AEGIS® Bearing Protection - Why Shaft Grounding?


Bearing Currents


Voltage Arcs through the Bearing:

Voltage arch through the bearings diagram
  • Discharge currents arc through the bearing, and EDM creates thousands of pits in the bearing race
  • Bearings are roughened, resulting in increased friction and noise
  • Eventually, the rolling elements can cause fluting damage to the bearing races
  • Bearing lubrication deteriorates, loses its viscosity, and the bearing fails
  • Potential for costly unplanned downtime

High Frequency Circulating Currents

High frequency circulating currents may be induced by magnetic flux imbalance, from the stator windings, around the motor shaft. These currents circulate along the shaft, through the bearing, then along the frame to the other bearing, and back to the shaft.

  • Occur in AC motors above 100HP (75 kW) and DC motors over
    10HP (7.5 kW)
  • High frequency circulating currents are always accompanied by capacitive EDM current


Best Practice: High frequency circulating currents should be interrupted by insulating one bearing (usually the non-drive end). Since these currents are always accompanied by capacitive EDM currents, an AEGIS® Shaft Grounding Ring should be installed at the other end (usually drive end) to prevent EDM from capacitive currents.