Arc discharge at switching contacts is one of the key phenomena, because it strongly affects material wear/transfer, contact resistance and electromagnetic interference (EMI). The arc discharge is classified into various types from the viewpoint of its sustaining mechanism and voltage waveform. They are mainly steady arc, showering arc and initial arc. Furthermore, a steady arc consists of two stages named metallic phase arc and gaseous phase arc. In the metallic, phase arc, metal ious from the electrodes mainly sustain the arc. On the other hand, gas ions from the surrounding atmosphere play an important role in the gaseous phase. Each phase arc has different influence on contact performance and EMI. The purpose of this paper is to review the arc discharges at light duty electrical contacts, and to survey the effects of arc discharges on material transfer and EMI.

The three major failures of electrical contacts for automotive relay applications are: contact welding (or contact sticking), high contact resistance and severe contact erosion due to switching arcing. With the demand of high power and multiple functions of automotive vehicles, the switching current has be dramatically increased, it results in higher failing rate, in particular for contact welding. On the other hand, the miniaturization of electromechanical relays has lead to the reduction of mechanical spring force. This not only results in the earlier contact welding but also makes the relay more susceptible to the contact resistance and arc erosion failures. This paper is a review of most recent studies on these three failure aspects. It describes the progress in the understanding of contact welding caused by short arcing and high contact resistance due to contamination of particles and films in relay manufacturing process and also it review the material transfer due to switching arcing. At the end, the brief considerations of electromechanical relays used in 42 volts have also been given.

The electromagnetic interference (EMI) induced by steady arc has been demonstrated to be dependent on arc voltage fluctuation when the arc transfers from the metallic phase to the gaseous phase. In order to give the physical understanding of this arc voltage fluctuation and EMI, several typical materials, such as Ag, Cu and Zr, were tested and their arc behavior was determined and compared. The experimental results indicated that the arc behavior, in particular the arc voltage fluctuation in the moment that metallic phase transfers to the gaseous phase was different for different materials. Based on the test results and former investigations, a plausible mechanism is proposed for understanding these phenomena.

The former experimental results have already shown that it is oxide films formed on contact surface causing the contact resistance to degrade in dc. breaking arcs for Ag and Pd materials. In order to understand the detailed information about it, the experiments are performed to break dc. inductive load at 20 V, 0.5 A and 1.0 A in nitrogen gas with different oxygen concentrations. The contact surface morphology and surface contamination are evaluated by SEM and AES, respectively. The tested results demonstrate that, for Ag contact, the severe oxidation occurs with increasing oxygen concentration, and the critical value of oxygen concentration is found to be about 10% and 5% in 0.5 A and 1.0 A, respectively, above those values the contact resistance degrades due to the oxide films formed on the contact surface, especially on the anode surface. While, for Pd contacts, a remarkable contact resistance degradation is not found even at 1.0 A in oxigen. Evidence shows that the arc duration, in particular the gaseous phase arc duration affects the anode oxidation, which in turn causes the significant fluctuation of contact resistance.