nema three phase ac horizontal motor home study course · nema three phase ac horizontal motor home...

NEMA THREE PHASEAC HORIZONTAL MOTORHOME STUDY COURSE

U.S. ELECTRICAL MOTORSDIVISION OF EMERSON ELECTRIC CO.

NEMA THREE PHASE AC HORIZONTAL MOTORHOME STUDY COURSE

TABLE OF CONTENTS

Introduction ................................................................................................................................. 1

Chapter 1- AC Motor Fundamentals

Electromagnetism........................................................................................................................................... 1

AC Motor Components ................................................................................................................................... 4

Principles of Operation ................................................................................................................................... 5

AC Motor Fundamentals - Quiz ....................................................................................................................... 6

Chapter 2 - The Nameplate

Industry Standards ......................................................................................................................................... 7

Nameplate Data .............................................................................................................................................. 7

Load Considerations ...................................................................................................................................... 14

Additional Motor Data .................................................................................................................................... 17

The Nameplate - Quiz .................................................................................................................................... 27

Chapter 3 - Application Considerations

Variable Frequency ........................................................................................................................................ 28

Environmental Considerations ........................................................................................................................ 31

Efficiency and Energy Legislation .................................................................................................................. 32

Starting Methods ........................................................................................................................................... 35

Application Considerations - Quiz ................................................................................................................... 40

Chapter 4 - Product Offering

Standard and Premium Efficient Open Dripproof Motors .................................................................................. 42

Standard and Premium Efficient Totally Enclosed Motors ................................................................................ 43

Hostile Environment Motors ........................................................................................................................... 44

841 Plus ........................................................................................................................................................ 45

Explosionproof Motors ................................................................................................................................... 45

“C” Face and Pump Motors............................................................................................................................. 48

Special Purpose Motors ................................................................................................................................. 48

U.S. Motors’ Product Offering - Quiz ............................................................................................................... 52

General Formulas and Conversion Tables ................................................................................ 53

Quiz Answers ............................................................................................................................ 57

Glossary .................................................................................................................................... 61



1

INTRODUCTION

Approximately 90% of all industrial applications use three phase induction motors. Why? The standard utility service isthree phase, 60 hertz. It is the most practical motor for uses requiring over five horsepower. Special mechanical or electricalfeatures for unusual conditions can be readily incorporated into a three phase induction motor. The three phase inductionmotor is simpler, more rugged, more easily maintained and less expensive than any other motor type. It is truly the workhorseof the industry!

The purpose of this home study guide is to familiarize you with AC motor fundamentals, motor terminology and the U.S.Motors product offering. AC motors are used all over the world in residential, commercial, industrial and utility applications,and U.S. Electrical Motors manufactures a wide variety of these motors for a wide variety of applications.

You will find a brief quiz at the end of each section in the course - we urge you to take a few minutes to answer the questionsbefore moving to the next section. A thorough understanding of this material will give you the ability to select and price theright AC motor for you or your customer’s application.

We hope that you find the format of this course user-friendly; it has been designed to provide you with simple, straightforwardanswers to your AC motors questions.

ELECTROMAGNETISM

About three thousand years ago, an unusual mineral was discovered in Asia Minor. The mineral had the ability to attract ironobjects. It was the first known magnetic material. Man-made magnets were put to practical use in about the twelfth century,but the connection between magnets and electricity was not made until the mid-1800’s. This discovery led to the inventionof the first electric motor in 1887 by John Tesla.

A substance is called a magnet if it has the property of attracting materials, such as iron. Magnets are comprised of twopoles: a north pole and a south pole. These poles represent the points of maximum attraction. In the case of a bar shapedmagnet, the strongest magnetic effect is produced at each end. Magnets not only have south poles and north poles, butthey also have magnetic lines of force, often called magnetic flux.



2

The most basic law of magnetic force is that unlike poles attract each other, and like poles repel. Two important considerationsapply to magnetism:

1. Every magnetic object creates a magnetic field that can affect other magnetic objects.

2. Every magnetic object can be acted upon by the magnetic field of another object.

The following diagram shows a device that demonstrates how magnetic fields can transmit mechanical torque withoutmaking contact. A change in cranking speed would produce a change in output speed.

Magnetic fields are important because of the relationship between magnetism and electricity. A moving charge produces amagnetic field and a magnetic field exerts force on a moving charge. These two parts of the relationship between magnetismand electricity have a great practical value. They form the basis for understanding motors, generators and many otherelectrical devices.

Every moving electrical charge produces a magnetic field. The charge may be moving along a conductor, or it may bemoving through a vacuum. The strength of the magnetic field depends on the speed and the strength of the charge.

One of the most important magnetic devices using electricity is the electromagnet. An electromagnet consists of a coil ofwire that carries an electric current. Electromagnets are the same as permanent magnets, except they only have magneticproperties when electrical power is applied to the coil.

As the example below shows, the paper clips will cling to the bar of metal when electrical power is applied. When electricalpower is removed, the bar of metal no longer has magnetic properties and the paper clips fall.



3

One other important feature of the electromagnet is its ability to change magnetic polarity due to a change in the direction ofelectric current flow through the coil. A reversal of magnetic poles brought about by a reversal of connections to the batteryterminals is shown below.

In the majority of alternating current (AC) motors, the realignment of the magnetic poles takes place due to the normal voltagereversals of the AC power. Alternating current, as the name implies, is continuously reversing at a rate determined by itsfrequency. The figure below shows an example of how AC current changes with time.

SINGLE PHASE

The figure shown above is a “single phase” current. However, if we mounted three coils of wire about the shaft equaldistances apart, each coil would produce an alternating current. This would then be “three phase” or “polyphase” current. Butsince the coils are equally spaced around the “circle of rotation”, each coil will have a different amount of current at a particularmoment.



4

THREE PHASE

The stator currents that flow in the three phases of a 3-phase motor are identical to each other. They have the samemagnitude and lag their respective phase voltages by the same angle. The phase voltages are 120 electrical degrees apart,the 3-phase currents are also 120 electrical degrees apart.

AC MOTOR COMPONENTS

Two major assemblies make up an AC motor: the rotor and the stator. The rotor is made up of the shaft, rotor core (a stackof steel laminations that form slots and aluminum conductors and end rings formed by either a die cast or fabricationprocess) and sometimes a fan. This is the rotating part of the electromagnetic circuit. A fabricated rotor core with air ductsis shown here.

The other major part is the stator. The stator is formed from thin steel laminations stacked and fastened together so that thenotches (called slots) form a continuous lengthwise slot on the inside diameter.



5

Insulation is inserted to line the slots, and then coils wound with many turns of wire are inserted into the slots to form a circuit.Each grouping of coils, together with the steel core it surrounds, form an electromagnet. Electromagnetism is the principlebehind motor operation. The stator windings are connected directly to the power source.

To explain the relationship of the coils we can use an example of six coils, two coils for each of the three phases. The coilsoperate in pairs. The coils are wrapped around the iron material of the stator. These coils are referred to as motor windings.Each motor winding becomes a separate electromagnet. The coils are wound in such a way that when current flows in themone coil is a north pole and its pair is a south pole.

The stator is connected to a 3-phase AC power supply. Each of the pairs of coils are connected to the three phases of thepower supply. The three phase windings are placed 120 degrees apart.

PRINCIPLES OF OPERATION

A motor is a device that converts electrical energy into mechanical energy. It is also known as a torque producing device.Torque is defined as a turning or twisting force supplied by a drive to the load. The induction motor derives its name from thefact that the rotor is not connected electrically to the source of power supply. The currents that circulate in the rotorconductors are not produced directly by the voltage of the power supply. They result from the voltage being induced in therotor by the magnetic field of the stator.

For its operation, the induction motor depends on a rotating magnetic field. This field is set up by the current flowing in thestator windings. The magnetic field, rotating around the outer surface of the stator, cuts across the conductors embedded inthe rotor and induces voltages in the conductors. The voltages induced in the rotor windings (squirrel cage) cause currentsto flow in the rotor conductors. The current-carrying conductors are then exposed to a magnetic field. This causes a repellingforce between the conductors and the field, and produces a torque that causes the rotor to turn.



6

AC MOTOR FUNDAMENTALS - QUIZ

1. The most basic law of magnetic force is that unlike poles attract and like poles repel each other.True _____ False _____

2. What is the main difference between a permanent magnet and an electromagnet?

3. What is the difference between single phase and three phase alternating current?

4. What are the two major components of an AC motor?

5. High electrical currents produced by the stator do not produce any magnetic field in the rotor. True_____ False _____

6. An electromagnet has the ability to change magnetic polarity due to a change in the direction ofelectric current flow through the coil. True _____ False _____

7. Alternating current is continuously reversing (changing polarity) at a rate determined by its frequency.True _____ False _____

8. In three phase alternating current, each winding produces an alternating current of the same amountat any given moment. True _____ False _____

9. Explain what is meant by an “induction” motor.



7

INDUSTRY STANDARDS

Motor development began in the 1800’s with Oersted and Faraday’s research on magnetism, and Sturgeon’s development ofthe electromagnet in 1825. Davenport received the first patent on an electric motor in 1837. By 1890, AC generating stationscame into being, but many diverse routes were being taken at this time. Edison was working in his Pear Street station - onDC. The city of Manhattan was on DC, Niagara Falls was generating at 25 cycles, California at 50 cycles, and Philadelphiawas utilizing two phase power.

Because of this, a number of organizations were established to standardize the motor industry. Many of today’s motorstandards have been established through organizations such as the National Electrical Manufacturers’ Association (NEMA).NEMA will be referred to frequently in this course; they have established standards for a wide range of electrical products,including motors. NEMA is primarily associated with motors used in North America. The standards developed representgeneral industry practices and are supported by the motor manufacturers. These standards can be found in NEMA StandardPublication No. MG-1.

IEEE is another agency that has established electrical standards and recommended practices for the motor industry.International standards exist as well, with organizations such as the International Electrotechnical Commission (IEC), theCanadian Standards Association (CSA), the Japanese Standards (JEC), the British Standards (BS) and at least one organizationfor each country that exists.

IEC is the organization responsible for motor standards in the European community. These standards differ from NEMAstandards, and can be found in IEC 34-1-16. These motors are referred to as IEC motors. This course will limit itself to NEMAstandards.

Underwriters’ Laboratories (UL) is an independent testing organization that sets standards for motors and other electricalequipment. The National Fire Protection Association, which sponsors the National Electrical Code (NEC) is used by insuranceinspectors and many government bodies regulating building codes.

These regulating agencies assist in the proper selection and application of motors. Standards established include definitions,ratings, dimensions, tests and performance, application data and safety.

NAMEPLATE DATA

As a basic requirement of the National Electrical Code (NEC), the induction motor nameplate must show eight specificitems, including the manufacturer’s name; rated volts and full load amps; rated frequency and number of phases; rated fullload speed; rated temperature; time rating; rated horsepower and locked rotor indicating code letter.



8

Additional information will normally appear on most nameplates as well. This information might include the motor servicefactor, enclosure type, the frame size, connection diagrams and unique or special features. The best way to approach a basicunderstanding of what standardization means and to cover some of the material fundamental to standard induction motors isto examine in detail the nameplate information contained on a typical motor.

Manufacturer’s Name.

You will also note that we have logos of additional agencies shown on the nameplate, including the UL recognition label, the‘CE’ mark for sales to the European Community and the Canadian Standards Association logo.

Rated Volts and Full Load Amps.

Each AC motor is designed for optimum performance with a specific line voltage applied. The most frequently used domesticvoltages for three phase systems are 230 and 460. Motors rated for these voltages will operate within the limits establishedby NEMA at rated voltage.

Since line voltage is apt to vary over a period of time due to power system load conditions, the motor must be designed tocope with some voltage variations. Standard induction motors are designed to tolerate voltage variations plus or minus10%. Thus, a motor with a nameplate voltage rating of 230 could be expected to give satisfactory but not necessarily idealperformance when supplied with power ranging from a low value of 207 to a high extreme of 253 volts.

Rated Frequency and Number of Phases

This indicates the frequency for which the motor is designed in hertz (cycles per second). 60 Hertz power is utilizedthroughout the United States and Canada, as well as a few other countries. Motors are designed to tolerate a frequencyvariance of plus or minus 5%, and a motor should be able to handle both voltage and frequency variations at the same time.

In most industrial and commercial installations, the power systems, and consequently the induction motors, will either besingle phase or three phase. The cost effectiveness and efficiency of the three phase induction motor makes it the natural

s

s



9

choice for all requirements where three phase power is available.

Single phase motors may be used on fractional horsepower requirements (less than one horsepower) and in applicationssuch as agricultural installations, where three phase power is not available (usually through a maximum horsepower ratingof 10 HP).

Following are graphs showing the sine wave for both single and three phase alternating current. Alternating current isdefined as the flow of electrons which periodically changes in amount and direction. The single phase graph shows how ACcurrent changes with time. Most generators produce three separate current flows, all superimposed on the same circuit. Athree phase power system is built around a set of three equal AC voltages, each produced by a separate set of windingswithin an electric generator. Those windings are displaced by 120 electrical degrees within the generator so that thesinusoidal voltage produced by each is physically displaced by one-third of a cycle from each of the other two.

SINGLE PHASE

THREE PHASE

Rated Full Load Speed

The rated full load speed, or rpm (revolutions per minute) of a motor is the speed at which the motor will operate under fulltorque conditions when applied voltage and frequency are held constant at the rated values. On standard induction motors,the full load speed, or actual speed, will normally be between 95 and 99% of synchronous speed. This is also known as slip.

s



10

Synchronous speed is the theoretical speed of a motor based on the rotating magnetic field. The formula for obtainingsynchronous speed is

S = 120 x F where S = synchronous speed in revolutions per minute — — — F = frequency in hertz P P = number of poles in the motor

The number of poles and the speed of an induction motor are used interchangeably. If you know one, you can determine theother with the formula shown above. Standard rpms are as follows:

TYPICALACTUAL SYNCHRONOUS NUMBERSPEED SPEED OF POLES 3530 3600 2 1750 1800 4 1175 1200 6 880 900 8

Rated Temperature Rise Or The InsulationSystem Class and Rated Ambient Temperature

One of the most critical items relating to the life of any type of electrical equipment (ranging from televisions to giant powergenerators) is the maximum temperature that occurs at the hottest point within the unit and the length of time that the hightemperature is allowed to exist. The maximum allowable safe operating temperature occurring at the hottest spot within amotor is determined by:

1. The temperature of the air surrounding the motor. This is the ambient temperature. Motors are rated using a 40°Cambient (104°F).

2. The heat created within the motor due to its operation at a fully loaded condition. This is the temperature rise.

3. The thermal capability of all the insulating materials used within the motor. For simplicity, these materials have beenbroken into classes A, B, F and H.

This standard 20,000 hour life temperature class is based on ambient plus the heat created within the motor during operation.Please keep in mind that motors are designed to withstand some very high temperatures. As an example, Class B is ratedat 130°C, which is 266°F, or 54 degrees above the boiling point of water. Motors have been designed to withstand this typeof heat.

s

s



11

Insulating materials prevent metal to metal contact or interaction of phase to phase shorts. This is also known as dielectricstrength - it limits the effects of voltage variations. Insulation System Classes are as follows:

CLASS 20,000 HOUR LIFE TEMPERATURE

A 105°C B 130°C F 155°C H 180°C

Time Rating

General purpose motors will be rated for continuous duty. When motors are to be utilized for specific, well-defined applicationswhere they will be operating for short periods of time, it is possible to reduce their size, weight and cost by loading them tohigher torques than would be possible if they were to operate continuously. As an example, garbage disposals are normallyrated for 15 minutes, since they would rarely operate for a longer period of time. The standard time ratings are 5 minutes, 15minutes, 30 minutes, 60 minutes and continuous.

Rated Horsepower

This represents the rated horsepower output when the motor is loaded to rated torque at rated speed. NEMA has establishedstandard horsepower ratings, from fractional through thousands of horsepower. The standard horsepower ratings from 1through 4000 are shown below. When application horsepower requirements fall between two standardized values, thelarger size is usually chosen. This adds a margin of safety that will reduce the motor’s operating temperature rise andextend the operating life of the motor.

STANDARD HORSEPOWER RATINGS 1 THRU 4000 HP

1 30 300 12501-1/2 40 350 1500 2 50 400 1750 3 60 450 2000 5 75 500 2250

7-1/2 100 600 2500 10 125 700 3000 15 150 800 3500 20 200 900 4000 25 250 1000

s

s



12

The illustration below shows how the term horsepower came about. The work capacity of a horse was used to define thepower of an electric motor. It was determined that a horse could lift 1000 pounds, thirty-three feet, in one minute. It is theamount of work done in a given amount of time.

From this, our formula for horsepower is

HP =FOOT POUNDS PER MINUTE

FOOT POUNDS PER SECOND

-OR-

550

33,000

HP =



13

AC motors used in North America are generally rated in horsepower. Equipment manufacturing in Europe is generally ratedin kilowatts (KW). Horsepower can be converted to kilowatts with the following formula:

KW = .746 x HP

Kilowatts can be converted to horsepower with this formula:

HP = 1.341 x KW

The relationship between horsepower and torque should also be noted here. Torque is the turning or twisting force supplied bya drive to the load. Units of measure are inch pounds or foot pounds. Torque and horsepower are related to each other by abasic formula that states:

The following graph shows the relationship between horsepower and torque. With only speed as the variable, you will notethat a one horsepower, 600 RPM motor would have approximately the same output torque as a three horsepower, 1800RPM motor.



14

LOAD CONSIDERATIONS

Note that only after the load has been started and adequate torque is available to run the load, does speed become a factor.There are three basic load types, and these types are classified by the relationship of horsepower and speed. Constanttorque applications are those that have the same torque at all operating speeds, and horsepower varies directly with thespeed. About 90% of all applications, other than pumps, are constant torque loads. Examples of this type include conveyors,hoisting loads, surface winding machines, positive displacement pumps and piston and screw compressors.

Constant horsepower applications have higher values of torque at lower speeds, and lower values of torque at higherspeeds. Examples include lathes, milling machines, drill presses and center winders.



15

The drills in the diagram below are an example of a constant horsepower application. When a larger hole is being drilled, thedrill is operating at low speed, but it requires a very high torque to turn the large drill in the material. When a small hole is beingdrilled, the drill is operated at a high speed, but it requires a very low torque to run the small drill in the material.

Spring coilers, punch presses and eyeletting presses will frequently have torque requirements falling somewhere between thecharacteristics of constant horsepower and constant torque. A general test for deciding if a machine might require constanthorsepower would be to study the machine output. When a machine is designed to produce a fixed number of pounds perhour regardless of whether it is making small parts at high speed, or large parts at a lower speed, the drive requirement is aptto be constant horsepower.

The last basic load type is variable torque. The torque required varies as the square of its speed, and horsepower requirementsincrease as the cube of the speed. Examples include centrifugal pumps, turbine pumps, centrifugal blowers, fans andcentrifugal compressors.



16

And a discussion of load types would not be complete without including information on high inertia loads. A load is consideredto be ‘high inertia’ when the reflected inertia at the motor shaft is greater than five times the motor rotor inertia. Inertia is thetendency of an object that is at rest to stay at rest or an object that is moving to keep moving.

We tend to think of flywheels as having high inertia; but, many other types of motor driven equipment, such as large fans,centrifuges, extractors, hammer mills and some types of machine tools, have inertias that have to be identified and analyzedin order to produce satisfactory applications.

The high inertia aspect of a load generally only becomes a problem during acceleration. For example, if a standard motoris applied to a large high inertia blower, there is a possibility that the motor could be damaged or fail completely on its firstattempt to start. This failure could occur even though the motor might have more than adequate torque and horsepowercapacity to drive the load after it reaches the required running speed. A good example of high inertia that most of us arefamiliar with would be a ferris wheel or a large fan.

In most cases, equipment manufacturers will be able to provide the typical inertia values for a given application. Generalguidelines on the inertias that standard motors can safely accelerate are given in MG1-14.40.

Locked Rotor Indicating Code Letter

When AC motors are started with full voltage applied, they draw line currents substantially greater than their full load runningcurrent rating. The magnitude of the so-called inrush current is a function of motor horsepower and the design characteristicsof the motor.

In order to define the inrush characteristics and present them in a simplified form, a series of code letters group motorsdepending on the range of inrush in terms of kilovolt amperes. By using the kilovolt ampere basis, a simple letter can beused to define both the low voltage and high voltage inrush values on dual voltage motors. The electrician installing the motoruses this information to properly size the starter for the motor. Following is a listing of the code letter designations.

s



17

To determine the across the line starting inrush amperes from the code letter designation, the code letter value, horsepowerand rated operating voltage are inserted in the appropriate equation. The equation to be used is determined by whether themotor is single or three phase. The following simplified equations will give approximate results for three phase motors ratedfor 200, 230 or 460 volts:

200 Volts LRA = Code letter value x HP x 2.9230 Volts LRA = Code letter value x HP x 2.5460 Volts LRA = Code letter value x HP x 1.25

Generally, standard motors of 15 HP or larger will have code letters of G or lower; 10 HP and smaller motors will have codeletters of H or higher.

ADDITIONAL MOTOR DATA

We have now covered all of the required data on a nameplate. But, as you have probably noticed, much more information isgenerally provided by the motor manufacturer.

Motor Service Factor (SF)

NEMA defines service factor as a multiplier, when applied to the rated horsepower, indicates a permissible horsepowerloading, which may be carried under the conditions specified for the service factor at rated voltage and frequency. Thisservice factor can be used for the following:

1. To accommodate inaccuracy in predicting intermittent system horsepower needs.

2. To lengthen insulation life by lowering the winding temperature at rated load.

3. To handle intermittent or occasional overloads.

4. To allow occasionally for ambients above 40°C.

5. To compensate for low or unbalanced supply voltages.

NEMA does add some cautions, however, when discussing service factor:

1. Operation at service factor load will usually reduce the motor speed, life and efficiency.

2. Do not rely on the service factor capability to carry the load on a continuous basis.

3. The service factor was established for operation at rated voltage, frequency, ambient and sea level conditions.

s



18

Enclosure Type

The enclosure of the motor must protect the windings, bearings, and other mechanical parts from moisture, chemicals,mechanical damage and abrasion from grit. NEMA standards MG1-1.25 through 1.27 define more than 20 types of enclosuresunder the categories of open machines, totally enclosed machines, and machines with encapsulated or sealed windings.The most commonly used motor enclosures are open dripproof, totally enclosed fan cooled and explosionproof.

Open Dripproof. The open dripproof motor (ODP) has a free exchange of air with the ambient. Drops of liquid or solidparticles do not interfere with the operation at any angle from 0 to 15 degrees downward from the vertical. The openings areintake and exhaust ports to accommodate interchange of air. The open dripproof motor is designed for indoor use where theair is fairly clean and where there is little danger of splashing liquid.

Totally Enclosed Fan Cooled (TEFC). This type of enclosure prevents the free exchange of air between the inside andoutside of the frame, but does not make the frame completely airtight. A fan is attached to the shaft and pushes air over theframe during its operation to help in the cooling process. The ribbed frame is designed to increase the surface area for coolingpurposes. There is also a totally enclosed non-ventilated (TENV) design which does not use a fan, but is used in situationswhere air is being blown over the motor shell for cooling, such as in a propeller fan application.

The TEFC style enclosure is the most versatile of all. It is used on pumps, fans, compressors, general industrial belt driveand direct connected equipment. The footless “C” face type is used as an input to speed reducers for material handlingequipment, and the multispeed version can be used on fans, blowers and machine tools. Conversion to brake motors areused on conveyors, speed reducers and other equipment requiring quick stops. Special protection can be added to the TEFCmotor to help it withstand hostile environments such as chemical and pulp and paper applications.

s



19

Explosionproof. The explosionproof motor is a totally enclosed machine and is designed to withstand an explosion ofspecified gas or vapor inside the motor casing and prevent the ignition outside the motor by sparks, flashing or explosion.These motors are designed for specific hazardous purposes, such as atmospheres containing gases or hazardous dusts.For safe operation, the maximum motor operating temperature must be below the ignition temperature of surrounding gasesor vapors. Explosionproof motors are designed, manufactured and tested under the rigid requirements of the UnderwritersLaboratories.

Hazardous location motor applications are classified by the type of hazardous environment present, the characteristics of thespecific material creating the hazard, the probability of exposure to the environment, and the maximum temperature level thatis considered safe for the substance creating the hazard. The format used to define this information is a class, group,division and temperature code structure.

Efficiency

Efficiency is defined as the ratio of the power output divided by the power input. Machine losses are in the form of heat, andinclude stator winding loss, rotor loss, core loss (hysteresis and eddy current), friction and windage, and stray load loss.

NEMA standard MG1-12.54.2 provides instructions for establishing the value of efficiency. The standard states that thenominal efficiency shown on the nameplate shall not be greater than the average efficiency of a large population of motorsof the same design. And, the full load efficiency, when operating at rated voltage and frequency, shall not be less thanthe minimum value associated with the nominal value.

Care should be taken in comparing efficiencies from one motor manufacturer to another. It is difficult to compare efficienciesbased on published, quoted or test data, due to the fact that there is no single standard method which is used throughout theindustry. The most common referred to standards are IEEE 112 (U.S.), IEC (International), JEC-27 (Japanese), BS-269(British) and ANSI C50.20 (same as IEEE 112). IEEE 112 is used more than any of the others in the United States. However,even it allows for a variety of test methods to be used. The preferred procedure is IEEE method B, where the motor isoperated at full load, and the power is directly measured.

s



20

Frame Size. Motor frame dimensions have been standardized with a uniform frame size numbering system. This systemwas developed by NEMA and specific frame sizes have been assigned to standard motor ratings based on enclosure,horsepower and speed.

The current standardized frames for integral horsepower induction motors ranges from 143T to 445T. These standards covermost motors in the range of one through two hundred horsepower.

The numbers used to designate frame sizes have specific meanings based on the physical size of the motor. The first twodigits are related to the motor shaft height and the remaining digit or digits relate to the length of the motor.

As a rule of thumb, you can calculate the shaft height on horizontal motors in inches, (“D” dimension), by dividing the first twodigits of the frame size by four. Please note that this works on all foot-mounted NEMA frame motors in 143T through 445Tframes.

The third digit of the frame size is related to the length of the motor but there is no rule of thumb that can be easily applied.It is important to note that when standard foot-mounted motors have frame sizes that differ only in the third digit, the shaftdiameters, shaft lengths, and distance from the end of the shaft to the bolt holes in the feet on the shaft end of the motor willbe the same.

The length difference in the examples above occur between the feet as shown by dimensions A and B. The suffix T indicatesthat the motor frame assignment conforms to the current, or so called “T” frame “Nu-Rate” standards which were adopted in1964.

Between 1954 and 1964, a different set of standard frame assignments were utilized. In many automotive manufacturing andsome process industries, there is still a preference for the “U” frame motors. The “U” frame motor is substantially larger andheavier than an equivalent “T” frame motor.

Prior to 1954, a third set of NEMA standard frame sizes existed. The table which follows shows the various NEMA frameassignments for totally enclosed motors based on speed and horsepower for the original (pre-1952), “U” frame (1952-1964)and “T” frame (current) standards.

s



21

TOTALLY ENCLOSED

The rerate, or frame size reduction programs were brought about by advancements in motor technology relating mainly tohigher temperature ratings of insulating materials, improved magnetic steels and improved bearings. At the present time,NEMA frame assignments do no exist for motors larger than 445T and each manufacturer may have different frame designationsfor these motors.

One additional suffix that may be used on standard motors in frames 284T and larger is an “S” inserted after the “T”. This “S”stands for short shaft. These motors are arranged to be directly coupled to loads, such as the centrifugal pump shown below.

In addition to having a short shaft, the motor will have a small diameter shaft (“U” dimension) and the bearing in the drive shaftend of the motor will be somewhat smaller than the equivalent long shaft motor. Short shaft motors are intended for use onlyon direct coupled centrifugal pumps and other direct coupled loads where there will not be a side pull (overhung load) exertedon the shaft by “V” belts.



22

Manufacturer’s Identification Number. This model and/or catalog number is used to establish motor identity and age forreplacement parts and warranty.

NEMA Design Letter

Changes in motor windings and rotor design will alter the performance characteristics of induction motors. Motors aredesigned with certain speed torque characteristics to match the speed torque requirements of the various loads. To obtainsome uniformity in application, NEMA has designated specific designs of general purpose motors having specified lockedrotor torque, breakdown torque, slip, starting current, or other values. The following graph shows the relationship betweenspeed and torque that the motor produces from the moment of start until the motor reaches full load torque at rated speed.

Locked rotor torque, or starting torque, is developed when the rotor is held at rest with the rated voltage and frequencyapplied. This condition occurs each time a motor is started. When rated voltage and frequency are applied to the stator, thereis a brief amount of time before the rotor turns. At this instant, a NEMA B motor develops approximately 150% of its full loadtorque.

The magnetic attraction of the rotating magnetic field will cause the rotor to accelerate. As the motor picks up speed, torquedecreases slightly until it reaches pull up torque. As the speed increases the torque increases until it reaches it’s maximumat about 200%. This is called breakdown, pullout or stall torque.

Torque decreases rapidly as speed increases beyond breakdown torque until it reaches full-load torque at a speed slightlyless than 100% of synchronous speed. Full load torque is the torque developed when the motor is operating with ratedvoltage, frequency and load. The speed at which full-load torque is produced is the slip speed or rated speed of the motor.

ss

s



23

Minimum acceptable values for different motor designs have been established and are identified by the letters A, B, C andD. The general shapes of the four typical torque-speed characteristics are shown here.

NEMA Design B motors have normal starting torque, with low starting current. These are the most widely used design, andhave locked rotor torques adequate for starting a wide variety of industrial machines and locked rotor starting currentsacceptable to most power systems. Some Design B applications would include machine tools, fans and blowers, compressors,chippers, and centrifugal pumps.

Design A motors have normal starting torque and high starting current. Typical applications would include equipment havingbrief heavy overloads, such as an injection molding machine.

NEMA Design C motors have high starting torque (approximately 225%) and low starting current. These motors have highlocked rotor torque and relatively high full load slip. They are especially suited for starting heavy loads such as reciprocatingcompressors, stokers, crushers and pulverizes, as well as positive displacement pumps.

Design D motors have high starting torque and low starting current, but with high slip. At no load the motor operates with littleslip. When peak load is applied the motor slip increases appreciably, allowing the unit to absorb the energy. This reducespower peaks supplied by the electrical system, resulting in a more uniform power requirement. These motors may beused on applications like a low speed punch press with a heavy flywheel, or hoisting applications.

Bearing Part Numbers. The bearing part numbers on U.S. Motors’ machines are made conveniently available on the nameplateso that, when required, procurement of replacement bearings can be carried out prior to motor disassembly.

s

s



24

Connection Diagrams. Connection diagrams can be found on the nameplate of some motors, or the diagrams may belocated inside the motor conduit box or on a special connection plate.

Unique or Special Features. This information could include special features such as refined balance, special insulationtreatments, space heaters, internal motor overheat protection, or any one of many other special construction features.

Obviously, information such as horsepower, speed, voltage and frequency are very important in determining the right motorfor your customer’s needs. However, after getting all the information on a motor requirement, if you don’t ask your customerabout the assembly position required, the motor you choose may be unusable. The standard assembly positions are:

And, what about the connection to the load? It could be direct connected by a coupling, a clutch or a spline. In this case, goodalignment is important, and this type of connection imposes a small load on the bearings.



25

It might be belt, chain, or gear drive connected to the load. This configuration imposes a radial load on the motor bearingsreferred to as overhung load. Good alignment and proper belt and chain tensions are important. Gear drives may also imposeaxial or thrust load on the motor bearings.

Perhaps your customer requires a face or flange connection. The male motor register is aligned with the female register of theload such as a gear drive or a pump. The shaft of the motor might even carry a pinion, a pump impeller or a blower.



26

And what about mounting? The most common type of mounting is the horizontal, rigid foot mounting. This configuration issuitable for any of the connections shown above, and the motor can be mounted on a solid foundation, adjustable bases orslide rails.

A NEMA C-Face end shield mounting, either footed or footless, can be used. The C-face has a male register with tappedmounting holes that attaches directly to the driven equipment.

Using a NEMA “D” flange end shield mounting is another method. Generally, this is the same as a C-face except mountingholes are thru-holes as opposed to tapped holes.



27

THE NAMEPLATE - QUIZ

1. What is the major purpose of organizations such as NEMA?

2. Rated Frequency and Number of Phases, Rated Volts and Full Load Amps and the ServiceFactor of a motor are all required nameplate data according to NEC. True _____ False _____

3. Induction motors are synchronous units. True _____ False _____

4. The standard temperature life of a motor is based on the ambient plus the heat created within themotor during operation. True _____ False _____

5. Explain how torque and horsepower are related.

6. What is the locked rotor indicating code letter used for?

7. Define efficiency.

8. The shaft height of a motor can be determined from the first two digits of the frame size.True _____ False _____

9. “U” frame motors are still in use today. True _____ False _____

10. What letter designates the superstandard and most widely used NEMA design?



28

VARIABLE FREQUENCY

The AC induction motor is normally a fixed speed device because the utility power is a fixed frequency supply. AC adjustablespeed drives eliminate this restriction because they are able to change the supply frequency to the motor. If we look back tothe previous chapter, we find that motor speed is a function of the number of poles (which is a constant once the motor ismanufactured) and the supply frequency.

If we accept the fact that the drive does change the supply frequency, then we can plug some values into the motor formulafor speed and see the results.

120 x frequencyMotor Speed =

# poles

120 x 601800 =

4

This represents the speed of a four pole motor. Now, let’s change the frequency to 30 . . . .

120 x 30900 =

4

and, 10 hertz . . . .

120 x 60300 =

4

Now you can see how a previously constant speed motor can operate at more than one speed, if the frequency can bechanged. An inverter, ASD, VFD, AFC, Adjustable Speed Controller, Adjustable Frequency Controller, Variable FrequencyDrive and PWM drive (many different terms for the same thing) allows a fixed speed motor to operate at an infinite number ofspeeds. Why would our customers want inverters? To solve a problem, improve a product, automate a plant - and, to savemoney.

The AC power at the output of the inverter is different from the AC power that is supplied by the utility. AC adjustable speedpower is a synthesized square wave power. Utility power is a sine wave type of power.



29

Drive Technology has changed by leaps and bounds - today, we see flux vector drives, micro-drives, and even variablefrequency drives in the motor. At the same time, costs have dropped, which makes the savings on energy and maintenancecosts and the improved process efficiency even more desirable.

The drive technology continues to evolve, originally utilizing current source and 6-Step Modulation, most manufacturerstoday use the PWM (pulse width modulated) technology, moving away from SCR’s to the IGBT. Analog circuits have beenreplaced by digital signals and fast acting computers. Custom components and circuits have replaced larger single componentsand many circuit boards.

Switching frequencies have increased from 360 hertz to 20k hertz or higher. Output frequency range has expanded from 6-60 hertz to 0-1000 hertz. Low performance standard drives are now high performance multifunction controllers.

Wall size units are now palm size. All of these innovations have made it necessary for motor manufacturers to adjust to thetechnical challenges presented by today’s drives. Please refer to the Inverter Duty Motor Home Study Course for a completediscussion of the application considerations of PWM inverters and AC induction motors to a total system. Obviously, thePWM waveform has a tremendous impact on the motor life and performance.

Motor manufacturers have accepted these new challenges by developing and publishing industry specifications that defineboth general purpose duty and definite purpose duty. U.S. Motors was the first to develop and produce a motor product thatmeets the definite purpose specification, and has continued its research and development as well as improving technical andapplication assistance for motors utilized on VFD power.

NEMA MG1-1993, Part 30 and 31 define what level of ‘Inverter Duty’ motor is required:

Part 30 - Level 1. General purpose product capable of reliable performance in inverter installations where peak transients donot exceed 1000 volts and/or rise times are not shorter than 2 microseconds.

Part 31 - Level 2. Definite purpose product capable of reliable performance in inverter installations where peak voltages donot exceed 1600 volts and/or rise times are not shorter than .1 microsecond.

U.S. Motors was the first motor manufacturers to develop a motor to meet customer expectations for inverter applications.The Varidyne Series Motor is a total AC Variable Frequency design package, including pulse resistant magnet wire, precisionphase, slot and cell insulation, and maximized steel and copper content. The Varidyne motor has a high rigidity stator coretreatment and low vibration rotor assembly. The Inverter Grade insulation system gives you reliable performance and iscompatible with all brands of variable frequency drives.

U.S. Motors also has a complete line of premium efficient and energy efficient products that can be used on AFD’s when thefollowing parameters are followed. Premium efficiency Unimount (type UTE), Dripproof (type DE/RE), Hostile Duty (typeCTE), Auto Duty (type JDE) and Corro-Duty (type TCE) motors meet NEMA MG-1, Section IV, Part 31.40.42. All motorshave 40°C ambient, 1.0 service factor on inverter power, 3300 feet maximum altitude and all enclosed motors have Class Finsulation and are suitable for use with adjustable frequency drives under the following parameters:

• Up to 10:1 speed range on variable torque loads• Up to 4:1 speed range on constant torque loads• 1.0 Service Factor• 600 volt or less line power• Cable limitations per the following table• Standard 2 year warranty



30

Maximum Cable Distance AFD to Motor

Switching 460 Volt 575 Volt 230 Volt 380 VoltFrequency Premium Premium Premium Premium

3Khz 196 ft 53 ft 482 ft 295 ft6Khz 138 ft 37 ft 340 ft 209 ft9Khz 113 ft 31 ft 278 ft 170 ft12Khz 98 ft 26 ft 241 ft 148 ft15Khz 88 ft 24 ft 215 ft 132 ft20Khz 76 ft 21 ft 186 ft 114 ft

For voltages and switching frequencies not listed above please use the following formula to determine maximum cabledistance:

1328 - (2.15 x Voltage)Square Root (Switching Freq)

Energy Efficient World Motors Unimount (type FUT), Dripproof (type FD/FR), Hostile Duty (type FCT) and Corro-Duty (typeFTC) motors meet NEMA MG-1, Section IV, Part 30.02.3.9. All motors have 40°C ambient, 1.0 service factor on inverterpower, 3300 feet maximum altitude and all enclosed motors have Class F insulation and are suitable for use with adjustablefrequency drives under the following parameters:

• Up to 10:1 speed range on variable torque loads• Up to 2:1 speed range on constant torque loads• 1.0 Service Factor• 460 volt or less line power• Cable limitations per the following table• Standard 1 year warranty

Maximum Cable Distance AFD to Motor

Switching 460 Volt 230Volt 380 VoltFrequency Energy Energy Energy

Efficient Efficient Efficient3Khz 103 ft 435 ft 218 ft6Khz 73 ft 307 ft 154 ft9Khz 59 ft 251 ft 126 ft12Khz 51 ft 217 ft 109 ft15Khz 46 ft 194 ft 98 ft20Khz 40 ft 168 ft 85 ft

If application requirements exceed these standards, an output filter must be applied or an inverter rated Varidyne motor ornew 841 Plus “S” model with Inverter Grade insulation must be used.

Again, please refer to the Inverter Duty Motor Home Study Course for full details of the affects of inverter drives on motorsand U.S. Motors full product offering.

= Feet



31

ENVIRONMENTAL CONSIDERATIONS

AC motors that are properly selected and used should give many years of satisfactory service. Motor life is prolonged bykeeping the motor cool, dry, clean and lubricated. Choosing the best motor for the application and the environment will insurethat long life. Because so many conditions contribute toward short service life, it is impractical to set forth all possibilities,but some discussion will help point out the need for application analysis where trouble is experienced.

Overheating. Heat is one of the most destructive stresses causing premature motor failure. Overheating occurs because ofmotor overloading, low or unbalanced voltage at the motor terminals, excessive ambient temperatures, or poor coolingcaused by dirt or lack of ventilation. If the heat is not dissipated, insulation failure and possibly lubrication and bearing failurecan damage a motor.

Moisture. Moisture should be kept from entering a motor. Water from splashing or condensation seriously degrades aninsulation system. The water alone is conducting. Nonconducting contaminants are readily converted into good leakagecurrent conductors. The proper type of motor should be chosen for use in a damp environment. Most motors can be equippedwith drains or breathers to allow moisture to drain from the motor. Space heaters are also available to prevent moisturecondensation in the motor during times the motor is not running like the heater shown below.

Contamination. Nonconducting contaminants such as factory dust and sand gradually promote over-temperature by restrictingcooling air circulation. In addition, these may erode the insulation and the varnish, gradually reducing their effectiveness.

Altitude. Standard motor ratings are based on operation at any altitude up to 3300 feet (1000 meters). High altitude deratingis required above 3300 feet because of lower air density.

Ambient Temperature. The standard ambient temperature is 40°C, or 104°F. This value was selected as one that wouldseldom be exceeded for any appreciable length of time in the majority of cases. Motors are usually designed for thistemperature unless there is a definite requirement for a machine with some other value.

Motors for use in abnormally hot places are usually designed to accommodate the higher ambient by having a lower windingtemperature rise, and are sometimes designed in a larger frame size. The opposite is also true. Operation of motors in verycold ambients can result in severe duty on the motor component parts. Arctic duty motors are available from U.S. Motors that



32

are rated for operation down to minus 60°C.A variety of modifications and accessories are available for use on AC motors to protect them from the environment. Inaddition to those mentioned above, a cast iron, TEFC motor with CORRO-DUTY protection, which resists the effects of saltwater, solvents, various acids and chemicals can be provided.

Screens can be placed on the openings of an ODP style motor to protect the inside electrical components from smallanimals. Seals or slingers can be placed on the output shaft of a motor to help prevent intrusion of liquids or particles.

EFFICIENCY AND ENERGY LEGISLATION

Enactment of the Federal Energy Act of 1992 took place on October 24, 1997, and this act, commonly referred to asEPACT92, governs the efficiency of general purpose motors, among many other products. This information is based on dataavailable from the Department of Energy, NEMA and other nationally recognized associations. It obviously is subject tochange, as the DOE formulates the actual Federal code that will regulate integral horsepower electric motors and releasesthat information through the Federal Register.

Product. Motor product covered by this act includes general purpose motors from 1 to 200 horsepower, open and encloseddesigns, with three digit NEMA T frames, single speed, 2, 4 and 6 pole designs, foot mounted, three phase, squirrel cageinduction Design A or B motors, rated for continuous duty, 230 or 460 volt, 60 hertz, that are manufactured after October 24,1997. Motor products not covered include definite purpose motors and special purpose motors.

Note that only Design A&B motors are regulated by this legislation; the remaining designs C and D account for a very smallportion of the market and the benefit to redesign may not be technically feasible or economically justifiable. Estimates byNEMA and its member companies put the affects of the energy act at approximately 75% of the 1 to 200 horsepower motorssold in the U.S. annually.

Labeling. The energy act requires that each motor manufacturer label general purpose product with a NEMA nominalefficiency. The accuracy of that number will be determined by a manufacturer’s use of a computer simulation program knownas correlation. The DOE has asked each manufacturer to verify the accuracy of their correlation method through a series ofactual motor tests that would demonstrate the overall reliability and repeatability of the method. The NEMA energy taskforcemembers have jointly developed a laboratory standard in conjunction with NVLAP (National Voluntary Lab AccreditationProgram) that will allow each manufacturer to certify the accuracy of test data within his own facility. It is also expected thatthird party labs, such as UL, will apply for similar status and accreditation.

Rewound Motors. The question of motor rewind comes up often in discussions of EPACT92. Rewinding of motors is notaddressed in the act itself. Several members of the DOE staff are aware of the affects of rewind, not only in potentiallyreducing efficiency of a rewound motor but also of prolonging the life of an older designed product with very low efficiency.EASA (Electrical Apparatus Service Association), as the representative of the rewind industry, has spent a great deal of timeand resource to develop standards of rewind for energy efficient motors. They have requested motor manufacturers to supplyan ever increasing amount of winding and test data to help them meet their standards.

Motor User Issues. To address a concern regarding adequate starting torque, U.S. Motors Engineering Department hascompleted some in depth studies on a wide range of motors and applications. The conclusions reached by this study supportthe hypothesis that energy efficient and premium efficient motors, when applied correctly, will offer the user a more reliableproduct that runs cooler and lasts longer than the standard efficient product being replaced.

The only significant difference in performance that may occur is a slight increase in speed. Since the energy efficient designbetter uses the motor’s active materials, the losses are less, which can result in slight speed increases.

The next two pages contain the tables from MG1-1993, Table 12-10, for both open and enclosed motors. These tables showthe nominal and minimum efficiency percentages for general purpose motors as enacted by EPACT92, from 1 through 500



33



34



35

horsepower, for both NAM and IEC motors.STARTING METHODS

There are a number of ways to start squirrel cage induction motors. Each method has its own characteristics and place ofcorrect application. You should refer to the motor manufacturer for any starting method other than across the line starting. Itis important to understand that applications requiring any other type of starting method necessitate careful consideration ofthe motor torque to accelerate the load.

Across the line.

Starting characteristics:Motor terminal voltage equals line voltage.Motor current equals line current.Starting torque equals rated starting torque.

Applications:Use where system capacity and stiffness are sufficient to stand the high starting current without excessivevoltage drop.

Series Resistance reduced voltage. In this method, a voltage-dropping resistance is placed in series with the motor duringstarting. The impedance seen by the power system then is the resistance of the resistor starter plus that of the motor.



36

Starting characteristics:Motor terminal voltage is reduced from line voltage.Starting torque is reduced by the square of the terminal voltage.

Applications:Usually on low voltage (less than 600 volts).Where load torque during acceleration is minimal.Not often used with large motors because of the high heat loss in the resistors.May be used for full acceleration or for system voltage recovery.

Solid state reduced voltage. In this method, a solid state starter, consisting of power SCR’s controlled by logic circuits, isused to chop the sine-wave system power so that only a portion of the wave is applied to the motor. The logic circuits can beprogrammed to respond to any of several sensors to control the voltage: internal time ramp, current sensor feedback ortachometer feedback. In addition, most starters have provisions to reduce the voltage when the loading on the motor is low,thus minimizing the no load losses of the motor.

Starting characteristics:Motor terminal voltage is reduced from line voltage.Motor current equals line current.Starting torque is reduced by the square of the terminal voltage.

Applications:Available through 4160 volts.Where rate of acceleration needs to be controlled.Where current limits exist, but load torque is high.Where the motor runs at no-load for significant periods.Where soft start (gradual taking up of slack) is desired.



37

Autotransformer Reduced Voltage. In this method, an autotransformer is placed in series with the motor during starting.The transformer action reduces the voltage applied to the motor terminals, which reduces the motor’s locked rotor current.

Starting characteristics:Motor terminal voltage is less than the line voltage (by transformer ratio).Motor current exceeds line current (by the inverse of the transformer ratio).Starting torque is reduced by the square of the terminal voltage.

Applications:Where complete acceleration at reduced amperes is needed.Where line ampere reduction requirements are severe and load torque is not minimal.

WYE Start/Delta Run. This method is similar to reduced voltage starting. Effectively, the voltage reflected to the stator isreduced by a factor of 1/3. Impedance seen by the power system is 3 times the impedance of the delta run connection.



38

Starting characteristics:Motor terminal voltage is reduced from line voltage by a û3 factor.Starting current is approximately 30% of normal.Starting torque is approximately 20-30% of full load torque.

Applications:Where load torque during acceleration is very low.May be used for partial acceleration.Used more often for European applications.Primary usage is on centrifuges.

Part Winding Start. This method uses only a portion (usually 1/2, but sometimes 2/3) of the motor winding when starting themotor. It is to be used only for voltage recovered and must not be left on the start connection for more than 1 to 2 seconds.The motor is not expected to accelerate on the start connection and may not even turn.

Starting characteristics:Starting current is 44-75% of normal, depending on the specific winding connection.Starting torque is very low (may not even turn the shaft) (45% to 0% depending on connection).Winding heating is very high on start connection.

Applications:Where power system has automatic voltage recovery and normal starting current would cause unacceptablevoltage dip. Should not stay on the start connection more than 1-2 seconds.



39

Double Delta. This method accomplishes the equivalent of reduced voltage starting by changing a delta connected windingfrom parallel groups to series groups during the start. The advantage of double delta is that all of the winding is connectedduring the start cycle, and the rate of heating is not so severe. Caution! May not work successfully on some PWSconfigurations (i.e. 4-2 starter).

Starting characteristics:Starting current is 60-75% of normal, depending on the specific winding connection.Starting torque is typically 45% of full load torque.

Applications:Where power system has automatic voltage recovery and normal starting current would cause unacceptablevoltage dip.



40

APPLICATION CONSIDERATIONS - QUIZ

1. What is the purpose of the motor enclosure?

2. What is TEFC an abbreviation for?

3. An open dripproof motor has a free exchange of air with the ambient. True _____ False ____

4. All explosionproof motors are UL approved. True _____ False ____

5. Name two examples of constant torque applications.

6. An example of variable torque application is a drill press. True _____ False _____

7. Pumps are almost always considered variable torque applications. True _____ False _____

8. What is the most destructive agent to a motor?

9. What type of motor would you suggest using in an extremely cold environment?

10. What purpose does a seal or slinger provide on the output shaft of a motor?



41

U.S. MOTORS PRODUCT OFFERING

U.S. Electrical Motors offers a full line of three phase AC induction motors for a variety of applications and environments.Following is our catalog numbering system which will aid you in identifying a motor product.

H 2 5 E 2 B S C R ( )Product Identifier8P - 841 PlusA - Auto DutyAB - Auto Duty Brakeless BrakeBM - Brake MotorC - Corro-DutyD - ODP Gen. PurposeDC - DC MotorsDJ - ODP CCPE - ElevatorFD - Farm Duty (1 ph.)H - Hostile DutyJ - Close Coupled PumpJT - Jet Pump MotorKT - Finished Goods KitM - IEC Metric MotorsP - Predator MotorsPF - Power Factor Correction CapacitorsT - TEFCU - UnimountUJ - Unimount CCPVB - Vector Blower CldVN - Vector Non-VentWD - Washdown DutyX - XP Dual LabelXC - XP Dual Lbl Corro-DtyXJ - XP Dual Label CCPXS - XP Dual Lbl Steel FrmY - XP Single LabelYC - XP Single Lbl Corro-DutyYJ - XP Single Label CCP

Horsepower14 = 1/413 = 1/312 = 1/213 = 3/41 = 132 = 1 1/22 = 23 = 35 = 57 = 7.510 = 1015 = 1520 = 2025 = 25 etc… ..

ElectricalA - Perm Split Cap.B - Split PhaseC - Cap StartD - Constant Torq 2WDGE - Energy EfficientF - Constant HP 1WDGG - Constant HP 2WDGH -K - KVAR Torq 2WDGL - KVAR Torq 1WDGM -N - Permanent MagnetP - Premium EfficientQ - Des ign CR - Constant Torq 1WDGS - Standard EfficientT - Inverter DutyConstant TorqueV - Inverter Duty Variable TorqueW - Shunt Wound

RPM @ 60Hz1 = 36002 = 18003 = 12004 = 9005 = 7206 = 6009 = Multi- Speed

Voltage2 = 2300A = 208-230/460B = 230/460C = 460D = 208-230/460 190/380E = 230/460 190/380F = 460/380G = 575H = 200I = 115/230J = 115/208-230K = 230L = 110/220M = 220/440N = 115P = 90Q = 180R = 220/380-440S = 460 (PWS)U = 230/460 190/380 220/415V = 4000W = 2300/4000X = 200/400Y = 500Z = Other

Mounting -Primy. (First Digit)Default = T Shaft or STD 48 or 56S = Short ShaftM = JMP = JPJ = WCCP2 = SpecialT = TM ShaftU = JMV Shaft V = JPV

Mounting-Flange (Second Digit)Default = NoneB = Roller BearingC = C-FaceD = D-FlangeK = TCH (Spcl ‘AK’)Q = Square FlangeY = Special

Mounting(Third Digit)Default = Rigid base F-1R = No base2 = F-2 Assembly3 = F-0 Assembly4 = Resilient Base5 = W-5 Assembly7 = Yokemount8 = W-8 Assembly

Mounting Single Phase(Fourth Digit)Default = 56 Frame or NEMA 4 = 48 Frame14 = 140 Frame18 = 180 Frame21 = 210 Frame

CATALOG NUMBER



42

ENERGY AND PREMIUM EFFICIENT OPEN DRIPPROOF MOTORS

A variety of three phase, open dripproof motors are available from U.S. Motors. These energy efficient and premium efficientmotors are for normal duty industrial equipment, such as compressors, conveyors, pumps and fans. They are generallysupplied with Class F insulation, are for continuous duty, with ball bearings and available in standard voltage ratings of 200,208-230/460, 230/460 and 575 volts. The Open Dripproof offering consists of two types of products: the steel frame, typesFD and DE on 56-320 frames from 1/3 HP to 60 HP and the cast iron frame types FR and RE on 360-440 frames, from30 HP to 400 HP.

WorldMotor FD and type DE are energy efficient and premium efficient. These motors fully comply with EPACT ‘92 andNRCan efficiency standards. The steel frame FD and DE are available with die cast aluminum brackets with steel bearinginserts for improved reliability in severe load applications. The base is steel welded and the 180 frame and larger has adiagonally split conduit box for ease in wiring. Double-shielded bearings with regreasing provisions are standard on the 180frame and larger, and lifting lugs are available on the 210 frame and larger. A new designed steel frame was introduced in1996 that extended the frame of the motor, utilizing a more pancake style end shield, resulting in a motor that is more efficientwith greater cooling capacity.

The WorldMotor FD motor also has dual voltage (230/460) with 12 leads out and is suitable for wye delta start on eithervoltage. World Motor products are suitable for use on 50 or 60 Hertz applications. The product has aluminum end shields on56-250 frames and cast iron end shields on 280-440 frames. In addition to the stock product offerings, we are able to extendthe product range to additional ratings and requirements with production models that incorporate modifications and accessoriessuch as space heaters, thermostats, screens and ambients above 40°C.



43

FR and RE

Our type WorldMotor FR and type RE are cast iron frame motors and are available from 30-400 horsepower, in speeds of3600, 1800, 1200, 900 and 720 RPM. The motor has both cast iron frame brackets and a diagonally split conduit box. Allbearings are double-shielded (open on 440 frame) with regreasing provisions. “C” Face, is available on all sizes from production.The FR meets federally mandated efficiency levels, and the RE is a premium efficient product.

ENERGY AND PREMIUM EFFICIENT TOTALLY ENCLOSED MOTORS

Our first offering of enclosed motors is our aluminum frame UNIMOUNT motor, available from 1/4-30 HP. This motor lineoffers the widest range of electrical and mechanical features, including a 1.25 service factor, full Class F insulation system,and 50 or 60 Hertz operation. The aluminum alloy extruded motor frame improves heat dissipation for cool operation andlong life on 180 frame and larger.

Mechanical Features include an oversized diagonally split conduit box for easier connections; lifting lugs on 180 frame andlarger; die cast aluminum brackets that have steel or cast iron inserts to ensure reliable performance under severe loadapplications. The rugged motor base is removable to allow conversion to footless configuration. Sturdy plastic fan and fancover are provided for maximum cooling and extended life. Other features include horizontal and vertical mounting (Canopycap kit), Shur Stop brake kits (1-1/2-35 ft. lbs.) and F-1 to F-2 convertibility (180 frame and larger). “C” Face kits with clampedbearing and “D” Flange kits (140 and 180 frames) complete the long list of mechanical features of the Unimount.



44

The Unimount can be used on pumps, fans, compressors, general industrial belt drive and direct drive equipment. The FUTdesignates an energy efficiency motor; the UTE the premium efficient model. A UTF is a “C” Face footless type motor. Thefootless “C” Face type can be used as an input to speed reducers for material handling.

The Unimount Air Over, type UTN, is used on propeller fans where fan air blows directly over the motor. The UnimountMultispeed is used on fans, blowers and machine tools where more than one standard speed is required (also available fromstock). The conversion to brake motors is used on conveyors, speed reducers and other equipment requiring quick stops.The Unimount Plus is used for pumps, fans, compressors, general industrial belt drive and direct connected equipment where12 lead, wye-start, delta-run starting is required.

HOSTILE ENVIRONMENT MOTORS

Our first offering of hostile duty cast iron enclosed motors is our FCT line, which is an energy efficient motor from 1-350 HP.The FCT offers tri-voltage through 25 HP and offers “C” Face and “D” Flange conversion kits from stock. The exterior of theFCT is protected by a polyphenolic paint, and it has an external neoprene shaft slinger on the pulley end. Stainless steelnameplate and plated hardware for additional protection. The conduit box is steel and the fan cover guard is plastic through286T frame and steel or aluminum from 324T and above. Also available as a premium efficient motor, type CTE.

CORRO DUTY MOTORS

The TCE is our next cast iron, TEFC product, which has all the features of the CTE, plus CORRO-DUTY. The CORRO-DUTYfeatures include a cast iron conduit box with non-braided, non-wicking leads, as well as compression type grounding lugs andlead positioning gasket. It also includes a cast iron fan cover guard. Epoxy varnish on rotor core, brass condensation drainsand internal bearing caps make this suitable for mill and chemical plants and other hostile environments.



45

841 PLUS MOTOR

U.S. Motors was the first to introduce a motor that meets or exceeds the IEEE 841 specifications for pretroleum and chemicalapplications. The 841 Plus is now the leader within the petroleum and chemical industry. The first to offer the VBX Inpro/Seal as a standard feature; the first to offer a five year warranty; and, the first to offer inverter duty designs from stock.

In severe duty applications, the 841 Plus motor offers superior protection and premium efficiency. The 841 Plus motor,exceeds the 1997 federally legislated efficiency levels, has as standard our patented Inverter Grade insulation system, andhas the same size bearings on 250 frame and larger. A smart ring is located on the fan end bracket that allows fieldadaptability to a standard Inpro/Seal. Machining to the bracket or disassembly is not required to retrofit an Inpro/Seal.

EXPLOSIONPROOF MOTORS

Hazardous location motor applications are classified by the type of hazardous environment present, the characteristics of thespecific material creating the hazard, the probability of exposure to the environment and the maximum temperature level thatis considered safe for the substance creating the hazard. The format used to define this information is a class, group,division and temperature code structure.

The term ‘class’ is used to define the form of the hazard that is present. The term ‘group’ defines the actual characteristics ofthe substance that is hazardous, and the term ‘division’ is used to define the type of exposure that is expected. The term‘temperature code’ is used to define the maximum level of temperature that the hazardous substance will be exposed toduring normal or abnormal operation of the motor. Typically, this is a reference to the maximum frame temperature the motorwill experience. Following are the categories for class, group, division and temperature codes.



46

Class I (Gas or Vapor)

Group:A - AcetyleneB - Hydrogen and Manufactured GasesC - Ethyl-Ether, Ethylene and CyclopropaneD - Gasoline, Hexane, Naphtha, Benzine, Butane, Propane, Alcohol Lacquer Solvent Vapors and Natural Gas

Division II:Hazard of fire or explosion is present only as a result of an accident. Motors may bedripproof or TEFC.

Class II (Dusts)

Group:E - Metal Dust (Special Seals)F - Carbon Black, Coal or Coke DustG - Flour, Starch or Grain Dust

Division I:Hazard is always present due to normal conditions. (Dust suspended in theatmosphere.) Motors must be explosionproof construction with Underwriter’s label.

Division II:Motors may be TEFC or externally ventilated:

(A) Where dust deposits on electrical equipment prevent safe heat dissipation.(B) Where deposit or dust might be ignited by arcs or burning material.

Class III (Fibers) Fibers that are easily ignitable but not apt to be suspended in the air to producemixtures. Examples include rayon, nylon, cotton, saw dust and wood chips.

Division II:Location in which easily ignitable fibers are stored or handled. TEFC enclosure canbe used if there is a minimal amount of fibers or flyings in the air.

In addition to the identification of the class, group and division, it is necessary as well to obtain the temperature code for theexplosionproof motor. This code indicates the maximum surface temperature for all conditions including burnout, overload,single phasing and locked rotor. This “T” code must be identified on the nameplate.

IGNITION TEMPERATURE vsTEMPERATURE MARKINGS

MAXIMUM TEMPERATURE FOR ALL CONDITIONS: w BURNOUTw OVERLOADw SINGLE PHASEw LOCKED ROTOR



47

T - CODES ON NAMEPLATE

Our explosionproof offering begins with our Type L, which is a high efficiency motor, available from 1/2 through 350 HP.Classifications vary, but most of these products are available for Class I, Groups D and C, and Class II, Groups F and G (andon the smaller frame sizes, Group E). The Type LF is a “C” Face, footless design, available from stock from 1/3 through 15HP.

Our Type LC combines both our explosionproof and CORRO-DUTY features into one UL listed product. 50 Hertz operation isavailable at 190/380 or 380 volts. These motors are upgraded from the Type L design to include class F insulation, a shaftslinger, brass drain and breather and all of our standard CORRO-DUTY features. Available from 1-200 HP for Division I, ClassI Group D, Temperature Code T2B.

A relatively new addition to the explosionproof family is the Explosionproof CORRO-DUTY Type NC for Division II applications.These products are now available from stock from 1-200 HP.



48

“C” FACE AND PUMP MOTORS

As previously mentioned, our Type D high efficiency ODP product is available from 40 to 60 HP with a “C” Face. TheUnimount design is also available as a “C” Face, in stock from 1/4-30 HP footed and footless. “C” Face and “D” Flange kits areavailable in frames 140-360 for Types FCT and TCE.

Our close coupled pump motors are designed for the specific requirements of centrifugal pumps. This product is used in theheating, ventilating and air conditioning market cooling systems to move water up in multistory buildings. Agricultural use isin the center pivot market.

A number of shaft types are available on our CCP motors. The JP shaft has packing glands that are the sealing deviceswhich are manually packet and adjusted using braided cotton for the sealing material. The JM Shaft is a mechanical sealthat uses molded or preformed seals held in place by a spring. We also have available the West Coast shaft, which is similarin design to the JM style. The shaft of the close coupled pump motor is directly connected and mounted to the inside of thepump. In the open dripproof design, the CCP motor is available from 1-100 HP, in the Unimount design from 1-20 HP, fromstock.

SPECIAL PURPOSE MOTORS

Inverter Duty Motors. Three phase, open dripproof inverter duty motors are available from 1 through 250 horsepower. A 10!(6-60 Hertz) speed range is available for variable torque applications, and a 5:1 (12-60 Hertz) speed range for constant torque.These motors are used on pumps, fans, blowers and other industrial equipment using inverter powered applications.

The TEFC Unimount motor is available for the same speed ranges from 1 to 20 horsepower, and the TEFC hostile dutyproduct from 1 to 200 horsepower, plus 1 to 150 horsepower for 10:1 constant torque.



49

All of these motors have our Inverter Grade Insulation system which meets NEMA MG-1 Part 31, and a special three yearwarranty on inverter power.

Vector Duty Motors. For conveyors, presses, hoists and other flux vector applications, we offer the three phase, TENV,hostile duty, c-face vector duty motors from 1 to 15 horsepower.

This TENV motor can handle a 0-1800 RPM (0-60 Hertz) speed range for constant torque applications. The motor includesour Inverter Grade insulation system that meets NEMA MG-1 Part 31, and is delivered standard with a 5-28 volt 1024 PPRencoder.

Also for vector duty applications, U.S. Motors offers a three phase, TEBC, hostile duty motor for 0-1800 RPM (0-60 Hertz)speed range for constant torque applications having constant torque requirements at or near zero speed

The TEBC vector duty motor is available from 1 to 200 horsepower, 1800 and 1200 RPM. These vector duty motors also havea three year warranty on inverter power.

Automotive Duty Motors. The U.S. Motors’ “U” frame automotive duty line is designed to provide a long, trouble-free life.The automotive industry has formulated a set of specifications designed to provide the highest reliability for 24 hours per day,7 days a week service - and our totally enclosed fan cooled “U” frame motors meet the GM, Ford and Chrysler specifications.These motors are available from stock from 1/4 through 250 HP, in both high and premium efficiency.



50

Washdown Duty. Our Washdown Duty motor line offers a motor designed for the food processing industry and otherapplications that are routinely exposed to chemicals, washdown, humidity and other severe environments. This TEFC motorhas a stainless steel shaft and key and a 1.15 service factor with Class F insulation. It is rust and corrosion protected withUSDA approved white epoxy paint, and comes standard with a double dip and baked winding and lip seals in both endshields.The Washdown Duty motors are offered in 1/2 through 10 HP with the following mountings: rigid base; “C” face footless; and“C” face with rigid base.

IEC Metric Motors. For those OEMs exporting to Europe and Asia, and where a user requires a motor replacement onimported equipment, U.S. Motors offers an IEC metric motor, available from 1 through 100 HP, or .75 KW through 75 KW. TheIEC motors feature Class F insulation, and can be run on 460 volts 60 Hertz, or 380, 400 or 415 Volt, 50 Hz. These motorshave a stainless steel nameplate and a finned housing made of aluminum alloy with an exterior protective treatment ofpolyurethane vinyl finish.

Brakemotors. A brakemotor is an electric motor with a brake. The brake, normally operated by an electromagnet against aspring, is usually fitted to the non -drive end of the motor. Its purpose is to hold a load steady, high speed movements withshort stopping times and precise positioning, emergency stops, safety devices, slowing down and stopping high inertialoads. Our 2000 Series Brakemotors, Type FB, are available from 1/3-2 HP with rigid base, “C” face footed, or “C” facefootless configurations. These motors are used in applications where instantaneous response is required, such as palletizers,conveyors, baggage handling equipment and general material handling systems. A great brakemotor in a small package - the2000 Series brakemotor is just one inch longer than a standard motor.



51

2000 Series Brakemotor

The FC Series Brakemotor, is available from 1/3-20 HP, 1800 and 1200 RPM in a rigid base, “C” face footed or “C” facefootless configuration. These brakemotors can be used when manual release, brake torque adjustments, external air gapadjustments and high cycling is required. Typical applications would include bulk material handling equipment, conveyors,cranes and hoists.

FIRE PUMP MOTORSFor fire pump applications per NFPA 20 where contaminants are minimal, we have a line of motors from 5 to 250 HP withNEMA B design performance. These motors have rolled steel and cast iron frames that are suitable for wye-delta start on250T frame and above, and part wind start through 125 HP.

FC Series Brake Motor



52

U.S. MOTORS’ PRODUCT OFFERING - QUIZ

1. U.S. Motors offers open dripproof motors in both steel and cast iron frames.True _____ False _____

2. Name three types of kits available for the UNIMOUNT motor.

3. What type of applications would the multispeed version of the UNIMOUNT be used for?

4. The TCE is just like the FCT except it has a cast iron conduit box and a cast iron fan cover guard.True _____ False _____

5. Name three possible applications for the TEFC hostile duty Type FCT and CORRODUTY TypeTCE motors.

6. For explosionproof motors, the term “class” defines the actual characteristics of the substance thatis hazardous. True _____ False _____

7. What is our type designation for an explosionproof motor with CORRODUTY?

8. Name the three different types of shafts available on the close coupled pump motors.

9. Washdown Duty motors are painted white. True _____ False _____

10. What material is the frame of the IEC metric motor?



53

GENERAL FORMULAS AND CONVERSION TABLES



54




55




56




57

QUIZ ANSWERS

AC MOTOR FUNDAMENTALS

1. True.

2. An electromagnet only has magnetic properties when power is applied.

3. In three phase AC, three different sets of current are present as compared to only one in singlephase.

4. Stator and rotor.

5. False.

6. True.

7. True.

8. False.

9. The rotor is not connected electrically to the source of power supply, but rotation is “induced” bythe magnetic fields of the stator.

THE NAMEPLATE

1. To assist in the proper selection and application of motors.

2. False.

3. False.

4. True.

5. Horsepower is equal to torque times speed over a constant.

6. It is used by the electrician installing the motor to properly size the power supply wiring andstarter.



58

QUIZ ANSWERS

THE NAMEPLATE (continued)

7. Efficiency is the ratio of the power output divided by the power input.

8. True.

9. True.

10. NEMA Design B.

APPLICATION CONSIDERATIONS

1. The motor enclosure must protect the windings, bearings and other mechanical parts from moisture,chemicals, mechanical damage and abrasion from grit.

2. Totally Enclosed Fan Cooled.

3. True.

4. True.

5. Conveyors, hoisting loads, surface winding machines, screw compressors.

6. False.

7. True.

8. Heat.

9. Arctic Duty.

10. Keeps moisture and debris from entering the motor.



59

QUIZ ANSWERS

U.S. MOTORS’ PRODUCT OFFERING

1. True.

2. Brake kits, “C” bracket kits, “D” flange kits and double “C” face brake kits.

3. Fans, blowers and machine tools.

4. True.

5. Petro-chem plants, mines, foundries, pulp and paper plants, waste management facilities andchemical plants.

6. False.

7. Type LC.

8. JM, JP and Westcoast.

9. True.

10. Aluminum alloy.



60

GLOSSARY

Alternating Current - Electricity that changes direction at a regular rate.

Ambient Temperature - The temperature of the medium, such as air, water or earth, into which the heat of the equipmentis dissipated.

Back of a Motor - The back of a motor is the end which carries the coupling or driving pulley (NEMA). This is sometimescalled the drive end (D.E.) or pulley end (P.E.).

Bearing (Ball) - A ball shaped component that is used to reduce friction and wear while supporting rotating elements. Fora motor, this type of bearing provides a relatively rigid support for the output shaft.

Breakaway Torque - The torque required to start a machine from standstill.

Breakdown Torque - The breakdown torque of an AC motor is the maximum torque which it will develop with rated voltageapplied at rated frequency.

C-Face - This type of motor mounting is used for close coupled pumps and similar applications where the mounting holes inthe face are threaded to receive bolts from the pump. Normally, the C-Face is used where a pump or similar product is to beoverhung on the motor. This type of mounting is a NEMA standard design and available with or without feet.

Circuit - An electrical network of conductors that provide one or more closed or complete paths for current.

Continuous Duty - A motor that can continue to operate within the insulation temperature limits after it has reached normaloperating temperature.

Definite Purpose Motor - A definite purpose motor is any motor design, listed and offered in standard ratings with standardoperating characteristics and mechanical construction, for use under service conditions other than usual or for use on aparticular type of application (NEMA).

D Flange - This type of motor mounting is used when the motor is to be built as part of the machine. The mounting holes ofthe flange are not threaded. The bolts protrude through the flange from the motor side. Normally D Flange motors aresupplied without feet since the motor is mounted directly to the driven machine.

Dimension Drawing - A dimension or outline drawing (base plan, floor plan, etc.) is one which shows the physical spaceand mounting requirements of a piece of equipment. It may also indicate ventilation requirements and space provided forconnections or the location to which connections are to be made.

Duty Cycle - The relationship between the operating and resting times or repeatable operation at different loads.

Dynamic Braking - A system of electric braking in which the motor, when used as a generator, converts the kinetic energyof the load into electric energy dissipated in resistors, and in doing so, exerts a retarding force on the load.

Efficiency - The ratio of power output to power input indicated as a percent. In motors, it is the effectiveness to which amotor converts electrical power into mechanical power.

Electrical Conductor - A material having many free electrons that can move easily. An object so constructed from conductingmaterial that it may be used as a carrier of electrical current.



61

GLOSSARY (continued)

Electrical Insulator - A material having a few free electrons that cannot move freely. A material or combination of materialswhich effectively resists the passage of an electric current.

Electric Current - The result when many free electrons move in the same direction.

Electromagnet - A coil of wire that carries an electric current. A magnet in which the field is produced by an electric current.Upon removal of the electrical current it exhibits little or no magnetic influence.

Energy - A quantitative property of matter indicating capacity to do work.

Foot Pound - A unit of work. The work done by a force of one pound acting through a distance of one foot.

Force - The tendency to change the motion or position of an object with a push or pull. It is measured in ounces or pounds.

Frame Size - The physical size of a motor, usually consisting of NEMA defined “D” and “F” dimensions at a minimum. The“D” dimension is the distance in inches from the center of the motor shaft to the bottom of the mounting feet. The “F”dimension relates to the distance between the centers of the mounting feet holes.

Frequency - The number of complete alternations per second of an alternating current.

Front of a Motor - The end opposite the coupling or driving pulley (NEMA). Also called the opposite pulley end (O.P.E.).

Full Load Torque - The full load torque of a motor is the torque necessary to produce rated horsepower at full load speed.

General Purpose Motor - This motor has a continuous Class B insulation rating and NEMA B design, listed and offered instandard ratings with standard operating characteristics and mechanical construction for use under usual service conditionswithout restriction to a particular application or type of application (NEMA).

Horsepower - A measure of the amount of work that a motor can perform in a given amount of time.

Hysteresis Loss - The resistance offered by materials to becoming magnetized results in energy being expended andcorresponding loss. Hysteresis loss in a magnetic circuit is the energy expended to magnetize and demagnetize the core.

Induction Motor - An alternating current motor in which the primary winding on one member (usually the stator) is connectedto the power source. A secondary winding on the other member (usually the rotor) carries the induced current. There is nophysical electrical connection to the secondary winding; its current is induced.

Inertia - A measure of a body’s resistance to changes in velocity, whether the body is at rest or moving at a constant velocity.The velocity can be either linear or rotational.

Integral Horsepower Motor - A motor built in a frame having a continuous rating of 1 HP or more.

Locked Rotor Current - Steady state current taken from the line with the rotor at standstill (at rated voltage and frequency).This is the RMS current when starting the motor with or without load.

Locked Rotor Torque - The minimum torque that a motor will develop at rest for all angular positions of the rotor (with ratedvoltage applied at rated frequency).



62


Multispeed Motor - An induction motor that can obtain two, three or four discrete (fixed) speeds by the selection of variousstator winding configurations.

NEC - The National Electric Code is the recommendation of the National Fire Protection Association and is revised everythree years. City or state regulations may differ from these code regulations and take precedence over NEC rules.

NEMA - The National Electrical Manufacturers Association is a nonprofit organization organized and supported bymanufacturers of electrical equipment and supplies.

No Load - The state of a machine rotating at normal speed under rated conditions, but when no output is required from it.

Open Motor - A machine having ventilating openings which permit passage of external cooling air over and around thewindings of the machine.

Power - Work done per unit of time. Measured in horsepower or watts: 1 HP = 33,000 ft.lb./min/ = 746 watts.

Power Factor - A measurement of the time phase difference between the voltage and current in an AC circuit. It isrepresented by the cosine of the angle of this phase difference. Power factor is the ratio of real power (kW) to total kVA orthe ratio of actual power (W) to apparent power (volt-amperes).

Pull-Up Torque - The torque required to accelerate the load from standstill to full speed (where breakdown torque occurs),expressed in percent of running torque. This is the minimum torque the motor develops between locked rotor and breakdowntorque.

Reactance - The opposition to the flow of current made by an induction coil or a capacitor.

Reversing - Changing the direction of rotation of the motor rotor. An AC motor is reversed by changing the connection ofone leg on the three phase power line.

Rotor - The rotating member of a machine with a shaft.

Service Factor - When used on a motor nameplate, a number which indicates the maximum loading permissible above thenameplate rating without causing serious degradation.

Slip - The difference between rotating magnetic field speed (synchronous speed) and the rotor speed of an AC inductionmotor. Usually expressed as a percentage of synchronous speed.

Special Purpose Motor - A motor with special operating characteristics, special mechanical construction or both, designedfor a particular application and not falling within the definition of a general purpose or definite purpose motor (NEMA).

Speed - The speed at which an induction motor operates is dependent upon the input power frequency, the load and thenumber of electrical magnetic poles for which the motor is wound. The higher the frequency, the faster the motor runs. Themore poles the motor has, the slower it runs.

Starting Torque - The torque exerted by the motor during the starting period.



63


Stator - The stationary portion of the magnetic circuit and the associated windings and leads of a rotating machine.

Synchronous Speed - The speed of an AC induction motor’s rotating magnetic field. It is determined by the frequencyapplied to the stator and the number of magnetic poles present in each phase of the stator windings.

Torque - A turning force applied to a shaft, tending to cause rotation. Torque is normally measured in pound / feet and isequal to the force applied times the radius through which it acts.

Totally Enclosed Motor - A machine so enclosed as to prevent the free exchange of air between the inside and the outsideof the case, but not sufficiently enclosed to be termed airtight.

Wiring (or Connection) Diagram - A wiring diagram is one which locates and identifies electrical devices, terminals andinterconnecting wiring in an assembly.

Work - A force moving and object over a distance. Measured in foot / pounds (ft.lbs.). Work = Force x Distance.

©1999 U.S. Electrical MotorsPrices, specifications and ratings subject to change without notice.

Printed in the U.S.A

REGIONAL OFFICES PHONE FAXMONTREAL, QUEBEC/CANADA (800) 361-5509 (514) 332-5912TORONTO, ONTARIO/CANADA (905) 475-4670 (905) 475-4672MONTERREY, MEXICO (52) 8-389-1300 (52) 8-389-1310CARACAS, VENEZUELA (58) 2-237-7522 (58) 2-232-9727BOGOTA, COLOMBIA (571) 439-5420 (571) 439-5417

U.S. Electrical Motors Division, Emerson Electric Co.8100 West Florissant Avenue, St. Louis, MO 63136

WWW Home Page: http://www.usmotors.com

REGIONAL OFFICES PHONE FAXORANGE, CONNECTICUT (800) 243-2700 (203) 891-1077CHICAGO, ILLINOIS (800) 323-5223 (630) 893-0182MEMPHIS, TENNESSEE (901) 794-5500 (901) 794-0741DALLAS, TEXAS (800) 683-4126 (972) 644-0254SANTA FE SPRINGS, CALIFORNIA (800) 854-3302 (562) 941-1858INTERNATIONAL SALES (314) 553-2196 (314) 553-2135

HSC-246-125 8/99

nema three phase ac horizontal motor home study course · nema three phase ac horizontal motor home...

Documents