a pipe with the spools of wire. If you arent careful and the end of the wire comes off the spool it can do allot of damage as it is extremely heavy and hard. Easily breaking bones and worse...

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