All major manufacturers of three-phase ac induction motors offer “inverter-duty” or “inverter-ready” models, but while these motors have inverter-rated insulation to protect the windings, the bearings — their most vulnerable parts — are too often ignored. Unfortunately, many customers who purchase these motors do not understand this. The National Electrical Manufacturers Association (NEMA) has yet to recommend that new motors have bearing protection against damaging electrical discharges.
It is now common knowledge that inverters, also known as variable frequency drives (VFDs) and adjustable speed drives, can induce unwanted motor shaft voltages that, without effective mitigation, can destroy bearings, causing premature motor failure.