Due to the continuous switching of the contacts, the arc of the opening and closing occurs continuously, and abnormal heat is generated at the center of the contact portion, the contact is melted, melted, dissolved and solidified, the operation is poor. An abnormal overcurrent exceeding the rated current of the contact (there is also a case of short-circuit current) may cause the circuit inside the relay to be blown and the contact melting and solidification, resulting in malfunction. Applying an overvoltage to the coil causes a partial short-circuit of the coil to break and the coil to break. There will be traces of abnormal heating of the coil.
The low voltage of the power supply and the voltage applied to the coil can cause repeated switching and vibration to occur, causing abnormal heat generation. In particular, for AC-rated relays, the voltage should not be less than 90% of the rated voltage. For DC-rated relays, the voltage should not be less than 70% of the rated voltage.