Page 2 of 4 FirstFirst 1234 LastLast
Results 11 to 20 of 39

Thread: MV Pulls

  1. #11
    Join Date
    May 2005
    Location
    Richmond, Virginia
    Posts
    23,725
    Quote Originally Posted by don_resqcapt19 View Post
    As far as pulling, for the above reason, it is always best to have the bends closer to the feed end, than to the pulling end. However you are limited by the installed configuration.
    Seems like the opposite would be true.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  2. #12
    Join Date
    Sep 2012
    Location
    NJ
    Posts
    2,279
    Quote Originally Posted by don_resqcapt19 View Post
    As it gets below 40°F the wire is much stiffer and harder to handle. Most conductor types cannot be handled below 14°F without risk of damage to the insulation.

    Someone will have to do the pulling calculations. With 3 90s in an 800 foot run, there is risk of exceeding the maximum permitted sidewall pressure. To find the sidewall pressure you need to find the pulling tension coming out of each 90, and also know the radius of the 90. The sidewall pressure and not the actual pulling tension, is most often the limiting factor in a pull.

    As far as pulling, for the above reason, it is always best to have the bends closer to the feed end, than to the pulling end. However you are limited by the installed configuration.
    So what happens if you do exceed sidewall pressure? Have to still make pulls.

    Sent from my SM-N960U using Tapatalk

  3. #13
    Join Date
    Jan 2009
    Location
    3 Hr 2 Min from Winged Horses
    Posts
    15,950
    Quote Originally Posted by mstrlucky74 View Post
    So what happens if you do exceed sidewall pressure? Have to still make pulls.

    Sent from my SM-N960U using Tapatalk
    Bad things happen. Usually conductor insulation damage.

    Google it.
    "Electricity is really just organized lightning." George Carlin


    Derek

  4. #14
    Join Date
    Feb 2003
    Location
    Illinois
    Posts
    23,816
    Quote Originally Posted by mstrlucky74 View Post
    So what happens if you do exceed sidewall pressure? Have to still make pulls.

    Sent from my SM-N960U using Tapatalk
    Excessive sidewall pressure damages the insulation and can result in complete cable failure. Ever without a complete failure, there may be enough damage that the cable will not pass the acceptance testing.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  5. #15
    Join Date
    Feb 2003
    Location
    Illinois
    Posts
    23,816
    Quote Originally Posted by LarryFine View Post
    Seems like the opposite would be true.
    The tension on the conductor itself increases along the pull. You want the bends in the locations with the least pulling tension. If you have a 90 and the pulling end of the run, the cable will have almost 100% of the total pulling tension. As I recall the sidewall pressure is the pulling tension divided by the radius of the 90 in feet. Typical maximum sidewall pressure is 500 to 600.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  6. #16
    Join Date
    Sep 2012
    Location
    NJ
    Posts
    2,279
    Quote Originally Posted by don_resqcapt19 View Post
    The tension on the conductor itself increases along the pull. You want the bends in the locations with the least pulling tension. If you have a 90 and the pulling end of the run, the cable will have almost 100% of the total pulling tension. As I recall the sidewall pressure is the pulling tension divided by the radius of the 90 in feet. Typical maximum sidewall pressure is 500 to 600.
    So if you have a 90 near where you are pulling that will be a to of pressure on that 90 because it's close to the pull point? Thanks.

  7. #17
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    19,755
    Quote Originally Posted by mstrlucky74 View Post
    So if you have a 90 near where you are pulling that will be a to of pressure on that 90 because it's close to the pull point? Thanks.
    Yes, because the tension in the wire is the friction around the 90 multiplied by the downstream tension of the long straight section.
    If you feed at the 90 the overall pulling tension will be lower, the tension at the 90 will be much lower, but the remainder of the pull, from 90 to pull point will be under the full pulling tension. Usually there is no downside to that, unless there is a chance of multiple wires wedging.

  8. #18
    Join Date
    Sep 2012
    Location
    NJ
    Posts
    2,279
    So how does one determine where splicing/pull points would take place in a pull. FOr instance on the attached it's a 900' run with three manholes and bends. THe routing is in bluee.
    Attached Images Attached Images

  9. #19
    Join Date
    Dec 2012
    Location
    Placerville, CA, USA
    Posts
    19,755
    Calculate pulling tension for segments individually, then in various combinations. Analyze whether you can lay wire out at a given manhole to pull in and repull out. Is the dark area in/near substation 10 vault, duct bank, tunnel? Lots of bends there.

  10. #20
    Join Date
    Sep 2012
    Location
    NJ
    Posts
    2,279
    Quote Originally Posted by GoldDigger View Post
    Calculate pulling tension for segments individually, then in various combinations. Analyze whether you can lay wire out at a given manhole to pull in and repull out. Is the dark area in/near substation 10 vault, duct bank, tunnel? Lots of bends there.

    The dark part of the ductbank are the new conduits connecting to the existing conduit duck bank. THey go to substation 10,11 & 12.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •