Failures in Bearings on Electric Motors: Why They Happen and How to Prevent Them

Explore the most common bearing failure reasons and what to do before they shut down your electric motor.

Most Motor Failures Start with the Bearings

Failures in bearings are responsible for around 60% of motor breakdowns. Whether it’s poor installation, misalignment, or lubrication mistakes, bearing failures start small but escalate quickly.

This article covers the most common bearing failure reasons, the symptoms to watch for, and how to get ahead of them before they take your equipment out of service.

Top Bearing Failure Reasons and How to Prevent Them

1. Lubrication Mistakes

Improper lubrication is a leading cause of bearing failures. Issues with the type, amount, or frequency of grease application all contribute to breakdowns.

Common lubrication-related bearing failure symptoms include:

• Excessive heat at the bearing housing

• Grease leakage or discoloration

• Abnormal noise or vibration

  
  

Prevention tips:

• Follow OEM and EASA lubrication standards based on your motor’s speed and environment

• Avoid overgreasing; too much grease leads to heat buildup and loss of lubricating properties

• Use an infrared gun to monitor bearing temperature

• Establish a clear greasing schedule tailored to your application and operating conditions

  
  

2. Shaft Currents from Variable Frequency Drives (VFDs)

When motors run on VFDs, they often develop shaft currents, which are electrical charges that seek the path of least resistance. Without proper grounding, the current will arc through the bearing, causing internal damage.

Bearing failure analysis in these cases typically reveals:

• Pitting on the race surfaces

• Burn marks or fluting damage

• Shortened bearing life despite regular lubrication

Prevention tips:

• Install grounding brushes or rings on VFD-powered motors

• Verify grounding systems during new installations or as part of routine maintenance

• Evaluate the need for shaft current mitigation based on motor speed and load variability

  
  

What are grounding brushes?

Grounding brushes are small conductive devices installed on electric motors to safely redirect stray electrical currents away from the motor’s bearings. Installing a grounding brush helps protect the motor from premature bearing failure and extends its service life. We often help our customers with shaft current mitigation and will recommend the right approach depending on your application. We can also outfit your current equipment with grounding brushes during scheduled maintenance.

3. Misalignment and Soft Foot

Misaligned motors apply side loads to bearings, and bearings aren’t designed to handle it. “Soft foot” conditions, where a motor’s feet sit unevenly on the base, also cause housing distortion and vibration.

Symptoms of misalignment-related bearing failures:

• Early bearing wear on one side

• Unusual motor vibration

• Recurring bearing replacements in the same unit

Prevention tips:

• Have our team perform precision laser alignment between the motor and driven equipment

• Get an expert to correct soft foot with proper shimming and frame adjustments

• Inspect alignment during each install, after repairs, and any time unusual vibration appears

  
  

4. Improper Installation

Even brand-new bearings can fail quickly if installed incorrectly. Forcing a bearing into place, failing to check tolerances, or skipping proper heat installation techniques all lead to early failure.

Common indicators in bearing failure analysis reports:

• Cracked or distorted raceways

• Loose or tight fits between the shaft and bearing

• Lack of documentation or installation records

Prevention tips:

• Follow the EASA AR100-2020 standard for bearing installations

• Use a micrometer to verify proper fit

• Heat the inner race before installation to avoid mechanical stress

  
  

Early Bearing Failure Symptoms to Watch For

Catching bearing failures early is key to preventing larger system breakdowns. Watch for:

• Vibration that increases over time

• Audible noise changes (grinding, humming, or rumbling)

• Temperature spikes at the bearing housing

• Leaking or discolored grease

• Drops in system performance or efficiency

If you’re seeing any of these bearing failure symptoms, it’s time for further inspection or a vibration analysis.

Our Approach to Bearing Failure Prevention

At Independent Electric, we approach bearing failure analysis with both the data and hands-on experience to back it up. Our certified technicians provide:

• On-site vibration analysis and inspection

• Laser alignment and soft foot correction

• Grounding brush installation for VFD protection

• Bearing replacements installed to industry-best specifications

Whether you're troubleshooting an active problem or building a proactive maintenance schedule, we can help extend the life of your equipment and prevent unplanned downtime.

Your next motor failure is preventable! Let’s talk.