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Course 410-500 Industrial Motor Maintenance11/01/98 Exercise

1998 Design Assistance Corporation 02-1

Exercise E410-S02.wpd

Interpreting Motor Nameplate Data

Objective

Using the Electric Motor Repair Training Manual #562-MAN,the DAC #410-#419 Motor Fundamentals Training Systemmotor nameplates and the nameplates on motors in yourworkplace, identify common motor types and operational

characteristics.

Performance Standard

Identify all the italicized terms and components with 100%accuracy.

Foundation Competencies

Knowledge of AC motor terminology and construction (Exercise

E410-S01).

Required Background Reading

Electric Motor Repair Manual, pgs. 12, 99-101. (DAC, #562-MAN)

Tools Required

Pencil and paper.

Components Required

Any of the DAC #410-#419 Motor Devices.

Introductory Discussion

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The National Electric Code (NEC) Article 430 requires all motors to havenameplates with certain information useful in the identification of the type of motor,

selection of motors for applications, and the repair and troubleshooting of the motor.It is the first place to look to determine exactly what you have or to verify on whatyou are working.

In this exercise you will have the opportunity to investigate the nameplatesof several motors and determine what types of information they provide.

Given the many functions throughout industry that motors perform, it isimportant that you know how to recognize the proper motor when you see one. Thebest way is to become thoroughly familiar with what information is available on amotors nameplate.

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Figure 1 DAC #410 Split Phase, Capacitor-Start AC Motor Nameplate

Performance Steps

Step 1. Identify the basic terms and types of information found on the

typical motor nameplate.

Identify the information listed on typical motor nameplates.

Manufacturer Phase/Frequency NEMA Design Letter

Type or Style Service Factor KVA Code Letter

Frame Size Insulation Class Efficiency

Rated Power (HP) Ambient Temp. Power Factor

Rated Voltage Rated RPM/Speed Enclosure Type

Full Load Amperage Duty or Time Connection Diagrams

Note that not all nameplates contain all this information andsome can even contain additional information.

Using the motors in the DAC Motor Fundamentals Training

Figure 2 DAC #412 Three-Phase,Capacitor-Start AC Motor Nameplate

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System and/or the motors in and around your workplace,identify and record for each the information contained on theirnameplates, as each type of entry is discussed in this exercise.

List the motors available on individual sheets of paper or largeindex cards for this exercise by their Name, ID Number, Usageor Location, so that you know which is which physically.

Step 2. Identify theManufacturers Names on available motors.

List at the top of each page or index card the name of themotors manufacturer. In some cases additional manufacturersinformation is included such as their address.

To obtain the most experience from this exercise it would bebest if you are including a variety of different manufacturers.

List also any identification numbers or serial numbers thatidentifies the motors in your facility and/or this exercise.

Some nameplates also include a Catalog #or aPart No. whichcan be used to re-order an exact replacement from themanufacturer.

Some nameplates also include a user numberwhich would bean identification number for your company with themanufacturer.

Step 3. Identify the Typeof each motor available.

List under the Manufacturers Name on each page or indexcard the type or model letter designator for that motor.

This letter designation tells you the specific style of the motor,

which you need to know to be able to troubleshoot and repairthe motor, such as a Split Phase, Capacitor-Start Motor or aThree Phase Squirrel Cage Rotor Motor.

Step 4. Identify the Frame Sizeof the motors available.

List the Frame Number on each page or index card.

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The National Electrical Manufacturers Association (NEMA)Frame Size Number is a code that can lead you to all thecritical dimensional measurements of the motor, such as shaft

height, shaft length, shaft diameter, distances betweenmounting bolts, overall length of the motor, and the diameter ofthe motor. This is an attempt to help ensure interchangeabilityof motors between manufacturers. The full load torque of amotor has more impact on the frame size than its horsepower.

Note: The industry went through two re-ratings of motors; onein 1952 and the second in 1964. Older motors (before 1952)are called pre-U frames, (after 1952 but before 1964) are Uframes, and newer motors (after 1964) are T frames for motors

up to 250 HP. There are other letter designations that describethe motor and/or its usage. The data can be found by lookingup this indicator in a copy of the National Electrical CodeHandbook.

Step 5. Identify the Power Ratingof the motors available.

List the stated horsepower (HP) rating of each motor on eachpage or index card.

This is the rated mechanical horsepower or full load kilowatt(KW) rating output of the motor. It is the measure of work themotor can do. It is measured at the rated voltage and currentand at the proper applied frequency. Motors can be thought ofas Torque Generators, a device that produces a twisting orturning force to provide rotation to a load. The measurementdescribes the weight moved, the distance it is moved and thetime it takes to do it in accordance with the formula below:

F x R x N Load Torque (ft.-lbs.)xRPMMotor HP = ----------------- or ------------------------------------

5252 5252

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where:F = Force or scale in poundsR = Radius of the motor pulley in Feet

N = Speed of the motor in RPMF x R = Load Torque

Step 6. Identify the Voltage Ratingof the motors available.

List the voltage rating or ratings of each motor on each page orindex card.

The rated voltage on the motor nameplate is usually lower thanthe voltage source of the electrical system. An assumption is

made by the motor manufacturer that there will be a voltagedrop of some amount from the systems transformer down tothe motor terminations. For example, a 460 volt motor isdesigned to operate on a 480 volt system; the assumed voltagedrop would, therefore, be 20 volts. The following chart showsthe most common system 3 Phase Systems and the typicalmotor rated voltages associated with each phase-to-phaselevels:

System and Rated Voltages for Induction Motors

3 Phase RatedSystem Motor Voltage Voltages

216 Volts 208 Volts240 230480 460600 575

2400 23004160 40004800 4600

The rated voltage or voltages on the nameplate represent thevoltage(s) at which the motor operates most effectively. Whenother than rated voltages are applied, the performance of themotor will change and the life of the motor may be reduced.Note: Efficiency remains about the same from 100% to 110%of rated voltage; it will drop off if much lower or much higher.

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Motor current varies inversely with the applied voltage. Higherload currents from lower than rated voltages can causeoverload protective devices to trip or can overheat the motor

resulting in premature failure.

The following chart shows the effects of lower and higher thanrated voltages at startup and running conditions:

Speed, Torque, and Current Changes

Caused ByVoltage Variations From Rated Values

90% of 110% of 120% of

Voltage Voltage VoltageFull Load Current 11% 7% 11%

Increase Decrease DecreaseFull Load Speed 1% 1/2% 1%

Decrease Increase IncreaseStarting Torque 19% 21% 44%

Decrease Increase IncreaseStarting Current 10% 10% 20%

Decrease Increase Increase

The motor develops less starting torque with lower motorvoltage. This results in longer accelerating time to full speedand can cause the motor to stall.

In three phase motors operating near full power, an unbalancein the voltages across phases of only 3.5% can produce a 25%increase in temperature in some windings. This can severelyshorten the life of a motor.

Step 7. Identify the Voltage Connection Diagrams of the AC motorsavailable.

If provided, copy the voltage connection diagrams for each ACmotor on each page or index card.

Many three phase motors have two voltages listed on thenameplate, such as 230/460 volts meaning the motor can beconnected for either 230 or 460 volt operation. In theseinstances different numbers of internal phase coils are being

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utilized or bypassed. This gives the motor more flexibility. Aconnection diagram is usually found on the nameplate orattached to the housing or conduit box which identifies each

voltage, often only marked Hi Volts and Low Volts oppositethe side for the Line connections. Note also that theseconnection points are numbered or color coded to indicate theterminals they represent inside the motor.

Step 8. Identify the Full Load Amperage Ratingof the motors available.

List the full load amperage (FLA) rating or ratings of each motoron each page or index card.

The full load amperage rating or ratings listed on the motornameplate indicates the current the motor draws at nameplatehorsepower, frequency, and voltage. If two currents are listed,the higher current is associated with the lower voltageconnection and the lower current is associated with the highervoltage connection. The National Electric Code (NEC) requiresthat the rated full load current be used as a basis fordetermining the proper sizing of cables, overload protectivedevices, and other overcurrent protection circuitry.

Step 9. Identify the Frequency Ratingof the AC motors available.

List the stated frequency (HZ: Hertz) rating of each AC motoron each page or index card.

This is the number of cycles per second that an AC motor isdesigned to utilize. Induction motors are able to operate at+/- 5% of the rated frequency with no deviation from ratedvoltage. The changes which do occur under these conditions,however, are:

Starting Power Load

Torque Speed Efficiency Factor CurrentFreq.High Decreases Increases Decreases Inc. Dec.Freq.Low Increases Decreases No Change Dec. Inc.

The most significant result of a decreasing frequency is theload current increase it can cause, and the damage that this

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can do if the motor runs at the lower frequency for a substantialtime period.

Step 10. Identify the Speed Ratingof the motors available.

List the speed, in number of rotations or revolutions per minute(RPM), for each motor on each page or index card.

This is the number of rotations the motors moveable elementand shaft completes in a minutes time if at full load operatingconditions. If the driven load, however, is less than thenameplate horsepower rating of the motor, the shaft will turnfaster than the full load speed. If the motor is operating

unloaded or disconnected from the load, the shaft will turn atvery close to what is called synchronous speed. The motor willoperate at speeds from synchronous speed down to its ratedspeed as the load increases from zero to full load. An inductionmotor cannot exceed its synchronous speed unless thefrequency to the motor has changed. The relationship betweenfrequency and speed of a motor is as indicated by the followingformula:

120 x FrequencySpeed = --------------------------------------

Number of Motor Poles

NEMA speed standards for T Frame AC motors are: 3600,1800, 1200, 900, 720, and 600 RPM; for DC motors: 3500,2500, 1750, 1150, 850, 650, 500, 400 and 300 RPM. Actualspeeds measured, even of unloaded motors, will be lower thanthese due to the friction of their bearings. The difference in themeasured speed and the ideal synchronous speed is calledslip. Therefore, the above synchronous speeds are rarelyfound listed on the nameplate. The full load slip of an inductionmotor is often expressed in a percent, rather than in RPM. It is

calculated as shown below:

Synchronous Speed - Nameplate Speed% F.L. Slip = ------------------------------------------------------- x 100%

Synchronous Speed

Note: NEMA design A, B, and C motors commonly have a fullload slip of less than 5%. Design D motors have 5% or more

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slip.

Multi-speed motors are mostly designed in either a single

winding or two winding configuration, but it is possible to findmultiple speed motors. Multi-speed motors are also availablein three application types:

Constant torque: A constant torque motor delivers thesame torque at each of the nameplate speeds. Ratedhorsepower output will change proportionately withnameplate speeds.

Constant horsepower: A constant horsepower motor has

the same horsepower rating at each of the nameplatespeeds. Torque output, however, will change inverselyproportional to the change in nameplate speed.

Variable torque: A variable torque motor has a torqueoutput that changes directly with the nameplate speed. Thehorsepower output at full load also changes, but with thesquare of the speed change.

Step 11. Identify the number ofPhasesthe AC motors available use.

List the number of phases each AC motor uses on each pageor index card.

This is the number of phases of AC power the motor isdesigned to utilize.

Step 12. Identify the Service Factorof the AC motors available.

List the Service Factor (SF) multiplier for each motor on eachpage or index card.

This is the multiplier applied to the motors rated horsepower todetermine how much the motor can run overloadedcontinuously without damaging the motors winding insulation.For example, a 1.15 SF multiplied to a 1 HP motor means itcan safely run at 1.15 HP without damage at listed ambienttemperature or lower. The benefits of a high Service Factor arethat the motor will probably have an extended life, it is

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insurance for temporary overloads, and the motor can be usedat high altitudes.

Caution: Whenever a motor is operated above its ratedpower, the temperature of the motor windingswill increase. For every 10 degrees centigraderise in insulation temperature, the life of themotor is cut in half! It is strongly recommendedthat motors be operated within the range of theirstated ratings and overloaded only for briefperiods.

Step 13. Identify the Ambient Temperature Ratingof the motors available.

List the Ambient Temperature Rating for each motor on eachpage or index card.

If this is listed, it is the maximum temperature in degreescentigrade of the surrounding air, which will allow operation atrated horsepower without damage.

Step 14. Identify the Insulation Classof the motors available.

List the Insulation Class of each motor on each page or indexcard.

The class of insulation used on the motor windings indicatesthe maximum operating temperature of the coil windings in themotor. This has more impact on the life span of a given motorthan any other single construction decision. Approximately 60%of motors brought to repair shops are there due to prematurefailure due to overheating the electrical insulation of the motors.There are four temperature classes: A, B, F and H:

Degrees Ambient Temp. Hot Spot Hot SpotCentigrade: Temp. Rise Allowance Temp.Class A - 40 40 40 40Class B - 60 80 105 125Class F - 5 10 10 15Class H - 105 130 155 180

Classes A and B insulations are considered hydroscopic,

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which means that if they operate in a moist environment, or ifmoisture in the air is allowed to condense on the insulation,some of that moisture is absorbed and retained. As a result, the

insulation dielectric effect is reduced and the motors life willalso be reduced.

Classes F and H insulations are considered non-hydroscopic,which means that they tend not to retain the moisture. Theseclasses should be used in humid environments and insituations where condensation can occur during a motors offcycle.

Step 15. Identify the Duty Classificationof the AC motors available.

List the Duty or Time Rating for each AC motor on each pageor index card.

This is the length of time the motor can run at full load withoutoverheating and/or shortening the life of the motor. It is alsoreferred to as a motors Duty Cycle. The time or duty rating ofa motor is determined by operating the motor at full load andmeasuring the time it takes for the winding to heat up to thetemperature rating of the insulation. A motor with a time, orduty rating other than continuous is a smaller motor that isgiven a higher horsepower rating for a limited period of time.Continuous duty means that the motor could run 24 hours aday if all other factors are within specifications. Other ratingsare: short-time duty, intermittent duty, periodic duty or varyingduty. Within these classes there can be manufacturerestablished time ratings of 5, 15, 30 or 60 minutes. A short timerated motor is used in applications where sufficient rest timeexists for the motor to cool down before it is likely to be usedagain. Examples wound be a garbage disposal or a crane.

Step 16. Identify the Enclosure Typeof the motors available.

List the type of enclosure for each motor on each page or indexcard.

NEMA has classified motor enclosure types and defined themin accordance with the environment in which the motoroperates. The two major groupings are Open or Totally

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Enclosed. The open motors are best suited for cleanenvironments and indoor service; motors that must operateoutdoors, but still in a relatively clean environment use

weather-protected open designs. Totally enclosed motorsprevent the windings and rotor from being directly exposed tothe external air. Totally enclosed motors find use in applicationsthat are dirty, corrosive, or extremely wet. A fairly complex setof ratings exist for those enclosures considered Explosion-Proof. Overall, the most common enclosure types are:

( 1) Open Enclosure - An open end frame structure thatpermits maximum air circulation. This construction isdesigned to prevent falling objects from making contact

with electrically live or moving parts.( 2) Drip-Proof Enclosure - An open machineconstruction that protects the motor from drops of liquidor solid particles striking the enclosure at angles from0 to +/-15 degrees downward from the vertical plane.

( 3) Splash-Proof Enclosure - An open machineconstruction that protects the motor from drops of liquidor solid particles striking the enclosure at angles from0 to +/-100 degrees downward from the vertical plane.

( 4) Guarded Enclosure - An enclosure arranged so that

no accidental or intentional object can penetrate.( 5) Weather-Protected Type 1 - An open constructionthat minimizes the entrance of rain, snow and air-borneparticles.

( 6) Weather-Protected Type 2 - A construction that hasintake and discharge ventilating passages that allowhigh velocity air and air-borne particles to bypass themotor internals.

( 7) Totally Enclosed Nonventilated (TENV) - A totallyenclosed motor which is not equipped for cooling bymeans external to the enclosing parts.

( 8) Totally Enclosed Fan Cooled (TEFC) - A totallyenclosed motor which is equipped for exterior coolingby means of a fan or fans integral with the motor butexternal to the enclosing parts.

( 9) Explosion Proof Motor - A totally enclosed motorconstruction that prevents the ignition of any gases orvapors surrounding the machine and contains sparks,flashes or explosions of specified gas or vapor

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occurring within the motor casing.

(10) Dust Ignition Proof - A totally enclosed motordesigned to exclude ignitable amounts of dust. It does

not permit arcs, sparks, or heat generated inside theenclosure from igniting exterior accumulations oratmospheric suspensions of a specific dust.

(11) Water Proof Enclosure - A totally enclosed motor soconstructed that it excludes water from entering whenapplied in the form of a stream coming from a hose.

Step 17. Identify the Locked-Rotor Code Letterof the motors available.

List the locked rotor KVA per HP, if provided, for each motor on

each page or index card.

The code letter (found in NEC Article 430-7b for motors of HP or more) refers to the starting or locked rotor characteristicsof the motor. These motors draw initial in-rush line currents thatdepend upon the construction of their rotors. This must beconsidered when providing overcurrent protection for the motor.Code Letters are listed as follows:

Code Letters for Locked Rotors:

Code KVA/HorsepowerLetter: with Locked Rotor:

A 0.00 - 3.14B 3.15 - 3.54C 3.55 - 3.99D 4.00 - 4.49E 4.50 - 4.99F 5.00 - 5.59G 5.60 - 6.29H 6.30 - 7.09

J 7.10 - 7.99K 8.00 - 8.99L 9.00 - 9.99M 10.00 - 11.19N 11.20 - 12.49P 12.50 - 13.99R 14.00 - 15.99S 16.00 - 17.99

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T 18.00 - 19.99U 20.00 - 22.39V 22.40 and up

Locked-rotor current values are used when sizing fuses orwhen determining a circuit breaker setting in an induction motorcircuit. The circuit breakers instantaneous trip setting shouldbe adjusted slightly above the locked-rotor current value inorder to allow the motor to come up to speed properly.

Step 18. Identify the NEMA Design Letterof the motors available.

List the NEMA Design Letter for each motor on each page or

index card.

The NEMA Design Letter defines the starting torquecharacteristics of an induction motor. The load on a motor isessentially the torque required by the load. The formula foroperating load torque is:

5252 x Horsepower (HP)Load Torque (ft.-lbs.) = ----------------------------------

RPM

However, two loads with the same load torque requirements atoperating speed can have very different starting load torquerequirements. Failure to take this rating into account whenreplacing a motor can lead to serious mis-applications. NEMAhas designated 5 classes:

Motor Characteristics by Rotor Design Class:

NEMA Full-Load Start Torque Start CharacteristicDesign Speed % X Rated Current Name

Class Regulation Torque x Rated

A 2 - 5 1.5 - 1.75 5.0 - 7.0 Normal

B 3 - 5 1.4 - 1.60 4.5 - 5.0 Gen. Purpose

C 4 - 5 2.0 - 2.50 3.5 - 5.0 Hi Torq. DoubleCage

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D 5 - 8 Up to 3 3.0 - 8.0 Hi Torq.,8 - 13 Hi Resistance

F Over 5 1.25 2.0 - 4.0

Step 19. Identify the Power Factorof the AC motors available.

List the Power Factor for each AC motor on each page or indexcard.

The Power Factor of a motor is the ratio of true power used inwatts and the apparent power delivered. It is expressed as apercentage. Note: Power Factor is not optimal at full ratedvoltage; the optimal Power Factor occurs at about 85% of rated

voltage.

Step 20. Identify the Efficiencyof the motors available, if provided.

List the Efficiency for each motor on each page or index card.

Efficiency is occasionally placed on the nameplates, and isexpressed as a percent of output watts (horsepower watts)compared to input watts at full operating conditions. Anefficiency rating of 85% means that 85% of the input electricalwatts are converted to mechanical output watts or horsepower.The percent efficiency of any energy conversion system can beexpressed as:

Power OUT% Efficiency = ---------------------- x 100%

Power IN

No energy conversion is perfect, so the efficiency is alwaysless than 100%. In the case of an electric motor the conversionis from electrical energy IN (Kwatts) to mechanical energy OUT(HP). Math relationships for this conversion are shown below:

Horsepower OUT x 0.746% Efficiency = -------------------------------------------- x 100%

Kwatts IN

and

Power Out Power IN - Losses

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-------------- = ------------------------ x 100%Power IN Power IN

Summary

Congratulations! You have just demonstrated your ability to read thenameplates of a variety of motors.

It is important for the maintenance electrician to have a completeunderstanding of how to read and interpret the nameplate of any motor they arecalled upon to service. Having acquired this skill an electrician will be able toperform more advanced motor maintenance and troubleshooting with increasedconfidence.

Optional Tasks

None.

Resources

National Fire Protection Association, National Electrical Code. Quincy, MA: 1984.Anderson, Edwin P., and Miller, Rex, Electric Motors. New York: Bobbs-Merrill Co.

Inc., 1983.Bos, Michael H., and Brown, Michael V., Whats In A Name(Plate): A Practical

Guide To AC Induction Motors. Milford, CT: New Standard Publishing, 1990.Putz, Herb, IPTs Electrical Training Manual. Edmonton, Alberta, Canada: IPT

Publishing and Training, Ltd., 1994.Rosenberg, Robert, and Hand, August, Electric Motor Repair, 3rd Ed. Orlando, FL:

Harcourt Brace Jovanovich, 1988.

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