Significant increase of contact resistance of silver contacts by mechanical switching actions

When Ag contacts were operated in mechanical break-make actions without switching load current in air (laboratory atmosphere), contact resistance increased significantly on about three quarters of the test samples. No contaminant products were detected in the contact area with AES (Auger electron spectroscopy) analysis. However, SEM (scanning electron microscopy) observation revealed an interesting relationship between the contact resistance characteristic and contact surface condition. The samples on which contact resistance increased had a mirror-like plain contact surface, while those with low and stable contact resistance had a rough surface which looked severely damaged by mechanical actions. The contact resistance characteristic was also found to be influenced by measuring current levels and contact force levels. With these experimental results, a possible hypothetical mechanism for the phenomenon is discussed considering the influence of wear types of the electrode surface.<>