Sliding contacts — Electrical characteristics

Experiments with oxidized and oxide-free materials indicate that the electrical characteristics of the ordinary sliding contact, such as that between a carbon or graphite brush and a copper slip ring, are dependent upon the oxide film on the surface of the ring. Results of these experiments are presented in this paper, together with an explanation of the breakdown of this oxide film by the increase of current through the contact, based upon these results. Tests to determine the effects of liquid films on the contact voltage drop, and the variation of thermal voltage in a sliding contact also are reported.