The faults of main circuit element in a solid state contactor happenbecause:1. Excessive overcurrent that is over permissible current flows due to loadcircuit short-circuit2. Starting current exceeds permissible value and thyristor exceedspermissible temparature3. Surge voltage is applied and the internal element is broken4. Due to incorrect load selection, load current flows to thyristor elementand exceeds the permissible temparature (of thyristor element)5. Operating ambient temparature is higher and thyristor exceedspermissible temparature6. The performance of cooling fin decreases (for example, insulatingmaterial such as dust interrupt heat conduction) and thyristor exceedspermissible temparature