I hope / suspect that Langmuir will chime in here with advice, but from what I recall I think these are some of the things you can do to help improve your chances with the Lotos cut60d:
Install a ground rod for the table. (There are a couple ways to achieve this. One is drilling a hole through your concrete pad and driving a ground stake right there by the machine. You can go “one better” by running two ground rods outside that are more than 6’ feet apart. (I would do 2 each 8’ ground rods that are about 8 ’ apart from eachother and run the large copper wire (6 gauge or 4 gauge for strength) to the two ground rods in series. (run to the first rod, clamp it down, continue the run to the second ground rod, clamp that down). Two ground rods give you a very low resistance path to ground for any stray electrical noise right from the table. The other end of this ground cable is clamped onto the plasma table itself.
EDIT: Thanks to @Lil_Abners_Kustoms below I’d like to point out that the table should be grounded to the service ground and the 2 ground rods in series. Instead of calling the ground rods dedicated, I should call them supplemental ground rods. You can see HyperTherm’s link below, and just like HyperTherm says, you should follow all codes and consult an electrician before taking any ol’ yahoo’s advice on the internet.
Second, you can buy cheap clamp on magnetic ferrites for all your computer cabling (especially USB cables). Ferrites act like inductive “chokes” and keep stray surges from traveling through cables. When I setup a CNC Mill, I put ferrites near both ends of the USB cable. This might be a little overkill, but they were cheap and easy to install, so I figured why not. If one falls off or gets knocked loose, I still have the other one in place.
Third, move the plasma cutter as far away from the control module and your computer as your plasma cutting lead will allow.
Fourth, (This might be considered part of #1, but it is worth spelling this out) Make sure that your plasma cutter power has its own dedicated ground going all the way back to the main panel. Bad Example: If your computer / Langmuire controller are plugged into a 120V outlet that is right next to your 240V outlet and let’s say the wiring wasn’t done properly and they end up sharing a ground connection, that is bad. The 240V outlet should have its own dedicated ground wire going all the way back to the main panel. The 120V outlets should have their own ground wire going back to the main panel. If you aren’t familiar with outlet wiring, I suggest you get an electrician to help you verify this.
Fifth, (I would probably try the other stuff first, and only try this if it was absolutely necessary), you can try wrapping your plasma cutting lead and ground cable in metal foil and grounding the metal foil at one end. (Not both ends, because that can create a noisy ground loop)
I believe they got the Lotos Cut60D working, but they did have to go through a number of things to isolate the noise it was generating. Sounds like you may have already read about it, but if you haven’t seen what ended up working, I suggest you dig back through the forum and find it. I think the solution that worked for that one was in the thread that had people with several different plasma cutters all in one tracking thread.