the reason uncontrolled electrical arcs in apparatus become so destructive since once initiated, an arc will draw more and more
current from a fixed-voltage supply until the apparatus is destroyed.
Electric arc - Wikipedia
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An electric arc is the form of electric discharge with the highest current density. The maximum current through an arc is limited only
by the external circuit, not by the arc itself.
An arc between two electrodes can be initiated by ionization and glow discharge, when the current through the electrodes is increased.