That was what I was saying . Might not be the cause but if all other options fail just maybe. It is like was just said the last answer a lot of things are made in china and I dont think they are conserned about interferance. 

That was what I was saying . Might not be the cause but if all other options fail just maybe. It is like was just said the last answer a lot of things are made in china and I dont think they are conserned about interferance. 

Well, not to hijack the thread, but in my situation I'm running a Miller spectrum 3080 (an older model of their current model Spectrum 875) and it worked fine for several years. Then all of a sudden without any changes to either the plasma or the cnc table or the computer, cabling, etc it just started interfering with the computer. I'm not sure about the specifics of the CandCNC thc so I can't really help the original poster much. If it works occasionally then I would work in the direction of interference in the cabling. Does the THC have the capability to Estop MACH?

Ive been busy tearing into this and pulling just about all my hair out..  I found my problem,    well at least it stops faulting now.  Heres what I found out.  I'm using a Gecko G540 motor controller, this is tied directly to my computer.  When the torch was firing I was using the external relay on the LCTHC that is tied into the G540 and the fault light would trip on the G540 as soon as the arc fired.  I came to the conclusion that it was interfering with the onboard relay.  My solution was to add another relay, using the onboard one to trip the extra relay that I had installed.  It solved the faulting out.

How I came to this,  I tried everything, having the motors disconnected, it still tripped. All the limits are disconnected. Re grounded everything including my computer,  When I unplugged the wires that are connected to my torch switch it wouldn't fault, but reconnect them and it did.  there must be some interference in there to cause some kind of backfeeding into the G540.

But at least my controller box looks good again..

I hope it helps anyone that is having the same problem...

Glad to hear you got it working. Thanks for the update.

Put a diode across the relay terminal so that when you hit the button the emf feild will feed back through it . It will work as a electical feed back neutralizer I think you know what I mean. I had the same trouble last year when I built a contol panel for a machine . It used 5 relays and when I made or broke the curcuit on the relay It sent a pulse back through the wiring and made  the other relays pulse  on.  I couldnt figure it out at first either but a electical freind told me what to do Never had any more problems. It allows the electricity to bleed of the coil so you dont get the feed back which can be a lot more than the input power almost 10 times as much.