Conduit Bank
Conduit Bank
(OP)
Currently working on the design of a concrete encased electrical conduit bank, have to install 600V feeds and about 1200A, currently looking at3/phase of 750kcmil.
My question comes with the conduit bank and how many bends I can have before it starts getting hard to pull the cables through, the run I have is only about 40m or 130ft. Right now I am thinking I will have a 90 at the start of the run and a 90 at the end, will the installing contractor be able to pull this cable?
Does anyone have any links to literature, I might need something to justify the need of a pull pit?
Thanks
Hank
My question comes with the conduit bank and how many bends I can have before it starts getting hard to pull the cables through, the run I have is only about 40m or 130ft. Right now I am thinking I will have a 90 at the start of the run and a 90 at the end, will the installing contractor be able to pull this cable?
Does anyone have any links to literature, I might need something to justify the need of a pull pit?
Thanks
Hank





RE: Conduit Bank
This might get you started.
RE: Conduit Bank
http://www.polywater.com/pullplan.html
RE: Conduit Bank
RE: Conduit Bank
RE: Conduit Bank
The NEC limit of 360° is also high arbitrary; there can be pulls where one 90 is enough to make the pull impossible while in other cases a pull through 720° would work just fine.
RE: Conduit Bank
RE: Conduit Bank
On the other hand, I designed a rather nasty run in a hospital remodel with pull points as often as possible and then the contractor proceeded to pull the whole 7 x 90° run as a single pull figuring there would be more risk to the cable from piling it up on the floor at each pull point than pulling it all the way in one pull.
RE: Conduit Bank
RE: Conduit Bank
Bill
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"Why not the best?"
Jimmy Carter
RE: Conduit Bank
I don't have my Southwire Power Cable manual (the only document that I have that shows the pulling calculations) here at home, but I don't recall the ratio between conduit and cable diameters having a big impact on the side wall pressure. As I recall it is just the pulling tension coming out of the bend divided by the radius of the bend in feet. What is the formula to take the diameter ratio into account?
Don
RE: Conduit Bank
I had some time and found the pulling calcs in the Southwire book. The ratio tells you what configuration the wire will take in the conduit when it is pulled...either cradled or triplexed. If it is cradled the side wall pressure will be reduced as compared to triplexed. I also found that the side wall pressure calc is a lot more involved than just the pulling tension divided by the radius in feet when there is more than on conductor.
Don
RE: Conduit Bank
I don't have the calculations handy, but the point that I was trying to make is that there is a range of diameter ratios that tend to jam badly in bends.
Bill
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"Why not the best?"
Jimmy Carter
RE: Conduit Bank
RE: Conduit Bank
Keith Cress
kcress - http://www.flaminsystems.com
RE: Conduit Bank