Floating switch problem with plasmac

Grounding/shielding issue, use shielded cable, ground everything at a single point inside the electronics box.
Trying to use the plasma while not properly grounded/shielded usually ends up badly.
Open up the "show hal configuration" and watch othe input pins, most probably the rest of them will also flash.
There is a very nice PDF by Hypertherm about grounding practices on the net, so do a search for it.

First link is to the PDF the second to a video on the same subject by Hypertherm, those are just the ground rules that can not be skipped for plasma.
www.google.com/search?q=hypertherm+groun...wAEB&sclient=gws-wiz