ELECTRIC MOTOR STANDARDS BASIC INFORMATION AND TUTORIALS



Motors and generators are required to meet various industry and national standards and in some instances specific local codes and customer specifications. The more important of these standards may be briefly described as follows:

1. NEMA Standards are voluntary standards of the National Electrical Manufacturers Association and represent general practice in the industry. They define a product, process, or procedure with reference to nomenclature composition, construction, dimensions, tolerances, operating characteristics, performance, quality, rating, and testing. Specifically, they cover such matters as frame sizes, torque classifications, and basis of rating.

2. IEEE Standards (AIEE) concern fundamentals such as basic standards for temperature rise, rating methods, classification of insulating materials, and test codes.

3. USA Standards are national standards established by the United States of America Standards Institute, which represents manufacturers, distributors, consumers, and others concerned. USA Standards may be sponsored by any responsible body and may become national standards only if a consensus of those having substantial interest is reached.

Standards may cover a wide variety of subjects such as dimensions, specifications of materials, methods of test, performance, and definition of terms. USA Standards frequently are those previously adopted by and sponsored by NEMA, IEEE, etc. The chief motor and generator standard of USASI is C50, “Rotating Machinery,” which is substantially in agreement with current NEMA Standards.

4. National Electrical Code is a USA Standard sponsored by the National Fire Protection Association for the purpose of safeguarding persons and buildings from electrical hazards arising from the use of electricity for light, heat, power, and other purposes. It covers wiring methods and materials, protection of branch circuits, motors and control, grounding, and recommendations, regarding suitable equipment for each classification.

5. Underwriters’Laboratories, Inc. is an independent testing organization, which examines and tests devices, systems, and materials with particular reference to life, fire, and casualty hazards. It develops standards for motor and control for hazardous locations through cooperation with manufacturers.

It has several different services by which a manufacturer can indicate compliance with Underwriters’ Laboratories Standards. Such services are utilized on motors only in the case of explosion proof and dust-ignition proof motors where label service is used to indicate to code enforcing authorities that motors have been inspected to determine their adherence to Underwriters’ Laboratories Standards for motors for hazardous locations.

6. Federal Specification CC-M-641 for integral-horsepower ac motors has been issued by the federal government to cover standard motors for general government uses. Standard motors meet these specifications, but other Federal Specifications issued by various branches of the government for specific use may require special designs.

7. World Standards. Standards similar to our NEMA Standards have been established in other countries. The most significant are

a. IEC (International Electrochemical Commission) Standard 72-1, Part 1
b. German Standard DIN 42673
c. British Standard BSI-2960, Part 2
These standards specify dimensions, classes of insulation, and in some cases horsepower ratings.

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