How far?

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hardworkingstiff

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Wilmington, NC
Can anyone help me with how far you can pull 3/0 THHN/THWN in a PVC conduit before you overstress the wire? I'm bidding a job that I need to pull over the river and through the woods to get from point a to point B. The path is winding and the PVC would not be a straight shot, but a gradual winding left then right, etc. etc.

I would like to hear comments on how you would deal with the winding conduit as far as degrees of bend in the conduit. I normally don't worry too much about gradual changes, but this is a long ways and there are a lot of changes (the path is not straight).

Overall distance is about 1600 feet. I'm stepping up the voltage from 240 to 480 and then back down (POCO has an existing 120/240 volt transformer in place, and I don't think they carry single phase transformers that deliver 480 volts).

Thanks,
HWS
 
Re: How far?

By the way, 1,600' with 3/0?

How much load are you feeding, 3/0 seems small.

I come up with 3% drop with only 55 amps of load.

[ August 21, 2005, 08:41 AM: Message edited by: iwire ]
 
Re: How far?

Originally posted by iwire:
By the way, 1,600' with 3/0?

How much load are you feeding, 3/0 seems small.

I come up with 3% drop with only 55 amps of load.
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It's just a few lights and receptacles, plus some future boat lifts (I would guess 2 - 1 H.P. max use at a time). I figured a 25 KVA transformer would be more than sufficient. I would be interested in your thoughts on this.

I'm acutally considering seeing if I can step up to 600 volts and back down instead of 480. Any pitfalls you know in doing that? I've never done it but can't see the problem since all of the equipment you would use at 480 is rated 600 volts.
 
Re: How far?

I would also be concerned with the conduit. If you had a number of bends or PVC elbow near the end of the pull I would be concerned that pulling 1600' of pulling rope through this run may damage or cut right through the conduit bend. Will you have any splice points in the run?
 
Re: How far?

Originally posted by infinity:
I would also be concerned with the conduit. If you had a number of bends or PVC elbow near the end of the pull I would be concerned that pulling 1600' of pulling rope through this run may damage or cut right through the conduit bend. Will you have any splice points in the run?
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That is what is under consideration right now. I've had good luck with using a 7/8" pull rope not damaging conduit in the past, but have seen POCO use a steel cable and cut into the PVC (can't believe they did that, but...). Right now I'm leaning towards using AL wire, one 90 (long radius) at each end and a lot of "S-ing". I'd prefer not to splice in the pull, but if I have to of course I will.
 
Re: How far?

I have never tried a 1600' pull but I have done around 1000' with bigger cable. The things that I have done to make it go easier. One thing is to rent a big compressor an blow any dirt and gravel out of the pipe with high pressure air. 100 psi or better. Then I take the time to pull a rag through the pipe to make sure there are no bad connections or burrs. If the rag comes through with no tears I'm sure the pipe is clean. Then lots of soap and a big enough crew to do the job. The radio man should not be feeding the cable. a good slow and steady pace with frequent applications of soap. Last thing is to meg the cable to prove that no damage was done. at least it wont be cold, I hate it when the soap starts to freeze. Good luck.
 
Re: How far?

By the way, 1,600' with 3/0?
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Did you consider additional bends other that the 2 end 90's? If not you would need ot include these also.
HWS would have to give the angles of each bend and distance between.
 
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