A dynamic wire melting phenomenon is found in rotating arc welding since self-regulation of the arc length is not fully performed. Consequently welding current and electrode extension vary rapidly in high speed rotating arc operation. This paper presents the dynamic simulation of wire melting by using the variable space network method and by modelling the heat flux from the molten end of the wire into the electrode. The simulations are compared with experimental results from other references to show a fairly good agreement. By using simulation analyses, it is clarified how the characteristics of the welding power source affect the sensitivity of the arc sensor.