#Grease can reach the motor windings from the open bearing side of an electric motor for several common reasons:

1. Lack of sealing or damaged seals

In #motors with open bearings, there is often no effective barrier between the bearing housing and the internal #motor cavity.
If:
• there is no labyrinth #seal,
• the felt ring is worn, or
• the oil seal is damaged,

grease can freely migrate into the motor interior.

2. Over-greasing of the bearing

This is one of the most frequent causes.
When too much grease is applied:
• centrifugal force acts on the grease during shaft rotation,
• grease is pushed out of the bearing,
• it is thrown into the motor housing and reaches the #windings.

This is especially typical for vertical motors or motors that are frequently re-lubricated.

3. Elevated bearing temperature

When the bearing overheats:
• grease becomes less viscous,
• its ability to stay in place decreases,
• it more easily leaks from the #bearing and moves toward the stator windings.

#Overheating may be caused by bearing wear, shaft misalignment, or motor overload.

4. Bearing wear or worn seating surfaces

As the bearing and its fits wear:
• clearances increase,
• grease distribution becomes uncontrolled,
• paths open for grease to escape toward the windings.

5. Motor design features

In some motors (especially older or small-frame designs):
• the open bearing is located very close to the windings,
• there are no grease deflectors or protective shields,

which increases the risk of contamination by design.

6. Incorrect type of grease

Grease with:
• too low #viscosity,
• an unsuitable NLGI grade, or
• poor thermal stability

is more likely to be thrown off and migrate into the motor interior.

Why this is dangerous

Grease on the windings can lead to:
• reduced heat dissipation,
• degradation of the insulation varnish,
• dust adhesion and formation of conductive paths,
• reduced insulation #resistance and eventual breakdown.

Typical preventive measures
• Lubricate #bearings strictly according to the specified quantity.
• Use only the grease recommended by the motor manufacturer.
• Inspect and restore bearing seals.
• Install grease deflectors or protective shields if possible.
• If contamination is severe, clean and dry the windings and measure #insulation resistance.