NEMA

NEMA Grade G-11 Nemathelminthes Nematic liquid crystal Nemato cide Nemato cides... 

Each segment of the insulated wire and cable industry has its own set of standards, and cables are built to conform to specifications provided by a large variety of technical associations such as The Institute of Electrical Electronic Engineers (IEEE), The Insulated Cable Engineers Association, (ICEA), National Electrical Manufacturers Association (NEMA), Underwriters Laboratories (UL), Rural Electrification Administration of the U.S. Department of Agriculture (REA), Association of Edison Illumination Companies (AEIC), MiUtary Specifications of the Department of Defense (MIL), American Society for Testing and Materials (ASTM), National Electrical Code (NEC), etc. 

High Pressure Decorative Eaminates, Standards PubHcation No. LD3-1991, National Electrical Manufacturers Association (NEMA), Washington, D.C., 1991. 

Most of the laminates used for rigid printed circuit boards have been classified, by the National Electrical Manufacturers Association (NEMA), according to the combination of properties that determine the suitabiHty of a laminate for a particular use. Eiber reinforcements make laminate-effective properties orthotropic. 

EET-NEMA Standards for Connectors for Use Between Hluminum or Hluminum—Copper Overhead Conductors, EEIPub. No. TDJ-162, Edison Electric Institute, New York, Aug. 1973. 

Electrical Laminates. A significant use for epoxy resins is in the manufacture of copper-clad epoxy-glass printed circuit boards. Systems are available that meet the National Electrical Manufacturers Association (NEMA), GIO, Gil, FR3, FR4, FR5 specifications. Currently the majority of boards are manufactured to the fiame-retardant FR4 specification. The flame retardance is achieved by the use of a soHd epoxy resin based on... 

Environmental Enclosures Enclosures for valve accessories are sometimes required to provide protection from specific environmental conditions. The National Electrical Manufacturers Association (NEMA) provides descriptions and test methods for equipment used in specific environmental conditions in NEMA 250. Protection against rain, windblown dust, hose-directed water, and external ice formation are examples of environmental conditions that are covered by NEMA standards. 

FIG. 29-2 Typical speed versus torque curves for various NEMA-design squirrel-cage induction motors. (See Table 29-2 for an explanation of design types.)... 

When maldug any economic analysis, care should be taken to be certain that the efficiency ratings of all motors being considered are on the same basis. While this should not be a problem for motors rated 1 to 500 horsepower as covered by the NEMA Standards for efficiency marldug, it is common practice for several different test methods to be used when measuring the efficiency of motors rated over 500 horsepower. A particular test method may need to be selected by the test facility on the basis of available test equipment and power supply. All test methods that may be used to test any one motor will not necessarily give the same result for efficiency. 

The speed control operates the governing valve to maintain steam flow commensurate with load demand while holding speed essentially constant. For sudden load changes there will be a short-time overshoot, and a special case is the instantaneous loss of load, load dump at full load. The usual specification states that the overshoot on load dump must not exceed 9 to 10 percent of rated speed. The settled speed rise will of course be equal to the regulation, 4 or 6 percent for a NEMA Class C or B governor and less than I percent for Class D. 

MG-I Reference to a publiealion on Motors and Generators by NEMA (National Electrical Manufacturers Association. USA) which is adopted universally. 

IEC 600.14-12 has recommended four rotor designs, i.e. N. H and NY. HY, to define starting performance for DOL and 17A startings respectively. They are along similar lines, ones to those in NEMA MG-I. They define minimum torques, though the manufacturer can produce better ones. 

NEMA, in its publication MG-1 for induction Motors, has prescribed four rotor designs. A, B, C, and D, covering almost all sizes of LT motors, to possess a prescribed minimum 77, Tp and pull-up torques. These torques are generally as drawn in Figure 2..3 to meet all normal industrial, agricultural or domestic needs. (Refer to the said publication or lEC 60034-12 for values of these torques. lEC 60034-12 has also provided similar stipulations.)... 

Figure 2.3 Speed-torque characteristics of motors as per NEMA standard...

NEMA recommendations on starting currents 2.5 Load torqUO Of Opposing torqUO... 

With a view to achieve yet more standardization in motor design, NEMA Standard MG-1 has also recommended the maximum locked rotor current of single-speed three-phase motors for the various rotor designs A, B, C, and D, for various recommended torque values. These have been derived for a 415 V a.c. system and are shown in Table 2.2. 

Note For motors beyond 200 h.p., NEMA has not covered these data. It is, however, recommended that larger motors may be designed to have even lower locked rotor currents than the above to reduce the starling transient effects on the distribution system as well as on the motor windings. ... 

NEMA/MG-1/1993 NEMA/MG-2/1989 Motor and generators ratings, construction, testing and performance Safety Standards (enclosures) for construction and guide for selection, installation and use of rotating machines ... 

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