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Thread: Torque Specs on lugs

  1. #1
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    Feb 2003
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    Torque Specs on lugs

    Is there a standard torque spec for lugs according to there size? Or are they according to manufacturers? I have a 3000 amp transfer switch with the lugs
    so close together that i barely get a "L" 1/2 in Allen wrench in to tighten them. How does one torque them to specs if you can't get a torque wrench on them? If I remove a set of lugs to be able to use a torque wrench, do I blow the manufacture warranty on the transfer switch, if any thing was to go wrong. Thank you

  2. #2
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    Jul 2003
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    Smile

    I made my own drivers to torque terminals. I cut the "L" off of some long allen wrenches and got 1/4" drive, hex sockets to fit the different sized allens and taped them on.
    I can use the drivers and any needed 1/4" extensions to reach just about anything inside a panel. Using a 1/4" drive makes it easier to get the tool into tight places. I adapt to my 3/8" torque wrench with a 1/4 x 3/8 socket reducer.
    What is the listed torque on the screws? A 1/4" drive may not withstand the torque required for the 3000A lugs.
    You can buy the allen wrenches with the driver attached, but the ones that I've seen have a 3/8" drive, plus I like to make my own tools if I can.
    I use the torque spec. that's listed on the enclosure, and always torque to maximum allowed. I don't know of a standard torque for each size although there probably is one. I know that GE panels have a standard label that gives the torque according to the internal dimension of the allen across its flat sides.
    hope this helps
    steve

  3. #3
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    I don't know of a standard torque spec, but has anyone else noticed the need to retorque the bigger lugs after install? It seems like they creep loose, and need torqued a week later. After that they seem to stay tight- maybe most of the creep is gone by then. I've had starters come in with the wire falling out of the lugs, and I'm pretty sure the factory actually torqued it.

  4. #4
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    This may help usually the manufacture will provide tissue paper with the information you are looking for

    Modified wrenches do not guarantee acurate torques.


    http://www.ilsco.com/newweb/IlscoHom...ue+Information
    Charlie

  5. #5
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    Smile

    [QUOTE=cpal]
    Modified wrenches do not guarantee acurate torques.

    Torque is torque. The skill of the installer and the accuracy of the torque wrench guarantees accurate torque (or not).
    (IMO) Straight line torsion of the extension has no effect on the sum of the applied torque.
    How's that for a thesis?
    steve

  6. #6
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    I assume that these lugs are side by side, with the set screw facing the ajacent lug preventing the use of any tool other than a "L" hex key wrench. In some cases, even the short end of the "L" is too long to fit in the space between the lugs. I have seen a number of panels built this way. Not sure how you torque these.
    Don
    Don, Illinois
    "It is the first responsibility of every citizen to question authority." B Franklin

  7. #7
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    [QUOTE=hillbilly]
    Quote Originally Posted by cpal
    Modified wrenches do not guarantee acurate torques.

    Torque is torque. The skill of the installer and the accuracy of the torque wrench guarantees accurate torque (or not).
    (IMO) Straight line torsion of the extension has no effect on the sum of the applied torque.
    How's that for a thesis?
    steve
    I'm not sure of stright line I would expect the torque would be accurate, I've used offset wrenches that were modified as such and I watched the arms bend to some degree I would not have a lot of confidence in accurate torque in those conditions.
    Charlie

  8. #8
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    Aug 2006
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    Alexandria, VA
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    Quote Originally Posted by don_resqcapt19
    ... Not sure how you torque these ...
    With an offset adaptor.

    Correction formula to be used for an extension is at:
    http://www.engineersedge.com/manufac...e_wrench_1.htm

    or for a reducer:
    http://www.engineersedge.com/manufac...e_wrench_2.htm

    The "Open Calculator" link on both pages provides a nifty tool once you understand the theory.
    Few "standards" exist w/o something really bad happening first.

  9. #9
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    Wisconsin
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    Torque values go back to the point where the lug is tested with the cable for temperature rise and a "pull test" per UL requirements. When a lug is torqued to that as specified by the mfg. that value goes back to that which it was tested and should guarantee that the lug/cable combo will operate within the temp. rise allowed as well as being able to pass a pull test.

  10. #10
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    Quote Originally Posted by don_resqcapt19
    I assume that these lugs are side by side, with the set screw facing the ajacent lug preventing the use of any tool other than a "L" hex key wrench. In some cases, even the short end of the "L" is too long to fit in the space between the lugs. I have seen a number of panels built this way. Not sure how you torque these.
    Don

    I have seen equipment constructed in that fashion with lugs facing each other. The reality is the L shaped hex key goes in the lug, an 18" pipe is sleeved over the key handle, and the thing is tightened as tight as it will go. It should be in the part of the manufacturers' design process to not design things that cannot be torqued.
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

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