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IndustryArena Forum > CNC Electronics > Spindles / VFD > Spindle grounding- manufacturer says to not ground
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  1. #1
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    Spindle grounding- manufacturer says to not ground

    Hello. Firstly, I am new to the forum. I know this horse has been beaten for some time now. I will try to remain to the point.

    I purchased one of those Chinese spindles from Amazon. I haven't checked yet, but I believe that like everyone else, my ground is not connected. A piece of paper that came in the package says specifically NOT to ground the spindle, otherwise damage will occur when cutting metals. I will update (when I get home) exactly what the paper says. I also noticed that the ground terminal on the VFD has red paint on it.

    So the questions are;
    -Why would it be advised to NOT ground the spindle?
    -If I do take steps to ground it, how could this be bad?
    -Is it possible the VFD isn't wired properly to handle a ground connection? (I mean by design..)

    Ultimately, I am concerned that there is no ground, and apparently should be no ground.


    SPINDLE KIT DETAILS (copied from amazon title):
    RATTMMOTOR 1.5KW Air Cooled Spindle Motor ER16 CNC Kit + 1500W 1.5kw Inverter Variable Frequency Drive 220V + 80mm Clamp Mount Bracket for CNC Router Engraving Milling Machine

    Nick

  2. #2
    Community Moderator Al_The_Man's Avatar
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    Re: Spindle grounding- manufacturer says to not ground

    Sounds like a load of guff to me, the spindle frame should be earth grounded for operation as well as per NFPA70. (N.A. & EU).
    The Chines are notorious for bad/non-grounding of machinery.
    Do you have a link for the spindle?
    Maybe the person you spoke to was non-technical?
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  3. #3
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    Re: Spindle grounding- manufacturer says to not ground

    I don't know how to edit my post, so here is what the extra piece of paper says (relevant text):

    "Notice: On the spindle motor air plug 1,2,3 connection to on the inverter: U,V,W, the mean is 1=U, 2=V,3=W, 4 is blank, can't connection to GND, otherwise the spindle motor will be damaged, Because your metal machine body have been connection to ground, and the motor can't use for heavy metal (E.g: Steel, Iron, Stainless steel, etc.)"

  4. #4
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    Re: Spindle grounding- manufacturer says to not ground

    I think "the motor can't use for heavy metal" is a separate statement, unrelated to the grounding.

  5. #5
    Community Moderator Al_The_Man's Avatar
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    Re: Spindle grounding- manufacturer says to not ground

    I can't quite understand the statement that the spindle will be damaged, I would be interested in seeing the logic behind the instruction.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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    Re: Spindle grounding- manufacturer says to not ground

    Al the man, here is the link to what I bought:

    https://www.amazon.ca/gp/product/B07...?ie=UTF8&psc=1

    Also, upon opening up the back of the spindle, it is indeed not grounded.

  7. #7
    Community Moderator Al_The_Man's Avatar
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    Re: Spindle grounding- manufacturer says to not ground

    Quite common to find that.
    Just to bring a sense of reason, the gantry, mill head etc that is installed on the machine should have an earth ground/bonding conductor to it.
    So the frame of the motor would be earth grounded through the mounting anyway, but it is not wise to rely solely on that method.
    Most remove the 4pin receptacle and fit an earth GND from pin to motor frame. Then use a 4 conductor cable to the motor.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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    Re: Spindle grounding- manufacturer says to not ground

    So the ground terminal on the VFD would have two wires on it, correct? --> One from the spindle ground that I create, and the other on the ground wire for the 220v supply into the VFD... Yeah, I'm pretty new at this..

    I'd like to guess about the Chinese note on causing damage if the spindle is grounded. They refer to the problem being when cutting metal (pretend for a moment that is possible with this spindle). Would they be referring to creating a ground loop? When your cutter engages the material, it would be possible depending on your machine construction that the spindle ground and the chassis ground are connected?

    What kind of damage are we talking about with a ground loop here? Death? Destroying the VFD or spinlde?

    Nick

  9. #9
    Community Moderator Al_The_Man's Avatar
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    Re: Spindle grounding- manufacturer says to not ground

    Bonding all frame points to an earth ground prevents ground loops, It is also known as equi-potential bonding.
    You should have a service earth GND to the VFD, this then continues on to the spindle motor frame.
    If you omit this, then there is a possibility of a ground loop via the metallic frame of the machine.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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    Re: Spindle grounding- manufacturer says to not ground

    Quote Originally Posted by Norkamus View Post
    I don't know how to edit my post, so here is what the extra piece of paper says (relevant text):

    "Notice: On the spindle motor air plug 1,2,3 connection to on the inverter: U,V,W, the mean is 1=U, 2=V,3=W, 4 is blank, can't connection to GND, otherwise the spindle motor will be damaged, Because your metal machine body have been connection to ground, and the motor can't use for heavy metal (E.g: Steel, Iron, Stainless steel, etc.)"
    This what they call in China population control. No Earth Ground Required

    Your spindle requires the Ground connection to be connected in the plug and in the spindle, do you have an air cooled or water-cooled spindle for water-cooled you will need to take the top off and connect the 4th pin Ground like this snip, for Air Cooled it is a little more difficult to do, but still has to be done.
    Mactec54

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    Re: Spindle grounding- manufacturer says to not ground

    Quote Originally Posted by Norkamus View Post
    So the ground terminal on the VFD would have two wires on it, correct? --> One from the spindle ground that I create, and the other on the ground wire for the 220v supply into the VFD... Yeah, I'm pretty new at this..

    I'd like to guess about the Chinese note on causing damage if the spindle is grounded. They refer to the problem being when cutting metal (pretend for a moment that is possible with this spindle). Would they be referring to creating a ground loop? When your cutter engages the material, it would be possible depending on your machine construction that the spindle ground and the chassis ground are connected?

    What kind of damage are we talking about with a ground loop here? Death? Destroying the VFD or spinlde?

    Nick
    Electrical shock is what you can expect to get with an un-Grounded spindle, the rotor voltage has to go somewhere and if it can't go through a Grounding conductor, then when you touch the spindle to change a cutter you will get Zapped.

    Can this damage a spindle motor No not at all. it is an electrical code requirement to have it Grounded so don't run this until you have all the correct wiring in place that means from the VFD to the Spindle you need a 4-wire shielded cable and the shield correctly terminated at each end with 360 Degree clamp

    You should use a Star-Point Ground stud or Bus in your cabinet all Grounds connect to this one point
    Mactec54

  12. #12
    Community Moderator Al_The_Man's Avatar
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    Re: Spindle grounding- manufacturer says to not ground

    One other error by omission is in the case of a motor that is mounted on a gantry together with other electronic devices etc, It is imperative to earth ground the moving gantry as well as the GND to the VFD/Spindle .
    CNC, Mechatronics Integration and Custom Machine Design

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    Mactek, you say I can expect electric shock. This is only if something has gone wrong correct? Such as one of the hot wires coming loose and contacting the case.
    This is an air-cooled unit. The cap is plastic. I don't see how this impeller/ fan can move any air. I guess I'll have to get creative with grounding.

  14. #14
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    Re: Spindle grounding- manufacturer says to not ground

    Hi,
    there is one drawback to having the spindle grounded, and that is if your VFD is supplied via a Residual Current Device.

    Under the normal circumstance if the VFD draws nnn.nn A on the phase wire then nnn.nn A will return on the neutral wire. If there is any difference
    between the go and return currents its presumed that current is leaking to earth....and that is a fault. If over 30mA it will trip the RCD within a few milliseconds.
    This would happen if a winding in the motor started 'leaking current' say due to coolant ingress.

    The electrical code in New Zealand it that all (new) domestic circuits will be protected by an RCD.

    There are a few devices which can cause nuisance trips however, VFDs are one of them. Welders can do the same.

    The issue is that the magnetic fields within the motor, which should ideally be balanced, but in reality are not quite balanced can induce currents in the frame
    of the motor which will in turn trip the RCD. This is called 'homopolar current' and would appear to violate Kirchoffs Law, but is understood if you allow for induction
    in the manner of Faraday's Law.

    Nuisance RCD trips due to homopolar current are infrequent and so I would never suggest that the spindle frame NOT be earthed.....if a genuine electrical fault occurs
    it MUST be earthed for safeties sake.

    My VFD occasionally trips the RCD despite the fact that I've done repeated high voltage insulation tests on the spindle......with no fault. I now have a separate supply to the VFD
    that does not have RCD protection.

    Craig

  15. #15
    Community Moderator Al_The_Man's Avatar
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    Re: Spindle grounding- manufacturer says to not ground

    Quote Originally Posted by joeavaerage View Post
    Hi,
    there is one drawback to having the spindle grounded, and that is if your VFD is supplied via a Residual Current Device.

    Craig
    If the OP is in NA, the practice of a RCD at the main supply is rare, generally individual RCD or GFI is carried out locally at the socket or final power location.
    So very likely that the VFD is not RCD fed.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
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  16. #16
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    Re: Spindle grounding- manufacturer says to not ground

    Hi,
    the electrical code in New Zealand changed about ten years ago now to REQUIRE RCDs on all new installation domestic circuits where you might be expected to plug in an
    appliance. By and large they are very good, they protect the user rather than the electrical circuit breaker. In schools, hospitals, preschools and the like the threshold
    is 5mA (I think?), so as to even better protect vulnerable people.

    99.9% of appliances behave themselves with respect to RCDs, but some don't....my VFD among them.

    Craig

    Craig

  17. #17
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    Re: Spindle grounding- manufacturer says to not ground

    Quote Originally Posted by Norkamus View Post
    Mactek, you say I can expect electric shock. This is only if something has gone wrong correct? Such as one of the hot wires coming loose and contacting the case.
    This is an air-cooled unit. The cap is plastic. I don't see how this impeller/ fan can move any air. I guess I'll have to get creative with grounding.
    No, when using a VFD Drive to power a spindle or any Ac motor you will have rotor voltage, so without a Ground there is no easy Parth for the rotor voltage to go, so a Ground is necessary, as well is a code requirement for safety.

    With you air cooled spindle you have to get creative, where one of the cap screws is screwed into the spindle body, this is where you will connect the Ground wire, so you will lock nut a wiring lug at this point, will have to clear the plastic cover around this mounting, the attached snip is just for an idea of how to do this.
    Attached Thumbnails Attached Thumbnails Rotor Voltage-1.PNG  
    Mactec54

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    Re: Spindle grounding- manufacturer says to not ground

    I am in North America. Thank you guys for your responses.

    Nick

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    Re: Spindle grounding- manufacturer says to not ground

    In schools, hospitals, preschools and the like the threshold is 5mA (I think?), so as to even better protect vulnerable people.
    Don't let preschoolers or vulnerable people like Joe Biden use your CNC. You should be good at 30mA

    I don't know if the "damage" comment is supposed to refer to shorting the induced spindle voltage to ground via the bearings. This voltage is only very small but can lead to spark erosion of the bearings. I've seen this is a classic problem in heavy machinery and special slip ring contacts are used to prevent this voltage appearing across the bear contact surface which is NOT designed to pass an electrical circuit.

    I do not know whether that is pertinent to this kind of light powered spindle.

  20. #20
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    Re: Spindle grounding- manufacturer says to not ground

    Quote Originally Posted by reg.miller View Post
    Don't let preschoolers or vulnerable people like Joe Biden use your CNC. You should be good at 30mA

    I don't know if the "damage" comment is supposed to refer to shorting the induced spindle voltage to ground via the bearings. This voltage is only very small but can lead to spark erosion of the bearings. I've seen this is a classic problem in heavy machinery and special slip ring contacts are used to prevent this voltage appearing across the bear contact surface which is NOT designed to pass an electrical circuit.

    I do not know whether that is pertinent to this kind of light powered spindle.
    So why post you are perthitic. (wedge)

    Any Ac 3 phase motor driven with a VFD Drive produces Rotor Voltage, a small voltage will not cause erosion of the Bearings

    Damage is when they use a touch prob that connects to their Breakout board, it will fry the input to the Breakout Boad the first time they do a tool touch off, if they have no spindle Ground, most hobby users use a Touch Probe. this has happened to lots of users that have posted here on the Zone.
    Mactec54

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