In a molded-case circuit breaker，a high current arc burns in air at an atmospheric pressure during current interruption process. It is thus important to find out the properties of the various phenomena resulting from the high current arc. One of the phenomena is contact erosion due to the high current arc. To understand the phenomenon of electrodes erosion, erosion masses of an anode and a cathode made of copper were measured over the gap length from 1 to 30 mm for ten or more kA. Vaporizing masses of the anode and the cathode were nearly 10% of total erosion masses of the anode and the cathode. From the relation between energies used for the anode and cathode erosions and ones inputted into the anode and the cathode，simple model of electrodes erosion was constructed. For the gap length of 1 mm, the erosion mass of the anode was larger than simulated value. These large amounts of the erosion mass of the anode were caused by an arc jet blasted from the cathode.

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