Common Reasons for Contactor Failure

Contactors fail due to a wide range of reasons.  Some of the common reasons are excess current flowing through the contacts.  High current can be either due to overload or due to short-circuit.  High current can cause the contacts to melt.  The electrodynamic forces during a short circuit can mechanically damage the contactor.

Another cause of contact failure is overvoltage.  Overvoltage causes high current to flow in the coil damaging it.  Chattering can be another reason for failure.  Continual chattering damages the contacts and causes arcing. 

Contactors should be properly sized keeping in mind their current closing and interrupting capacities. 

Only Genuine spare parts should be used.

Age is another reason for contactor failure.  The winding in the coil are bonded together with a varnish (encapsulation).  This prevents movement of the coil windings when current passes through the coil.  Age can cause these coils to crack or move causing the insulation to break.   

Temperature can also cause the contactor to fail.  Hence, adequate provision for ventilation needs to be provided.  The contactor should not be installed in placed which are too hot.

Power Quality too has an impact on the life of the contactor.  Transients, voltage and frequency fluctuations can cause the coil to get damaged. 

A corrosive environment which contains damaging chemicals or vapors can also cause damage to the contactor coil.

Mechanical shock or excessive vibration can also cause contactors to fail.