Some things do not add up here, but most of the discussion is OK in general, so i did not reply till now.
As for the "Copper tip is electrically connected to the work piece", most probably you are both right, as that would have to be connected to something (even work) for it to be able to strike an arc, but also most probably it will have to be disconnected as soon as the cutting current is engaged, otherwise it would just eat through the tip that is copper and would be a puddle in under 1 second, as RDA said it will take the path of least resistance.
All this is perfectly explained in HyperTherm documentation for blow back start plasma sources, service manuals, if you can find them as they showed those behind a paywall lately.
Sorry, but i do not recall the exact procedure and inner workings, it's been 8 years since i read that.
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As for
Code:
It would be quite unusual, not really sure if unusual is the correct word, to have the table completely separated from PE.
Unusual = yes for sure, but possible as almost all my machines have a separate cutting table that is not grounded as there is no need for it since the electronics and the surrounding machine frame are all grounded properly, so despite that table acting as a huge antenna, no issues with interference at all. And some are grounded through the plasma source clamp, hence avoiding ground loops.
But, and this is a big but:
Ground everything, properly, in star formation, avoid at all cost "ground loops", use good shielded cable, that will get rid of 90% of issues, and ground the cutting table if the plasma source has no connection between PE and clamp.
