Electrical Apparatus magazine, March 2005 How To (and Not To) Write a Motor Repair Specification

Major users of electric motors often produce detailed specifications for new purchases, especially for machines of large size. Specifications governing motor repair and reconditioning can be equally important. Writers of such a document should avoid several troublesome practices, such as:

1. Mismatch between the document title or scope and its content. If a specification is written only for a particular motor type or size range, its content should be confined to those topics. If meant to be general, it should cover the entire product scope. One common mistake is to include provisions meaningful only for horizontal motors, but apply the specification to the servicing of vertical machines.

2. Lack of distinction between repair in general, rewinding only, and reconditioning. Specifications written solely for rewinding should be so titled, and not invoked for general repairs.

3. Failure to cite or make use of pertinent industry standards prescribing test and measurement procedures.

4. Inaccurate or imprecise language. Measurable quantities should be quantified, not described in subjective terms such as "large," "small," "excessive," "normal," or "adequate." Such descriptions will not mean the same thing to every service shop.

5. Technical inaccuracy or incompleteness. For example, some have specified replacement of aluminum rotor cage bars with copper in the same slots, with the bars sized to produce the same cage resistance. That inherently changes cage reactance also, thereby altering locked-rotor current and breakdown torque. Another common error is in requiring high potential testing of a reconditioned winding at the standard test voltage for a new winding.

6. Undefined test procedures, such as "checking for unbalanced phase impedance" without specifying a procedure or providing a basis for judging the results, or calling for use of a "motor circuit analysis tester."

Specification writers should also consider instructing the service center to stop work at certain "hold points" where the user can inspect the work to gather information or choose an alternative procedure.

No matter how the specification is written, it should never be a substitute for careful evaluation of service center capability before having the work done.

Industry news...

Featured Technical Article
March 2005

On this page is a summary of the Electrical Apparatus March 2005 featured technical article, by Richard L. Nailen, P.E. , "How To (and Not To) Write a Motor Repair Specification" Spezifikationen für eine Motorreparatur vergasst (und wie nicht) ... Comment écrire (et ne pas écrire) une spécification de réparation de moteur ... Cómo Escribir (y No Escribir) una Especificatión para Reparación de Motores

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