Critical temperature rise can be a failure mechanism for contact materials in power applications. The use of contact materials with reduced silver content to be more cost effective and the smaller sizes of devices impact this failure mode. Furthermore this effect is enforced by reductions in the volume of contact material and lower contact forces, due to energy saving by less power consumption of the driving coil. This paper presents influences of metal oxide content to contact resistance and temperature rise by experiments in a break-only model switch and in contactor applications. Temperature rise tests according to IEC standards show the influences of contact force on temperature rise of contactors and the effect of different switching conditions/loads on temperature rise. Therefore results of AC-3 and AC-4 standard contactor lifetime tests have been compared.contact material; contactor; Ag/SnO 2 ; temperature rise; contact resistance

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Higher power density and longer electrical lifetime at the same time are the main technical targets in development of contactors. Therefore, a close matching of contact material and switching device as well as the understanding of the material-device-interactions is necessary to achieve those demands. The paper will demonstrate the general influence of different material parameters based on Ag/SnO 2 in model switch tests and off-the-shelf contactors under various load conditions. The basic tendencies of the materials can be seen in both test series, but are partially counterbalanced by device specific effects like electrodynamic lift-off, unbalanced erosion between single pairs of contacts or the rise in contact resistance. Since under different load conditions welding, erosion and contact resistance vary, contact materials with 12-14% metal oxide content and special additives appeared to be the best choice for contactor development.