I’m running into this issue with a Hypertherm Powermax 600. I have the USB cable with the supplied choke, with two loops through it, installed. As soon as the torch fires the USB connection is lost. This happens if trying to use Firecontrol or the torch trigger. Using the manual torch fire in FireControl I had the torch stay stuck on, almost put a hole in the water table… anyway…
I have another CNC machine which uses USB, from day one I’ve always used a USB isolator between it and the PC. Mounted right next to the machine are two VFDs, which are known to be noisy. I’ve never had a problem, my machining runs are measured in hours (8 hours is typical).
All that to say I grabbed the USB isolator and used it and the problem was solved. Here is a short video showing the problem and the solution with the isolator. You can find the isolators on ebay/amazon for relatively cheap. Although the exact model I use no longer seems to be sold.
FWIW I measured the USB to table for continuity and found none, I also disconnected the VIM from the electronics enclosure, and the problem persisted.
On edit - Perhaps one reason this is showing up on the Hypertherm is that I’ve run the torch trigger wires out the same strain relief fitting as the raw arc lines that go to the VIM. Perhaps the trigger wires are picking up the noise and propagating it to the enclosure/USB. Might be worth documenting how others with this issue have their lines run/ or if they have factory CNC ports…
Here’s a link to one with US Stock, as most of the ones on ebay seem to be shipping from China, although it lacks a nice case
https://www.mouser.com/ProductDetail/Olimex-Ltd/USB-ISO?qs=hO3QYTFrOd09eOKVRIujMQ==
Manufacturer link https://www.olimex.com/Products/USB-Modules/USB-ISO/
Another one with a case but more $$
https://www.mouser.com/ProductDetail/Keterex/KXUSB-150?qs=sGAEpiMZZMuos25lhNoLahchgXDNv7iT
Mouser has other options too, by most are around $100 and up.