When you switch to the expanded metal mode on a Hypertherm system....the system senses the loss of current flow through the metal and switches back to pilot arc current at high speed to maintain the arc. As soon as the torch approaches the metal again, the current rapidly ramps up again.
It takes a bit of experimentation to make this work...to get the speed right so that the arc cuts all the way through the material when it has to restart. I have had good luck cutting perforated steel up to about 5/16" thick with my Powermax45. (perforated steel has a lot of holes punched in it....the arc often has to cut accross the holes). Expanded metal is generally quite a bit thinner gauge and seems to work pretty well. For hand cutting...simply drag the torch and hold the trigger. For mechanized cutting shut off the height control....or the torch would be diving on all of the holes!
Make sure for normal cutting that your plasma is in the cutting mode. Normal cutting with the switch in the expanded metal position will cause shorter nozzle life, and may also affect cut quality.
Jim Colt Hypertherm