Proper grounding

[monte55]

I have been searching for answers but can't find one for me...so I did try before posting.

First...I have a Xylotex 4 axis driver and their power supply. I am driving 4- 495 oz steppers through four wire shielded cable with ground. From the steppers they go to the driver which is mounted in a plastic box mounted to the steel table. There is no electrical path between the driver, power supply,
and computer to the table.
Question........grounds and shielding has never been connected. What is the
best way to ground?
Do I ground the ground wire, shielding, or both?

Does the cable shield/ground need to be commom with the driver/power
supply and or computer?

I assume the grounding of the stepper wiring is for RF noise.

Can I just ground each cable at each stepper location to steel table and leave the ends in the plastic box by the driver disconnected?
The easiest way for me would be to tie all four stepper cables grounds
or shields together after they enter the driver box. If that's ok do they need to be grounded to the table, driver board etc. I am not having any problems
but this should be completed properly.
I hope I have made myself clear............thanks.............Nick

[jkeyser14]

Shielded cable should only be grounded at one end. Normally you ground it on the controller side, though I'm not sure of the exact reason.

[Geetar-ist]

the reason for only connecting to ground at one end is that the "noise" - electrical interferance which can cause crosstalk in control systems - especially analogue systems (0-10v etc) by raising the actual ground value to a positive voltage which loses the control ground reference.

noise is introduced to the system and then like any other type of electrical voltage/signal looks for the route of least resistance (ground hopefully). this is where the shield comes in ! it routes this signal to ground before it can effect the signal cables inside.

if you ground the shield at both ends you are creating an earth loop effectively keeping those signal from leaving the shield quickly..

these shields should be grounded at source - the controller as jkeyser14 rightly says!

sorry its not a very good explanation but thats the way I understand it !

[JRoque]

Hi. I have my steppers and spindle grounded to the frame of the machine as close to the motors as possible. I also ground the shields on both ends since I don't want any potential to develop along that. The frame is then connected to power earth on the AC outlet. All of my logic connection bundles run their own ground returns and are connected only to a common place at the PC controller end.

JR

[Al_The_Man]

Originally Posted by JRoque I also ground the shields on both ends since I don't want any potential to develop along that. JR

Actually a potential is what can happen if you ground both ends.
The reason you only ground one end is, If you have both ends grounded and some part of the circuit seeks a ground path (also known as ground loop) and your shield is the lowest resistance path, then the shield passes current and the resultant field is impressed on the conductors within, which you certainly do not want.
The whole concept of grounding is to produce a common plane ( ground, Earth etc) This is done by setting up a common point in the form of a copper bus or strip of grounded terminals where every shield, ground, incoming service ground, power suppy commons etc, are connected to.
This means that there is a common point where no potential should exist anywhere common to this point and ground ( the machine and the planet (Earth) you are standing on!)
See this post also http://cnczone.com/forums/showthread.php?t=28227
Al.

[JRoque]

Hi Al. Right, but chances are the large frame on my machine is a better conductor than the shield on my cables. If a noise spike is introduced at the open end of the shield, it would have to travel all the way to the other end before finding it's way to ground. That means that there's a better chance of picking it up along the way.

I would agree that for the larger potentials - as is with lightning - you certainly want to ground only one end. The small resistance difference to ground between the ends would create a huge potential in that scenario.

I just did a quick search on this topic and there are two camps: one that grounds at one end and another that grounds at both. It seems to depend on the nature of the signals being carried and how much current they are likely to carry.

JR

[Geetar-ist]

yes, there are two camps when it comes to grounding, I work with large servo motors which control conveyor systems. - xxkW

these are grounded at the servo motor controller only and very rarely experience issues.

as for grounding on the frame, that really depends on the construction of your frame, when we ground to the chassis etc a proper resistance test should be conducted to ensure a true low resistance route to ground at each proposed earth point...

[Al_The_Man]

Originally Posted by JRoque I just did a quick search on this topic and there are two camps: one that grounds at one end and another that grounds at both. It seems to depend on the nature of the signals being carried and how much current they are likely to carry. JR

That surprises me as in all the years I have been involved with industrial machinery, I have never seen a manufacturer specify or read of a recommended practice to ground both ends of a shielded cable, because of ground loops.
Co-incidentally, if you go to the link I showed above, he has just cured his problem, which could easily been caused by shields grounded at both ends or at least, would have aggravated the situation.
Al.

[NinerSevenTango]

The grounds for everything should be configured as a star, meaning all of them connect to one point only.

If you ground both ends of a shield in a cable, then consider what happens if a power line ever accidentally zaps to ground. It's the fault current that you really want to watch for. If there are ground loops in your system, then when an accident happens or someone decides to weld a bracket on the side of your machine, the currents can pass through the common traces on your circuit boards. And yes, copper wire has lower resistance than a huge steel machine. So an appreciable fraction of any fault current will try to find its way home through your expensive controls.

As for noise control, if the shield is grounded at both ends, and there is a noise generator near your cable, then there is a current path for inductively coupled noise. The current gets generated and can pass through the machine and back to the other end. This now floats the ground reference at one end of the cable relative to the other, or it inductively couples the noise into your signal wires. So the best thing is to pop that loop open. With it open, any noise generator near the cable will allow the shield to wiggle a harmless voltage on the ungrounded end of the shield, but none of the noise gets through into the signal wires you are protecting.

I do analog and digital control with huge noise generators, and this kind of practice is mandatory. If we start a new machine up and it acts illogically, the first thing we do after double checking all the obvious stuff is try to find out where somebody created a ground loop. It takes vigilance to keep them out of a sizable system.

--97T--

[monte55]

I read all the posts and still don't quite have an answer to my questions.
I got some good info though.
My 60X60" table is steel. The driver is in a plastic box not grounded to table.
If I take each stepper wires shield and ground as it enters the plastic driver
box and connect them all together, what do I connect that to or do I leave
it in space?
I don't think I want it ground with the driver in case the router would short and maybe harm the electronics. The only ground the table has now is the ground on the router motor.

[NinerSevenTango]

Monte, I'll go out on a limb and suggest you connect the grounds and shields together at one point, with a single connection to ground.

[DayneInfo]

Monte55 - I emailed Jeff at Xylotex with the sme question...here is his answer.

Dwayne

support@xylotex.com wrote:
> >> Hi,
> >> The sheilds should be connected to the Earth Ground (green wire) on
> >> the
> >> power supply.
> >>
> >> Jeff