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This paper describes the arc behavior in the transverse-magnetic-field (TMF) contacts at intermediate frequency (400-800 Hz). With high-speed photography, three different arc modes were identified: expansion arc column, moving arc, and diffuse arc. In the expansion arc column mode, the arc column is immobile and the diameter of the arc column increases with the current. During this stage, the bright anode spots appear with high amplitude noise of arc voltage at high current. The expansion arc column mode plays an important role in the anode erosion. In the moving arc column mode, the average velocities were observed about 10-100 m/s, and the arc velocity increases with the increased frequency at the same current. The arc voltage expressed by arc current and frequency was obtained in this paper. The cross-section area of the arc column decreases with the increased frequency at the same current. The current density increases with the increased frequency at the certain current. Consequently, it is deduced that the arc velocity increases with the increased frequency at the same current. The mean power input concentrates in a smaller area at a higher frequency. It may be one of the reasons why the anode local melted.