[Nametag]

I’m building my first hobby CNC and could use some help with grounding my stepper motor and limit switch cables.

I’m using shielded cable for stepper motors and limit switches, but I am clueless on where to attach the drain wires.

The build videos for my CNC (CNC4Newbie New Carve) use a Demon Controller, which has a ground screw. However I have an Openbuilds Blackbox controller, which doesn’t appear to have a ground point to attach the drain wires.

The only ground point that I know of is on my Huanyang VFD, which is where I will be attaching the drain wire for the spindle cable. Should I attach the stepper and limit switch drain cable to the VFD ground as well, or is there a better place?

Thanks in advance for the help!

[Al_The_Man]

You normally would set up a Star ground point, and take all ground conductors to this point. including any shields conductors, grounded from the source end.
The service ground conductor also is connected to the star point.
Al.

[mactec54]

I’m building my first hobby CNC and could use some help with grounding my stepper motor and limit switch cables.

I’m using shielded cable for stepper motors and limit switches, but I am clueless on where to attach the drain wires.

The build videos for my CNC (CNC4Newbie New Carve) use a Demon Controller, which has a ground screw. However I have an Openbuilds Blackbox controller, which doesn’t appear to have a ground point to attach the drain wires.

The only ground point that I know of is on my Huanyang VFD, which is where I will be attaching the drain wire for the spindle cable. Should I attach the stepper and limit switch drain cable to the VFD ground as well, or is there a better place?

Thanks in advance for the help!

You Don't attach the drain wire to anything, you can wrap it around the shield, all shields must be clamped or they will not work correctly, and you will have noise problems, here are some snips of how to Ground a Shield

A Ground plane is required for everything to be mounted on, ( A metal Plate that is Grounded to you main Power supply Ground )

A Power Filter is required mounted close to the VFD Drive for the input Power to the VFD Drive , all Grounds wires go to the ( 1 ) mounting Point on the Ground Plane ( Star Ground this can be a stud or a Bus mounting block )

[Al_The_Man]

If you adopt a tried and true method of something called equi-potential bonding, where all sections of the machine are grounded, you can actually connect both ends of the shield to ground, if left unconnected, the shield is floating and essentially useless with no EMI protection and you may as well not use shielded cable...
This is why it is referred to a drain wire.
See the Siemens paper on it. Section 6
They have been a leader in industrial electronics in Europe since after the second world war!
Al.

[Dankata]

Hi, AI
I see you are very knowledgeable about cnc builds and familiar with EMI problem. Im planning to build a very budget CNC for my plasma cutter , I know i will experience many EMI problems and im trying to make my plan around this issue, but im not sure if i understand it right. It will be great if you can give me some guidance on the ideas i have.
Im going to use GRBL controller(https://github.com/Macrobase-tech/MKS-DLC32), first i was going to use it with plugin stepper drivers TMC2209 but because i wont be able to use shielded wires i change my mind and ill go with TB6600. My plan is to use a closed metal box to hold all the electronics and shielded cables on all signal wires. But i have a bit hard time understanding the proper technics of grounding the shielding wires.
As far i understood from your post all drain wires should be connected to the AC neutral wire(or maybe im totally wrong My idea is to use one of those ground rows and attach all drain wires from all the shielded cables and the metal box to it and then connect this to the AC Neutral wire.
What do you think about my idea and please correct mw if im wrong( most probably im)
Thanks!

[Dankata]

Which one will be the correct grounding of the signal cable drain wire
Thanks

[servtech]

In my experience, shielded signal cables work best if only one end is grounded in the electrical panel. Particularly those wires where induced frequency noise can be problematic. Grounding both ends is not best practice and can in some cases short a servo or other device to ground.

[Al_The_Man]

In my experience, shielded signal cables work best if only one end is grounded in the electrical panel. Particularly those wires where induced frequency noise can be problematic. Grounding both ends is not best practice and can in some cases short a servo or other device to ground.

That was the original thinking in order to prevent ground loops, the down side, is that the shield then acts as a good Antenna!
Now it is recommended to bond all metallic parts of the system to earth ground with allows the preferred method of grounding shields at both ends.
I have previously posted a PDF from Siemens which outlines this method, it is called equi-potential bonding.

- - - Updated - - -

Which one will be the correct grounding of the signal cable drain wire
Thanks

The one on the right would be the preferred method.

[servtech]

That was the original thinking in order to prevent ground loops, the down side, is that the shield then acts as a good Antenna!
Now it is recommended to bond all metallic parts of the system to earth ground with allows the preferred method of grounding shields at both ends.
I have previously posted a PDF from Siemens which outlines this method, it is called equi-potential bonding.

- - - Updated - - -











The one on the right would be the preferred method.

With respect, that is not the case or thinking on current Siemens and Fanuc controlled machines out of Switzerland and Germany.

Frequency noise can cause chaotic axis behaviour such as standstill vibration and data transfer loss. Machines I have worked on are very large 5 axis aerospace machines, weighing from 20 to 230 tonnes holding 5mu fighter aircraft component tolerances, signal and power cables can run 80 metres and more.

However, I do accept in some cases both ends being grounded would not be an issue

[Dankata]

Thanks for the tips.
AI, if i want to add capacitors to reduce the noise to each line going to the motors can I connect it to the shield like ground or it will disturb the shielding .

[Al_The_Man]

With respect, that is not the case or thinking on current Siemens and Fanuc controlled machines out of Switzerland and Germany.

However, I do accept in some cases both ends being grounded would not be an issue

Here is the Siemens paper, see section 6 for shield grounding.

[Al_The_Man]

Thanks for the tips.
AI, if i want to add capacitors to reduce the noise to each line going to the motors can I connect it to the shield like ground or it will disturb the shielding .

Motor conductors should be twisted the full length, this often eliminates radiated energy.
BTW, normally a grounded neutral is earth grounded at only one point, the source.
Obtain a copy of NFPA79 if you can, there is often a copy out there on the web.

[mactec54]

Thanks for the tips.
AI, if i want to add capacitors to reduce the noise to each line going to the motors can I connect it to the shield like ground or it will disturb the shielding .

Correct that is why you don't Terminate Grounds and Shields together.

No, you can't add capacitors to each line or the shield to reduce noise this snip will tell you what works and what does not.

If you need more methods for shield Termination, I have lots of snips I can post for you

Note for servtech some of what I post are from Siemens and how they do it.

[mactec54]

In my experience, shielded signal cables work best if only one end is grounded in the electrical panel. Particularly those wires where induced frequency noise can be problematic. Grounding both ends is not best practice and can in some cases short a servo or other device to ground.

It is not possible for the shield to cause a short in any way for a Servo, the Shield is independent of any other wiring when correctly Terminated.

This snip is from Siemens

[Dankata]

The only dual shielded cable with twisted wires that i can find around here is SFTP CAT7 AWG23 - do you think this will work for powering the motors?

[Al_The_Man]

If that is the stranded version with individual shielded pairs and OA shield, then it should be OK, if 23AWG is sufficient for the motors. It is only rated for just under 3amps.!
For motor wires, you attempt to keep radiated energy to a minimum, I have never used shielded cables for motors, and never had any problems, and these have been large motors, I ensure the motor conductors are of the twisted together variety. This eliminates radiated energy.
Signal wires are different and do require adequate shielding.

[Dankata]

I really cannot understand that 360 part, can you send me something visual , thanks
The motors are nema 17 with peak 1.7 amps so it will be fine.

[Al_The_Man]

I really cannot understand that 360 part, can you send me something visual , thanks
.

360?

[servtech]

It is not possible for the shield to cause a short in any way for a Servo, the Shield is independent of any other wiring when correctly Terminated.

This snip is from Siemens

Clearly you've never been a CNC manufacturer's electronic field service engineer. I've had plenty of servos shorted to ground where shielding has chafed cutting into the power cables, axis movement can cause a shield to pierce the insulation of an axis 3 phase servo cable. Also signal cables damaging the drive logic boards. Poor shielding can cause a host of issues, many due to being connected both ends.

Now please, comment on the question, not your response to legitimate replies from others.

I have 30 years experience on CNC machine tools, including Siemens 3, 8, 800, 840d, 870 and Fanuc from Fanuc 5 to 31i.

I was trained by Siemens in Germany and the UK, also Fanuc but I don't pretend to know everything, just make recommendations based on my field and factory experience.

[Dankata]

About this. But as far i get it . The best way will be to use those ground clamps and clamp everything to the metal box and then ground the box with a fat wire