[0Jw]

Hello, I hope someone can help me. I am trying to use a stepper motor as a welding wire feed and I don't know if the motor shaft should be electrically isolated from the welding wire. Similarly I have not seen the motors isolated on plasma tables so maybe the opto-isolation is good enough as long as I have a good ground on the welder or plasma side?
Any help is appreciated.

[big iron]

I am only assuming this is a home brewed robotic wire welding operation...
So I would assume you have worked out the welding power source contactor control as well as shielding gas solenoid control.
Wire feed speed must be consistent at the point of arc start ,incorrect feed speed at start will most likely cause a bad arc start or burn back of the wire.
All your preset weld parameters will come on instantaneously, primarily a concern would be the constant voltage if wire speed is not ramped to match your preset voltage then you have a stumbling arc start or wire burn back.
When this happens current starts to go a little crazy as on constant (CV) machines wire diameter for the most part determines correct current, all parameters set correctly.
There's more to this such as burn back control etc
On most commercial wire feeders the constant voltage and( current depending on wire size) are transferred to the welding wire through the wire liner. Even short guns like spool use the same principle.
It may very well be easer to purchase a ready to roll wire feeder.