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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