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Earth Bonding Points - Use of 'Double Nutting' or 'Jam Nuts'

Toby Lewis
Hi,


We have earth bonding points on our electronic enclosures and the general opinion is that the use of 'double nutting' or a second locking nut on an earth bonding stud is considered good practice (even where a coil or shakeprook washer is provided).


Problem is no-one that I talk to can find any evidence for the practice of double nutting or a standard or 'good practice' guidelines to hang this on.


Can anyone on this forum provide any information about a standard or code of practice/guidelines that state this?


Many thanks,


TL
  • 0
    Toby,

    I am not so familiar with BS 7671 as I am involved in the marine industry where it is not applicable as other standards apply. However the Lloyd's Register Rules and Regulations (and presumably other Classification Society requirements) contain a requirement which states:
    All nuts and screws and clamping devices used in connection with current-carrying, supporting and working parts are to be provided with means to ensure that they cannot work loose by vibration and shock as arise in normal practice.


    You may find similar requirements which apply to the enclosures you are dealing with in the applicable standards.

    Alasdair
  • 0

    Toby Lewis:

    Hi,


    We have earth bonding points on our electronic enclosures and the general opinion is that the use of 'double nutting' or a second locking nut on an earth bonding stud is considered good practice (even where a coil or shakeprook washer is provided).


    Problem is no-one that I talk to can find any evidence for the practice of double nutting or a standard or 'good practice' guidelines to hang this on.


    Can anyone on this forum provide any information about a standard or code of practice/guidelines that state this?


    Many thanks,


    TL




    Double bolting, non-slip washers, self-locking nuts will all do the same job, do a degree. Low current appliations are less likely to suffer the effects of vibratioin unless the installation is near a generator,on a boat, automotive control, mobile  transmission vans, temporary installs

    BS7671 gives us 134.1.4 as an introduction with more advise at section 526.


    Legh

  • 0
    It's not in the standards, but 'double nutting' or lock-nuts, are only good at stopping the nut rotating on the thread, it does not help you if thermal cycling causes the lug-eye or the stud itself to slowly relax, you can end up with a very tight nut, but  not really holding the joint. You are better off with a  washer design with some spring in it, either a star washer or in extreme environments, (like a tracked vehicle for example) purpose built fastener like a Nordlock.

    From about 1.25 onward https://www.nord-lock.com/insights/videos/watch-the-junker-vibration-test-video/

    this video is intersting... As things come undone. At about 2.20 the demonstrate a double nut under vibration.

    The Junkers test is unusually harsh however.

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