Publisher Summary This chapter highlights the investigations pertaining to the diagnosis of rolling-element bearings of motors and alternators failed because of the causes generally unforeseen during design and operation. These generally unforeseen causes found to lead to the passage of electric current through bearings of the motors and alternators and deteriorate them in due course. The vibration and shaft-voltage data, characteristics of the grease used in various rolling-element bearings, and other related aspects were analyzed and unforeseen causes of failure of bearings diagnosed. The surveys of the failure of rolling-element bearings indicate various causes including that of failure, because of corrugations. The investigations pertaining to shaft voltage, vibration, and shock pulse levels were carried out on various motors, both at non-drive end and drive-end, and various other related aspects were inspected. The prolong operation of bearings under vibration, leads to the ageing of insulation, depending on quality of insulating material. This results in the breakage/crack of the bearing insulation. Consequently, it generates a resistance-free path of bearing current that leads to catastrophic failure of the bearings. This has been detected in a few motor bearings. By the detection of the flux density on the bearing surfaces along with the corrugated pattern on the tracks surfaces, by analysis of deterioration of greases used in the bearings, and by measurement of stray and shaft voltages, the failure of bearings by the passage of electric current can be established. The extent of deterioration is ascertained by the vibration analysis. The bearings can be shielded against any unforeseen causes for precluding any possible means of leakage of current, for ensuring their trouble-free operational life.