Motor Grounded
 
Next to a severe mechanical failure, a ground fault can be the most destructive.  A ground fault almost always involves the stator lamination.   Hot spots can develop in the lamination and expensive core rebuilds may be required.
A ground fault occurs when the insulation that separates the winding from the lamination develops a void and the conductor makes contact with the lamination. 

 A ground fault can be compounded by attempting  to start the motor again after it has tripped on a ground fault   Measuring the insulation resistance should always be done before a re-start is attempted. 

As mentioned above a ground fault occurs when the insulation fails.  Some of the causes are as follows:

§ Windings experience a surge during start up and try to move.  during  operation the conductors will vibrate.  If a winding has not been properly consolidated and excessive movement and/or vibration can occur, the moving conductors will eventually wear through the insulation.  Sometimes the movement will wear through the turn to turn insulation causing a turn to turn short.  The heat from the short will   compromise the ground wall insulation.
§ Environmental stresses will eventually cause insulation failure.  Moisture, Chemicals, Abrasive contaminants, will all lead to ground faults.  Motors subject to contaminants should be overhauled on a regular basis.
§ Overheating will cause thermal aging of the insulation.
§  Electrical stresses will cause dielectric aging of the insulation.
§ Natural causes:  very often insulation fails because it is old and dried out.

Magneto Electric can custom build a winding analysis program to suit your needs!