Motors & Drives Information

The advent of electronic drives, as well as emphasis on efficiency, has led to countless revisions, as well as to a more readable version

WHAT'S A "STANDARD" ELECTRIC MOTOR? For decades, the best answer has been "one that complies with NEMA MG1."--The National Electrical Manufacturers Association has been publishing its "Motor & Generator" MG1 standards-hundreds of individual provisions combined into a single document-- for generations. Now, the first complete rewrite since 1993, MGI-1998, a 538-page volume, is available.

Comparison with the 1993 edition, for which partial revisions had been issued several times since, reveals numerous major changes. The most sweeping revisions, however, are cosmetic, aimed (successfully) at making both text and illustrations more readable.

Look at the visual impact first. The golden yellow binder familiar to MG1 readers since the 1980s has been replaced by a white version of much more modem appearance. Inside, the text has gone from a two-column format to a single page-width column. All numbered paragraphs-each technically an individual standard-now carry boldface tides. Line drawings have been made much clearer. Tables have been expanded for easier readability of columns of figures.

The format of paragraph numbering has been simplified and made more consistent. Consequently, even though much of the content is unchanged, the numerical identity is changed. As an example of hundreds of such revisions, see Table I, on the facing page.

Because of these revisions, searchers of the technical literature are likely to find numerous incorrect published references to various MG1 standards. Anyone citing such standards by number for any purpose needs to have the latest edition.

If most of the text remains the same, how does one determine what exactly did change? Must the reader place the 1993 and 1998 publications side by side, to compare paragraph by paragraph, or even word for word?

Unfortunately, the answer is yes. In January 1995, a NEMA spokesman acknowledged the problem in these words: "In trying to streamline NEMA Standards publications-that is, by removing approval dates-NEMA is forcing users to read and compare the standard and revision to identify changes. We lost sight of the importance of this feature to users." Future provisions would show, he said, "in a way not yet determined, what actually changed."

# posted by Medical Information : 2:22 AM