Grounding and ground-loops are part science and part black-magic. 
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Mostly black magic… 
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Hey where did you ground to the table? I’ve got an 8’ copper rod I put in the ground for powder coating figure I might as well ground the table while I’m at it. You just put it right to a leg?
I set my table up just like this file says. I have Never had a problem at all. Used copper buss bar to connect it all.
https://www.hypertherm.com/Download?fileId=HYP103900&zip=False
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Hey I’m getting my pro soon and wondering if you could post or send a picture of your bonding setup on yours…. I see how they have it the doc but I’m wondering how you set it up exactly on fhe Langmuir so I have something to go from for cable mgmt
Here you go. All the motors are tied to the buss bar on the back of the table. It is connected to the copper buss near the floor that ties the plasma cutter and table to the earth’s ground. The ss sleeve on the positive work clamp creates a Faraday shield around it. It does not
connect the Langmuir control box to the grounding system. It must be isolated from everything.
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This awesome thank you so much…. I appreciate you going out of your way to take so many… and I was thinking I understood that part about the braided shielding sheath/tube, and see I sort of do… but I definitely need to find that stuff then. This kind of bonding regime probably seems extreme to some but I’m sure it’s probably a good CYA.
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Is that white cord with the non grounded adapter for the plasma controller box?
Yes it has a two prong adapter to isolate the computers and control box from the electrical service ground. Not the earth ground. This prevents ground loops though the electrical panel.
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understood. thanks, good to know, again much appreciated. yeah i’m just trying be pretty serious about the bonding and grounding of it all as i have some expensive electronics in addition to the laptop that may or may not be used in the shop concurrently with the new crossfire running on the same electrical service… 3d scanner and possibly a separate cnc eventually. i might need to look at changing the service config too bc i think the house and big shop share the same 100amp… inexplicably it looks like the other 100amps of my 200 service goes to the small 2 car detached. no clue there. that and someone did some BS before i got this place with neutral ground… which i understand is acceptable in certain specific configs but mostly not.
do you use usb isolators? ive seen them used for ground loop stuff… but if you’ve effectively eliminated possibility of ground loops with simpler methods its probably not needed?
No I don’t use one. Its not a bad $19/investment. 
Now, If you decide to do this chassis earth ground setup be aware that in theory some of your positive DC voltage (work clamp) will be lost into the earth ground rod. With that being said, I have seen NO difference in the plasma cutter performance. Zero.
I run a Everlast 82i and have cut 3/4 steel without any problems at all. Well, that is my disclaimer. Also,I have had zero problems with EMI even with 300 amp Tig machine welding right next to it.
As for your neutral and ground being connected together. The only place this should be done is at the main service panel being feed from your utility.
Now, this may be a hard fix if the prior owner buried the wrong cable. Will it work, yes. Is it to code no.
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yeah thankfully the big shop is grounded properly with a rod, its the small 2 car next to the house thats got the funny wiring. i’m just going through everything beforehand making sure i’m not gonna fry anything and assuming that i might possibly use the small garage/outbuilding as a home for the cnc stuff later on so i can sit in the office in the house right next to it and possibly save on having to subdivide space and do too much ventilation work … just have a designated dirty area i guess. and thats really good to know considering i have a lesser quality tig nearby that i use for stainless … and i can definitely hear the high freq start in my shop radio every time… maybe i keep that on the other end of the shop? you know its one of those amazon $500 combo machines with dc tig stick plasma lotos or something. so i’m sure it makes dirty interference. was thinking of selling it and upgrading so i can do aluminum but can’t quite yet after buying the langmuir. anyway your advice and insight has been highly appreciated… and i’ll get to setting this up and try to report back. in the meantime cheers!
the better quesion i should have asked is how did you get the rs232? plugs on the ends of the stepper wires thru the shielding braid? cut/reattach/solder? if it messes with a warranty or something just pm/email me or something or i’ll deduce it?.. deaglebingo outlook… but again thanks for replying before especially when you already commented on this so much earlier and i just didn’t see it in my searching… so also:
i’m posting another link to this thread too that you already commented on to further cement anyone’s understanding if they find this later… sometimes my search skills catches up later after i understand the concept better. Grounding interference solved!.....I wish
edit: wait a second i’m dumb… looking at pics a second time you didn’t shield the actual stepper motor cables… i need to re-read the hypertherm pdf etc you posted and get my shit together on concepts here.
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ok now that i’ve finally gotten over covid and gotten the big shop cleaned up set up and insulated… and finally assembled the table… i’m at the point where my replies originally started. understanding a bit more about the whole thing, just to clarify once and for all… the control box itself shouldn’t be grounded to anything despite the psu of the control box having a ground prong. also i’m extending the cnc pigtail to keep the thc break-out box away from the plasma cutter unit itself because i’ve read that velcroing it to the cutter itself is probably not a good idea. i don’t have any shielded cable but i bought a bunch of that tinned copper braid sleeve, do i connect that shielding sleeve to the same “star” (the bus bar that goes to earth)? i’ve seen someone use a phrase “shield away from the field”? maybe i’m getting that wrong. does it go on one end or the other of the extended thc voltage sensing wires and if i run that wire along with the trigger wires in the same shielding sleeve would that be a problem? also are your braided straps from said bus bar to steppers just connected to the metal case of the steppers with ring terminals like under one of the socket head cap screws? i just wanted to make sure i have this right in my head before i start soldering and crimping stuff… sorry for the ton of rambling questions and thank you in advance.
Thats all correct. Except my VMI box is double sticked to the side of the plasma cutter.
I run an Everlast with a chassis ground lug on it. If yours doesn’t, add one to the outside cover and bring it to the Star buss bar.
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that makes sense. trying to do this right but on a slightly shoestring budget, so ended up going with a new primeweld cut60 as it looked like the most affordable one on the approved list while still having enough amps to do 3/8 well. hopefully that wasnt a mistake, time will tell. soldering the pins on the cnc connector reminded me why i should have been a surgeon or electrician instead of an icu nurse as a career. ha. regardless thank you for your advice. much appreciated.
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Not a fan of the Cut60. But it is what it is. Hopefully, it will be a trouble-free machine. A lot of guys swear by them.
i’ll give it a fair shake. but i’ll definite let ppl know if it turns out to have been an indiana jones and the last crusade type situation.
aka “he chose… poorly”
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I’m running a cut60 and so far no real issues that weren’t my own fault. I did however end up wiring mine to Raw voltage after running divided for a short time and see no real difference between them
I’m new to it all so nothing to compare the cut60 to but so far it’s been working fine. I’m still working on dialing in my speeds and amps but book settings will get you in the ball park