Variable Frequency Drives (VFDs) have become a standard technology for improving motor efficiency and speed control. However, many engineers and maintenance professionals are surprised to discover that VFDs can also contribute to a hidden source of motor failure: electrical bearing damage.
Understanding how shaft voltage develops and how it affects motor bearings is essential for improving equipment reliability.

What Is Shaft Voltage?

In a VFD-driven motor, high-frequency switching creates electrical energy that can accumulate on the motor shaft. As this voltage builds up, it seeks a path to ground. Unfortunately, the motor bearings often become that path. When the voltage exceeds the insulating capability of the bearing lubricant, an electrical discharge occurs through the bearing. This phenomenon is commonly known as Electrical Discharge Machining (EDM).

How Bearing Damage Develops

A single electrical discharge may be microscopic, but thousands of discharges can occur every second. Over time, these discharges can create:

• Microscopic craters on bearing surfaces
• Fluting patterns on bearing races
• Increased operating noise
• Excessive vibration
• Premature bearing failure

Many bearing failures that appear mechanical are actually caused by electrical current passing through the bearing. Industries Most Affected. Bearing current problems are commonly found in:

• Manufacturing facilities
• HVAC systems
• Water treatment plants
• Mining operations
• Renewable energy systems
• Electric vehicle applications

As VFD technology becomes more widespread, the need for shaft voltage mitigation continues to grow.

How Shaft Grounding Rings Help

One of the most effective methods of protecting motor bearings is the installation of a shaft grounding ring. The grounding ring creates a low-resistance path that safely redirects harmful shaft currents to ground before they reach the bearings.

Benefits include:

• Reduced risk of bearing failure
• Lower maintenance costs
• Improved motor reliability
• Longer equipment service life
• Increased operational uptime

Learn More at EASA 2026

If your organization operates VFD-driven motors, understanding shaft voltage protection is an important step toward improving reliability and reducing maintenance expenses. Volsun will be exhibiting at EASA 2026 in Orlando, Florida, where visitors can learn more about shaft grounding technology and bearing protection solutions.


Exhibition Information

Event: EASA 2026
Date: June 14–16, 2026
Location: Orlando, Florida, USA
Booth Number: 1429

Visit Volsun at Booth 1429 to discuss shaft voltage challenges and discover practical solutions for protecting your motor bearings.

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