Each year, more motors are repaired than are sold new. For every new motor sold, approximately 2.5 motors are repaired. It is estimated that motors are repaired on average every 5 to 7 years.  Since motors are frequently operated for 20 to 30 years, a motor may be repaired 3 to 5 times in its service life (Schueler, Leistner, & Douglass 1994).

If properly repaired at the time of failure, most motors can be restored to about their original efficiency. However, improper repair of motors can decrease efficiency by up to 5 percent. Recently, sound research linking quality repair practices to greater retained motor efficiency and reliability provided clear guidance on how to maintain motor efficiency during repair (as described in the text box).

The average efficiency loss observed in studies of repaired motors is 1 percent for motors under 100 hp and 0.5 percent for larger motors. While this change may appear small, it can be about the same size as the difference between a standard and an energy-efficient motor (Schueler, V., P. Leistner, and J. Douglass. 1994. Industrial Motor Repair in the United States. Portland, Oreg.: Bonneville Power Administration.). Improperly repaired motors also operate at higher temperatures, which has been demonstrated to significantly reduce the operating life of the motor (Energy-Efficient Motor Systems Handbook). We now understand that a quality repair involves testing the motor prior to and after repair, attention to procedure, access to information on the original design of the motor, and availability of the correct bearings and wire for rewinding.

The least costly motor repair procedure, referred to as reconditioning, is performed on motors that are electrically sound but whose bearings have worn out. This procedure involves cleaning the motor, replacing the bearings, and checking the electrical leads for deterioration. If the motor has experienced an electrical failure due to a short or overloading, then the motor is rewound. Rewinding involves removal of the old windings, replacement with new windings, and reconditioning. Rewinding costs are typically more than twice that of reconditioning. If the repair is an emergency, additional "overtime" charges can increase this cost significantly, while rushing the repair shop may reduce the quality of the repair.

Many electrical failures result from mechanical failures, such as bearings. If a motor problem can be identified through a preventive maintenance program before an electrical failure occurs, significant costs can be avoided. In addition, the motor can be removed from service when it is convenient and the repair shop can take the time for careful reconditioning.

Efficiency losses in motor repair are derived from the following three major sources:

1. Improper bearing installation or replacement with low quality or out-of-spec bearings;
2. Changes in size and pattern of motor core windings from manufacturer's original design; and
3. Overheating of the motor core during the winding removal process, resulting in changes to the magnetic properties of the steel.

The quality of service provided by repairers varies, with some doing an excellent job, but others doing poorly. Almost half of the 4,100 motor repair shops in the United States are members of the Electrical Apparatus Service Association (EASA), the trade association for the repair industry in North America. EASA member shops account for about two-thirds of the motors repaired and three-quarters of the horsepower. Non-EASA shops are smaller and tend to repair smaller motors (Schueler, V., P. Leistner, and J. Douglass. 1994. Industrial Motor Repair in the United States. Portland, Oreg.: Bonneville Power Administration.).

EASA has provided guidelines for efficient motor repair and established a standard for a quality repair, EASA-Q, which is a comprehensive quality standard that is ISO-9000 compliant. Because of its rigor, however, few repair shops qualify. In addition to EASA-Q, a number of groups have developed guidelines for repair shops and customers to identify the key points that characterize a quality repair. Advanced Energy has developed a guide to good motor repair.