584,861 active members*
4,894 visitors online*
Register for free
Login
Page 2 of 3 123
Results 21 to 40 of 42
  1. #21
    Join Date
    Sep 2005
    Posts
    1740

    Re: Size for ground wires

    Quote Originally Posted by millhouse_ View Post
    @mactec54

    As far as I know those 2.2kw + VFD sets won't exceed 8A.
    If your running them on 3 phase, yes but your input to the VFD would still be greater than 8 amps. Running a single phase 230 volt line to the VFD you will need at least 20 amps input line to line 230 volts. My Hitachi called for 30 amp circuit in and I have it on #10 wire, 30 amp breaker. Never had any issues. Check your drive spec's for use on 230 volts, single phase Input.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router Mach4 Kimber 1911 45ACP

  2. #22
    Join Date
    Jan 2005
    Posts
    15362

    Re: Size for ground wires

    Quote Originally Posted by millhouse_ View Post
    @mactec54

    As far as I know those 2.2kw + VFD sets won't exceed 8A.
    Not on single phase, if you where using 3 phase that would be the case, just remember you only have ( 1 ) Hot/live conductor your spindle motor requires ( 3 ) hot/live conductors, so the VFD Drive makes up the requirement by needing more input current to drive the 8.5 amp spindle
    Mactec54

  3. #23
    Join Date
    Mar 2017
    Posts
    411

    Re: Size for ground wires

    Quote Originally Posted by millhouse_ View Post
    Ok. Thanks. Another question:

    As you can see on the picture the panel has three line-in wires. Each one with hot/neutral/ground.


    I would like to crimp their grounds together and use them like one large ground wire. Is this a problem?

    What you want to do is try not to create a ground loop. If you connect all the grounds together from the three sources you have created 3 loops. Most likely the 3 ground wires from the power panel are all connected together in the panel. So, only a single wire is needed for your ground. It should be a large enough gauge to carry the load of the 3 lines combined.

    The purpose of the ground wire is to provide any stray energy in your device the path of least resistance to ground. If there was no ground connection then a short of a main wire could cause the cabinet to be at a high potential. When you touch the cabinet, then you become the shortest path to ground (this is bad).

  4. #24
    Join Date
    Jun 2010
    Posts
    4252

    Re: Size for ground wires

    Not mentioned yet is the function of a Ground wire - why have one? There are two reasons, and really two different sorts of ground wires.

    The first is safety. If something exciting goes wrong, you want the Ground wire to be able to handle as much current as the Active can supply which might be 30 - 40 A. This is why you often see instructions that the ground wire should never be smaller. Note this well.

    The second reason for a 'Ground' wire is to serve as a screen, to block EMI or radiated interference. For instance, you should Earth the screen around your spindle PS cable. In general, the Ground wire from such a screen does not need to carry 30 A. Within reasonable limits of distance, quite light electronics hookup or signal wire is adequate for the screening. I won't go into the fact that high-frequency interference usually sits on the exterior of a copper conductor anyhow.

    The tricky bit can be when there is a risk of a Mains fault to a low-voltage power supply lead. This is a bit of a cross-over case. In practice, we usually use slightly more than 'light electronics hook-up wire' for this.

    My 2c.
    Cheers
    Roger

  5. #25
    Join Date
    Sep 2005
    Posts
    1740

    Re: Size for ground wires

    The equipment grounding wire is required by electrical code for safety, and sized to the main power input source, the EMI drain is a bonus. Yes your shields should be grounded to this ground as your metal cabinets are also.

    To clear up confusion, the DC and signal power negative
    ( - ) should not be tied to equipment ground unless instructed (?) as its not the same thing as it carries voltage.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router Mach4 Kimber 1911 45ACP

  6. #26
    Join Date
    Dec 2003
    Posts
    24216

    Re: Size for ground wires

    Quote Originally Posted by wmgeorge View Post
    To clear up confusion, the DC and signal power negative
    ( - ) should not be tied to equipment ground unless instructed (?) as its not the same thing as it carries voltage.
    Yeah, there is two thoughts on this, some practice never grounding the power commons of different sections of equipment, IOW keep all power separate, and the opposing view on grounding at all times if it is possible.
    I have always prescribed to the latter, whether the equipment supplier has decreed it or not.
    I know of a few instances here in the past where posters have had 'noise' issues caused by false triggering of inputs due to injection of noise which can be inductive or capacitively coupled. Such problems were cured after grounding all power common.
    There is also a practice that was outlined in a Siemens paper covering the importance of something called equi-potential bonding, this ensures that all metallic parts of a machine are at the same ground potential, this practice virtually eliminates the occurrence of Ground Loops.
    The above has so far kept me in good stead!
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

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

  7. #27
    Join Date
    Mar 2018
    Posts
    70

    Re: Size for ground wires

    Thanks for the feedback. I thought that it will create ground loops but someone said it is not a problem because of equal potential.


    The wire shields from the incoming wires will go into shield clamps on a rail. The four other shields will use the same rail. The information I was able to find said that wire shields should only contact the enclosure or the mounting plate through a rail or something like that.

  8. #28
    Join Date
    Jun 2010
    Posts
    4252

    Re: Size for ground wires

    I have a single solid brass bolt on the main control chassis. This is directly connected to the Mains Earth wire. ALL my power supplies (the negatives) are connected to this bolt as well. I am not sure what its not the same thing as it carries voltage even means. ALL wires carry voltage, even if it is 0 V.

    Equi-potential bonding across all the metal is in some ways the ideal for keeping everything quiet. In some cases I have seen this required 1" wide copper braid straps - but it worked.

    Cheers
    Roger

  9. #29
    Join Date
    Sep 2005
    Posts
    1740

    Re: Size for ground wires

    Quote Originally Posted by RCaffin View Post
    I have a single solid brass bolt on the main control chassis. This is directly connected to the Mains Earth wire. ALL my power supplies (the negatives) are connected to this bolt as well. I am not sure what its not the same thing as it carries voltage even means. ALL wires carry voltage, even if it is 0 V.

    Equi-potential bonding across all the metal is in some ways the ideal for keeping everything quiet. In some cases I have seen this required 1" wide copper braid straps - but it worked.

    Cheers
    Roger
    Talking about machine or equipment grounds for safety and to drain off EMI. DC power supply negative or black wires are not the same as they carry current. The equipment ground is for safety and should never be considered a power conductor… because its not.

    Whither or not you ground your DC power supply ground wire to the equipment depends on the maker of that equipment your using.

    Your confusing equipment ground which only carries current during or under a fault condition with a negative DC ground wire which does carry current.
    Retired Master Electrician, HVAC/R Commercial. FLA Saturn 2 4x4 CNC Router Mach4 Kimber 1911 45ACP

  10. #30
    Join Date
    Jan 2005
    Posts
    15362

    Re: Size for ground wires

    Quote Originally Posted by millhouse_ View Post
    Thanks for the feedback. I thought that it will create ground loops but someone said it is not a problem because of equal potential.


    The wire shields from the incoming wires will go into shield clamps on a rail. The four other shields will use the same rail. The information I was able to find said that wire shields should only contact the enclosure or the mounting plate through a rail or something like that.
    The problem is each device will not be at the same potential, so you will have a Ground loop which happens when you have more than one source supplying a cabinet like this

    Yes your shield Termination is the correct way to do it

    I also see not sure but it looks like you have added Circuit Breakers to the Neutral lines, this is normally something that you do not do to a Neutral line only Hot / Live should have a Circuit Breaker
    Mactec54

  11. #31
    Join Date
    Mar 2018
    Posts
    70

    Re: Size for ground wires

    @mactect54

    You see correct but those breaker are temporary. They get replaced by 2 pole or a 6 pole circuit breaker to disconnect hot & neutral at the same time or with a 6 pole breaker everything at once. Since it uses normal Schuko-plugs better not rely on the brown=hot, blue=neutral scheme.

  12. #32
    Join Date
    Dec 2003
    Posts
    24216

    Re: Size for ground wires

    Quote Originally Posted by RCaffin View Post
    I have a single solid brass bolt on the main control chassis. This is directly connected to the Mains Earth wire. ALL my power supplies (the negatives) are connected to this bolt as well.
    Roger
    Basically the same method I have always used regarding DC power supply commons.I use a section of copper bus-bar and drill and tap to take several bolts and connect all star grounds including the service ground.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

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

  13. #33
    Join Date
    Aug 2019
    Posts
    339

    Re: Size for ground wires

    Get the machinery cabinet and wiring inspected and signed-off by a licensed electrician/engineer when completed. I'm not trying to say that you aren't fit for the task or the advice given in your thread weren't accurate, I do this myself for any "custom electrical/electronics" above 2 amps running constant in the shop or at home (for insurance and safety/qc purposes). I'm still having a hard time visiting a friend who is now serving time because he couldn't afford the law suit from the insurance co nor able to re-pay the 6 apartments building he completely burnt down (6 years ago, so called home-made HI-FI Amplifier).

    Sorry for the bomb, you seem like a good guy with good intentions (ground/question worried me a bit). Looking good otherwise!

  14. #34
    Join Date
    Mar 2018
    Posts
    70

    Re: Size for ground wires

    I'm form germany and the whole machine must get inspected if it's going to run in a shop. And it is planned to do so. But on my budget it would be good if this only needs to be done once.

  15. #35
    Join Date
    Dec 2003
    Posts
    24216

    Re: Size for ground wires

    While on the subject of safety, this is what NFPA79 has to say about E--stop, at least as far as N.A. is concerned.
    The electrical code allows for a controlled stop, where the controlled stopping of a VFD can be done according to code using a Safety Relay, these can be obtained with all kinds of features such as issuing a stop input to the VFD PLC input followed by a disconnect via the supply contactor.
    Safety relays are typically one device that can achieve this and have been in used on European machines for some years, they are slowly becoming more popular and eventually mandatory for N.A.

    The E-Stop process required by industrial machinery is spelled out in NFPA79 (Electrical Standard for Industrial Control).
    There are three categories of stop outlined, 0,1 & 2.
    Cat 0: Is stopping by immediate removal of power to the whole machine, i.e. an uncontrolled stop.
    Cat 1: A controlled stop with power to the machine actuators available in order to achieve a the stop and then power removed, the controlled stop is where a Cat: 0 may cause damage to both machine and personnel.
    Cat 2: Basically is a the same as Cat1 but power is left on to actuators such as input devices such as PLC inputs etc which will still allow monitoring their current state.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

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

  16. #36
    Join Date
    Jan 2005
    Posts
    15362

    Re: Size for ground wires

    Quote Originally Posted by millhouse_ View Post
    @mactect54

    You see correct but those breaker are temporary. They get replaced by 2 pole or a 6 pole circuit breaker to disconnect hot & neutral at the same time or with a 6 pole breaker everything at once. Since it uses normal Schuko-plugs better not rely on the brown=hot, blue=neutral scheme.
    I'm not sure of your counties electrical code but you do not normally use a disconnect for a Neutral wire so for each single phase connection Live / Hot wire this is the only wire that should be connected through the disconnects

    So you should only require ( 3 ) single pole breakers or it could be a 3 phase breaker then if there was a fault all 3 would trip

    I know what you mean with the Schuko plugs, don't you have a 16A single phase supply at each plug

    Check your electrical code requirements as for what you are doing I don't think they will allow you to wire it like this
    Mactec54

  17. #37
    Join Date
    May 2005
    Posts
    3920

    Re: Size for ground wires

    Good info Al.

    Have you noticed safety relays being the heaviest maintenance item in modern control panels? Maybe semi modern. Maybe it is the implementation of the specifier but I have machines that all electrical failures over the years, inside the control panel, have been safety relays.

    Quote Originally Posted by Al_The_Man View Post
    While on the subject of safety, this is what NFPA79 has to say about E--stop, at least as far as N.A. is concerned.
    The electrical code allows for a controlled stop, where the controlled stopping of a VFD can be done according to code using a Safety Relay, these can be obtained with all kinds of features such as issuing a stop input to the VFD PLC input followed by a disconnect via the supply contactor.
    Safety relays are typically one device that can achieve this and have been in used on European machines for some years, they are slowly becoming more popular and eventually mandatory for N.A.

    The E-Stop process required by industrial machinery is spelled out in NFPA79 (Electrical Standard for Industrial Control).
    There are three categories of stop outlined, 0,1 & 2.
    Cat 0: Is stopping by immediate removal of power to the whole machine, i.e. an uncontrolled stop.
    Cat 1: A controlled stop with power to the machine actuators available in order to achieve a the stop and then power removed, the controlled stop is where a Cat: 0 may cause damage to both machine and personnel.
    Cat 2: Basically is a the same as Cat1 but power is left on to actuators such as input devices such as PLC inputs etc which will still allow monitoring their current state.
    Al.

  18. #38
    Join Date
    May 2005
    Posts
    3920

    Re: Size for ground wires

    Quote Originally Posted by millhouse_ View Post
    I'm form germany and the whole machine must get inspected if it's going to run in a shop. And it is planned to do so. But on my budget it would be good if this only needs to be done once.
    A few comments:

    A lot of the responses here are reflective of North American practices. Since most of us know little about code specifics in Germany you need to take comments here under consideration.

    Second I’d strongly suggest working with a local panel builder if this build needs to be compliant. Again they will be able to correctly build for local codes. Yes this costs money but if you really want to do it once then you have little choice because I don’t think you are at the point right now where you can DIY a compliant build.

    By the way things like color codes for wiring and other considerations for wiring, should not be dismissed. In some cases screwing up color coding can fail an inspection. In the same way electrical codes have all sorts things that must be complied with. Depending upon the machine there may be other organizations that need to approve the build or your build must meet regulatory requirements. So it isn’t just an issue of meeting electrical code requirements. For instance we have tools with high power RF sources and thus must comply with FCC regs. I have no idea what might come into play in Germany.

    As for grounding I do not like Din Rail grounding solutions at all. They seem to be routinely installed poorly and frankly grounding to steel doesn’t make a lot of sense to me. This may be old fashion but the engineer that steered me this way was pretty old ??, we used copper grounding blocks and in some cases aluminum grounding bars that you might see in a load center. One reason for this approach was the capability for visual inspection. Of course you effectively force a star ground instead of grounding terminal blocks spread all over a high impedance terminal mounting rail.

    There is a bit of a side discussion about leaving DC supplies floating. There is considerable danger from floating DC supplies that go to field, as such I don’t recommend the approach. In most cases you want negative bonded to ground.

    One other point if the panel / wiring project doesn’t look good and by that I mean professional workmanship, expect the inspector to go over the machine with a fine tooth comb. At least locally you will get a very complete inspection if your build looks like an amateurs effort.

  19. #39
    Join Date
    Jan 2005
    Posts
    15362

    Re: Size for ground wires

    Quote Originally Posted by wizard View Post
    There is a bit of a side discussion about leaving DC supplies floating. There is considerable danger from floating DC supplies that go to field, as such I don’t recommend the approach. In most cases you want negative bonded to ground. .

    When did you last check the electrical code for this, I think you will find that it is not recommended, ( Old methods don't apply anymore ) DC Negative is never floating it is the return path if you want extra noise /voltage on your Grounds then it's your choice how you want to terminate it but the electrical code says different

    Din Rail Grounding is completely to Code and can be more affective than what you are suggesting
    Mactec54

  20. #40

    Re: Size for ground wires

    Most supplies have a grounded neutral, so the DC negative wouldn't appreciate being grounded, you'd pop the breakers and possibly damage the PFC / rectifier. Not something to try!

    Some installations such as safety critical applications like escalators (and steel mills, paper mills etc with multiple drives) are designed with their own isolation transformer, which allows for the DC bus to float. The reason for that is to allow tolerance to a single short circuit to ground. It is possible to detect that short (usually an insulation breakdown) and flag it up as a warning without causing or forcing the system to shut down uncontrolledly. You can imagine the carnage if a steel mill tripped out at full speed - if it's capable of continuing to operate and shutting down in a controlled manner, you can see the benefit in terms of safety and cost in doing so..

Page 2 of 3 123

Similar Threads

  1. Stepper motor wires size, possible step loss?
    By QinX in forum Stepper Motors / Drives
    Replies: 15
    Last Post: 03-24-2017, 05:39 PM
  2. help with wires
    By linkintiger in forum DIY CNC Router Table Machines
    Replies: 15
    Last Post: 02-25-2011, 04:00 AM
  3. Frame ground vs. Electrical ground.
    By polaraligned in forum CNC (Mill / Lathe) Control Software (NC)
    Replies: 2
    Last Post: 11-24-2008, 11:21 PM
  4. To Ground or not to Ground That is the question!
    By Mr.Chips in forum DIY CNC Router Table Machines
    Replies: 1
    Last Post: 03-16-2008, 09:10 PM
  5. Motor supply ground vs Logic ground?
    By Gashmore in forum CNC Machine Related Electronics
    Replies: 11
    Last Post: 06-07-2005, 11:21 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
  •