What I consider very important to reduce the problem of noise etc is to make sure that every thing is grounded, including the commons of all power supplies. I always set up a large copper plate to terminate all grounds and shields to a common point which in turn goes to a the main ground conductor. this is especially important when you CNC the plasma, where It is a good idea to ground the plasma table to the plasma common and sink a ground rod if possible. If you use a 120vac or 240vac step-down/isolation transformer for the AC control make sure you set up a neutral by grounding one side of the secondary at the transformer. If you have a PC based system, make sure the power supply DC common goes to the same ground point, on all the retro-fits I where I have followed this method I have not had a problem with noise.
Al
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.