Contactor main contacts prone to erosion or welding Symptom

In the machine tool equipment electrical maintenance practice, often encounter such a fault , that bear cage type motor forward and reverse control relay - contactor main contacts prone to  air circuit breaker  or welding failure phenomenon . The reason is nothing more than the main circuit or motor load , line occurred phase , overcurrent , overvoltage , overload and short circuit , or main contact capacity is too small , the device intrinsic poor quality, poor performance interrupter contacts , or action too frequent , and other mechanical factors . As a general rule , the causes of such failures are mostly obvious faults are relatively easy to exclude . But for other failure reasons, many maintenance personnel tend to notice , such as the device 's own action delay caused by the failure of its  mcb circuit breaker  device characteristics are mainly caused by differences contacts competitive mistakes, resulting in a system control the disorder causes the main contacts ablation or welding . For brief , it can do a simple closed  electric meter  test . See Figure back below. As we all know , the relay - contactor operation of its contacts off characteristics , always follow such a principle ; namely when the coil is energized regardless of the release will or power of the moment, by its own structural reasons , The control break before make contacts all follow the principles .