Ask Rick: Bearing Life | What is L10?

Bearing Life

Thermotech Wheel Bearing

Wheel Bearing from Thermotech

Bearings are a critical component in all HVAC equipment.  Bearing life is usually expressed as the number of hours an individual bearing will operate before the first evidence of metal fatigue develops.  The usual life rating for industrial applications is called “L-10” life.  Simply put the L-10 life  is the number of hours in service that 90% of bearings will survive.  Or, conversely,  10% of bearings will have failed in the L-10 number of service hours.  

L10 life:   is the preferred term in specifying bearing life and is defined by The American Bearing Manufacturers Association (ABMA). 

L50 or average life:   is accepted as the bearing life associated with a 50% reliability, i.e., after a stated amount of time, only 50% of a group of identical bearings will not yet have developed metal fatigue.

L50 life equals five times the L10 life.  The following chart shows a comparison of L10 to L50 equivalents.                                 

Required L10 – Life Hours       Equivalent L50 (avg) Life Hours
20,000       100,000
40,000       200,000
80,000       400,000
100,000       500,000
200,000       1,000,000


No Guarantee

Failed Wheel Bearing

Failed Wheel Bearing

The bearing life rating is theoretical and based on statistics. Specifying a L10 life does not guarantee that the bearings will have a 90% reliability when installed in real world applications.  The calculation for Basic Rating Life assumes proper lubrication, no shock or vibration, perfect alignment, debris free environment and temperatures that are not extreme.   In the real world, none of these conditions are realistic and the “installed life” of the bearing will depend on the application and maintenance.

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