Understanding the Limitations of Inverter Duty Motors: Why Bearing Protection is Essential 

The introduction of Variable Frequency Drives (VFDs) has revolutionized motor control, offering greater efficiency, precise speed regulation, and enhanced operational flexibility. However, with these benefits come additional stresses on the motor, which manufacturers have addressed by creating “inverter duty” motors. These motors are built to handle the higher voltages on the windings and increased operating temperatures associated with VFDs. But there’s a significant gap in protection that many inverter duty motors fail to address: bearing protection against VFD-induced shaft voltages. 

The Incomplete Promise of Inverter Duty Motors 

“Inverter duty” suggests a motor is robust enough to handle the unique stresses that come with VFD operation. This typically means reinforced insulation to withstand voltage spikes and designs that manage higher thermal loads. Yet, despite these enhancements, many inverter duty motors lack adequate protection for the bearings—one of the most critical components for ensuring motor longevity. 

VFDs can induce high-frequency electrical currents that travel along the motor shaft and discharge through the bearings, causing electrical discharge machining (EDM). This leads to bearing damage characterized by frosted bearings and fluted races, often resulting in premature failure. Without bearing protection, even an inverter duty motor can fall well short of its rated service life, creating a costly cycle of repairs and replacements. 

The Impact on Motor Repair Shops 

For motor repair shops, this oversight presents a significant challenge. A customer may bring in an inverter duty motor for bearing replacement, expecting it to last for years after the repair. However, if the motor lacks bearing protection and is returned to service in a VFD-driven application, it’s likely to fail again in a short time. This puts the repair shop in a difficult position, as customers expect the motor to perform reliably, not realizing that the issue lies in the lack of bearing protection rather than the quality of the repair. 

Repair shops are then caught between the expectations of their customers and the technical limitations of the motors they’re servicing. The motor manufacturer, having delivered a product that meets “inverter duty” standards, may not acknowledge the need for additional bearing protection. Meanwhile, the VFD manufacturer also claims no responsibility for motor failures caused by shaft voltages. This leaves the repair shop in the middle, absorbing the cost of rework and risking their reputation over an issue they did not cause. 

The Importance of Education and Proactive Solutions 

The solution to this problem lies in education and proactive intervention. Repair shops need to inform their customers that even inverter duty motors require additional protection for bearings when used with VFDs. Installing motor shaft grounding modules (MSGMs) is a proven method to prevent VFD-induced bearing damage. MSGMs divert harmful shaft currents away from the bearings, protecting them from EDM damage and significantly extending the motor’s service life. 

At Aaki, we recognize the importance of supporting repair shops with not only reliable products but also the educational tools needed to communicate these critical issues to their customers. We offer a range of resources, including videos and brochures, that clearly explain the risks of VFD-induced bearing damage and the benefits of installing MSGMs. 

Aaki’s Commitment to Supporting the Industry 

For almost 40 years, Aaki has been dedicated to providing motor repair shops with high-quality solutions that address the real-world challenges they face. Our FleXform™ brackets make it easy to install MSGMs on any motor, reducing installation time and ensuring a secure, effective fit. This innovation allows repair shops to confidently equip motors with the protection they need, without worrying about complex installations or risking the motor’s reliability. 

By adding MSGMs to every motor that could potentially be paired with a VFD, repair shops can break the cycle of premature failures and costly returns. It’s not just about protecting motors—it’s about protecting the trust and satisfaction of your customers. 

In an industry where reputation is everything, Aaki is here to help repair shops deliver lasting solutions that keep their customers’ operations running smoothly. For more information on how our products and educational resources can support your business, reach out to Aaki today. We’re committed to helping you provide the best service possible with products that perform faithfully and reliably.