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  1. 26th December 2010, 09:03 PM #1
    Stustoys
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    Default Machine earthing problem

    So first up to save anyone else saying it, we better have a electrical warning please mods.

    I'm running a machine off an inverter so it doesn't have 415V power as such. So therefore the control side of things is run at 32V from its own 240V supply.

    My problem is that this leaves me with two earth wires one from the inverter and one from the 240V supply. Now it is unlikely but not impossible that the inverter would be connected to the machine without the 240V supply being plugged in so I don't want to leave that one out.

    So basically my question is this. Is it bad to have two earths on one machine?

    Stuart

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  3. 26th December 2010, 09:42 PM #2
    Dave J Guest

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    I am not up on electrics like you guys, but I don't think 2, or even 10 earths would hurt anything as their all going back to the same place.
    Better to be safe than sorry.

    Dave
  4. 26th December 2010, 10:23 PM #3
    Stustoys
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    Yeah I'm pretty sure you're right Dave. I'm pretty sure what I am thinking about is the bonding of the neutral to the earth at the panel. But I thought I would ask.
    Stuart
  5. 26th December 2010, 11:15 PM #4
    cava
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    More earthing points are better. Please ensure that the main earth point for the house/shed is in good condition, or drive an ancillary earth point as well.
  6. 26th December 2010, 11:58 PM #5
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    Hi Stuart,

    As a general rule...
    The neutral should only be tied to earth at one point on the premises, and that is the main switchboard where your RCD's are located.

    However,
    The inverter is producing a 415 v 3 phase which creates a new (derived) neutral that doesn't relate to the existing mains 240v neutral... so it's a bit more complex. I suspect that it might be already tied to the chassis which is earthed inside the inverter.

    By all means make sure that the machine is properly grounded (to earth). But I'm not so sure about connecting the "inverter derived neutral" to ground.

    Regards
    Ray
  7. 27th December 2010, 12:18 AM #6
    Stustoys
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    Quote Originally Posted by RayG View Post
    Hi Stuart,

    As a general rule...
    The neutral should only be tied to earth at one point on the premises, and that is the main switchboard where your RCD's are located.
    Yes I'm pretty sure this is what I was thinking of.

    Quote Originally Posted by RayG View Post
    However,
    The inverter is producing a 415 v 3 phase which creates a new (derived) neutral that doesn't relate to the existing mains 240v neutral... so it's a bit more complex. I suspect that it might be already tied to the chassis which is earthed inside the inverter.

    By all means make sure that the machine is properly grounded (to earth). But I'm not so sure about connecting the "inverter derived neutral" to ground.

    Regards
    Ray
    The chassis of the inverter is earthed to the 240V supply with a link to join that earth to the 3 phase wiring.

    Its looking like I am making up the problem

    Stuart
  8. 27th December 2010, 04:19 PM #7
    .RC.
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    What does the manufacturer of the inverter say?
  9. 27th December 2010, 04:25 PM #8
    Stustoys
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    Quote Originally Posted by .RC. View Post
    What does the manufacturer of the inverter say?
    About what?
  10. 27th December 2010, 08:02 PM #9
    .RC.
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    The earth
  11. 27th December 2010, 08:30 PM #10
    Stustoys
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    Nothing about connecting it to two machines each with their own supply.
  12. 28th December 2010, 12:09 AM #11
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    Hi
    Running a machine off an inverter vfds transformers
    YOUR safety RCDS will mostly not trip..

    tony
  13. 28th December 2010, 12:14 AM #12
    Stustoys
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    Quote Originally Posted by antoni View Post
    Hi
    Running a machine off an inverter vfds transformers
    YOUR safety RCDS will mostly not trip..

    tony
    I dont understand what you are talking about.
    Stuart
  14. 28th December 2010, 10:06 AM #13
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    2 earths is not an ideal situation, but for what you are doing it's unlikely to cause any issues - I assume the two earths go back to the same point.

    Your earth leakage/RCD will still work fine. It would only be a problem if you connect the two neutrals together at the machine (don't do it).
    Cheers.

    Vernon.
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  15. 28th December 2010, 11:02 AM #14
    Stustoys
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    Vernonv
    There will only be one neutral at the machine.
    Thanks

    Stuart
  16. 28th December 2010, 11:46 AM #15
    .RC.
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    If you installed a second earth (to it's own earth stake) wouldn't it then bypass the ELCB and create a risk?
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