Arc mobility on new and eroded Ag/CdO and Ag/SnO/sub 2/ contacts

The mobility of break arcs in a magnetic blast field was investigated in both a model switch and a commercial contactor. After contact separation, three arc motion phenomena were measured independently: initial reduced arc motion (immobility and creeping), subsequent running, and final commutation from the contacts to the arc runners. Contacts made from Ag/CdO and from Ag/SnO/sub 2/ were compared in both initial and eroded states. The time of reduced arc motion was much shorter on uneroded Ag/SnO/sub 2/ than on uneroded Ag/CdO contacts, especially at low values of current and magnetic induction. Ag/SnO/sub 2/ contacts lost their superiority during their life when stressed according to AC-4 duty. Arc running velocity was independent of the material but considerably increased with increasing electrode distance. The commutation time was significantly higher on uneroded Ag/SnO/sub 2/ than on uneroded Ag/CdO contacts. After AC-4 erosion rounded the edges of Ag/SnO/sub 2/, the commutation time decreased to the unaltered value of Ag/CdO.<>