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IndustryArena Forum > CNC Electronics > General CNC Machine Related Electronics > Grounding two different circuits to prevent loops
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  1. #1
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    Question Grounding two different circuits to prevent loops

    Hey folks, this is my first post! hoping to learn alot from this forum and the knowledge you guys have to offer.

    I currently have 2 circuits (110v 20a hard wired to a VFD which powers a 2.2kw spindle) & (110v 20a wall outlet that powers my 24v power supply for motion controller)

    I want to make sure I have my grounds proper. My plan is:

    Spindle grounded to VFD, as well as the shield on the spindle cord will ground to VFD.

    For my other circuit, I will use a brass ground "post" which will be a single point ground for all 4 stepper motors (cord shields), it will also host ground for all axes of my machine, and the 24v power supply. This one point post will ground from the incoming ground wire from the wall which supplies the 24v power supply.

    am I close to being correct with this design? I assume I would not ground my spindle to the ground post (on a different circuit , as this would create a ground loop?)

    Thank you very much for any guidance with doing this right. I seem to have alot of noise coming from my steppers and want to eliminate that as well as being safe.

  2. #2
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    Re: Grounding two different circuits to prevent loops

    Attached is a diagram of what I have going on.
    Attached Thumbnails Attached Thumbnails Untitled-6.jpg  

  3. #3
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    Re: Grounding two different circuits to prevent loops

    That's very close to what I do - even to the brass post (M6 brass bolt). Everything goes to it, and it goes to the earth pin on the mains connection. It is not far from there to a decent earth stake in the ground.

    Cheers
    Roger

  4. #4
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    Re: Grounding two different circuits to prevent loops

    Thanks for posting Roger! The Earth (ground) stake that's outside, is that grounding your main electrical panel as well, or did you use a separate ground rod for your cnc?

  5. #5
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    Re: Grounding two different circuits to prevent loops

    As in main electrical panel for your shop / house

  6. #6
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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by JBrown4220 View Post
    Hey folks, this is my first post! hoping to learn alot from this forum and the knowledge you guys have to offer.

    I currently have 2 circuits (110v 20a hard wired to a VFD which powers a 2.2kw spindle) & (110v 20a wall outlet that powers my 24v power supply for motion controller)

    I want to make sure I have my grounds proper. My plan is:

    Spindle grounded to VFD, as well as the shield on the spindle cord will ground to VFD.

    For my other circuit, I will use a brass ground "post" which will be a single point ground for all 4 stepper motors (cord shields), it will also host ground for all axes of my machine, and the 24v power supply. This one point post will ground from the incoming ground wire from the wall which supplies the 24v power supply.

    am I close to being correct with this design? I assume I would not ground my spindle to the ground post (on a different circuit , as this would create a ground loop?)

    Thank you very much for any guidance with doing this right. I seem to have alot of noise coming from my steppers and want to eliminate that as well as being safe.
    The answer is easy, for Grounds, the incoming Power to your Machine you should have a Ground Bus this is where you connect all Ground wires. some photos of your cabinet and I will have a better idea of what you have to do

    You can't have 2 individual Mains power suppling a Machine this will give you an instant Ground loop no matter how you try to do it.

    Your supply is not 110v if you live in NA it is 120v/240 for single phase

    Your 2.2Kw Spindle will not run very well on a 120v 20A supply, the max for a 120v supply is a 1.5Kw spindle
    Mactec54

  7. #7
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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by JBrown4220 View Post
    Thanks for posting Roger! The Earth (ground) stake that's outside, is that grounding your main electrical panel as well, or did you use a separate ground rod for your cnc?
    You can't use a separate Ground Rod / Stake, electrical code would not allow you to do this, unless the (2) Rods are bonded together, using (2) Ground Rods can have lethal consequences
    Mactec54

  8. #8
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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by JBrown4220 View Post
    As in main electrical panel for your shop / house
    It does not matter where it is Shop or House, everything must be install for Safety and comply to Electrical Codes.

    Here are some examples of what is required, need to see some photos to see what you have, I have many more examples if you need more.
    Mactec54

  9. #9
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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by mactec54 View Post
    The answer is easy, for Grounds, the incoming Power to your Machine you should have a Ground Bus this is where you connect all Ground wires. some photos of your cabinet and I will have a better idea of what you have to do

    You can't have 2 individual Mains power suppling a Machine this will give you an instant Ground loop no matter how you try to do it.

    Your supply is not 110v if you live in NA it is 120v/240 for single phase

    Your 2.2Kw Spindle will not run very well on a 120v 20A supply, the max for a 120v supply is a 1.5Kw spindle
    Thank you for the help! I've read through some of your posts, and understand now what you are saying about the ground loop issue. So, that being said; if I eliminated one incoming circuit, could I run both my VFD/Spindle & 24v power supply / controller off from the 10AWG 120v incoming? How do you suggest to "split" the leads once inside my enclosure to go to each component?

    As far as the spindle, it seems to run just fine. I do hear a fair amount of noise in my steppers however

  10. #10
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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by mactec54 View Post
    You can't use a separate Ground Rod / Stake, electrical code would not allow you to do this, unless the (2) Rods are bonded together, using (2) Ground Rods can have lethal consequences
    I do know that. That is why I asked Roger how he had it setup

  11. #11
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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by JBrown4220 View Post
    Thank you for the help! I've read through some of your posts, and understand now what you are saying about the ground loop issue. So, that being said; if I eliminated one incoming circuit, could I run both my VFD/Spindle & 24v power supply / controller off from the 10AWG 120v incoming? How do you suggest to "split" the leads once inside my enclosure to go to each component?

    As far as the spindle, it seems to run just fine. I do hear a fair amount of noise in my steppers however
    The Spindle will run fine but won't have much power, you would need 40A supply to run this 2.2Kw spindle on 120v single phase for it to have full power

    You would use a Power Distribution Block, like these
    Attached Thumbnails Attached Thumbnails Mains Power .jpg   Mains Power-2.jpg  
    Attached Files Attached Files
    Mactec54

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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by mactec54 View Post
    ,,,,,
    Mactec54 is this new diagram how I should have it? I will also get you a picture this evening when I am home.. Thank you again for your assistance!
    Attached Thumbnails Attached Thumbnails Untitled-6 copy.jpg  

  13. #13
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    Re: Grounding two different circuits to prevent loops

    Mactec54 I was reading through some of your older posts, and thought you mentioned that a DC power source should never be connected to a star ground from ac incoming. It is confusing no doubt with all the conflicting opinions out there. I feel like I'm on the right path. I am going to eliminate that extra circuit tonight and use one main incoming line. I appreciate the help so far

  14. #14
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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by JBrown4220 View Post
    Mactec54 I was reading through some of your older posts, and thought you mentioned that a DC power source should never be connected to a star ground from ac incoming. It is confusing no doubt with all the conflicting opinions out there. I feel like I'm on the right path. I am going to eliminate that extra circuit tonight and use one main incoming line. I appreciate the help so far
    The DC Power supply has a 120v Ac input you have a Hot / Neutral / Ground this Ground must be connected to the Bus along with any other Mains Power Grounds you have.

    The 24v Dc Negative / Com should only be connected to the Power supply this is it's return path, this return in some circumstances can be tapped to Ground but must first return to the source first, this being the Power Supply. don't get tripped up with this, remember in all circuits. No matter what your Power supply source is it must return to the the source to complete the circuit.

    Your Attachment in the other post is not there
    Mactec54

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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by mactec54 View Post
    The DC Power supply has a 120v Ac input you have a Hot / Neutral / Ground this Ground must be connected to the Bus along with any other Mains Power Grounds you have.

    The 24v Dc Negative / Com should only be connected to the Power supply this is it's return path, this return in some circumstances can be tapped to Ground but must first return to the source first, this being the Power Supply. don't get tripped up with this, remember in all circuits. No matter what your Power supply source is it must return to the the source to complete the circuit.

    Your Attachment in the other post is not there
    Here is my rudimentary cabinet. Until I get a proper ground bus, I used a brass post. I still need to eliminate the 12 gauge incoming circuit and tie it into the 10awg i have. As far as he 24v power supply, I thought I had that correct?
    Attached Thumbnails Attached Thumbnails Untitled-7.jpg  

  16. #16
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    Re: Grounding two different circuits to prevent loops

    .
    Attached Thumbnails Attached Thumbnails sd.jpg  

  17. #17
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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by JBrown4220 View Post
    Here is my rudimentary cabinet. Until I get a proper ground bus, I used a brass post. I still need to eliminate the 12 gauge incoming circuit and tie it into the 10awg i have. As far as he 24v power supply, I thought I had that correct?
    Still nothing attached how are you attaching your photos
    Mactec54

  18. #18
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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by mactec54 View Post
    Still nothing attached how are you attaching your photos
    I am attaching them through this forum. they show up for me as attached? I will upload them through a third party website and post them again

  19. #19
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    Re: Grounding two different circuits to prevent loops


  20. #20
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    Re: Grounding two different circuits to prevent loops

    Quote Originally Posted by JBrown4220 View Post
    Ground wires can only be GREEN and your 10 AWG wire is incorrect you can not use that type of cable for machine wiring

    The Power supply Ground is incorrect, I'm not sure what you are doing with that Input Power to the Power Supply

    The single point Grounding is not correctly done, you need to use crimp ring terminals if doing it to a single point and each Ground wire has to be separated and use a lock nut and washer to be correct, A bus is better than a single point for Grounding

    Is that a metal cabinet, all your competents need to be mounted on a paint free surface so you have a good Grounding bond, the paint must be removed where ever you mount something to the metal surface
    Mactec54

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