This webpage article provides a systematic overview of the generation mechanisms, adverse effects, and mitigation strategies for shaft currents in variable frequency drive (VFD)-fed induction motors and permanent magnet synchronous motors (PMSM). It explains that the high‑frequency switching of the VFD generates common‑mode voltages, which induce shaft voltages on the motor rotor. When these voltages exceed the dielectric strength of the bearing lubricating oil film, they trigger microscopic electrical discharge machining (EDM) events. Repeated millions of times, these discharges cause pitting, fluting, and progressive damage to bearing surfaces, ultimately reducing bearing service life by more than 50%. Compared with traditional line‑start motors, VFD‑driven and PMSM systems are inherently more susceptible to shaft currents due to the inverter’s high switching frequency, higher power density design, and the reflected wave effect from long motor cables. The article emphasizes that single countermeasures, such as using only insulated bearings, have limited efficacy because shaft currents are a multi‑path high‑frequency phenomenon. Drawing on OPD’s practical experience in industrial applications—including blowers, pumps, and wastewater treatment—the most effective approach is a comprehensive system‑level protection strategy. This combines insulated bearings, shaft grounding devices, optimized grounding systems, and VFD output filtering, which collectively reduce shaft voltage accumulation, significantly prolong bearing life, and enhance overall system reliability.