Sorry to revive an ancient thread but I would really like to get some understanding of what you posted previously about cable shielding. I am in the middle of grounding/shielding my CNC. I have just grounded the entire CNC chassis to earth ground via the case of the controller box. I am about to replace all of my unshielded stepper motor cables with shielded cables and I was planning to terminate all of the shield drains to the controller case as well but you are saying not to do this and I donât understand why. If I understand correctly, youâre saying to connect all of the shield drains to the ground of the power supply inside the controller box. The power supply inside the box has what appears to be a floating or isolated ground but it is not easily accessible from outside the box. The terminals marked âGâ for ground donât have continuity to the chassis of the power supply. I should therefore find a way to connect the 4 stepper motor shield drains to this ground instead of chassis/earth ground? Can you explain why this is and why is connecting the shield drains to earth ground bad? Thanks
(Edit) I just found a very similar post where a user grounded his cable shields to the chassis of the X-Controller. Just to make sure I understand this correctly, youâre saying that what he did here is incorrect?
Thanks again
Hello @I.weinspar,
All I am saying is that the stepper motor shield/drain wires should be connected to the âCommonâ (or negative DC) side of where the actual stepper drivers are receiving power from. This will allow any stray voltage induced on the shield/drain wire to bleed back to the source. What you aim to do is have any errant magnetic field induce a voltage on the shield/drain instead of the stepper motor phase wires. This is the entire intent of these extra wires.
You would NOT want to connect both sides (at the controller AND the stepper motor) to the common. This can allow a current loop to form and would make any issue that you are trying to resolve worse. All you need is one side connected. I always like to drain it back to a source instead of at the machine itself that way any current that is flowing due to induced voltage does not have the chance to go through machine components to get back to a source. It would not be a common thing in hobby CNC, but induced voltage can build to be very large with respect to âEarthâ if it is not provided a path to ground. This could provide a shock hazard⌠It is similar to static electricity buildup on dry days when a person touches something and gets a small zap; that is voltage potential buildup in/on a personâs body with respect to âEarthâ ground.
Does that make sense?
FYI, I still have my original 2015 Arduino Uno and gShield running. I have had the stepper motorâs shield/drains grounded from day one, and I have never had any connectivity or errant stepper activity issues with the machine.
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Brandon Parker
Hi Brandon,
Thank you for taking the time to respond.
Everything you are saying makes perfect sense. I completely understand the purpose and function of the shield/drain and that only one end, the end at the control box, should be connected. Got it. Iâm totally with you.
What I am still not clear on is why you prefer to connect the shield/drain to Common on the power supply instead of to earth ground. Why is that better? It seems to me that if the case of the control box is solidly connected to earth ground and the shield/drains are connected to that case, any errant voltage on the shield will be drained to earth ground through the case of the control box. It seems like it should work just as well to dissipate that stray voltage away from the signal wires. Am I wrong on this? Is it actually wrong to connect the shield/drain to the case of the control box instead of Common on the internal power supply? If so, can you explain why? Why is Common on the power supply better than earth ground? Or is this just a personal preference and both will work just as well?
I hope Iâm explaining my question clearly.
If you could clarify this, that would be REALLY great.
Thanks
@I.weinspar,
Depending on the scenario, one might be better than the other.
Typically, the shield/drain should be connected at the controller side only to the 0V potential of the circuit it protects. Generally speaking, this will shield control wires perfectly fine, but depending on the power supply design and system, connecting directly to Earth ground can be better. If connecting to an actual Earth ground, this also poses the scenario where the 0V potential of the control wires (which may not be actual Earth 0V due to a floating power supply) is in close parallel proximity to the shield/drain which would be at 0V Earth ground. This, couldâŚand I say this with a large COULD, cause issues. Anything that temporarily raises the potential of the local Earth ground would increase the 0V potential between the control wires and the shield/drain.
Many factors play into proper grounding, but I always try and keep it simple by grounding my control wires to the control wire parent controller ground/common that way they have the same 0V potential.
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Brandon R. Parker
AAAAHHHHHhhhhhâŚOK, that makes a lot of sense. Thank you for clarifying that.
In summary, connecting shield drains to actual earth ground is probably OK, but there is a chance it could create some problems. The more bulletproof way is to connect them to the 0V ground of the power supply if the power supply is floating. It is very helpful to finally understand that.
I really hope Iâm not pushing my luck here but would you mind answering one more ground related question? Could you give me your take on whether or not this chassis grounding is acceptable?
The ground wire runs from the Z axis > X axis > Gantry > Main Chassis > Control box case > Ground.
I have read that each item should have its own ground wire for true star grounding, but does that really matter in this scenario? I currently have it wired this way and at every point along the path from the tip of the spindle to the actual ground there is only 0.2 ohms of resistance. It seems like this should serve to dissipate any sort of charge on the frame quite well, but maybe Iâm missing something. If you wouldnât mind sharing your thoughts on this, I would really appreciate it.
Thanks again.
Sure⌠I apologize for the late reply!
This should technically work perfectly fine for the size of an X-Carve, but it is most likely overkill. As long as the electrical items are grounded correctly, there should not be any charge build-up on the frame.
It is perfectly acceptable to ground the chassis of the X-Carve, but I have never grounded mine. I have not heard of anyone having any issue with charge build-up on the frame either, but that does not mean it has not occurred.
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Brandon R. Parker
Thanks so much for chiming in and clearing that up for me. I really appreciate it.
