Tom,
I agree that the plasma work clamp is not ground....however in a properly designed plasma or welder..it is referenced to earth ground through a resistance back in the power supply....for safety reasons. I have hand cut in thousands of different positions....including underwater (in a dry suit) with a plasma torch in my hand....never felt a tingle. I have also unloaded many cutting tables over the years while as many as 4 plasma torches were cutting...often standing in puddles.....never a tingle from that either.
The plasma voltage is generally higher than tig, however the highest potential (electrode) is harder to get to in a plasma torch as compared to a tig torch. Pretty safe process....however it pays to be careful and properly install and ground your equipment.
Jim |