Contacts conduction and switching in DC levels

Electrical contact conduction and switching capacity are described by contact resistance and subsequent erosion due to arcing. Measurement of these parameters is therefore useful for testing contact materials under various conditions and applications. In various areas, nominal contact resistance, minimum erosion and material transfer are required with low cost materials working in a wide range of currents from 1 mA - 50 A and forces (1 to 200 N). In this paper we review our studies made during the last 10 years. We relate contact resistance versus force both in their initial state and during aging under fretting, climatic constraint and switching current conditions. The main results are that the contact resistance can be predicted by the experimental and theoretical law R_c = k_cF_c^-n where the constants k_c and n are related to material resistivity and contact shape characteristics. Furthermore, contact resistance enhancement during fretting and climatic tests are reported. Concerning arcing on break, it is found that anodic arcs occur at current levels below the common minimum arc current At higher currents and voltages (>2 A and >14 V) cathodic long arc durations appear and their durations seem to be linear with current. Material performance studies show that the AgSnO₂ family is adequate for short arcs and AgZnO is more appropriate for long arcs.