NEMA MG 1-2011 Manual técnico

NEMA Condensed MG 1-2011

Information Guide for General Purpose Industrial AC Small

and

Medium Squirrel-Cage Induction Motor Standards

Published by

National Electrical Manufacturers Association

1300 North 17th Street, Suite 900

Rosslyn, Virginia 22209

www.nema.org

reserved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary

and Artistic Works, and the International and Pan American copyright conventions.

NOTICE AND DISCLAIMER

The information in this publication was considered technically sound by a consensus among persons

engaged in its development at the time it was approved. Consensus does not necessarily mean there was

unanimous agreement among every person participating in the development process.

The National Electrical Manufacturers Association (NEMA) standards and guideline publications, of which

the document herein is one, are developed through a voluntary standards development process. This

process brings together volunteers and/or seeks out the views of persons who have an interest in the topic

covered by this publication. Although NEMA administers the process and establishes rules to promote

fairness in the development of consensus, it does not write the documents, nor does it independently test,

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contained in its standards and guideline publications.

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and makes no warranty that the information in this document will fulfill any particular purpose(s) or

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In publishing and making this document available, NEMA is not undertaking to render professional or

other services for or on behalf of any person or entity, nor is NEMA undertaking to perform any duty owed

by any person or entity to someone else. Anyone using this document should rely on his or her own

independent judgment or, as appropriate, seek the advice of a competent professional in determining the

exercise of reasonable care in any given circumstance. Information and other standards on the topic

covered by this publication may be available from other sources, which the user may wish to consult for

additional views or information not covered by this publication.

NEMA has no power, nor does it undertake to police or enforce compliance with the contents of this

document. NEMA does not certify, test, or inspect products, designs, or installations for safety or health

purposes. Any certification or other statement of compliance with any health- or safety-related information

in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker

of the statement.

Condensed MG 1-2011

Page i

CONTENTS

Page

Foreword.................................................................................................................................................iv

1PURPOSE........................................................................................................................................2

2SCOPE.............................................................................................................................................2

3DEFINITIONS...................................................................................................................................2

4CLASSIFICATION OF DEGREES OF PROTECTION PROVIDED FOR ENCLOSURES FOR

ROTATING MOTORS......................................................................................................................4

4.1 Single Characteristic Numeral.............................................................................................4

4.2 Supplementary Letters ........................................................................................................4

4.3 Letters Following Numerals.................................................................................................4

4.4 Letters Placed Immediately After the Letters IP..................................................................4

4.5 Degrees of Protection—First Characteristic Numeral.........................................................4

4.6 Degrees of Protection—Second Characteristic Numeral....................................................5

5METHODS OF COOLING ...............................................................................................................5

5.1 Arrangement of the IC Code ...............................................................................................5

6MECHANICAL VIBRATION—MEASUREMENT, EVALUATION, AND LIMITS OF AC MEDIUM

MOTORS..........................................................................................................................................5

7SMALL (FRACTIONAL) AND MEDIUM (INTEGRAL) MOTORS RATINGS..................................5

7.1 Voltages...............................................................................................................................5

7.2 Frequencies.........................................................................................................................6

7.3 Horsepower and Speed Ratings..........................................................................................6

7.3.1 Small Induction Motors...........................................................................................6

7.3.2 Single-Phase Medium Motors ................................................................................6

7.3.3 Polyphase Medium Induction Motors .....................................................................6

7.3.4 Basis of Single-Phase Horsepower Rating ............................................................6

7.4 Horsepower Ratings of Multispeed Motors .........................................................................6

7.4.1 Constant Horsepower.............................................................................................6

7.4.2 Constant Torque.....................................................................................................6

7.4.3 Variable Torque......................................................................................................6

7.5 Rating of 60-Hertz Motors Operated on 50-Hertz Power....................................................6

7.6 Time Ratings for Single-Phase and Polyphase Induction Motors.......................................6

7.7 Code Letters (for Locked-Rotor kVA)—Nameplate Marking...............................................7

7.8 Nameplate Temperature Ratings for Alternating-Current Small Motors .............................7

7.9 Nameplate Marking for Small Single-Phase and Polyphase Motors...................................7

7.9.1 Dual Voltage, Dual Frequency, and Dual Speed Motors........................................7

7.10 Nameplate Marking for Medium Single-Phase and Polyphase Induction Motors ...............8

7.11 Additional Nameplate Information for All Motors.................................................................8

8DIMENSIONS—AC SMALL (FRACTIONAL) AND MEDIUM (INTEGRAL) MOTORS...................9

8.1 System for Designating Frames..........................................................................................9

8.1.1 Small Motors ..........................................................................................................9

8.1.2 Medium Motors.......................................................................................................9

8.2 Frame Assignments ..........................................................................................................10

8.3 Lettering of Dimension Sheets..........................................................................................10

8.4 Tolerances for Shaft Runout .............................................................................................10

Condensed MG 1-2011

Page ii

8.5 Grounding Means for Field Wiring ....................................................................................10

9TESTS AND PERFORMANCE—AC SMALL AND MEDIUM MOTORS ......................................10

9.1 Routine Tests for Polyphase Medium Induction Motors....................................................10

9.2 High-Potential Test Voltages for Induction Motors [MG 1-12.3]........................................10

9.3 Test Methods.....................................................................................................................11

9.4 Performance Characteristics.............................................................................................11

9.5 Torque Characteristics of Single-Phase General-Purpose Induction Motors....................11

9.5.1 Breakdown Torque of Single-Phase Motors.........................................................11

9.5.2 Locked-Rotor Torque of Single-Phase Small Motors...........................................11

9.5.3 Locked-Rotor Torque of Single-Phase Medium Motors.......................................11

9.5.4 Pull-Up Torque of Single-Phase Medium Motors.................................................11

9.6 Locked-Rotor Current Characteristics of Single-Phase and Polyphase General-Purpose

Induction Motors................................................................................................................11

9.6.1 Locked-Rotor Current of Single-Phase Small Motors, Designs N, O,and General

Purpose................................................................................................................11

9.6.2 Locked-Rotor Current of Single-Phase Medium Motors, Designs L and M .........11

9.6.3 Locked-Rotor Current of 3-Phase 60-Hertz Small and Medium Squirrel-Cage

Induction Motors Rated at 230 Volts.....................................................................12

9.7 Torque Characteristics of Polyphase General-Purpose Induction Motors........................12

9.7.1 Breakdown Torque Characteristics of Polyphase Small Motors ..........................12

9.7.2 Locked-Rotor Torque of Single-Speed Polyphase Squirrel-Cage Medium Motors

with Continuous Rating.........................................................................................12

9.7.3 Breakdown Torque of Single-Speed Polyphase Squirrel-Cage Medium Motors

with Continuous Ratings.......................................................................................12

9.7.4 Pull-Up Torque of Single-Speed Polyphase Squirrel-Cage Medium Motors with

Continuous Ratings..............................................................................................12

9.8 Temperature Rise for Small and Medium Single-Phase and Polyphase Induction

Motors................................................................................................................................12

9.9 Variations from Rated Voltage and Rated Frequency.......................................................13

9.9.1 Running................................................................................................................13

9.9.2 Starting.................................................................................................................13

9.10 Voltage Unbalance............................................................................................................13

9.11 Variation from Rated Speed..............................................................................................13

9.12 Variation from Nameplate Amperes—Alternating-Current Medium Motors......................13

9.13 Occasional Excess Current...............................................................................................13

9.14 Stall Time ..........................................................................................................................14

9.15 Service Factor of Alternating-Current Motors....................................................................14

9.15.1 General-Purpose Alternating-Current Motors of the Open Type..........................14

9.16 Overspeeds for Squirrel-Cage Motors...............................................................................14

9.16.1 General Purpose Squirrel-Cage Induction Motors ...............................................14

9.16.2 General-Purpose Design A and B Direct-Coupled Squirrel-Cage Induction

Motors ................................................................................................................14

9.17 Machine Sound (Medium Induction Motors)......................................................................15

9.17.1 General ................................................................................................................15

9.17.2 Sound Measurement............................................................................................15

9.17.3 Sound Power Levels of Polyphase Squirrel-Cage Induction Motors at No Load .15

9.17.4 Sound Power Levels of Polyphase Squirrel-Cage Induction Motors at Rated

Load ................................................................................................................15

Condensed MG 1-2011

Page iii

9.18 Number of Starts...............................................................................................................15

9.19 Thermal Protection of Medium Motors..............................................................................16

9.19.1 Winding Temperature...........................................................................................16

9.20 Overtemperature Protection of Medium Motors Not Meeting the Definition of “Thermally

Protected”..........................................................................................................................16

9.20.1 Type 1—Winding Running and Locked Rotor Overtemperature Protection ........16

9.20.2 Type 2—Winding Running Overtemperature Protection......................................17

9.20.3 Type 3—Winding Overtemperature Protection, Nonspecific Type.......................17

9.21 Efficiency...........................................................................................................................17

9.21.1 Determination of Motor Efficiency and Losses.....................................................17

9.21.2 Efficiency of Polyphase Squirrel-Cage Medium Motors with Continuous Ratings18

9.21.3 Efficiency Levels of Energy Efficient Polyphase Squirrel-Cage Induction Motors 18

9.21.4 Efficiency Levels of Premium Efficiency Electric Motors......................................18

9.21.5 Effects of Load on Motor Efficiency......................................................................18

10 APPLICATION DATA—AC SMALL AND MEDIUM MOTORS.....................................................19

10.1 Service Conditions.............................................................................................................19

11 APPLICATION CONSIDERATIONS FOR CONSTANT SPEED DESIGN A AND B INDUCTION

MOTORS USED ON A SINUSOIDAL BUS WITH HARMONIC CONTENT .................................19

11.1 Efficiency...........................................................................................................................19

11.2 Derating for Harmonic Content..........................................................................................19

11.2.1 Harmonic Voltage Factor (HVF) Defined .............................................................19

11.3 Power Factor Correction ...................................................................................................20

12 APPLICATION CONSIDERATIONS FOR GENERAL PURPOSE DESIGN a AND b

INDUCTION MOTORS USED WITH ADJUSTABLE-VOLTAGE OR ADJUSTABLE-

FREQUENCY CONTROLS OR BOTH..........................................................................................20

12.1 Torque...............................................................................................................................20

12.1.1 Motor Torque During Operation Below Base Speed............................................20

12.1.2 Torque Derating at Reduced Speeds...................................................................20

12.1.3 Motor Torque During Operation Above Base Speed............................................20

12.2 Current...............................................................................................................................21

12.2.1 Running Current...................................................................................................21

12.2.2 Starting Current....................................................................................................21

12.3 Efficiency...........................................................................................................................21

12.4 Maximum Safe Operating Speeds ....................................................................................21

12.5 Sound................................................................................................................................21

12.6 Resonances, Sound, Vibration..........................................................................................22

12.7 Voltage Stress...................................................................................................................22

12.8 Power Factor Correction ...................................................................................................22

12.9 Operation in Hazardous (Classified) Locations.................................................................22

Condensed MG 1-2011

Page 1

Foreword

In the preparation of this publication, input of users and other interested parties has been sought and

evaluated. Inquiries, comments, and proposed or recommended revisions should be submitted to the

concerned NEMA product Subdivision by contacting the:

Senior Technical Director, Operations

National Electrical Manufacturers Association

1300 North 17th Street, Suite 900

Rosslyn, VA 22209

This publication was developed by the Motors and Generators Section. Section approval of the document

does not necessarily imply that all section members voted for its approval or participated in its development.

At the time it was approved, the section was composed of the following members:

A.O. Smith Electrical Products Company—Tipp City, OH

Baldor Electric Company—Fort Smith, AR

Brook Crompton North America—Toronto, Canada

Cummins, Incorporated—Minneapolis, MN

Emerson Electric Company—St. Louis, MO

GE Industrial Systems—Fort Wayne, IN

Howell Electric Motors—Plainfield, NJ

Peerless-Winsmith, Incorporated—Warren, OH

RAM Industries—Leesport, PA

Regal-Beloit Corporation—Beloit, WI

Leeson Electric—Grafton, WI

Lincoln Electric—Cleveland, OH

Marathon Electric—Wausau, WI

SEW-Eurodrive, Incorporated—Lyman, SC

Siemens Energy & Automation, Incorporated—Norwood, OH

Sterling Electric, Incorporated—Irvine, CA

TECO-Westinghouse Motor Company—Round Rock, TX

The Imperial Electric Company—Akron, OH

Toshiba International Corporation—Houston, TX

WEG Electric Motor Corporation—Suwanee, GA

Condensed MG 1-2011

Page 2

1 PURPOSE

This is a condensation of the standards on motors included in NEMA Motors and Generators, MG 1-2011.

Some standards are reprinted in their entirety while others have been combined or abbreviated. The

numbers placed at the end of many of the paragraphs in this condensation (e.g. MG 1 Part 6) refer to the

complete standard in MG 1.

2 SCOPE

The standards in this guide cover alternating-current squirrel-cage motors up to and including the ratings

built in frames corresponding to the continuous open-type ratings given in Table 1.

3 DEFINITIONS

ambient temperature: The temperature of the surrounding air which comes into contact with the heated

parts of the apparatus. [MG 1-1.56]

capacitor motor: A single-phase induction motor with main winding arranged for direct connection to power

source and auxiliary winding connected in series with a capacitor. There are three types of capacitor motors:

capacitor start, in which capacitor phase is in circuit only during starting; permanent-split capacitor which has

the same capacitance for both starting and running; two-value capacitor motor in which there are different

values of effective capacitance for starting and running. [MG 1-1.20.3.3]

current:

locked-rotor current: The steady-state current taken from the line, with the rotor locked and with rated

voltage and rated frequency applied to the motor. [MG 1-1.53]

no-load current: The current flowing through a line terminal of a winding when rated voltage is applied at

a rated frequencywith no connected load. [MG 1-1.54]

design letters: Identifies specific performance requirements for starting and operating characteristics. See

Table 8. [MG 1-1.19.1]

dimensions: Dimension are indicated bythe NEMA letters given in Table 19. [MG 1-4.1]

dripproof motor: An open motor in which the ventilating openings are so constructed that successful

operation is not interfered with when drops of liquid or solid particles strike or enter the enclosure at any

angle from 0 to 15 degrees downward from the vertical. [MG 1-1.25.1]

dripproof guarded motor: A dripproof motor whose ventilating openings are guarded. [MG 1-1.25.5]

energy efficient polyphase squirrel-cage induction motor: An induction motor having an efficiency in

accordance with 9.21.3. [MG 1-1.41.2]

frame number: The frame number for small motors is the "D" dimension in inches multiplied by 16. The

frame number for medium motors consists of three or four digits. The first two digits are equal to four times

the "D" dimension in inches. When this product is not a whole number, the first two digits of the frame

number are the next higher whole number. The third and, when required, fourth digit of the frame number is

obtained from the value of the "2F" dimension in inches as shown in the columns headed 1 to 15, inclusive, in

the Table 13. [MG 1-4.2]

general-purpose motor: A squirrel-cage induction motor, rated 500 horsepower and less, open or enclosed

construction. It is designed in standard ratings with standard operating characteristics and mechanical

construction for use under usual service conditions without restriction to a particular application or type of

application. [MG 1-1.6]

guarded motor: An open motor in which all openings giving direct access to live metal or rotating parts

(except smooth rotating surfaces) are limited in size by the structural parts or by screens, baffles, grilles,

expanded metal, or other means to prevent accidental contact with hazardous parts. Openings giving direct

access to such live or rotating parts shall not permit the passage of a cylindrical rod 0.75 inch in diameter.

The openings in the motor enclosure shall be such that (1) a probe such as that illustrated in Figure 1, when

inserted through the openings, will not touch an uninsulated live metal part or a hazardous rotating part and

Condensed MG 1-2011

Page 3

(2) a probe such as that illustrated in Figure 1, when inserted through the openings, will not touch film coated

wire. [MG 1-1.25.4]

high-potential tests: High-potential tests are tests which consist of the application of a voltage higher

than the rated voltage for a specified time for the purpose of determining the adequacy against breakdown

of insulating materials and spacings under normal conditions. [MG 1 Part 3]

IC code: Acronym for "International Cooling.” See Clause 5, Methods of Cooling. [MG 1 Part 6]

IP code: Acronym for "International Protection." See Clause 4, Classification of Degrees of Protection.

[MG 1 Part 5]

medium (integral) motor: An alternating-current medium motor is (1) built in a three-or four-digit frame

series (or equivalent for motors without feet); and (2) having a continuous rating up to and including the

information in Table 2. [MG 1-1.4.1]

Premiumefficiency electric motor: A continuous rated, single-speed, polyphase, squirrel-cage induction

motor of 2, 4, or 6 pole design meeting the performance requirements of Design A or Design B and having

a nominal full load efficiency not less than that shown in 9.21.4. [MG 1-1.16]

open motor: One having ventilating openings which permit passage of external cooling air over and around

the windings of the motor. [MG 1-1.25]

service factor: A multiplier which, when applied to the rated horsepower, indicates a permissible horsepower

loading which may be carried under the conditions specified for the service factor. [MG 1-1.42]

small (fractional) motor: A small motor is either (1) built in a two digit frame number series (or equivalent for

motors without feet); or, (2) a motor built in a frame smaller than that frame of a medium motor which has a

continuous rating at 1700-1800 rpm of 1 horsepower; or, (3) a motor rated less than 1/3 horsepower and less

than 800 rpm. [MG 1-1.3]

squirrel-cage induction motor: An alternating-current motor composed of a primary winding connected to a

power source and a squirrel-cage secondary winding which carries induced current. [MG 1-1.18.1.1]

starting capacitance for a capacitor motor: The total effective capacitance in series with the starting

winding under locked-rotor conditions. [MG 1-1.58]

temperature tests: Tests taken to determine the temperature rise of certain parts of the motor above the

ambient temperature, when running under a specified load. [MG 1-1.55]

torque:

breakdown torque: The maximum torque developed by the motor with rated voltage applied at rated

frequency, without an abrupt drop in speed. [MG 1-1.50]

locked-rotor torque: The minimum torque developed by the motor at rest for all angular positions of the

rotor, with rated voltage applied at rated frequency. [MG 1-1.47]

pull-up torque: The minimum torque developed by the motor during the period of acceleration from rest

to the speed at which breakdown torque occurs. For motors which do not have a definite breakdown

torque, the pull-up torque is the minimum torque developed up to rated speed. [MG 1-1.48]

totally enclosed motor: A motor enclosed to prevent the free exchange of air between the inside and the

outside of the case but not sufficiently enclosed to be termed air-tight. [MG 1-1.26]

totally enclosed fan-cooled motor: A totally enclosed motor equipped for exterior cooling by means of a

fan or fans integral with the motor but external to the enclosing parts. [MG 1-1.26.2]

totally enclosed fan-cooled guarded motor: A totally enclosed fan-cooled motor in which all openings

giving direct access to the fan are limited in size by the design of the structural parts or by screens, grills,

expanded metal, etc. to prevent accidental contact with the fan. Such openings shall not permit the passage

of a cylindrical rod 0.75 inch in diameter, and a probe such as that shown in Figure 1 and Figure 2 shall not

contact the blades, spokes, or other irregular surfaces of the fan. [MG 1-1.26.3]

totally enclosed nonventilated motor: A totally enclosed motor which is not equipped for cooling by means

external to the enclosing parts. [MG 1-1.26.1]

Condensed MG 1-2011

Page 4

voltage unbalance: The voltage unbalance in percent may be defined as follows:

percent voltage unbalance = 100 x maximum voltage deviation from average voltage average voltage

Example—With voltages of 460, 467, and 450, the average is 459, the maximum deviation from average is

9, and the percent unbalance = 100 x 9/459 = 1.96 percent. [MG 1-14.36.2]

4 CLASSIFICATION OF DEGREES OF PROTECTION PROVIDED FOR ENCLOSURES

FOR ROTATING MOTORS

The designation used for the degree of protection consists of the letters IP followed by two characteristic

numerals signifying conformity with the conditions indicated in Table 3. [MG 1-5.2]

4.1 Single Characteristic Numeral

When it is required to indicate degree of protection by only one characteristic numeral, the omitted

numeral shall be replaced by the letter X. For example, IPX5 or IP2X. [MG 1-5.2.1]

4.2 Supplementary Letters

Additional information may be indicated by a supplementary letter following the second characteristic

numeral. If more than one letter is used, the alphabetic sequence shall apply. [MG 1-5.2.2]

4.3 Letters Following Numerals

In special application (such as motors with open circuit cooling for ship deck installation with air inlet and

outlet openings closed during standstill) numerals may be followed by a letter indicating whether the

protection against harmful effects due to ingress of water was verified or tested for the machine not

running (letter S) or the machine running (letter M). In this case the degree of protection in either state of

the machine shall be indicated, for example IP55S/IP20M. The absence of the letters S and M shall imply

that the intended degree of protection will be provided under all normal conditions of use. [MG 1-5.2.2.1]

4.4 Letters Placed Immediately After the Letters IP

For open internally air-cooled motors suitable under specific weather conditions and provided with

additional protective features or processes, such as those required for open water-protected motors, the

letter W may be used. [MG 1-5.2.2.2]

Example of Designation

Characteristic letters

1st characteristic numeral

(see Table 3)

2nd characteristic numeral

(see Table 3)

4.5 Degrees of Protection—First Characteristic Numeral

The first characteristic numeral indicates the degree of protection provided by the enclosure with respect

to persons and also to the parts of the machine inside the enclosure. Table 3 gives brief details of objects

which will be excluded from the enclosure for each of the degrees of protection represented by the first

characteristic numeral. [MG 1-5.3.1]

The term “excluded” implies that a part of the body, or a tool or wire held by a person, either will not enter

the machine or, if it enters, that adequate clearance will be maintained between it and the live or

dangerous moving parts (smooth rotating shafts and the like are not considered dangerous). Table 3 also

indicates the minimum size of foreign objects which will be excluded. [MG 1-5.3.1]

Compliance of an enclosure with an indicated degree of protection implies that the enclosure will also

comply with all lower degrees of protection. In consequence, the tests establishing these lower degrees of

protection are not required, except in cases of doubt. [MG 1-5.3.2]

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