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Pulling Cable in PVC - Burning Through Elbows (Data)

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joozu6

Electrical
May 29, 2003
37
I'm looking for some data on determining when pulling rope burns though PVC conduit elbows in order to determine when to use rigid metal conduit elbows. My electric coop currently requires the use of rigid metal elbows for pulls over 250 feet. I would like to see data to support this. It's my opinion that it should be based on the sidewall bearing pressure, speed of pull, and the type of pulling tape (steel should generate less friction than nylon). Does anyone have any data or experience concerning this matter? My efforts to find specific data on this have been unproductive (Southwire, Carlon, IEEE, AEIC, etc.).

FYI: We pull 25kV urd XLP jacketed cable into 3" PVC, one cable per conduit.

Thank you in advance.
 
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The code specifies a maximum length you can pull befor putting in pull boxes or fittings. Also the maximum amount of bends.
Have you tryed using a wire pulling lubricant?
 
Yes, we do use a lubricant. What code are you refering to?
 
You might check with your local Okonite folks. They have told us that the PVC elbows are sometimes damaged by the pull wire, but generally not by a lubricated cable. I seem to remember that nylon pull cable can be a problem.

The requirement of steel elbows is seen frequently, but I'm not aware of any published data to support the practice.

 
According to our local Okonite folks, use of a steel rope will essentially eliminate all burn through of PVC elbows. The problem is the interaction of the nylon rope and the PVC.
 
Thank you all for you help.

Busbar, I read Thread238-61500 before I started this one, but I was looking more specifically for experimental data to support the use of rigid metal elbows. Thanks anyway.

I think this matter is in dire need of some specific experimental studies.
 
Our company has encased PVC elbows in concrete to disapate heat on runs more than 100 feet. I think it is more reasonable to pull the rope slower instead of tying it to the bumper of a truck and seeing how quick can get it pulled in.
I would be concerned about using metal elbows or conduit if you are only putting one phase in each conduit. I would also be concerned about bare steel if there is a copper ground grid.
 
It's been a while since I started this thread, but since then I found some info on the subject that someone may find useful:

EPRI has done extensive experiments on this and it is published in the document EL-3333-CCMV2. The cost of the document is around $2,500, which is quite pricey.

AEIC document CG5-90 ($25.00) is what I purchased and it was exactly what I was looking for. It has all the info you'll need for a succesful pull.
 
joozu6,

So when does pulling rope burn through PVC elbows? Or do we have to pay the 25 buck also to find out?
 
Best explained, perhaps, by quoting AEIC. It has a lot to do with the method of the pull:

"A coarsely braided fiber pulling line or stranded steel rope will wear through duct much more rapidly than a nylon jacketed pulling line."

"Typical cable pulling speeds for power cables range btwn 10 and 50 ft per minute."......"High pulling speeds also result in an increased rate of frictional heating in bends and can result in additional wear in PVC."

My conculsion is to try using steel tape(not stranded) without steel elbows and being sure to pull at proper speeds with a tension gauge attached. We will run cable pulling calculations prior and will be conservative.

Also concerning surging, AEIC states "Cable pulls with pulling lines that have a large amount of elasticity (nylon)surge more readily than pulls with lines that have little elasticity." (steel tape)

The document has a lot of other useful data on coefficient of friction, SWBP, tension calcs, etc.

Hope that helps.
 
Interesting. The AEIC opinion on steel rope vs nylon seems to contradict some of the earlier posts.
 
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