Ok, I’m starting to see a light in the tunnel now 
I hope it’s not the train comming…
Well, I don’t know about wrong planet, it’s just not this one. A voltage is a measurement in the difference in energy potentials between two points. If you plug a 12V power supply into the wall and measure the voltage between V+ and V- on it, you’ll probably get something like 12V. That’s because the power supply “wants” the V+ wire to be 12V higher energy than the V- wire. That’s how it regulates itself- to make that happen. With most voltage supplies, you can actually connect the V+ to ground and guess what happens? You’ll measure -12V on V- relative to ground! You just made yourself a negative power supply. You’ll notice that I never say “0V” or “zero volts” anywhere in this thread, and instead say ground voltage; that is because the earth is not 0V! It has energy in the form of free electronics, just like you and I do. The whole point of using ground is that it is an extremely stable reference from which to tie relative voltages to. I don’t know how much energy/ free electrons is in the soil under your house, and we don’t need to. What we do need to know is that all of your voltages are referencing the same thing, that they’re stable. The only universal energy potential we have to reference is the rock we’re spinning on, so we just go with that.
So! No, if you tie V- to your ground wire, 24V will not “flow out of it.” Not only because voltages do not flow, but because only the electrical components between the V+ and V- will experience a gradient in electrical energy, from common to to +24.
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Thnx again,
That was a very good explanation.
Thank you all for such a great and informative discussion! I have done a lot of electrical work and understand Grounds but this was very well done and also without the theatrics and bullshit prevalent in many forums. Obviously we are a group of adults here that what to learn. Thanks to all.
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It’s really not simple at all.
The short answer is Yes. The black wire from the limit switch and the shield wire can be connected to the negative terminal on the power supply and your X-carve should work fine. I have mine hooked up this way.
Hooking the negative terminal of the power supply to ground can be tricky.
Some power supply manufacturers connect the negative terminal of the power supply to ground internal to the power supply. This gives you a common ground between the AC source and the DC output. This can be problematic as sometimes you want to isolate the DC side from the AC side.
Others have what is known as “floating outputs”. Think of these like a battery. You have a voltage between the terminals of the battery but neither is connected to ground. This gives you options for paralleling power supplies and serializing power supplies and some isolation between the AC and DC circuitry.
In the simple case, normally it does no harm to connect the negative terminal of a DC power supply to ground.
… go on guys, I’m listening…
Personally, I wouldn’t hook the negative terminal to earth ground. Mainly because I don’t need to. By hooking the shield and negative wire to the negative terminal on the power supply all of my noise issues went away. Why add a complication if you don’t need to?
If you hook the negative terminal to earth ground and it is already hooked to earth ground inside the power supply then you have created a ground loop which current can flow in and cause problems. Unless the current is really high it is not a safety issue.
The assumption is not warranted. Switching power supplies don’t follow the conventions of linear supplies. You can assume that the power supply case is earth grounded, but the assumption that the negative terminal is earth grounded is not a good one (it may be connected, I just wouldn’t assume that).
I measured the X-Carve interface board, it isn’t internally grounded to DC common.
Hi there
Does it make sense to use the shield itself as the negative/return (-) wire for the homing/limit switches, or better ground it separately ?
Cheers
Isaac
@IsaacNeuman
You need to use a separate wire for the negative return. You only connect the shield on one end, not both. For the homing/limit switches you would ground the end of the shield wire at the gShield and leave the end at the switch open.
Hi Larry,
Thanks for clarifying this.
Cheers
Isaac
Sorry about bumping this thread but I figured the link I posted would be wort hit.
Concerning limit switches I found this article on instructables and have added it to my board. http://www.instructables.com/id/End-Stop-Limit-Switch-Problems/
I’ve been having problems with my project stopping at sorta random places (too long to explain) in the code. After trying a few things with the wiring and nothing helping I switched out the laptop for a desktop and it works fine so far.
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Each type of shield has its weak points and strong points, and not all braided shield is created equally. Coverage of the braided shield can typically vary from less than 40% to nearly 97% due to the manufacture changing the angle of the weave, strand diameter, number of carriers (strand groups) and the number of individual strands. Coverage of 100% is unattainable with a braided shield.
Foil shields do provide 100% cable coverage BUT foil shield is generally not as good because aluminum is not as good of a conductor as copper is, and aluminum has a higher transfer impedance. Foil shield also has a lower mechanical strength so bending can damage it. Braids can be combined with foil for maximum performance but will cost more.
Looong time off…
But, back again 
Update on my solution for shielding:
I had my shields, from motors and homing switches, connected to ground from the mains AC.
This must have generated a lot of noise around the cables. Nothing worked.
When removed, everything started up. Homing and jogging started to work and now I can carve.
I will now consentrate on the carving and try to use this machine for something
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