Going underground...


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Old 09-17-13, 07:59 PM
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Going underground...

Hey All,

So I've grown tired of going back into my shed at night only to step on a rake and rap myself on the head like one of the three stooges. So I'm running power.

I don't like the idea of direct bury cable....don't ask why...I just don't. Fear of something severing the line.

I've decided to run proper PVC conduit back there and I'm already trenched out. No problem except for a sore back.

My question is - given that I have proper pipe, buried at the correct depth over a bed of gravel, can or should I just run regular Romex through or even with the conduit, do I need something more waterproof or beefy?

Code aside here....I'd prefer a bit of over-kill as I don't want to do this again....ever!

Do I go direct bury cable through the pipe or is this a big waste of money?

Thoughts?
 
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Old 09-17-13, 08:04 PM
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should I just run regular Romex through
Never. NM-b can not be used in a wet environment. Conduit will eventually fill with water. It is a wet environment. Best practice is to use individual conductors such as THWN not cable. UF-b can be used but it is hard to pull, hard to strip, maybe more expensive, and really no reason to use it. Were you planing on a 20 amp 120 volt circuit?.
 
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Old 09-17-13, 08:20 PM
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I believe code here dictates that I can use regular romex through sealed PVC conduit as long as i'm below the frost line. I don't know about water. I mean, it's sealed PVC and in the event of a crack it's sitting on 5" of gravel.

It's also not what I'd consider a wet environment....Cold, but not wet.

I'm also not sure I understand the benefit of individual conductors vs grouped wire?
 
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Old 09-17-13, 08:23 PM
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Oh - yes. this is 120v 20amp
 
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Old 09-17-13, 09:17 PM
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It does not matter what you believe or consider, the code is adamant that buried conduit IS a wet environment. You may NOT use any wire or cable that is not listed for wet environment.
 
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Old 09-17-13, 09:33 PM
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Fair enough. But all due respect that's a statement and not really an answer.

What exactly would you use then?
 
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Old 09-17-13, 09:42 PM
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An answer IS a statement. You need to use a wire or cable that is "listed" (tested and stated to be suitable for the specific purpose by a Nationally Recognized Testing Laboratory or NRTL) for wet environments. You already mentioned type UF cable but the preferred method is to use individual wires with type THWN (or dual rates THHN/THWN) insulation. The individual wires are FAR easier to pull through the conduit so they are preferred over a cable.
 
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Old 09-17-13, 09:54 PM
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I believe code here dictates that I can use regular romex through sealed PVC conduit as long as i'm below the frost line.
Not only does it not dictate that, it prohibits it.

What exactly would you use then?
Originally Posted by ray2047 in post #2
Best practice is to use individual conductors such as THWN
The "W" designates the insulation as water-resistant.
 
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Old 09-18-13, 10:00 AM
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OK, Thanks. I did't figure that pulling the cable through would be a big issue. I'll take this advice and get wet rated cables.

I'm guessing I should still group all three conductors before pulling it? I can't see how it would be very easy to pull a second and third wire... Unless I'm missing something?
 
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Old 09-18-13, 02:03 PM
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I did't figure that pulling the cable through would be a big issue.
There aren't many cable assemblies rated for installation in wet locations. When you need 12-2/G or 10-2/G, you're pretty much limited to Type UF-B. That stuff is jacketed with molded-on rubber. The next time you're at the store, test it with your fingers for slickness and flexibility. It doesn't have a lot of either - it's made to be buried directly, without conduit.

I'll take this advice and get wet rated cables.
Conductors or wires. Cables are factory-made assemblies with two or more bare or insulated conductors inside a common jacket, or sheath.

I'm guessing I should still group all three conductors before pulling it? I can't see how it would be very easy to pull a second and third wire... Unless I'm missing something?
No, that's the way it's done. I like to make the head as a daisy-chain sometimes, but that's only if I have reason to believe the the pull might be tougher than normal.

Stranded conductors pull easier but are tricky to terminate. Solid conductors are a bit harder to pull but much easier to terminate.

Install the conduit with the bells pointing toward the location where you want to set up the wire stand to pull from. Feed the fish tape from the other end.

A piece of 1/2" pipe laid and taped between a tread and a back brace on a stepladder makes a good axle for the wire reels.

How long is the conduit going to be?
 
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Old 09-18-13, 02:30 PM
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You can thread masons twine through the conduit as you glue it up. Always use plenty of lubricant.
 
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Old 09-19-13, 07:26 PM
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There's always time for lubrication....

I wouldn't consider trying to pull more than a few feet without lube. the distance on this is only about 35' but there are two 45 degree bends. I've pulled much farther but only through steel pipe...and never underground, not that that really makes a difference.

I actually laid the pipe today. 1 1/2" PVC. I think it's larger than needed but I'm hoping bigger is easier. Of course I left 2 strands of twine inside to pull cable through.

I see what you mean about staggering the head of the cables to pull them through. Makes sense.

So it appears the solution is 12 ga NMW using separate conductors...

I think I'm going to avoid solid core. Such a pain and I'll never power anything that draws too much.

Thanks all
 
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Old 09-19-13, 07:34 PM
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so it appears the solution is 12 ga NMW using separate conductors...
No, it is individual THWN conductors. One black, one white, one green. I don't know what NMW is.
 
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Old 09-19-13, 07:37 PM
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I actually laid the pipe today. 1 1/2" PVC. I think it's larger than needed but I'm hoping bigger is easier. Of course I left 2 strands of twine inside to pull cable through.
So it appears the solution is 12 ga NMW using separate conductors...
That would be THWN and not NMW. Your conduit is WAY overkill for #12 conductors. You could have used 3/4" and not needed any lube.
 
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Old 09-19-13, 07:44 PM
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Old 09-19-13, 07:56 PM
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Yea, that must be a CANADIAN thing! You had mentioned separate conductors so I naturally thought of THWN. By the way, NMW is a cable and appears to be very similar to UF B cable except that it is only rated for 300 volts to ground. The NEC doesn't prohibit installing a cable in conduit, but that isn't a recommended installation either. I can't say about the CEC. Good luck with your project!
 
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Old 09-19-13, 08:01 PM
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I surrender. We can only tell you the best way not force you. If your more comfortable with cable then do use it.
 
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Old 09-19-13, 08:19 PM
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I must admit I'm more comfortable with cable. I just figure it leaves less to screw up.

I don;t get how it can be easier to pull separate wires.

You guys ARE awesome. thanks for the patience. I'm a concrete, wood, welding guy. Electrical is obviously not my strength so I really appreciate all this excellent advice.

Cheers
 
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Old 09-20-13, 01:53 AM
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I don;t get how it can be easier to pull separate wires.
You pull all conductors at the same time. By using individual conductors you don't have the extra material of a cable jacket and fillers to interfere.
 
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Old 09-20-13, 08:00 PM
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THHN, etc is coated with thin nylon. It pulls easier, it's cheaper, it's easier to use. Cable won't get you an advantage, but not an issue, either.
 
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Old 09-22-13, 12:38 PM
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I must admit I'm more comfortable with cable. I just figure it leaves less to screw up.
You pull the conductors you need, you terminate them. What's to screw up?

I don;t get how it can be easier to pull separate wires.
Each conductor (wire) flexes and snakes through the conduit on it's own. They are pulled in parallel, not as a spiral-twisted set, so they are far more flexible. Once they're in, if you make up the pulled end first, you can pull a bit more of any one or two if you need to. As already said, the insulation on individual conductors is made to ease pulling; the jacket on cables is not. Most cables are not rated for installation in closed conduit; the insulation and jacket on them is designed and rated for installation that allows heat to be dissipated into the air. They can overheat when enclosed in conduit.

I think I'm going to avoid solid core. Such a pain and I'll never power anything that draws too much.
So you're more comfortable with installing a crimp-on terminal on each end of each conductor before terminating it?
 
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Old 09-23-13, 07:52 PM
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Thanks. To be honest I've only tried pulling separate conductors once before. I wrapped them together. I'm guessing that's what made for it being a pain to pull around corners. Thinking back now, I can see how the wouldn't want to make corners while fastened. It didn't allow them to turn at different radius from one another.

I'm very comfortable with the crimp-on terminal actually. But don't think that's going to be necessary here.

This is all making a great case for using direct bury
 
 

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