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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
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  • 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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  • 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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