Selection of electric motor bearings for coupled & belted loads

The decision between which antifriction bearing type to specify on NEMA motors is not always easy or obvious. From an end users perspective, it would be simplest if each motor would only have one bearing configuration available, and have that bearing configuration be suitable for both direct connected and belted loads. Unfortunately, that is currently not the case. This is particularly true on the larger higher speed motors (larger than 125 Hp and faster than 1200 RPM). If a bearing is selected that is optimized for direct connect duty (i.e. deep groove ball bearing), and it is belted, the bearing may prematurely fail due to a mechanical overload condition. On the other hand, if a bearing is selected which is suitable for heavy belts loads (i.e. roller bearing), and the motor is direct connected, the bearing may prematurely fail due to a lack of maintaining the required minimum load. Oftentimes the nonoptimal bearing selection can work if special attention is given towards cleanliness, relubrication, alignments, etc. This paper discusses the relationships between these various factors and bearing selection, and helps the reader understand the tradeoffs involved in nonoptimal application of anti-friction bearings and suggests alternate solutions