A method for automatic detection of a critical point in voltage waveform in breaking contact arc has been developed. The point and a transition term from metallic to gaseous phase were detected by searching a peak in voltage fluctuation. Each phase differed in feature of corresponding waveform such as the gradient and the fluctuation.

The accumulated metallic phase arc duration in Ag electrical contacts was log-proportional to the amount of electrode mass change, and the relationship was irrespective of the air pressure condition. It can be considered that the electrode mass change closely depends on the metallic phase arc.