Thanks for your response....
1st the voltage..cant go more than 36 volts so not that
2nd coil ground short...not sure how this would happen but sometimes the machine behaves perfectly, other times it a real PITA..and it's different axis hence different motors.....so don't think it's a coil short.

The plasma 'wiring'? If you mean the mains input it's well away from the machine and electronics on it's own 30amp supply.

The 'switch' for the plasma...I made a litlle circuit - fully enclosed in a metal box - that takes the 5volts output from the BOB 'spindle enable' signal and thru a ULN relay driver to a relay that switches the plasma torch....my BOB doesn't have a relay fitted.

Most of the cable shields, but not all, are grounded both ends.

As I said, it seems to be whenever the plasma cutter (RTech P40 - which I'm not impressed with) fires or ends a cut....but not always!! It has a habit of stuttering the pilot arc and the drive electronics really don't like it. I've fitted an expensive mains filter to the drive electronics and I have a spare one. I could fit this to the plasma (it's rated at 55amps)...other thing I thought was a UPS for the PC and electronics...or different drivers??