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Thread: Long Sweep Ells

  1. #31
    Join Date
    Feb 2003
    Location
    Illinois
    Posts
    23,287
    Quote Originally Posted by electrofelon View Post
    Talking from a lot of practical experience, there is no way that larger radius sweeps do not make a pull easier. I dont care what the pulling tension calculators say. I have been out in the field pulling 500 quad and about 300,000 feet of PV wire for the last month, in the mud (do these calculators have a check box for mud?) not typing stuff into a computer This must be sort of analogous to friction/traction in that in theory, more surface area does not change the friction force, but in practice it usually does.

    I think there are two main things at play because the conductors are not infinitely flexible. First, you have the force need to physically bend then unbend the conductor as it traverses the sweep. Most of us on here have pulled big wire. Recall pulling say 750 or multiple conductors plexed off a spool. Most of the force to unwind the wire from the spool is not the inertial to get it going or the friction on the spindle. It is changing the shape of the wire from curved to straight. Secondly, the tighter the radius, the more friction we would have between the conductor(s) and the walls of the sweep. As someone mentioned, these forces are multiplied not added to the next point of resistance.
    And with small conduit I felt that the large radius concentric bends that we used on one project actually made it more difficult to pull than a standard 90.

    As far as the friction, I see that staying the same...more friction over a shorter distance or less friction over a longer distance. I think the only possible difference is the bending force that you talked about.

    I have never seen the radius used an any pulling force calculation over the years. I would expect that if it really made a difference there would be a calculation to support that. There is a huge difference in sidewall pressure and that is what normally triggers a requirement for a large radius bend.
    Don, Illinois
    Ego is the anesthesia that deadens the pain of stupidity. Dr. Rick Rigsby
    (All code citations are 2017 unless otherwise noted)

  2. #32
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    18,374
    Quote Originally Posted by don_resqcapt19 View Post
    Can we say that where we are using conduit with a bending radius at least equal to minimum permitted by Chapter 9, Table 2, that an increase in the bending radius does not decrease the required pulling force?
    I would not say that.
    The minimum bending radius is based on damage to the wire or insulation from bending, not whether the bending is inelastic enough to affect pulling tension.
    The other replies discuss other factors in play as well as personal experience.

    Sent from my XT1585 using Tapatalk

  3. #33
    Join Date
    Mar 2008
    Location
    Michigan. It's a beautiful penninsula, I've looked around.
    Posts
    9,429
    Quote Originally Posted by don_resqcapt19 View Post
    Did they show you the calculations to show that the large radius reduced the pulling force, or did the just assume, like most do, that the large radius reduces the pulling force?
    All I was given was the inside radius, which I don't remember.
    Cheers and Stay Safe,

    Marky the Sparky

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