To Grease or Not to Grease: Best Practices for Electric Motor Bearing Lubrication

I spend a significant amount of time in plants, partnering with companies to craft strategic lubrication plans that enhance motor performance and reliability. Whether in pharmaceuticals, mining, steel, or food processing, the core question remains: how should we lubricate electric motors?

For those who view lubrication as routine, a conversation between a maintenance mechanic, an electrician, and an operations manager can spark debate. Each stakeholder sees motor lubrication through a different lens: the operations manager is focused on preventing downtime, the electrician on electrical integrity, and the mechanic on mechanical longevity.

In my experience, many facilities adopt a “no grease” policy after a lubrication‑related failure. Often that failure was caused by excessive grease, which forced its way past the seal into the motor windings, triggering a fault. To avoid recurrence, management may ban grease entirely and rely on vibration analysis to detect bearing wear, hoping to replace bearings during scheduled outages.

Consequently, many plants install sealed bearings on all motors. Sealed bearings feature an elastomeric seal that blocks contaminants but are not designed for relubrication. While they protect against harsh environments—moisture, dust, or particulate contamination—sealed bearings typically fail when their lubricant (often a polyurea‑based synthetic or refined mineral oil) degrades under heat and shear stress.

In smaller motors, sealed bearings can offer sufficient service life, but in motors above 50–75 hp, their life can shrink to as little as two to four years. Nevertheless, I have observed sealed bearings used in 300‑hp and larger motors in production‑critical applications, which is a risky practice.

I contend that larger motors with open or shielded bearings should still be greased. Expecting a non‑lubricated bearing to outlast a properly greased one defies engineering logic. Claiming better reliability by omitting grease often masks poor maintenance practices.

So how should electric motors be lubricated? The most reliable strategy applies lubrication engineering principles to calculate the exact amount and frequency of greasing. Methods range from frame size to specific bearing dimensions, providing a solid baseline for developing lubrication procedures. Advanced tools—sonic or ultrasonic devices—can “listen” for adequate lubrication, further refining the relubrication schedule.

Many organizations entrust electricians with motor greasing because the electrical department is seen as responsible for motor reliability. However, electricians may lack the mechanical knowledge needed for proper greasing, leading to a “do‑nothing” approach that risks more failures. I believe that regreasing should remain the domain of the mechanical maintenance team.

The only scenario where a regreassable bearing should not be greased is if it has been ungreased for two to three years or more. In such cases, hardened grease can impede new grease distribution, potentially forcing it through the seal or damaging the bearing shield. Aside from this exception, a relubricated bearing will invariably last longer than one that is left untouched.

To avoid motor bearing failures and the associated downtime, ensure that bearings are properly lubricated. Proper greasing is the most effective way to extend bearing life and maintain motor reliability.