Managers typically make decisions involving motor replacements after motors fail or when technicians detect an impending failure. Time becomes a major — if not driving — force, resulting in managers making decisions based more on matching the characteristics of the existing motor and the replacement’s availability rather than on finding the motor best suited for the application.
To avoid this replace-in-kind approach to motor maintenance, managers must schedule an inventory of motors in their facility. Most facilities limit the program to motors of more than 5-10 horsepower.
For each motor, the technician should:
• identify the motor’s physical and electrical characteristics
• determine if the load connected is constant or variable and if the application would benefit from installing a VFD
• perform a load and efficiency test on each motor under normal operating conditions.
When the technician completes the survey and testing, the manager can divide the resulting inventory into three groups based on how well the motor matches the load.
The first group includes applications where the motor is significantly oversized. These motors are replacement candidates, even if they are in good operating condition.
The second group of motors includes those that are only moderately oversized. In these applications, it would take too long to recover the cost of the motor replacement, so managers should plan so that when the motor fails, technicians can install a properly sized, high-efficiency unit as a replacement.
The third group includes motors properly sized for the application but manufactured before the arrival of energy-efficiency standards in 1992.
James Piper, P.E., is a national consultant based in Bowie, Md., with more than 25 years of experience in facilities engineering and maintenance issues.
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