584,805 active members*
5,350 visitors online*
Register for free
Login
IndustryArena Forum > CNC Electronics > CNC Machine Related Electronics > Single or separate building circuits for Controller, VFD, PC
Page 1 of 2 12
Results 1 to 20 of 29
  1. #1
    Join Date
    Mar 2020
    Posts
    179

    Single or separate building circuits for Controller, VFD, PC

    Hello,

    I'm about ready to start drafting a wiring diagram for my controller, but one question I can't settle after many evenings of research is whether to run 2x 20amp circuits from the garage subpanel, or a single 30 amp circuit that can run everything.

    Some of my considerations:
    -I have plenty of 12awg wire so running 2x 20amp circuits would be significantly cheaper
    -I have read that separate mains circuit for the VFD can reduce noise/EMI
    -I've also read about avoiding ground loops: as far as I can tell, having separate circuits would create a workshop-size ground loop, as both the spindle and steppers/machine frame are conductively mounted to the same chassis and would be grounded to their separate circuits. Unless: I grounded the spindle to the CNC controller mains feed instead of the VFD mains feed, but that seems kind of weird.
    -my control PC is an older desktop PC and monitor, both of which can run on 240v. This could be ran from the controller circuit, or I could put it on the normal shop 120v circuit.
    -I'm planning on full implementation of EMI filters and ferrite toroids, as well as enclosure layout to separate AC voltage, high current motor circuits, and logic circuits
    -Having a single circuit on which everything runs seems necessary for true single point star grounding, which seems to be highly recommended. This is apparently in direct contradiction with the advice for separate circuits for controller and VFD, which would create multiple supply grounds.

    Additional related questions:
    1. I bought a giant 24"x16"x10" enclosure for the controller, thinking the VFD would be inside it. With good layout, emi filters and ferrites, should I still use a separate enclosure for the VFD?
    2. If i run 2 separate circuits and they're in separate conduits, do the conduits really need to be separated from each other, i.e. not running parallel along the walls?
    3. More theoretically, it seems there's two rivaling philosophies: equi-potential grounding where all metallic components are grounded to each other including both ends of cable shields, and, "single drain" where shields are only grounded at the controller/supply end. How do I choose between them when electrical engineers seem to disagree?

    So many questions! Sorry. This has been one of the more difficult topics to get to the bottom of, so would appreciate any advice.
    (my build thread is over in DIY Metalworking Machines but thought this warranted a separate post)

    Cheers

  2. #2
    Join Date
    Mar 2020
    Posts
    179

    Re: Single or separate building circuits for Controller, VFD, PC

    one more thing- i'm familiar with the Siemens guide to equi-potential grounding, but in all the diagrams it seems to suggest a single mains supply and earthing connection (pg 25 attached here)

  3. #3
    Join Date
    Nov 2013
    Posts
    4280

    Re: Single or separate building circuits for Controller, VFD, PC

    Hi,
    I don't think having two 20A circuits verses one 30A circuit will make a huge difference.

    The only thing that I can think of is that you are supposed to be able to isolate a machine from the incoming mains with one isolation switch, so I suspect that having
    two isolation switches would be frowned on legally.

    -I have read that separate mains circuit for the VFD can reduce noise/EMI
    VFD's are usually the biggest source of EMI and harmonic distortion in any CNC machine. There is some sense to the notion of having a separate supply but the two supplies
    are still connected back at the sub-board, so in truth little is gained. It is very worthwhile to have either a line reactor or a two stage EMI filter, or both on the input side
    of the VFD. This tends to contain the noise and harmonic distortion to the VFD and stop it polluting the power supply to other more sensitive parts of your machine.
    The recommendation to have some effective filtering applies whether there is one incoming AC supply or two.

    -I've also read about avoiding ground loops: as far as I can tell, having separate circuits would create a workshop-size ground loop, as both the spindle and steppers/machine frame are conductively mounted to the same chassis and would be grounded to their separate circuits.
    Ground loops can be a problem but it is not a common source of failure. Plasma tables seem to be rather more affected by ground loops, but most normal machines no. Remeber also that if you have two incoming AC circuits
    the cable runs are presumably adjacent to each other and therefore the ground loop area would be minimal. May I suggest try it and see. I doubt that it would cause a problem.

    1. I bought a giant 24"x16"x10" enclosure for the controller, thinking the VFD would be inside it. With good layout, emi filters and ferrites, should I still use a separate enclosure for the VFD?
    Try it and see. My VFD in in the same enclosure and without problem. Mind you I have a two stage line filter and a line reactor on the input side of the VFD. My experience was that attending to the 'conducted noise'
    ie noise induced onto the power supply by the VFD all but fixed whatever few noise issues I've ever had.

    3. More theoretically, it seems there's two rivaling philosophies: equi-potential grounding where all metallic components are grounded to each other including both ends of cable shields, and, "single drain" where shields are only grounded at the controller/supply end. How do I choose between them when electrical engineers seem to disagree?
    Simple, try it and see. I have what few shielded cables I have earthed at one end only, and it seems effective.

    Overall I would try to prevent the noise from being generated in the first place, its much easier to suppress at source rather than try to protect all the different circuits once the noise is already out there.

    Craig

  4. #4
    Join Date
    Dec 2003
    Posts
    24216

    Re: Single or separate building circuits for Controller, VFD, PC

    For two separate systems, which is not the ideal, you would have to ensure the E-Stop is interlocked, for each to act together.
    It has always been my experience it is more beneficial to put money into the 3 phase choke between VFD and motor, not only for noise suppression, but easier on the motor, the VFD itself has a huge capacitor bank right at the power input, so the biggest issue there, is power factor, which is not a great issue with just one installation.
    Never used an input filter ever.
    I also subscribe to equi-potential bonding, if done correctly, this allows grounding both ends of shielded cables.
    As to using the same enclosure, I have always done this, in some cases two VFD's in the same enclosure with the rest of the system electronics.!
    As to running conduits, as long as they are metallic whether solid or flexible they should all be bonded to earth GND
    There is a copy out there of NFPA79 which may help somewhat.
    CNC, Mechatronics Integration and Custom Machine Design

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

  5. #5
    Join Date
    Mar 2020
    Posts
    179

    Re: Single or separate building circuits for Controller, VFD, PC

    Thanks very much for the detailed replies. I may have somewhat fallen into the trap of the confirmation bias machine known as google- search about EMI issues and plenty more EMI issues you will be served.

    It's a good point about one switch to cut power to the machine. I think that alone is enough to push me to the single circuit. Which obviously means breakers/fuses for each of the sub components within the control box.

    Yes, conduits will all be connected to earth ground at the sub panel.

    Any thoughts on which circuit to run the control PC on?

  6. #6
    Join Date
    Jan 2005
    Posts
    15362

    Re: Single or separate building circuits for Controller, VFD, PC

    Quote Originally Posted by catahoula View Post
    Hello,

    I'm about ready to start drafting a wiring diagram for my controller, but one question I can't settle after many evenings of research is whether to run 2x 20amp circuits from the garage subpanel, or a single 30 amp circuit that can run everything.

    Some of my considerations:
    -I have plenty of 12awg wire so running 2x 20amp circuits would be significantly cheaper
    -I have read that separate mains circuit for the VFD can reduce noise/EMI
    -I've also read about avoiding ground loops: as far as I can tell, having separate circuits would create a workshop-size ground loop, as both the spindle and steppers/machine frame are conductively mounted to the same chassis and would be grounded to their separate circuits. Unless: I grounded the spindle to the CNC controller mains feed instead of the VFD mains feed, but that seems kind of weird.
    -my control PC is an older desktop PC and monitor, both of which can run on 240v. This could be ran from the controller circuit, or I could put it on the normal shop 120v circuit.
    -I'm planning on full implementation of EMI filters and ferrite toroids, as well as enclosure layout to separate AC voltage, high current motor circuits, and logic circuits
    -Having a single circuit on which everything runs seems necessary for true single point star grounding, which seems to be highly recommended. This is apparently in direct contradiction with the advice for separate circuits for controller and VFD, which would create multiple supply grounds.

    Additional related questions:
    1. I bought a giant 24"x16"x10" enclosure for the controller, thinking the VFD would be inside it. With good layout, emi filters and ferrites, should I still use a separate enclosure for the VFD?
    2. If i run 2 separate circuits and they're in separate conduits, do the conduits really need to be separated from each other, i.e. not running parallel along the walls?
    3. More theoretically, it seems there's two rivaling philosophies: equi-potential grounding where all metallic components are grounded to each other including both ends of cable shields, and, "single drain" where shields are only grounded at the controller/supply end. How do I choose between them when electrical engineers seem to disagree?

    So many questions! Sorry. This has been one of the more difficult topics to get to the bottom of, so would appreciate any advice.
    (my build thread is over in DIY Metalworking Machines but thought this warranted a separate post)

    Cheers
    Yes, you definitely don't want to have to have (2) sources feeding the same machine because of the Grounding problem! this creates.

    You should use (1) supply correctly sized for the whole machine, to your cabinet and then split it up from there, having a Breaker for each branch.

    No ferrite Rings / toroid's should be used or needed, if correctly wired and Shields correctly Terminated.

    You never use a Shielded cables drain wire for a Grounding Termination, this will be an antenna and emit EMI.
    Mactec54

  7. #7
    Join Date
    Jan 2005
    Posts
    15362

    Re: Single or separate building circuits for Controller, VFD, PC

    Quote Originally Posted by catahoula View Post
    Thanks very much for the detailed replies. I may have somewhat fallen into the trap of the confirmation bias machine known as google- search about EMI issues and plenty more EMI issues you will be served.

    It's a good point about one switch to cut power to the machine. I think that alone is enough to push me to the single circuit. Which obviously means breakers/fuses for each of the sub components within the control box.

    Yes, conduits will all be connected to earth ground at the sub panel.

    Any thoughts on which circuit to run the control PC on?
    If this is in your home, then you should be using PVC Conduit
    Mactec54

  8. #8
    Join Date
    Dec 2003
    Posts
    24216

    Re: Single or separate building circuits for Controller, VFD, PC

    I know of no regulation stipulating PVC conduit only in a residential location?
    There is also flexible metallic that is used extensively. Home depot sell it under liquid-tite flexible metallic
    CNC, Mechatronics Integration and Custom Machine Design

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

  9. #9
    Join Date
    Mar 2020
    Posts
    179
    It's in a detached garage, but EMT conduit and flex MC cable are standard products used widely in commercial and residential, quite sure they are explicitly permitted by code providing conduit fill charts and grounding are respected. The sub panel breaker box is grounded and all conduits ground to that.

  10. #10
    Join Date
    Dec 2003
    Posts
    24216

    Re: Single or separate building circuits for Controller, VFD, PC

    Quote Originally Posted by catahoula View Post
    It's in a detached garage, but EMT conduit and flex MC cable are standard products used widely in commercial and residential, quite sure they are explicitly permitted by code providing conduit fill charts and grounding are respected. The sub panel breaker box is grounded and all conduits ground to that.
    Agree
    One publication that is a help is the official guide used in N.A. in particular is NFPA79, "Elec. Standard for Industrial Machinery " there is an older copy available out there.
    One example in there is where there are conductors ran between say, a divided system for example, and live conductors exist in an enclosure that are sourced and switched by another part of the system, they shall be Orange in colour.
    N.A. changed this from yellow a few years back in order to conform to the European standard.
    CNC, Mechatronics Integration and Custom Machine Design

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

  11. #11
    Join Date
    Jan 2005
    Posts
    15362

    Re: Single or separate building circuits for Controller, VFD, PC

    Quote Originally Posted by Al_The_Man View Post
    I know of no regulation stipulating PVC conduit only in a residential location?
    There is also flexible metallic that is used extensively. Home depot sell it under liquid-tite flexible metallic
    There is no regulation why you would think that its just what is used mostly for residential, if he is on a farm and his workshop in a barn then metal conduit would most likely be used
    Mactec54

  12. #12
    Join Date
    Jan 2005
    Posts
    15362

    Re: Single or separate building circuits for Controller, VFD, PC

    Quote Originally Posted by catahoula View Post
    It's in a detached garage, but EMT conduit and flex MC cable are standard products used widely in commercial and residential, quite sure they are explicitly permitted by code providing conduit fill charts and grounding are respected. The sub panel breaker box is grounded and all conduits ground to that.
    There is no code regarding what type of conduit you use, residential normally use PVC or the Flex in some cases, older outbuildings like barns Etc. used metal conduit

    Metal conduit becomes a large antenna and emits EMI / EMC even if it is Grounded, that is way PVC is better to use.
    Mactec54

  13. #13
    Join Date
    Apr 2018
    Posts
    130

    Re: Single or separate building circuits for Controller, VFD, PC

    Hmmm, not everyone agrees that metal conduit "emits" RFI. The conductors inside any conduit, PVC or metal, emit RFI as a function of the alternating current in the wires. Grounded metal conduit can act to reduce EMI.

    Allied Tube & Conduit®’s Intermediate Metal Conduit (IMC) with Rigid Elbows, Couplings and Nipples (ECN) create an Electrical Raceway System recognized as an equipment grounding conductor which provides shielding from electromagnetic interference (EMI).

    https://www.alliedeg.us/imc-metal-conduit/
    A major element of Amuneal’s recommendations was the use of rigid steel conduit to enclose two large conductors running on the ceiling on to consider the use of steel conduit to mitigate the effects of electromagnetic fields,” he says. “It’s always the first option of choice.”

    https://www.wheatland.com/wp-content...-Institute.pdf

  14. #14
    Join Date
    Dec 2003
    Posts
    24216

    Re: Single or separate building circuits for Controller, VFD, PC

    Quote Originally Posted by RaderSidetrack View Post
    Hmmm, not everyone agrees that metal conduit "emits" RFI. The conductors inside any conduit, PVC or metal, emit RFI as a function of the alternating current in the wires. Grounded metal conduit can act to reduce EMI.
    Entirely agree, all the industrial CNC systems I have worked on over the years have either used solid metallic conduit or flexible metallic somewhere in their installations, as have I consistently with no apparent problems.
    On many machines metallic ducting was also used out on the machine itself.
    CNC, Mechatronics Integration and Custom Machine Design

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

  15. #15
    Join Date
    Jan 2005
    Posts
    15362

    Re: Single or separate building circuits for Controller, VFD, PC

    Quote Originally Posted by RaderSidetrack View Post
    Hmmm, not everyone agrees that metal conduit "emits" RFI. The conductors inside any conduit, PVC or metal, emit RFI as a function of the alternating current in the wires. Grounded metal conduit can act to reduce EMI.
    This is correct metal conduit keeps noise control, with in the conduit, then when it is Grounded then the noise is carried on it, just like any other Ground wire which then is just a very large antenna, PVC conduit does the same job without the noise from Grounding keeps the noise inside.

    Most of the articles are based on using 50Hz / 60Hz noise control this does not apply to High Frequency motors that are from 300Hz to 1000Hz the most used 400Hz this is a whole different situation for noise control.
    Mactec54

  16. #16
    Join Date
    Jan 2005
    Posts
    15362

    Re: Single or separate building circuits for Controller, VFD, PC

    Quote Originally Posted by RaderSidetrack View Post
    Hmmm, not everyone agrees that metal conduit "emits" RFI. The conductors inside any conduit, PVC or metal, emit RFI as a function of the alternating current in the wires. Grounded metal conduit can act to reduce EMI.
    This gives you a better Idea of what works at what Frequencies Note PVC is the most common used on the outside, other materials used on the outside are better than PVC but cost a lot more.

    https://www.electriflex.com/shield-f...xible-conduit/
    Mactec54

  17. #17
    Join Date
    Apr 2018
    Posts
    130

    Re: Single or separate building circuits for Controller, VFD, PC

    The shielded conduit linked above (linked again here: https://www.electriflex.com/shield-f...xible-conduit/) is still metal conduit, but with a plastic outer covering. I can appreciate that the various high-dollar copper & bronze braids overwrapping the core steel/metal conduit may offer a greater shielding effect, but that does not take away from the fact that a properly grounded plain steel/metal conduit reduces EMI compared to ordinary PVC conduit.

    If you believe otherwise, I'd like to see some credible links supporting that concept.

  18. #18
    Join Date
    Dec 2003
    Posts
    24216

    Re: Single or separate building circuits for Controller, VFD, PC

    Quote Originally Posted by RaderSidetrack View Post
    t, but that does not take away from the fact that a properly grounded steel/metal conduit reduces EMI.
    Especially if equipotential bonding is ensured, i.e. both ends at earth GND, the the "Antenna" is essentially neutralized.
    CNC, Mechatronics Integration and Custom Machine Design

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

  19. #19
    Join Date
    Mar 2017
    Posts
    411

    Re: Single or separate building circuits for Controller, VFD, PC

    If you are running cable, Run 2 circuits. One 12AWG for a 20 Amp 120VAC and one 10AWG for a 240VAC 30 Amp circuit. You could run the PC and electronics off 120VAC and the VFD off the 240VAC.

  20. #20
    Join Date
    Jan 2005
    Posts
    15362

    Re: Single or separate building circuits for Controller, VFD, PC

    Quote Originally Posted by RaderSidetrack View Post
    The shielded conduit linked above (linked again here: https://www.electriflex.com/shield-f...xible-conduit/) is still metal conduit, but with a plastic outer covering. I can appreciate that the various high-dollar copper & bronze braids overwrapping the core steel/metal conduit may offer a greater shielding effect, but that does not take away from the fact that a properly grounded plain steel/metal conduit reduces EMI compared to ordinary PVC conduit.

    If you believe otherwise, I'd like to see some credible links supporting that concept.
    How many links do you want, if you are a qualified EE than you would know what method is best for EMI control

    Yes, there is plenty of information if you know what to look for, here is one from EATON but I guess in your eyes they don't know either what is the best practice for EMI control

    Eaton Corporation
    VFD Wiring Best Practices
    Note: See the VFD User Manual for more information in regard to power wiring to the drive and to the motor.

    Grounding
    Grounding the equipment to the panel and system ground is the most important aspect to look at when trying to mitigate EMI issues and prevent high frequency currents from effecting other equipment throughout the power network. A specific ground connection should be made between the VFD and the motor with a direct point of contact. From there the VFD should be grounded to the facility ground along with any other devices that are in the cabinet or are used for controls. Painted back panel creates an insulation barrier between the Ground lug and grounding cable that can cause a bad ground connection.
    Ground cables should be sized to the same size of the power wiring to again maintain the proper current level protection. Braided ground connections have lower high frequency impedance than round conductors and are preferred.

    We view a three-level approach to a single drive installation, starting with the accepted standard.
    Use metal conduit that has a grounding strap on the outside of the conduit. Connect this strap to the VFD enclosure and also the motor grounded frame. Inside of the conduit, run a grounding conductor connecting the motor ground to the VFD ground. A shield is preferred over the cable, connecting the shield to the ground bus in the drive and terminating the motor end to the grounded motor.

    The better method would be to use shielded armor cabled or PVC jacketed shielded cable instead of conduit from the drive to the motor. Use similar grounding practices as above. The best method is to use shielded armored cable on the line and load side of the VFD, connecting all grounds as above.

    The preferred method of using shielded or armored power cable is due to the return path for common mode noise is the shield or armor. Unlike conduit, the shield or armor is isolated from accidental contact with grounds by a PVC outer coating. The coating makes the majority of noise current flow in the controlled path and very little high frequency noise flows into the ground grid. The armor prevents EMI coupling to other cables because the radiated emissions are minimal as the armor completely covers the power wires.
    Mactec54

Page 1 of 2 12

Similar Threads

  1. Replies: 1
    Last Post: 01-04-2014, 01:43 AM
  2. Will a VFD output single phase?
    By vladdy in forum Phase Converters
    Replies: 24
    Last Post: 11-28-2009, 07:51 PM
  3. VFD for a single Phase motor!!
    By Yepez in forum Servo Motors / Drives
    Replies: 4
    Last Post: 08-11-2009, 12:53 AM
  4. Can I control 5 axis using 2 separate controller cards?
    By bralwel in forum CNC Machine Related Electronics
    Replies: 2
    Last Post: 08-15-2008, 11:47 PM
  5. Single phase IR motor with a VFD?
    By in2steam in forum Phase Converters
    Replies: 2
    Last Post: 07-10-2007, 05:23 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •