Kent State University to Host AEGIS Training Session

February 2016

Thanks to Bob Stokes, Commissioning Project Manager for Four Seasons, Kent State University will be hosting a training session on the AEGIS Shaft Grounding Rings.

"For those not familiar the product," Bob explains, "it prevents stray current etching of bearing races associated with VFDs. I personally experienced such failures on a previous project. Not all motors listed as inverter duty are equipped with the technology. When the bearings fail, the owner is left holding the bag as this particular failure is not warranted even though the motor may be listed as inverter duty."

This plays a role in energy savings too. Many buildings are installing VFDs (also known as inverters) to help reduce energy consumption. However, VFDs can also induce currents that can damage bearings and shorten motor life. Repair costs can wipe out any savings for their use. Therefore, to make HVAC systems sustainable, as well as energy-efficient, a reliable method of bearing protection is required.

A representative for AEGIS notes that for years, the true cause of VFD-induced bearing failure was often misdiagnosed. Eventually, repair shops and testing consultants proved that the high-peak voltages, fast-voltage rise times, non-sinusoidal shaft currents, and parasitic capacitance associated with typical pulse-width-modulated VFDs lead to the cumulative erosion of bearings. Since many of today's motors have sealed bearings to keep out dirt and other contaminants, electrical damage has become the most common cause of bearing failure in VFD-controlled AC motors.

Training is scheduled for February 24th at 8 a.m. If any FSE employee would like to attend, please contact Reed Tarkington ( or Bob Stokes (

To learn more about AEGIS Shaft Grounding Rings, visit, or click here to see a Return on Investment sheet for the Grounding Rings.