This video clearly demonstrates that common mode chokes (inductive absorbers) installed on a VFD do not eliminate damaging shaft voltage, and that these chokes are no substitute for AEGIS® Rings.

In this video, we installed the common mode chokes exactly as recommended by the manufacturer and then operated the motor, with no AEGIS® Ring installed, while monitoring shaft voltages to see if bearing discharges occurred. With common mode chokes and no AEGIS® Ring, the oscilloscope detected continual shaft voltage discharge through the bearings. These discharges cause cumulative bearing damage, and lead to eventual bearing failure.

Then we simply stopped the motor, installed the AEGIS® Ring, and turned the motor back on while again monitoring the shaft voltage. All the shaft voltage was gone – as expected – since now the AEGIS Ring was discharging the voltage away from the motor’s bearings to ground. By providing a low-resistance discharge path to shaft voltages, the AEGIS® Ring protects the bearings from electrical damage.

Conclusion: Common mode chokes (cores) have zero benefit in reducing or eliminating shaft voltage, which can discharge through motor bearings and cause electrical pitting damage.

In contrast, AEGIS® Shaft Grounding Rings were found to eliminate the bearing discharges and effectively protect the motor’s bearings.