AEGIS® Bearing Protection - Why Shaft Grounding?


Bearing Inspection


Template Available

Cutting and inspecting every bearing in motors that come in for repair, especially motors operated on variable frequency drives, will often provide vital information to make the best repair recommendation and improve performance.

Report template available here.

Two primary sources of bearing currents

  1. Inspect the bearing and bearing cavity and retain a sample of the lubricant if further analysis is warranted. Look for:
    1. Contamination
    2. Signs of excessive heat
    3. Hardening of grease
    4. Abnormal coloration (blackened grease)
    5. Excess grease escaping the bearing

Voltage arcs through the bearing

  1. Cut the outer race into halves.
    Follow established safety precautions and use personal protective equipment including eye protection, hearing protection, face shield, gloves and protective clothing.

A third source of bearing currents

  1. Inspect the grease and contamination in the bearing.
    1. Burnt Grease: Continuous electrical arcing in the motor bearings will often rapidly deteriorate the lubricating capability of the grease and cause bearing race damage. When an arc occurs, the oil component of the grease is heated beyond its temperature capacity.
    2. Contamination: In addition to the burnt grease, the arcing causes small metal particles to loosen from the bearing races/balls which are distributed in the grease. These particles are abrasive and intensify the bearing wear.