This article investigates the thermal phenomena that are occurring in an electrode submitted to an electric arc in air at atmospheric pressure. Our purpose is to get a better understanding of the electrode erosion phenomena concerning vaporization or liquid droplets ejection. For that we propose an original experimental device allowing the measurement of the liquid and vapor quantities created under the arc root. The principle of this device is based on the ejection of the liquid metal through centrifugal movement of the electrodes during the arc. Some results are given relatively to Ag, Cu and AgSnO2 cathodes and anodes. Then we present a numerical modelling of the thermal phenomena induced in the electrode by the heat transferred from the arc root. We propose a method to solve the difficulties related to this kind of “free boundary” problems induced by the fact that the electrode material may undergo various phase changes. Finally we show how to use this numerical computation and the experimental results in order to estimate the power density input at a copper anode.