Pulling new wire through old conduit


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Old 09-02-08, 05:30 AM
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Pulling new wire through old conduit

I have an old conduit that goes from the crawlspace in the house to a lamp post out by the road. In the process, it goes under the driveway.

Anyway, when the house got rewired, the light post didn't get connected back up. I want to replace this wire and the light post.

I have removed the old light post. What I have now is an underground junction box (not sure if that's legal) with the old wires sticking out of it. I can't pull the wires by hand.

Is this a lost cause or is there something I can do to increase my success as pulling the old wires out (and in the process a new wire in).

It looks like it's about 1/2" or 3/4" conduit.

The alternative to pulling this through is putting a new light on the house side of the driveway (probably the easiest).
 
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Old 09-02-08, 07:16 AM
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I have not personally dealt with this issue, however from reading:

1) something as simple as flooding the conduit with water may help

2) there are wire lubricants specifically made for loosening stuck cables, eg http://www.polywater.com/cablfree.html

Don't use the old conductors to pull the new ones in; pull in a rope, and then use that to pull in something to clean the conduit, along with another rope, and _then_ pull in your new conductors.

-Jon
 
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Old 09-02-08, 09:09 AM
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If the conduit is old and metal, there's a good chance that it's rusted through and may be full of sediment and therefore junk.

You can try to gauge this with a shop vac. Hook it up to one end of the conduit and see if you're getting airflow through the other end. This will give you a clue if the conduit is obstructed.

If the conduit is open, you will probably need a cable loosening lubricant to get the wires moving. You can buy this product at an electrical supply house. You pour some of the liquid into the conduit, then use a compressor blow gun or shop vac in reverse to blow the lube through the conduit.

Once the loosener has soaked in, pull like hell! You might want to use some vice grips to get a good grab on the wires.

Also, follow Jon's advice. Pull a rope through first tied to the end of the old conductors, then use that to pull a couple passes of rags through to clean out the conduit.

You should not have an underground junction box. Once the old conductors are pulled out, you can replace this with a continuous sweep of conduit.
 
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Old 09-02-08, 01:31 PM
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I'll have to see what I can figure out with my shopvac this weekend.

What I found of the conduit seems to be in pretty good shape, so I'm hopeful that I won't have to dig a new trench.
 
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Old 09-02-08, 03:30 PM
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If it's rigid (threaded) conduit, as it should be, you may be in luck since that's pretty thick-walled.

If it is EMT or even intermediate, your chances are much reduced.

You might also try sticking a lubed fish tape in there to see how far you get. If you want to do that, I would unscrew the eye and push the female threaded part back down to the tape case so it doesn't go down the conduit. Most of the lube won't make it very far down the pipe but if it's not blocked some should. If the conduit does not slope so it can drain by gravity, expect it to be full of water.
 
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Old 09-21-08, 05:01 AM
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I got it out by filling the conduit with water and using brute force to pull on the wire with vice grips. Once it moved about 6", it was easy pulling.
The wires were tapes together, so I had to pull both at once instead of one at a time like I was trying to do.

I have a pull string through. I think I'm going to use that to pull a fish tape through, and then use the fish tape to pull the UF-B. I was using the UF-B because I don't know the condition of the conduit for 100%, and I have a short run inside I need to make and didn't want to transition.
 
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Old 09-21-08, 05:17 AM
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Originally Posted by chandltp View Post
I think I'm going to use that to pull a fish tape through, and then use the fish tape to pull the UF-B. I was using the UF-B because I don't know the condition of the conduit for 100%, and I have a short run inside I need to make and didn't want to transition.
I'd just use THHN/THWN. It would be much easier to pull. If my pull string made it through without getting abraded too much, and I pulled in a separate ground wire, I wouldn't worry about the conduit condition too much.
 
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Old 09-21-08, 08:52 AM
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Don't know what the distance is but if the conduit is only 1/2 or 3/4, the chances of pulling a piece of UF through it are probably slim to none even with some lube.
 
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Old 09-21-08, 08:58 AM
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Remember conduit is to protect from physical damage not moisture or water so even if there are a few small holes it is still good for THWN. Moisture even a bit of water is to be expected.
 
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Old 09-21-08, 01:56 PM
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Well, I didn't check back before I did it, because the electrician across the street had recommended UF-B. It was a 1" conduit, and I didn't have any issues pulling it to speak of (other than 2 small blockages that appear to have been dirt). But the wire is pulled everything went fine.

Thanks for all your help.
 
 

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