Electrical faults in refrigeration compressors are for the most part caused by: Power failure on one of the phases of a three-phase motor, too low voltage, defective winding, abnormal overheating, rotor friction against the stator or adjustment problems.
When a motor fails, it is recommended first of all to check the state of the windings; the look of these will generally lead to the apparent cause of the fault.

The friction of the rotor against the stator is one of the cause of electrical accidents. Since the space between rotor and stator is very small, wear of a bearing may be enough to cause such friction.
Contact between the stator and the rotor causes metal wear and deterioration of the magnetic circuit insulation, and therefore results in a short circuit between phase and ground.

Causes of Rotor Friction

It must be checked whether the wear of the bearings is such as to cause this type of failure. Excessive wear can result from a lubrication defect, caused by an oil dilution by abrasive residues.
Bearings that have a worn surface condition have certainly been damaged due of the dilution of the oil by the refrigerant.
An opaque oil containing suspended particles and a clogged oil filter indicate the presence of foreign elements, humidity or contaminating residues.
After restarting the compressor, it is advisable to periodically check the color and clarity oil.

In case of presence of suspended matter, the oil must be replaced until it remains clear. In some cases it may be useful to install a suction filter, which retains the particles contaminants before entering the compressor.
Of course if it is found that even after installation of the filter, the oil still contains suspended particles, it is very likely that another mechanical failure is occurring.