Causes:

1. Incorrect voltage
2. Loose conections
3. Worn or pitted contacts
4. Incorrect coil voltage

Solutions:

1. Verify the voltage on the line side of the contactor is balanced accross the phases.
2. Verify terminations of wires and connections are tightened.
3. verify the contacts are in good shape
4. Verify the coil coltage is correct. The rated coil voltage will be marked on the contactor. 

If a contactor has gotten to this point, there is not much that can be done other than to replace it with a properly sized contactor. Click here to see our contactos.

However, routine inspections can prevent this from happening.