The proper application and selection of low voltage motors can be a demanding task.
A good starting point would be to consider why motors fail in the first place. In this
issue, Toshiba will investigate some of the reasons why motors fail. If you talk to your local rewind shop,
you would most likely find that they also experience very similar, if not identical, reasons described in
Bearing Failures (60 to 70%)
- Over/Under Lubrication
- Misalignment/Belt Tension
- High Ambient
- Bearing Currents
- L10 Fatigue
Studies show that bearings fail more often than insulation systems, and the number one
cause of bearing failure is due to over/under lubrication. Improper lubrication causes a heat buildup in
the bearing cavity, and the added heat causes the grease to break down prematurely, eventually resulting in
failure. Ultimately, many of these bearing failures are a result of the bearing exceeding its temperature
limits in one form or another.
When evaluating motor bearing systems, the following important considerations should be
Bearing Temperature Rise: Temperature is the root cause of many of the failures
listed above. A larger thermal margin in the bearing design is ideal. For every 15°C temperature
decrease, the life of your bearing doubles.
Grease Nipples & Relief Valves: This is done to allow greasing and prevent
Sealed or Open-Style Bearings: Sealed bearings do not require as much greasing
maintenance and are commonly used on smaller frames that are often installed in hard-to-reach places.
As frames sizes increase, a transition to open-style bearings is important to allow for reduced
temperature rises, which in turn extends grease life and greasing intervals.
Bearing Clearance Rating: C3 'loose' fitting bearings allow for thermal
Shaft Seals: To protect against contaminants, a V-ring seal (forsheda seal) is
better than a flat seal. Librium-type seals provide IP55 protection and industry-leading bearing
Bearings Sizes on DE & ODE: Larger bearings run on lower temperatures. They
can handle larger radial loads, have longer L10 lives to extend the effects of fatigue, and are not as
sensitive to small misalignments. 300 series bearings are wider and have much larger outside
Inner Bearing Caps: Caps can prevent bearings from failing by damage caused to
the stator and rotor.
Drain & Breather Plugs: These allow for water to escape and prevents water
from entering the motor.
Grease Type: Premium-grade polyurea or lithium based greases extend grease life,
have wider operating temperature ranges, contain rust and oxidation inhibitors, run quieter, and have
higher operating speed capabilities.