Thank you kken for your clarifications. I don't know the physics modelling switching devices or arcs, but I do recall reading long ago that once an arc starts,

Thank you kken for your clarifications. I don't know the physics modelling switching devices or arcs, but I do recall reading long ago that once an arc starts, its resistance drops dramatically, continuing to drop as more current flows through it (within limits). So an arc becomes a runaway situation if current flow isn't ballasted or elsewhere interrupted. But if current flow is controlled, an arc has practical application in fluorescent lighting and arc welding.