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Old 04-05-2009, 01:46 PM   #1
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URD, Sand, Conduit


Can URD really be "directly" buried without being protected by conduit or sand, especially in conditions with highly rocky soil? If one had to choose between sand or conduit, which provides better protection, again in the setting of rocky soil?

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Old 04-05-2009, 02:18 PM   #2
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You can use it. BUT.. you never add rocks back into the trench. Always fill the trench with clean builders sand. Many inspectors will check what fill you intend to use. Rocks at the bottom of the trench should be removed. Pipe of course offers better protection but why spend the extra money for direct burial wire if you go this route.

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Old 04-05-2009, 02:31 PM   #3
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Many thanks. Do you mean that you would not use any of the excavated soil as backfill? Or would 6" of sand below URD cable and 6" sand above the URD cable be enough? And then rest of trench could be backfilled with excavated soil (removing the largest rocks, as much as possible)?
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Old 04-05-2009, 02:50 PM   #4
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6" of sand will be fine. Personally I always use clean builders sand to fill the trench... but I am set up for this and it is not much more work or cost for me.
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Old 04-05-2009, 03:48 PM   #5
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That's an interesting and excellent point. If one fills the trench with sand, it could well be more efficient--a bit more cost in sand but less work on backfilling with the excavated soil. Would you cart away the excavated soil or just spread it out, partly as a layer on top of sand and the rest on surrounding area? (I appreciate your insights.)
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Old 04-05-2009, 04:12 PM   #6
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URD, Sand, Conduit


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If one had to choose between sand or conduit, which provides better protection, again in the setting of rocky soil?
If one had to choose between a motorcycle or an SUV, which provides better protection?

Conduit is inexpensive insurance. I would never install any direct buried cable. Even the power compannys figured that out here in the 80's. Things don't last forever. When the time comes to repair/replace, the conduit is well worth the added expense.
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Old 04-05-2009, 04:28 PM   #7
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As long as you're digging anyway, you may as well put it once. Put it in conduit. Hate to see you dig it up again.
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Old 04-05-2009, 06:49 PM   #8
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Many thanks, this is very helpful.

I gather the conduit is SUV protection; sand is more like motorcycle. But here's my situation:

I have two separate runs of URD, one about 300' the other about 150'. Electrician cut corners and placed each run in its respective trench, with no conduit and no sand, in rocky soil. He has backfilled half of the long run already, so unless I dig it up (which, as he says, is bound to damage the cable) I don't see how I can use conduit on that run. Presumably, the best I can do is use sand for the remaining half. The shorter run has not been backfilled at all yet, so presumably I should encase that one in conduit while I still have the chance.

Is that the most sensible thing to do? And, on the short run, would you also use sand in addition to conduit?
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Old 04-05-2009, 07:00 PM   #9
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Is that the most sensible thing to do? And, on the short run, would you also use sand in addition to conduit?
I would install conduit in the short trench. Some protection is better than none.

There are miles of wire installed underground like this so I don't know that you should lose any sleep over it. Just make sure to inspect all of it and make sure there is adequate sand below and above the wire. I think 6" is kind of shy.

If you use scheule 40 conduit, sand isn't necessary, just use some discretion when backfilling. If you use something thinner like DB120, use sand.
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Old 04-05-2009, 07:14 PM   #10
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I wasn't fully clear on your suggestion:

--Short trench: Use conduit w/schedule 40 and no sand. Is that OK?

--Long trench: Just use sand on the half that's yet to be backfilled, and hope for the best on the half that's now buried with no protection (no sand, no conduit)? It is hard to see how to use conduit on half a run of cable; would presumably need to dig up the buried half to use conduit at all in long trench (?)
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Old 04-05-2009, 07:20 PM   #11
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The half that is in conduit is more protected is what is meant. Here for a main feed we still need to use sand around conduit. But for runs like you are doing it would not be a requirement but would still be better than using fill with rock. In any case, no rock. When the ground freezes the rock will move and possible move into the wire or conduit.

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