This paper deals with the fundamental aspects of cathode erosion for non refractory materials and highlights the importance of the system chemistry for cathode erosion. The experimental work was performed in a test chamber with concentric copper cylinders as electrodes. The arc current varied between 100 - 1 100 A. An external magnetic field, varying from 10 to 1 500 G was used to move the arc. Different plasma gases were used (Ar, He, N,, air, CO, Cl,, CH, and mixtures of the polyatomic gases with the inert gases) at atmospheric pressure. Heat transfer simulations included both transient two dimensional models and steady three dimensional models. It is shown that the cathode erosion is a physical phenomenon and that it is a function of three main parameters: arc residence time, arc attachment diameter and cathode spot distribution. The system chemistry affects all three parameters and it is of fundamental importance in cathode erosion phenomena.