Hi,
I found this within a few minutes.
There is an ARC_OK signal, its closing relay contacts called OK TO MOVE by Thermal Dynamics. The Start/Stop presumably you've already got sorted.
It would be no trouble to tap into the machine to read the torch voltage, I've had these things in 1000 bits on a number of occasions. They have an IGBT
to close the earth to nozzle circuit used at start up. If it fails short circuit, and it often does, the nozzle blows out repeatedly in short order. I used to keep the IGBTs in stock,
and given how tight my boss was that was a battle!
Craig