A growth process of damage shapes (specifically growth of a crater) on a cathode surface of a Ag contact pair and a AgSnO2 contact pair due to break arc discharges was observed and numerically evaluated with an evaluation system as well as a commercially-available digital microscope.From comparisons of three-dimensional images of the whole cathode electrode with a certain damage shape on its surface, clear crater growth was recognized on the Ag cathode, while a relatively large but shallow damage shape, instead of a deep crater, was observed on the AgSnO2 cathode surface.Numerical data obtained from the digital microscope analysis confirrned such differences in the damage shapes between these two contact materials.