Electric Motor Nameplate Details

1. Manufacturer’s Name, Model, & Serial Number

•The manufacturer’s name identifies the manufacturer of the motor

•The model number identifies the model of the motor produced by the specific manufacturer.

•The Serial number is specific for the manufacturer and identifies the specific motor and is useful in establishing the age of the motor for replacement parts and warranties.

2. Motor Type

•Identifies the type of motor

•Generally describes the starting method including

–DC Motors - Shunt wound, Series wound, Compound wound, Permanent Magnet, and  Universal.

–Single Phase Motors – Split phase, Shaded pole, Permanent Split Capacitor, Capacitor Start, Capacitor Start-Capacitor Run, Universal

–Three Phase Motors – Squirrel Cage Induction, Wound Rotor, Synchronous, Reluctance.

3.Enclosure Type

•The enclosure for the motor should be chosen to protect the motor from the expected operating environment.

–See the next slide for NEMA enclosure ratings

4. NEMA Frame Size Designation

•NEMA has assigned a series of standardized numbers and letters to describe various dimensions and mounting types of motor frames.

–When changing a motor, selecting the same frame size  regardless of manufacturer ensures the mounting mechanism and hole positions will match.

–As a general rule, as frame size increases, so does physical size and horsepower of the motor.

–There are many motors of the same horsepower and size built with different frame sizes so they can be mounted in various manners.

•NEMA Frame Designations may contain

–A prefix of letters

–The frame number

–A suffix of letters

•Frame Size Prefix

–Letter or number prefixes before the NEMA Frame Designation are the manufacturer’s and are not NEMA standardized.  The prefix meanings vary from manufacturer’s

•Example: EF56C

•Frame Size Number

–Two Digit Frame Size – Indicates a fractional horsepower motor of less than 1 horsepower.

•This number is the distance from the center of the drive shaft to the center of the bottom of the mount in sixteenths of an inch.

–Three Digit Frame Size – Indicates an integral horsepower motor 1 horsepower or greater

•Divide the first two digits by four to calculate the distance from the center of the driveshaft to the center bottom of the mount in  fourths of an inch. 

•Example 145 – 14 divided by 4 = 3.5 inches from the shaft to the mount.

•Frame Size Suffix  - Indicates the mounting type of the motor.

–Modern motors (post 1964) are designated with a “T”

•Example:EF145TD – A current T-Frame motor using a D-Flange mount

 

5. Insulation Class

•The type of insulation used in a motor depends on the operating temperature the motor will experience.

–Standard NEMA insulation classes are given by alphabetic classification according the the maximum temperature rating and include, A, B, F, H or J.

–These are an indication of the maximum temperature the motor insulation can withstand without degrading its life

•Modern “T” frame motors use class B insulation as the standard.

–Do not confuse the NEMA insulation classes with the NEMA motor designs which are also given by letters.

6. Horsepower Rating

•The full load output power at the shaft the motor can produce without reducing the motors operational life.

–If a motor produces more horsepower that it is rated for, the service life will be reduced.

–Motors below 1 horsepower are referred to as fractional horsepower motors and motors above 1 horsepower are referred to as integral horsepower motors.

–NEMA has established standard power ratings from fractional to thousands of horsepower.

–Motors have one power rating: Continuous Brake Horsepower

–When an application call for a horsepower between two sizes the larger size is chose to provide the appropriate power to operate the load.  

7. RPM

•RPM is the rated operating speed of the motor at full load.

–Normal speeds for 60 hertz motors vary depending on the number of poles in the motor stator.

–Some motors are dual speed motors and both the speed will be given

–The motor may be one of the following NEMA classification of speed characteristics:

•Constant Speed Motor

–One in which the speed of normal operation is constant or practically constant.

•Multi-Speed Motor

–Can operate at any two or more definite speeds, each being independent of the load power required.

•Varying Speed Motor

–Speed varies with the load.

•Adjustable Varying Speed Motors

–Speed can be adjusted gradually, but once adjusted for a given load, will vary with the change in load. 

8. Duty Rating 

•Duty rating is classified as the length of time the motor is expected to operate under full load. Motors can be classified as either continuous or Intermittent Duty.

–Continuous Duty – Rated to be run continuously without any damage or reduction in life of the motor.

–Intermittent Duty – Rated to be run continuously only for short time periods.  They must then be allowed to stop and cool before restarting. 

9. Phase, Rated Voltage, Frequency

•Phase describes the necessary phase of the electric power supply required for correct connection and operation of the motor – Single or Three Phase

–Single Phase- Generally may be operated on one phase of a three phase power supply with the correct voltage.

•Generally used in smaller motor sizes of less than 1 horsepower and where three phase in not available.

–Three Phase – The advantages of Three Phase often dictate its use

•Little or no voltage flicker when starting

•Cost less to purchase than comparable single phase motor

•Have longer life spans than single phase motors

•This is the electrical supply voltage at which the motor is rated to operate.

•NEMA Standard Motor Voltages

–Single Phase

•115, 230, 115/230, 277, 460, & 230/460

–Three Phase up to 125HP

•208,  230, 460, 230/460, 575, 2300, & 4000

–Three Phase above 125HP

•460, 575, 2300, & 4000

10. Current Rating

•This is the motors rated current at full load and rated voltage and is measured in Amps.

–The motor will draw the rated current when producing its rated output power when supplied its voltage.

–If the motor draws more current than it is rated, the motor is overloaded unless the motor has a service factor larger than 1.0.

–A motor that draws more current than rated will generally have their windings damaged due to the additional heat and the motor’s life will be reduced.

11. Service Factor

•NEMA defines service factor as the amount of continual overload capacity designed into the motor. 

–The amount over the overload over the nameplate rated power the motor can tolerate without reduced motor life.

–A service factor greater than 1.0 allows for a margin of peak horsepower demand without selecting the next larger size motor.  

12. Design Code

•An alphabetic letter used to indicate the NEMA design code for the motor.

–A replacement motor should have the same rating as its predecessor or the circuit fuses/breakers and wire may not be sized appropriately. 

–The code letter is an indication of the locked rotor KVA (kilo-volt-amps) per horsepower for the motor and its design function.

13. Power Factor

•The motor’s rated power factor at rated load and voltage

–The higher the rated horsepower, in general the higher the power factor of the motor.

14. Ambient Temperature

•The maximum ambient temperature the motor should be operated within.

–Ambient – Temperature of the air surrounding the motor.

–Generally standard is 104°F or 40°C.

–If the motor is operated at full load and above the ambient temperature rating service life will be reduced.

15. Temperature Rise

•Temperature rise is the increase in the motors internal temperature as it operates due to current flowing through the windings.

–The ambient temperature plus the temperature rise is the maximum temperature at which the motor should operate at full load.

16. Thermal Protection

•Indicates if the motor has its own internal automatic or manual thermal protection device.

–Can be used to sense excessive load, temperature rise, and/or current flow.

–These prevent the motor from getting too hot and damaging the windings or causing a fire.

–Never bypass a thermal protective device.  

17. Efficiency

•The ratio of mechanical power output of the motor compared to the electrical input.