Electrical and mechanical lives of Ag/C and Ag/WC/C Contacts

Several Ag/C and Ag/WC/C contact materials used as stationary contacts in MCCB (molded case circuit breakers) are compared for electrical and mechanical properties. The mechanical lives of the MCCB can be limited by the stationary contact chipping due to the impact by the much harder moving contacts of Ag/W and Ag/WC. Transverse Rupture Strengths are therefore measured by a 3 point bending test, and impact lives on a model switch designed to evaluate material cracking and chipping. The test results are discussed to illustrate the optimization of metallurgical and electrical properties.