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.


It is not always easy to read motor nameplates. Different manufacturers have different ways of displaying their information, and the nameplates are not always clean, they sometimes get damaged or removed. These are some of the factors that make it difficult to read a motor nameplate.  

You’ll need to get the entire history of the motor nameplate. The importance of gathering information on motor nameplate can never be overemphasized especially if you want to replace your motor, repair your motor, correct power factor, seize a VFD, buy parts, connect a motor, or any other thing that has to do with motors.


Horsepower is the name given to a motor’s mechanical output. Most people probably know a thing or two about it, so there’s really no need to go into much detail. That being said, I should probably mention that output rating outside North America is measured in kilowatts or watts. 


Motors are designed in a way that allows them to run at the particular voltage provided on their nameplate. A lot of industrial motors run with more than one voltage. For instance, some motors are dual rated, which means they run at both 230V and 460V.

The operating tolerance of most motors is about 10%± of the nameplate’s rated voltage. The implication of this is that, a motor that runs on 230V is capable of running at 208 or 240V. It is not advisable for motors to exceed that designated voltage, because it can cause grievous damage to the motor and equipment. Always remember to verify the corresponding lead connection and amperage rating when working with any motor that is designed for dual voltage.

Full Load Amp Rating

A motor’s FLA rating can be described as the consumption rate of the motor at 100% both at rated load as well as at balanced and rated voltage. The value of this number cannot be overemphasized particularly when electrical components are involved. The load amp rating has a great effect on the circuit breaker, thermal overloads, wiring and starter, particularly for sizing.

The FLA rating comes in handy when sizing a VFD.


If you don’t have a special application, it is safe to say you motor will be rated for either three phase or single phase input power.

RPM (Speed)

The RPM on the nameplate is actually the motor’s shaft speed. The motor’s speed is connected to the line voltage’s frequency as well as the number of poles that can be found in the motor. A 4 pole motor is capable of rotating at about 1800 RPM (7200/4 poles) when it’s at 60 Hz. However, the RPM might be listed as 1759 or 1755, depending on the motor’s rotor slip. This number is the rate at which the motor will rotate when it’s at full load at the frequency provided on the nameplate.

Design Letter

The design letter was created to provide information on the motor’s starting torque. The most common design letters are D – which has an extremely high stating torque, C – high starting torque and B – whose starting torque is normal. There’s a difference between torques during their regular operations and a motor’s starting torque.

For instance, it is possible for two motors with very similar running torques ratings to have dissimilar starting torque ratings. Also, the starting torque requirements of a centrifugal fan’s motor will probably be different from that of a conveyor belt.

Service Factor

Most motors are designed to cope with temporary upsurge in demand. The service factor is a representation of the ability of the motor to handle the temporary upsurge in demand. Service factor can be likened to an insurance policy. They are designed to handle imbalanced voltages, low and high line voltages, ambient temperatures and altitude. However, it is not a means for boosting motor horsepower.

 Decimals are used to express service factor. Most service factors are normally 1.00. In addition, motors on VFD will lose their service factor and giving them a 1.00. rating. You can check out your manual for additional information on this.


Frequency can be described as an AC sine wave’s (i.e. 60 HZ = 60 every second) duration peak to peak. A motor’s speed is directly connected to its frequency.

The standard frequency for North America is 60 HZ. But the standard frequency for places outside North America is 50 HZ. However, certain name plates might come with multiple frequency ratings.


AC motors at full voltage are likely to bring in higher current (amps) than they do in the course of their regular operations. This is known as starting current or inrush current. These codes are actually a range of different inrush currents.  

*If you want to find your motor’s perfect inrush current, match your motor nameplate code letter to its corresponding mid-range value from the chart; try multiplying your motor nameplate’s full load amp and mid-range value.


The job of a motor’s efficiency rating is to measure the capability of a motor to convert electrical energy into mechanical energy. This is displayed in form of a decimal.

The biggest operating expense incurred by a motor is probably its energy consumption. The general rule is that a motor that can run 24/7/for a year, can actually cost triple the purchase price when it comes to power consumption. When it comes to operational costs, VFD is a great way to save for a lot of applications. Centrifugal pumps are also a great way to save energy. You can also save about 50% energy by making use of a VFD to lessen speed by 20%. However, a lot of factors like the cost of energy in your area, applications, as well as motor conditions often have a profound effect on energy savings.


Insulation class is the ability of a motor to withstand long term temperatures. H, B and F are some of the common types of insulation. The last letters in the alphabet represent the type of insulation that can withstand temperature better. The implication of this is that class F is better equipped to withstand temperature than class B.

The motor nameplate will specify the motor insulation systems rated for inverter use. The wires of these systems should be rated for at least 1600 volt spikes, H or F insulation and processed with 100% resin through a vacuum pressure impregnated system.

Any motor that does not meet this requirement cab be modified to meet them.


VT is an acronym for Variable Torque while CT is an acronym for Constant Torque. The implication of having these ratings on your motor is that such a motor can be used for inverter. You can check out your manual for further information on this.


Duty can be described as the duration required for a motor to run without cooling. A high number of industrial motors are designed for continuous duty.

Frame Size

NEMA frame size is used to outline shaft dimensions and motor footprints. The first 2 numbers are used to represent the shaft height straight from its mounting base. To find the inches of the shaft height, divide the number by four representations. The third number is actually the dimension of the bolt mounting hole, there are motors with different holes for various mounting options.

Below are the frame sizes for each type:

The frame size for fractional type motors is 48 and 56.

The frame size for integral type motors is 143 and 449

Enclosure Type

The enclosure type is responsible for revealing how well protected the motor is against environmental factors. Totally Enclosed Fan Cooled (TEFC) and Open Drip-Proof (ODP) are the two most popular closure types.

An Open Drip-Proof ODP motor is a form of open enclosure that permits air to flow freely around the windings. This enclosure is safeguarded by liquid drops coming down from 0-15 degree angle, but it isn’t waterproof. 

Totally Enclosed Fan Cooled TEFC enclosure works by preventing free flow of air into the motor. This motor receives its coolness from a fan which blows air outside the enclosure. This enclosure is not completely water or air tight. The motor can be contaminated by substances from outside, but this does not have any effect on regular operations.

There are lots of other enclosure types that are not on this list.


There might be some bearing information on your motor nameplate.

A motor nameplate might have two bearing specifications, the opposite drive shaft bearing and the drive shaft bearing. Their location within the motor is the major difference between these two specifications. The drive shaft can be found close to the location where it extends away from the motor, while the opposite drive shaft is opposite the drive shaft.

Manufacturers all have their different methods of showcasing bearing information and it varies from manufacturer to manufacturer.

Don’t hesitate to contact your manufacturer for additional information on bearings.

Voltage Connection (Strapping) Diagrams

The role of a connection diagram is to display information on how to connect the motor to the right voltage. Since there are motors designed to handle more than one voltage, the diagrams might be more than one.

Serial Number and Model Number

Both the manufacturer and the equipment can be identified by the model number and the serial number.