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Home / Technical Articles / 19 Essential Information You Can Find On Motor Nameplate

Understanding motor’s nameplate

Motor nameplate is normally located on all produced electric motors. Understanding nameplate information can be hard sometimes, but is essential. In most countries it is a requirement for manufacturers to display all information on the motor’s nameplate, but often this is not the case.

19 Essential Information Found On Motor’s Nameplate
19 Essential Information Found On Motor’s Nameplate (on photo: Baldor Reliancer motor; credit:

However, when a motor has been in operation for a long time, it is often not possible to determine its operating information because nameplates of motors are often lost or painted over.

  1. Voltage
  2. Frequency
  3. Phase
  4. Current
  5. Type
  6. Power factor
  7. kW or Horsepower
  8. Full-load speed
  9. Efficiency
  10. Duty
  11. Insulation class
  12. Maximum ambient temperature
  13. Altitude
  14. Enclosure
  15. Frame
  16. Bearings
  17. NEMA // Letter code
  18. NEMA // Design letter
  19. NEMA // Service factor

Electrical input //

1. Voltage

This data tells you at which voltage the motor is made to operate. Nameplate-defined parameters for the motor such as power factor, efficiency, torque and current are at rated voltage and frequency. When the motor is used at other voltages than the voltage indicated on the nameplate, its performance will be affected.

Voltage on motor nameplate
Voltage on motor nameplate

2. Frequency

Usually for motors, the input frequency is 50 or 60 Hz. If more than one frequency is marked on the nameplate, then other parameters that will differ at different input frequencies have to be indicated on the nameplate as well.

Frequency on motor nameplate
Frequency on motor nameplate

3. Phase

This parameter represents the number of AC power lines that supply the motor. Single-phase and three-phase are considered as the standard.

Phase on nameplate
Phase on nameplate

4. Current

Current indicated on the nameplate corresponds to the rated power output together with voltage and frequency. Current may deviate from the nameplate amperes if the phases are unbalanced or if the voltage turns out to be lower than indicated.

Current on nameplate
Current on nameplate

5. Type

Some manufacturers use type to define the motor as single-phase or poly-phase, single-phase or multi-speed or by type of construction. Nevertheless, there are no industry standards for type. Grundfos uses the following type designation: MG90SA2-24FF165-C2.

Motor type designation
Motor type designation

6. Power factor

Power factor is indicated on the nameplate as either “PF” or “P .F” or cos φ . Power factor is an expression of the ratio of active power (W) to apparent power (VA) expressed as a percentage.

Numerically expressed, power factor is equal to cosine of the angle of lag of the input current with respect to its voltage.

The motor’s nameplate provides you with the power factor for the motor at full-load.

Power factor also known as cosFI
Power factor also known as cosFI

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Mechanical Input //

7. kW or horsepower

kW or horsepower (HP) is an expression of the motor’s mechanical output rating – that is it’s ability to deliver the torque needed for the load at rated speed.

8. Full-load speed

Full-load speed is the speed at which rated full-load torque is delivered at rated power output. Normally, the full-load speed is given in RPM. This speed is sometimes called slip-speed or actual rotor speed.

Motor efficiency label; Full-load speed; Efficiency in percent and kW or horsepower
Motor efficiency label; Full-load speed; Efficiency in percent and kW or horsepower

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Performance //

9. Efficiency

Efficiency is the motor’s output power divided by its input power multiplied by 100. Efficiency is expressed as a percentage. Efficiency is guaranteed by the manufacturer to be within a certain tolerance band, which varies depending on the design standard, eg IEC or NEMA.

Therefore, pay attention to guaranteed minimum efficiencies, when you evaluate the motor’s performance.

10. Duty

This parameter defines the length of time during which the motor can carry its nameplate rating safely. In many cases, the motor can do it continuously, which is indicated by an S1 or “Cont” on the nameplate. If nothing is indicated on the nameplate, the motor is designed for duty cycle S1.

Motor duty
Motor duty

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11. Insulation class

Insulation class (INSUL CLASS) is an expression of the standard classification of the thermal tolerance of the motor winding. Insulation class is a letter designation such as “B” or “F”, depending on the winding’s ability to survive a given operating temperature for a given life. The farther in the alphabet, the better the performance.

For instance, a class “F” insulation has a longer nominal life at a given operating temperature than a class “B”.

Insulation class. CI.F(B) = class F with temperature rise B
Insulation class. CI.F(B) = class F with temperature rise B

12. Maximum ambient temperature

The maximum ambient temperature at which a motor can operate is sometimes indicated on the nameplate. If not the maximum is 40°C for EFF2 motors and normally 60°C for EFF1 motors. The motor can run and still be within the tolerance of the insulation class at the maximum rated temperature.

The power output reduction curve
The power output reduction curve shows the performance reduction with increased ambient temperature or increased installation height above sea

13. Altitude

This indication shows the maximum height above sea level at which the motor will remain within its design temperature rise, meeting all other nameplate data.

If the altitude is not indicated on the nameplate, the maximum height above sea is 1000 metres.

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14. Enclosure

Enclosure classifies a motor as to its degree of protection from its environment and its method of cooling. Enclosure is shown as IP or ENCL on the nameplate.

Motor frame, enclosure ,bearing and grease information on nameplate
Motor frame, enclosure ,bearing and grease information on nameplate

15. Frame

The frame size data on the nameplate is an important piece of information. It determines mounting dimensions such as the foot hole mounting pattern and the shaft height. The frame size is often a part of the type designation which can be difficult to interpret because special shaft or mounting configurations are used.

The frame size data on the nameplate
The frame size data on the nameplate

16. Bearings

Bearings are the component in an AC motor that requires the most maintenance. The information is usually given for both the drive-end (DE) bearing and the bearing opposite the drive-end, non drive- end (NDE).


Besides the above mentioned information, NEMA nameplates have some supplementary information. The most important ones are:

  1. Letter code,
  2. Design letter and
  3. Service factor.

17. Letter code

A letter code defines the locked rotor current kVA on a per horsepower basis. The letter code consists of letters from A to V. The farther away from the letter code A, the higher the inrush current per horsepower.

NEMA code letterLocked rotor kVA/HPNEMA code letterLocked rotor kVA/HP 
A0 – 3.15L9.0 – 10.0
B3.15 – 3.55M10.0 – 11.2
C3.55 – 4.0N11.2 – 12.5
D4.0 – 4.5ONOT USED
E4.5 – 5.0P12.5 – 14.0
F5.0 – 5.6QNOT USED
G5.6 – 6.3R14.0 – 16.0
H6.3 – 7.1S16.0 – 18.0
INOT USEDT18.0 – 20.0
J7.1 – 8.0U20.0 – 22.4
K8.0 – 9.0V22.4 AND UP

18. Design letter

Design letter covers the characteristics of torque and current of the motor. Design letter (A, B, C or D) defines the different categories. Most motors are design A or B motors.

A design A motor torque characteristic is similar to the characteristic of a design B motor; but there is no limit in starting inrush current. With a design B motor, the motor manufacturer has to limit the inrush current on his products to make sure that users can apply their motor starting devices.

So, when replacing a motor in an application, it is important to check the design letter, because some manufacturers assign their products with letters that are not considered industry standard which may lead to starting problems.

19. Service factor

A motor designed to operate at its nameplate power rating has a service factor of 1.0. This means that the motor can operate at 100% of its rated power.

Some applications require a motor that can exceed the rated power. In these cases, a motor with a service factor of 1.15 can be applied to the rated power. A 1.15 service factor motor can be operated at 15% higher than the motor’s nameplate power.

However, any motor that operates continuously at a service factor that exceeds 1 will have reduced life expectancy compared to operating it at its rated power.

Go back to Index ↑

Reference // Motor book by Grundfos (Download)

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More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. Clovis
    Mar 16, 2023

    From the point of view I see this site to helpful were motors are concerned.

  2. Douglas Mackinnon
    Aug 12, 2022

    Edvard, Novice question here In regard to 3 phase motors: Is a measured RLA of around 27 amps on each line too high for a motor whose data tag list 30 amps?
    Does a technician need to take a reading or average of 3 then multiply by 1.73 and compare this to the data tag? Or should no phase be operating above 30 amps + service factor?

  3. Sean
    Mar 09, 2022

    I have an old mill and the nameplate has some info I’m not familiar with. In order it reads : H.P._ R.P.M._ FR. 254 VOLTS_ AMPS_ PH._ CYC 60. The info with number values are the two I’m unsure of. My best guess is that FR. is frequency and CYC is duty cycle? But I really don’t know :/

    • chris
      Mar 13, 2022

      Hi Sean, the FR likely refers to the frame dimensions (25/4 = 6.25″ base to shaft) and CYC probably refers to the frequency or cycles per second which will be 60Hz in North America.

    • Art
      Sep 17, 2022

      Frame and frequency

  4. Giannis
    Jun 08, 2021

    Does the voltage refer to line-to-line or line-to-neutral values?

  5. Joe King
    Mar 28, 2021

    Is the motor nameplate rated current the current in one phase leg or the sum of all three phase legs (current in one phase * 1.73)?

  6. Aniket
    Sep 12, 2020

    How to know motor is suitable for VFD operation from motor nameplate. Here in given nameplatethere is no info is mentioned about VFD operation.

  7. Callixte Kayigire
    Mar 14, 2020

    How to know the quantity grease to fill in the bearing by reading the motor nameplate

  8. Callixte Kayigire
    Mar 14, 2020

    1.What is the function of duty cycle on motor nameplate?
    2. How to know the time to regrease a motor by reading it’s nameplate?

  9. Gabriel
    Aug 26, 2019

    Good evening Sir. I have a question?How can a single phase motor can be made self starting

    • Ankit
      Feb 24, 2020

      Single phase induction motor cant be self starting because in this motor when current induce in rotor(due to emf) then rotor experience a force but it can’t not decide direction to rotate (because rotor are inner part and both upper side like stator have a same magnetic field).in that case rotor create a hum sound when we give some torque on a particular direction then the rotor rotate start that direction by an auxiliary supply when rotor start rotate then auxiliary supply automatically disconnect and motor run properly

    Jul 03, 2019



  11. Robery
    May 29, 2019

    How would you determine FLA with this info?

  12. Benny
    May 07, 2019

    Is it safe or even allowed to apply higher voltage than the voltage indicated on the equipment name plate? Ex. Applying 480 volt to a 208 stamped nameplate?

    • Edvard
      May 07, 2019

      Why would you do this? You could burn the windings…

      • Carl
        Dec 04, 2020

        Love your site…
        There is a case its to do with the VF ratio
        So you connect the motor in delta …but run on the star rated voltage. Then adjust the drives VF ratio to suit.
        Its to do with delivering more torque above the nominal speed of the motor.
        …I’ve seen this and done it. …but you are now working outside of the manufactures guidelines.
        Not a commonly known trick and I’ve only seen it done twice….
        Your dealing with an inverter so you can set max current trip etc etc..if you think it will cook the motor

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