I have come across four 7 1/2 HP Baldor motors, each one controlled by a Danfoss Graham VSD (VFD). Two of these motors supported two chiller units in one building and the other two supported two chiller units in the building adjacent. All four motors went bad on the same day around the same time. The megger shows no insulation between the motor windings and ground. How can this be possible? What could be the cause, or have all four motors failed simultaneously for no apparent reason? and if so how is it possible that all twelve fuses have blown in the vfd cabinets and all four breakers tripped at the 480 volt panels, yet did not stop the motors from burning up? Any ideas?... Keep in mind, these are two completely separate buildings.