Motor Repair Best Practices for VFD-Driven Motors

Motors operated by variable frequency drives (VFD) are vulnerable to premature bearing failure from VFD induced shaft voltages and bearing currents – sometimes within only weeks or months – and the result is costly down time and production interruptions. Avoiding these costs makes economic sense and pays a high return on investment.

VFD-Driven Motors Can Fail From Destructive Bearing Currents - Costing Downtime and Lost Production

ANSI/EASA Standard AR100-2015

Motor Repair Best Practices
VFDs induce destructive shaft voltages and high-frequency currents which will cause electrical discharge machining (EDM) pitting, fusion craters, and fluting damage to the motor’s bearings and deteriorate the bearing lubrication by allowing electrical arcing to burn the grease.

Cost Avoidance - Follow Best Practices to Ensure Up-time and Reliability

Motor repair best practices will provide bearing protection from these destructive bearing currents by adding AEGIS® Shaft Grounding Ring Technology and, when needed, insulating a bearing to prevent high frequency circulating currents.

  • Motors up to 100 HP - Add AEGIS Shaft Grounding Ring to discharge shaft voltages to ground.
  • Motors over 100 HP - Add AEGIS Ring at one end and insulate the bearing at the opposite end.
  • Detailed recommendations are contained in the AEGIS Bearing Protection Handbook.

Motor Bearings are the Most Vulnerable Parts and the Cost of a Failed Motor Adds Up Quickly

Failed motor costs

The return on investment in repairing motors and following the AEGIS Bearing Protection Handbook’s best practices recommendations will pay dividends day after day and ensure the most reliable repair to the motor.


AEGIS Rings also come with a 2-year extended warranty against bearing fluting damage. No other form of protection against VFD-caused bearing damage offers a warranty like this.

2-Year Extended Warranty

To learn more about AEGIS shaft grounding and best practices for electrical bearing protection, sign up for a training. We offer monthly live training webinars, and - pandemic restrictions permitting - we can also visit your facility to review your exact application.

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