[sploo]

I have an old CNC machine (K2 KG3925) I’ve been running for years with a router, but having recently upgraded to a 3 phase spindle + VFD I’d like to take the time to improve the wiring (specifically grounding and noise suppression).

The not-very-good diagram attached below shows the basic layout of the system as it is now.

The CNC controller PCB is driven by a parallel port connection from the PC, and is powered by a 5VDC line taken from one of the PC’s USB ports (ugly, but that’s how it was delivered).

The VFD is a Huanyang 2.2kW unit, that was supplied with the spindle.

In terms of earthing paths, the PC, Controller and VFD are all connected to UK 240V mains (live, earth, and neutral). The controller enclosure is earthed via its mains connection.

On the CNC machine, there is continuity between the spindle can, all servo motor cans, and the CNC body itself; by virtue of metal-on-metal contact for all parts.

The first thing I need to do is wire the 4th pin on the spindle connector to the spindle can (as it’s not connected to anything on these cheap Chinese spindles), and then run that line to the earth on the VFD.

I understand the correct way to do it is to have a 4 core shielded cable (U, V, W plus E), where the E core would go to the spindle 4th pin, and also connect the cable shield to that earth core in the cable at both ends. However, I have some suitably rated 3 core shielded cable to hand. Would it be acceptable to connect the shield to the 4th pin on the spindle, and the earth connector on the VFD, rather than use 4 core cable?

The above would mean the CNC machine body itself is now earthed, but only by virtue of its continuity to the spindle body. Should I also add a separate earth line between the CNC machine body at the earth point on the VFD? I’m aware that with the spindle installed in the CNC machine that would then create a loop of earth wiring.

I notice there is no continuity between the three earth (E) points on the VFD, so should I wire the spindle earth (and possible CNC machine body earth) to the left earth point in the VFD on my diagram; so they are definitely connected to the mains earth?

Finally, what other changes should I make? The encoder and limit switch connections between the CNC machine and the controller use Cat (Ethernet) cables; which I assume will have some degree of protection against noise. None of the mains power leads I’m using have any ferrite beads, and I have no EMI filters - would it be advisable to add some?

[Al_The_Man]

It is always best to bond the frame of the motor to Earth GND by means of a dedicated conductor, rather than leave it to galvanic conduction through machine/metallic ground.
The general method is from service ground point, to VFD to motor frame.
The method used to earth ground all metallic parts of the machine is known as equi-potential bonding and when this is done, the elimination of ground loops etc is virtually eliminated.
Also best to set up a star point ground system, where all, or most earth points end up connected together.
Al..

[sploo]

It is always best to bond the frame of the motor to Earth GND by means of a dedicated conductor, rather than leave it to galvanic conduction through machine/metallic ground.
The general method is from service ground point, to VFD to motor frame.
The method used to earth ground all metallic parts of the machine is known as equi-potential bonding and when this is done, the elimination of ground loops etc is virtually eliminated.
Also best to set up a star point ground system, where all, or most earth points end up connected together.
Al..

Thanks. That sounds logical. So if I understand correctly, that means taking an earth lead from CNC machine body to the left earth (E) connection in the VFD on my diagram, and also connecting the earth from the spindle to that same earth point.

Question is; does the earth line from the spindle to VFD need to be a fourth core, or can I get away with using the shield on a three core cable?

[Al_The_Man]

Thanks. That sounds logical. So if I understand correctly, that means taking an earth lead from CNC machine body to the left earth (E) connection in the VFD on my diagram, and also connecting the earth from the spindle to that same earth point.

Question is; does the earth line from the spindle to VFD need to be a fourth core, or can I get away with using the shield on a three core cable?

It should be an independent conductor from earth ground point to either the plug ground pin or the frame of the motor itself, which is essentially the same thing. It can either be part of the 4 conductors or a ground conductor ran separately.

[mactec54]

It should be an independent conductor from earth ground point to either the plug ground pin or the frame of the motor itself, which is essentially the same thing. It can either be part of the 4 conductors or a ground conductor ran separately.

No it can not be run as an independent Ground wire in this case, it needs to be shielded , and part of the 4 core cable

[Al_The_Man]

No it can not be run as an independent Ground wire in this case, it needs to be shielded , and part of the 4 core cable

Just another opinion! What basis?
There is a lot more likely hood of spurious signals being imposed on a conductor that is ran twisted with hi-current carrying ones.
The earth GND is best kept away from these if at all possible, this is what can and does cause ground loops!.
This is why when the 3 separate conductors are used ran as twisted motor power conductors, the earth is kept along side and non twisted, this is the preferred method.

[mactec54]

I have an old CNC machine (K2 KG3925) I’ve been running for years with a router, but having recently upgraded to a 3 phase spindle + VFD I’d like to take the time to improve the wiring (specifically grounding and noise suppression).

The not-very-good diagram attached below shows the basic layout of the system as it is now.

The CNC controller PCB is driven by a parallel port connection from the PC, and is powered by a 5VDC line taken from one of the PC’s USB ports (ugly, but that’s how it was delivered).

The VFD is a Huanyang 2.2kW unit, that was supplied with the spindle.

In terms of earthing paths, the PC, Controller and VFD are all connected to UK 240V mains (live, earth, and neutral). The controller enclosure is earthed via its mains connection.

On the CNC machine, there is continuity between the spindle can, all servo motor cans, and the CNC body itself; by virtue of metal-on-metal contact for all parts.

The first thing I need to do is wire the 4th pin on the spindle connector to the spindle can (as it’s not connected to anything on these cheap Chinese spindles), and then run that line to the earth on the VFD.

I understand the correct way to do it is to have a 4 core shielded cable (U, V, W plus E), where the E core would go to the spindle 4th pin, and also connect the cable shield to that earth core in the cable at both ends. However, I have some suitably rated 3 core shielded cable to hand. Would it be acceptable to connect the shield to the 4th pin on the spindle, and the earth connector on the VFD, rather than use 4 core cable?

The above would mean the CNC machine body itself is now earthed, but only by virtue of its continuity to the spindle body. Should I also add a separate earth line between the CNC machine body at the earth point on the VFD? I’m aware that with the spindle installed in the CNC machine that would then create a loop of earth wiring.

I notice there is no continuity between the three earth (E) points on the VFD, so should I wire the spindle earth (and possible CNC machine body earth) to the left earth point in the VFD on my diagram; so they are definitely connected to the mains earth?

Finally, what other changes should I make? The encoder and limit switch connections between the CNC machine and the controller use Cat (Ethernet) cables; which I assume will have some degree of protection against noise. None of the mains power leads I’m using have any ferrite beads, and I have no EMI filters - would it be advisable to add some?

The Spindle to VFD drive needs to be one cable the Earth / Ground wire being a separate wire will carry noise everywhere so 4 core shielded cable is required and the shield is connected to the plug body not the Earth / Ground pin

Yes an EMI Power Filter mounted close to the VFD Drives input power will help with noise also TDK Lambada RSEN-2030L is the ideal filter for your VFD Drive but must be mounted as close as possible to the VFD Drive input power connection

[sploo]

The Spindle to VFD drive needs to be one cable the Earth / Ground wire being a separate wire will carry noise everywhere so 4 core shielded cable is required and the shield is connected to the plug body not the Earth / Ground pin

I've attached an image showing the top of my spindle, with the plug disconnected. Just to be clear, by "connected to the plug body" you mean that I should ensure there's continuity between the metal plug at the top of the picture and the outer metal shield in the cable?

There's no continuity between the plug body and any part of the spindle; so assuming I used a 4 core cable (and ensure the earth pin in the spindle socket is connected to the spindle can) then:

1. Would I connect the earth core in that 4 core shielded cable to the 50Hz mains earth (the bottom left circled 'E' in the VFD drawing in my original post), or the earth point E to the right of the U, V, W connectors in the VFD?
2. To what would I connect the cable shield at the VFD end?

Yes an EMI Power Filter mounted close to the VFD Drives input power will help with noise also TDK Lambada RSEN-2030L is the ideal filter for your VFD Drive but must be mounted as close as possible to the VFD Drive input power connection

Great. I see there are sources where I can get it in the UK. Is there any value to putting one of these in front of the CNC controller too? Inside the controller enclosure the 240VAC mains passes through a transformer (to produce 24VDC), and then goes into a circuit board with a number of capacitors before it goes to the Gecko G320 drives, so perhaps this combination of transformer and caps means a filter would be unnecessary?

[mactec54]

I've attached an image showing the top of my spindle, with the plug disconnected. Just to be clear, by "connected to the plug body" you mean that I should ensure there's continuity between the metal plug at the top of the picture and the outer metal shield in the cable?

There's no continuity between the plug body and any part of the spindle; so assuming I used a 4 core cable (and ensure the earth pin in the spindle socket is connected to the spindle can) then:

1. Would I connect the earth core in that 4 core shielded cable to the 50Hz mains earth (the bottom left circled 'E' in the VFD drawing in my original post), or the earth point E to the right of the U, V, W connectors in the VFD?
2. To what would I connect the cable shield at the VFD end?



Great. I see there are sources where I can get it in the UK. Is there any value to putting one of these in front of the CNC controller too? Inside the controller enclosure the 240VAC mains passes through a transformer (to produce 24VDC), and then goes into a circuit board with a number of capacitors before it goes to the Gecko G320 drives, so perhaps this combination of transformer and caps means a filter would be unnecessary?

This is very common that the 4th is not connected and you have to connect this inside under the cap mot of the air cooled spindle you need to mod the cap where it mounts and attach the 4th pin with the Ground connector one of the snips is a stud that you attach a crimp fitting to and lock it to the spindle body you then mod the plastic cover to clear the crimp fitting nut and washer

Is your spindle only 3 pin or is it 4 pin ??? if 3 pin it will have to be changed to a 4 pin connecter , these 3 Pin where a China only spindle but people buy them anyway not understanding that 4 pin plug is connector is required

Yes any power supply can have a EMI Power Filter on the input power, they are not always needed though

In your cabinet you will have a metal plate that everything is mounted on ( Ground Plane ) you can mount a Bus for all your Ground wires to attach at this point so your input mains power supply Ground /Earth will attach at this point, all other parts of your system that have a Ground / Earth wire or connection will attach to this point

Do you need to have a shielded cable for the Input Mains Power No it is not normally needed , if you have lots of Shielded Cable then you can put it to use for this cable, the Shield must be correctly terminated or can cause problems

Grounding the Shields are important for the spindle plug you don't have many choices you can roll it back ( not easy to do ) and clamp it under the cable restraint clamp

Because your spindle has a plastic cap you will have to mount a Ground wire under the cap and connect it to the 4th pin you will have to mod the cap is mounted to allow for the connection

A few snips to give you a picture of how you should connect Shields Etc.

Grounding a Shield is done by using a 360 degree clamp this clamp is attached /fastened to the Ground Plane a saddle can also be used but a 360 degree clamp is better and must be a tight clamp around the Shield

[sploo]

This is very common that the 4th is not connected and you have to connect this inside under the cap mot of the air cooled spindle you need to mod the cap where it mounts and attach the 4th pin with the Ground connector one of the snips is a stud that you attach a crimp fitting to and lock it to the spindle body you then mod the plastic cover to clear the crimp fitting nut and washer

Is your spindle only 3 pin or is it 4 pin ??? if 3 pin it will have to be changed to a 4 pin connecter , these 3 Pin where a China only spindle but people buy them anyway not understanding that 4 pin plug is connector is required

Fortunately the spindle does have 4 pins, so I opened it up today and added a lead between that unused 4th pin and a ring connector, that will be held in place by one of the screws used to hold on the plastic cap (I shortened the appropriate "leg" on the underside of the cap so everything seats correctly). The attached image shows what I did. There's now continuity between that 4th pin and the spindle body.

I've also ordered some shielded 4 core cable and will rewire the spindle plug accordingly.

Yes any power supply can have a EMI Power Filter on the input power, they are not always needed though

I suppose that adding one to the CNC controller power input isn't doing to cause problems, so it's probably worth having one there too, just in case.

In your cabinet you will have a metal plate that everything is mounted on ( Ground Plane ) you can mount a Bus for all your Ground wires to attach at this point so your input mains power supply Ground /Earth will attach at this point, all other parts of your system that have a Ground / Earth wire or connection will attach to this point

The metal enclosure of the control box is earthed through the mains line that supplies the controller, but as that's the same mains line as used for the VFD (and indeed the PC) does it matter if the spindle is earthed via the VFD or the control box?

Do you need to have a shielded cable for the Input Mains Power No it is not normally needed , if you have lots of Shielded Cable then you can put it to use for this cable, the Shield must be correctly terminated or can cause problems

I was considering using the 3 core shielded cable for the mains-to-VFD line; though I'm unsure how the shield would be "correctly terminated"?

Grounding the Shields are important for the spindle plug you don't have many choices you can roll it back ( not easy to do ) and clamp it under the cable restraint clamp

Agreed. I was thinking the cable restraint clamp would be the way to grip the shield.

Because your spindle has a plastic cap you will have to mount a Ground wire under the cap and connect it to the 4th pin you will have to mod the cap is mounted to allow for the connection

Ah. OK. So the shield should be connected to the 4th pin (and therefore to the earth core inside the cable), or does the above only apply if I only had a 3 core cable? I assume then that the shield also needs to be clamped appropriately and connected to the earth code at the VFD end?

[mactec54]

Fortunately the spindle does have 4 pins, so I opened it up today and added a lead between that unused 4th pin and a ring connector, that will be held in place by one of the screws used to hold on the plastic cap (I shortened the appropriate "leg" on the underside of the cap so everything seats correctly). The attached image shows what I did. There's now continuity between that 4th pin and the spindle body.

I've also ordered some shielded 4 core cable and will rewire the spindle plug accordingly.



I suppose that adding one to the CNC controller power input isn't doing to cause problems, so it's probably worth having one there too, just in case.



The metal enclosure of the control box is earthed through the mains line that supplies the controller, but as that's the same mains line as used for the VFD (and indeed the PC) does it matter if the spindle is earthed via the VFD or the control box?



I was considering using the 3 core shielded cable for the mains-to-VFD line; though I'm unsure how the shield would be "correctly terminated"?



Agreed. I was thinking the cable restraint clamp would be the way to grip the shield.



Ah. OK. So the shield should be connected to the 4th pin (and therefore to the earth core inside the cable), or does the above only apply if I only had a 3 core cable? I assume then that the shield also needs to be clamped appropriately and connected to the earth code at the VFD end?

No the Shield is only clamped by the cable restraint in your case at the spindle and by a clamp at the other end near the VFD Drive

Where you have added the Ground wire is correct except you have to lock it in place with a star washer and lock nut so you need a long thread like the snip I posted

You need to make a Star point Ground By adding a Bus all Ground connect at this one point

You can not use a 3 core Shielded cable for the Spindle to VFD connection you can get your cable from IGUS CF6-15-04 https://www.igus.com/search?q=CF6-15-04

Just use stranded wire Twisted to make the input connections to the VFD Drive using shielded cable if not done correctly will cause you more problems

[machinehop5]

...stay grounded.

High Voltage can kill.