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Is a Repaired Motor "Less Reliable" than a new one?

Purchase of the newest premium efficiency motors is optional. Some technologists feel that their higher price is justified not only by lower operating cost but also by higher reliability compared to a repaired motor of lower efficiency. Although electrical apparatus reliability is seldom precisely defined, it's generally expressed by 1.0 minus an annual failure rate.

That isn't especially helpful for electric motors. First, little information exists on failure rates of large groups of identical motors operating under identical conditions. Secondly, motor "failure" can take many forms. Motors may be sent to the repair shop for cleaning because of blocked ventilation passages (equally likely for either new or repaired units); for replacement of a noisy bearing; or for many other reasons other than a burned-out winding. Some repairs can be completed quickly. Others take much longer. Once returned to the owner, a repaired motor may go into long-term spare storage (with consequently misleading service life data). Hence, failure rate surveys performed in the United States between 1960 and 1990 are of limited value in assessing reliability of new vs. repaired machines.

More recently, one manufacturer published data based on warranty claims that indicated no difference between reliability of standard and higher efficiency motors. Following the 1997 effective date of the Energy Policy Act (EPACT), that issue became unimportant. Older, less efficient designs could no longer be sold in the United States. However, a new standard product line of still higher efficiency ("Premium") motors is now being marketed as a higher-priced option. That has led to the question of relative reliability of those motors compared to repaired units of either EPACT or pre-EPACT design.

Too few "Premium" motors are now in service to support a useful failure rate survey. And no survey has ever been made of repaired motor reliability. That would have to examine the nature of the repairs; how they were made; and how often. A comparison would have to recognize that higher efficiency motors do not necessarily operate at lower temperatures (and that few motors fail from simple thermal overload). For the present, then, there is no reason to suppose that a properly-repaired motor is less reliable than a new machine.

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