How to Read a Motor Nameplate

Posted by Trevor Fullwood 20/03/2014 15 Comment(s)
Motors & Drives International


The Big Picture

Reading a motor nameplate can sometimes pose a unique challenge. Most manufacturers display information differently, and nameplates often get dirty, damaged, and occasionally are removed. This can make reading a motor nameplate a difficult or frustrating task.

You will need information from the motor nameplate throughout the life of the motor. If you ever need to size a VFD, repair a motor, replace a motor, connect a motor, correct power factor, purchase parts, or do just about anything with a motor you will need the information on the motor nameplate.


Horsepower is the mechanical output of a motor. You probably already have a good understanding of what horsepower is, so we won’t go into too much detail. However, it is probably important to mention that outside of North America the output rating is commonly expressed in watts or kilowatts.

Did you know?
Horsepower was a term coined by James Watt. He used this term to help market his steam engine.

Remember to be conservative. Using an under powered motor or drive could damage equipment and lead to unnecessary downtime and expense.



Motors are designed to run at the voltage listed on their nameplate. Many industrial motors are designed to run at more than one (line power) voltage. For example, many motors are dual rated and are designed to run at 230V and 460V.

Typically, motors have an operating tolerance of 10%± of the rated voltage on the nameplate (consult your manual). This means that a motor designed to run on 230V can run at 208V (or 240V). Motors should not run outside their designated voltage range, doing so will damage your motor and or equipment. When working with a motor rated for dual voltages don’t forget to verify the corresponding amperage rating and lead connection.

Your service factor rating will drop if you utilize your motor’s voltage tolerance.


Full Load Amp Rating

The FLA rating is the rate at which a motor will consume power at 100% of rated load and at rated and balanced voltage. This number is extremely important, especially when dealing with electrical components. The wiring, starter, circuit breaker, and thermal overloads are all sized based upon the full load amp rating.

When it comes to sizing a VFD the FLA rating is a very important piece of information. Learn more about sizing VFDs at our VFD Buying Guide.


Unless you have a unique application your motor will be rated for single-phase or three-phase input power.

RPM (Speed)

The RPM listed on the nameplate is the shaft speed for the motor. The speed of the motor is directly related to the frequency of the line voltage and the number of poles in the motor. At 60 Hz, a 4 pole motor will rotate at approximately 1800 RPM (7200/4 poles). However, depending on the amount of rotor slip the motor was designed for you may see the RPM listed as 1775 or 1750, et cetera. This number represents what the manufacturer has engineered the motor will rotate at under full load with the set frequency listed on the nameplate.

Design Letter

The design letter provides information about a motor’s starting torque. B (normal starting torque), C (high starting torque), and D (very high starting torque) design letters are the most common. A motor’s starting torque is different than torque during normal operations.

For example, two motors with similar running torque ratings may have very different starting torque ratings. A motor being used for a centrifugal fan is likely to have different starting torque requirement than a conveyor belt.

Service Factor

Motors are often designed to handle a temporary increase in demand. Service factor represents the motor’s ability to handle these temporary demand increases. Think of service factor as an insurance policy. It is designed for ambient temperatures, altitude, high and low line voltages, and imbalanced voltages. It should not be used as a method of increasing motor horsepower.

The service factor is expressed as a decimal. If you do not see a service factor rating on the motor nameplate the service factor is typically 1.00. Additionally, all motors running on a VFD (even at 60 HZ) will lose service factor and be rated at 1.00. Please consult your manual for more information.

You can dramatically reduce the life of your motor by consistently running into the service factor rating.



Frequency is the duration peak to peak of an AC sine wave (60 HZ = 60 cycles per second). Frequency is directly related to the motor’s speed.

In North America, the standard frequency is typically 60 HZ. Outside North America 50 HZ is often the standard. Some nameplates will have multiple frequency ratings.


AC motors that are started at full voltage will draw a greater current (amps) than during normal operations. This is commonly referred to as inrush current or starting current. These codes represent a range of inrush current.

Code LetterKVA/HPApproximate Mid-Range Value*

*To find approximate inrush current for your motor match the code letter on your motor nameplate with the corresponding approximate mid-range value on the chart; multiply the mid-range value and the full load amp rating on your motor nameplate.


A motor’s efficiency rating measures how well the motor converts electrical energy (input) into mechanical energy (output). This is usually displayed as a decimal.

A motor’s energy consumption is by far its largest operating expense. As a general rule, a motor that runs 24/7/365 for one year could cost three times more than the purchase price in power consumption. In many applications a VFD can provide considerable savings with regards to operational costs. Centrifugal pumps often have great potential for energy savings. Under some circumstances using a VFD to reduce speed by 20% can result in energy savings of 50%. However, energy savings will vary based upon several factors, such as motor conditions, application, and energy costs in your area.


The insulation class describes a motor’s ability to withstand temperatures over time. B, F, and H are commonly used insulation types. Letters occurring later in the alphabet represent insulation that is better able to withstand temperature. So class F can withstand temperature better than a class B.

Motor insulation systems that are rated for inverter use will be specified on the motor nameplate (or a sticker). These systems should have wire rated for a minimum of 1600 volt spikes, F or H class insulation, and will be processed with 100% sold resin in a vacuum pressure impregnation (VPI) system.

Motors that do not fit this specification can be rewound to meet these requirements.


CT stands for Constant Torque and VT stands for Variable Torque. If these ratings are on your motor nameplate it typically means your motor is rated for inverter use. Consult your manual for more information.


Duty is the length of time a motor can run without a cooling period. Most industrial motors are rated for continuous duty.

Frame Size

NEMA frame size outlines motor footprint and shaft dimensions. The first two numbers represent the shaft height from the mounting base. This number divided by four represents the shaft height in inches. The third number is the bolt mounting hole dimensions, some motors may have multiple holes for different mounting options.

The letter is the type of frame, each type is provided below:

Fractional type motors (frame size 48 and 56)

CFace mounting (can be round body or footed)
GGasoline pump motor
HIndicates a frame with a larger “F” dimension
JJet pump motor
YSpecial mounting dimensions
ZAll mounting dimensions are standard except shaft extension and or design

Integral type motors (frame size 143 to 449)

ADC motor or generator
CFace mounting (can be round body or footed)
DFlange mounting (can be round body or footed)
PVertical hollow and solid shaft with P-base flange
HPVertical solid shaft with P-base flange, normal thrust
JMClosed coupled pump motor with C-face mounting and special shaft extensions
JPClosed coupled pump motor with C-face mounting and special long shaft extensions
LPVertical sold shaft with P- base flange, medium thrust
SStandard short shaft
TStandardized shaft (1964 and newer)
UStandardized shaft (1964 and older)
VVertical mounting
YSpecial mounting dimensions
ZAll mounting dimension are standard except shaft extension

Enclosure Type

The enclosure type displays information about how well the motor is protected from the environment. The most common enclosure types are Open Drip-Proof (ODP) and Totally Enclosed Fan Cooled (TEFC).

ODP – An Open Drip-Proof motor is an open enclosure that allows air to flow freely inside around the windings. It is protected from drops of liquid falling downward from a 0 to 15 degree angle, but is not waterproof.

TEFC – A Totally Enclosed Fan Cooled enclosure prevents air from flowing freely into the motor. The motor is cooled by a fan that blows air on the outside of the enclosure. A TEFC is not fully air or water tight. Outside contaminants can enter the motor, but this typically doesn’t interfere with normal operations.

There are several other enclosure types not listed here.


Your motor nameplate may include bearing information.

There may be two bearing specifications on a motor nameplate, the drive shaft bearing and the opposite drive shaft bearing. The different between these two are location in the motor. The drive shaft bearing is located close to where the drive shaft extends out of the motor. The opposite drive shaft bearing is on the opposite side of the drive shaft.

Every manufacturer has their own way of displaying bearing information and this can vary widely between manufacturers.

Consult your manufacturer for more information about bearings.

Voltage Connection (Strapping) Diagrams

Connection diagrams display information about connecting your motor to the proper voltage. Some motors are designed to handle multiple voltages, so there may be more than one diagram.

Carefully select the correct diagram. Incorrectly connecting wiring will damage your motor.


Model Number and Serial Number

The serial number and model number are used to identify the equipment with the manufacturer.


Leave a Comment

15 Comment(s)

Accura EX:
13/01/2017, 06:09:18 AM

I have a question for ya Yin.
I can not find the frame size of my motor!
Help appreciated.

Yin (Admin):
13/01/2017, 09:02:23 AM

You are welcome to send us a photo of your nameplate to

Accura EX:
17/01/2017, 05:51:19 AM


11/01/2017, 06:13:47 AM

How to determine frame size???

Yin (Admin):
12/01/2017, 02:02:56 PM


The frame size should be specified on the motor name plate. Some common frame sizes are 185T, 254T, 365T, etc.

11/11/2016, 02:39:50 PM

I have motor with nameplate ratings for 208-230 VAC and ratings for 460 VAC. My VFD input is single phase 240 VAC but output is 3 phase. Which settings do I enter in VFD from motor name plate?

Yin (Admin):
11/11/2016, 02:49:44 PM

Hi George,

You enter whatever your input voltage is from your power supply. I assume it would be single phase 230V or 240V. Check out this programming video: How to program a Mitsubishi D700.

13/12/2016, 08:04:03 AM

George, most drives will trigger a fault state called "Phase loss". You may deactivate the triggering of this fault in your configuration, but have in mind the power drop you will get.

Gabriel Bimpong:
23/10/2016, 11:21:44 PM

thank you very much for the information you gave me,it was very accurate.

11/07/2016, 05:23:21 PM

Thisis my motor - I can't seem to locate the frame size - can someone help?
Here are the specs I can read
3 HP
3 PHase
230/460 v
60 Hz
1740 RPM
7/3.5 or 3.6 Amps
1.15 Service factor
Still not sure on the enclosure type it is a shaft motor
and the model seems to read Reliance Electric Duty Master 7342308-001
Any help appreciated

Yin (Admin):
11/07/2016, 05:33:04 PM

Hi Collin,

Is 7342308-001 the serial number? Category number? Or model number?

Joshua Hrouda:
21/06/2016, 08:46:15 AM

Hi. Nice info! :) But you failed to mention "Date" and "Temp".
Sadly, often the date is left blank on motors I've looked at.
But I have a motor on my bandsaw, that was made in 1985, and for temp, it has 60°C. I don't know if that's temperature rise, or just max. operating temp. And if the latter, at the surface of the motor, or internal!!?
I don't think it mentions the insulation, but I will check next time I go to work to have a look at it.

29/05/2016, 03:45:09 AM

Dear Sir,

I have 2 nos of AHU fan motor (A & B) with below rated nameplate info.

Volts: 380-415/460
Amps: 57.4-52.6/46.3
RPM: 1475/1773
kW: 30
Hz: 50/60
Eff: 0.923
PF: 0.86

While both are running, the avg (RYB) amp reading from True RMS clamp meter for motor A is 47.7A and motor B registered at 28.4A. Both motor A&B have no VFD installed.

May I get advise what could cause the above scenario.

Thank you Edward

Yin (Admin):
01/06/2016, 12:40:17 PM

Hi Edward,

This is because the torque of one shaft is greater than the other. There could be many reasons, here are some potential causes:

- The shimming on the two fans are different
- The air duct size is different
- One of the motors' bearing is smooth and the other isn't
- One of the motors needs greasing

We think it is most likely the shimming. You can start by checking the angles of the the blades. Hope this helps.

CK Loh:
16/01/2016, 05:34:28 AM

Very informative. Tq

12/01/2016, 01:29:18 PM

Hie l am new please send me basic information on hw to wire motor and generators

05/01/2016, 04:36:45 AM

Hi . I have a motor with this specification :P=4500 kw, V=6300 v , I=479 A = cos phi=0.89 .but According to the power Formula for an electrical motor P=1.73*v*i*cos phi ,my calculation is P=1.7*6300*479*0.89= 4651860 w, and my question is why there is different ?

05/01/2016, 10:32:49 AM

The power you calculated is actually applied (true) power (P_True), not power output (P_O, motor nameplate HP or kW). If we perform an energy balance on a motor, the power flowing into the motor is applied (true) power (P_T) and reactive power (P_R) [1], both provided by the power source (utility, generator, etc.) [2]. The power flowing out of the motor is power produced by the motor (P_O, motor nameplate HP or kW) and any energy losses resulting from resistance in windings or mechanical friction (P_L):

P_R + P_T = P_O + P_L


P_R – reactive power
P_T – applied (true) power
P_O – output power (motor nameplate HP or kW)
P_L – energy losses

Calculating for P_T, as you have done:

P_T = sqrt(3)*I*V*cos(phi)


cos(phi) = PF – power factor [3].

The difference between the motor’s output power and true power can be given by the motor’s efficiency (EFF. or greek letter mu on motor nameplate):

mu = P_O/P_T * 100%,

which, in your case, is:

mu = 4500 kW/4652 kW * 100% = 96.7%.

[1] The reactive power is only used to magnetize the motor and create the magnetic field inside of the motor, and is not useful power.

[2] These calculations were performed assuming a positive current in the AC cycle. The calculations for negative current (power flowing to utility) are only slightly different, however, the result is the same.

[3] Power factor is the ratio of applied (true) power to apparent power. Apparent power is the vector sum of applied (true) power to reactive power. Any power factor less than 1 means that the circuit's wiring has to carry more current than what would be necessary with zero reactance in the circuit to deliver the same amount of (true) power to the resistive load.

If you are sizing a VFD or a motor for an application, please give us a call at 1-800-800-2261, and we would be happy to help. We sell VFDs and motors for both medium and low voltage.

25/10/2015, 01:53:09 AM

Hi i have a 3 phase cmg motor 3hp 415volts 4.2 amps it was wired up in star configuration but have since changed it to run on delta
just wondering what type/size vfd i would need to run this on 240 single phase household
Regards James.

robin rose:

I am trying to match a Hitachi miter saw listed at 15amps with a portable generator that is listed to 8000 running watts and 10000 surge watts (Generac XT8000). So help me, I can't find the motor code or surge watts for the miter saw! In fact, I can't find any motor codes for circular saws, etc. The portable generator people are vague about what tools their generators will run AND the tool people are vague about the surge watts of their tools. Any notion as to where to look? The notion that running watts times 3 does not always work... it is a guess and the companies know it!

10/03/2015, 08:34:00 AM


We have discussed your questions with our motor specialist. Here is a summary of his answer.

Power tools are universal motors, not your standard single phase motor. There will not be power codes on the plates.

Universal motors are different than induction motors in both starting and running. Starting inrush is higher with universal motors. Motor infuse is the current to bring the motor from rest to full speed. Everything the motor turns at starting adds to the energy to break it from rest to speed. Gear boxes are multipliers for either speed or torque. The blade also adds load requiring more current to bring from rest to speed. If the blade is against wood then the starting current would rise more depending on the hardness of the wood, the pressure against the wood and how long the cut is.

If possible, you should test the inrush while on commercial power.

06/10/2015, 10:51:19 AM

8000 watts/120 volts = 66 amps. Your saw is 15 amps, so you're good.

Lowell Weeks:
23/01/2015, 01:14:42 PM,

I am looking to size a VFD for a 10HP, 380V, 50Hz pump. If a 60Hz motor is producing 10HP then a 50Hz motor is producing 8.33HP? So a 10HP 50Hz motor is equivalent to a (6/5)10Hp motor at 60Hz or approximately 12HP? What HP/KW drive would I use for the 10HP 50Hz drive? I am assuming that I should size for the 12Hp current? I feel I am missing something that is fairly obvious here.

26/01/2015, 09:53:00 AM

Hi Lowell,

You cannot equate HP/kW with Hz, because they are two different calculations. To size your 10HP motor, regardless of what frequency if you are running it, we will need the FLA of your motor to properly size a VFD. The FLA (Full Load Amps) can be found on the motor nameplate. Feel free to send us an e-mail ( with the FLA, and we will provide you with a couple of options. Let us know if you have other questions!

03/10/2014, 12:16:11 AM,

I am trying to identify a replacement motor for the following GE Model Number:


it need to run on 240V ph1

Any help will be most welcome

26/05/2014, 01:02:48 PM

Code FZ ---does this have anything to do with a dual rotational motor? I have an old commercial garage door opener with a Westinghouse 1/3hp 317P193 AD81 that quit, what can I replace it with and does the motor have 2 field windings?