Faulty insulation in electrical motors can lead to current passing through the bearings to earth through the housing, causing damage to the bearings. The form and extent of the damage will depend upon the magnitude of the current and the duration of the conditions.

Where a voltage difference exists across a motor bearing, current will tend to flow from one ring to another through the contact zones at the loaded rolling elements, since they offer the path of least resistance. As the bearing rotates, these contacts are broken and the current produces arcing between the rolling elements and raceways, causing pitting in their surfaces.

Examples of this type of damage caused by the passage (for only a brief period of time) of an electric current are well illustrated in Figures 1 and 2. The pitting on the components of the ball bearings as shown in Figure 2 is the more common indication but in both cases it will be noted that there is a replica of the raceway pitting on the rolling element involved. Figure 3 shows the pitting on the surface of a ball less under x 100 magnification.

Options - reclamation of parts damaged by wear or corrosion:

• Reclaiming bearing bores to size
• Reclaiming location spigot areas to size
• Corrosion protection on outer body and end shields
• Reclaiming seal diameters on shafts - building-up or shrinking-on coated sleeves
• Reclaiming bearing diameters on shafts to size reclaiming all threads or keyways.