How To Read a Motor Nameplate

Friday - 21/01/2022 08:35

How To Read a Motor Nameplate

Found on all types of electric motor, the motor nameplate provides information about the motor’s construction and performance characteristics.
Whilst motor standards are established on a country by country basis, most motors fall under the two main industry bodies: the International Electrotechnical Commission (IEC) and the National Electric Manufacturers Association (NEMA) and their nameplates adhere to the standards set out by the body.

Understanding how to read the nameplate of a motor can help identify faults more accurately, ensure that the right motor is being used for the job and can result in a more efficient service from a motor repair company if there is a fault.

What Information Can Be Found On a Nameplate?

A nameplate contains a large amount of useful information relating to the motor including the type, RPM. frame size and power of the motor. Whilst the exact layout and format of the motor nameplate will be dependent on the manufacturer and what standards are being adhered to (IEC or NEMA), once you understand one motor it’s much easier to understand another.

Number of Phases

This shows the type of power supply for which the motor is designed. There are single phase and three phase motors.

Rated Operating Voltage (Volts)

This shows at which voltage is the motor is designed to operate most efficiently. Motors are designed to operate at +/-10% tolerance of this value. Other parameters shown on the nameplate including: power factor, efficiency, torque and current are at rated voltage and frequency. Using the motor at voltage outside this tolerance will most probably lead to different performance.

Service Duty

In this case, S1 shows that this is a continuous duty motor that works at a constant load for enough time to reach temperature equilibrium. The parameter Duty/Time rating represents the period of time during which the motor can run at its nameplate rating/rated load safely and indicates whether the motor is rated for continuous duty.

This is shown as “CONT” for continuous duty 24/7 but they can also have a short-time rating from 5 to 60 minutes, most motors are rated for continuous duty. The rating of the motor is the ambient temperature vs. the time it can operate at that temperature, the EIC break this down into ten ratings.

Efficiency Code

This shows the percentage of the input power that is actually converted to work output from the motor shaft. The motor will have a “nominal” efficiency shown on the plate, this is the average efficiency. The closer this value is to 100%, the lower the electricity consumption cost is going to be.

The four levels of motor efficiency are

    IE1 – Standard Efficiency
    IE 2 – High Efficiency
    IE 3 – Premium Efficiency
    IE 4 – Super Premium Efficiency
ie3 electric motor

In our example, we are shown an IE Code of IE3 which indicating premium efficiency.

Frame Size

This shows the frame size. The frame size determines the mounting dimensions such as the foot openings pattern and the shaft height.

The dimension of the electric motor based on the NEMA system for fractional hp motors (micro motors) have two digits and represent the shaft height from the base’s bottom in sixteenths of one inch.

For large motors the frame size has three digits, the first two digits stand for the shaft height in one quarter of an inch. The third digit is the bolt mounting holes dimension, the longer the motor body, the longer the distance between mounting bolt holes in the base. Finally, the letter is the type of frame.

The same concept applies for IEC type motors (metric motors) but the height is measured in millimeters instead of inches.

Degree of Protection

The IEC uses a two-digit ingress protection (IP) rating to measure how well the motor is protected from the environment. NEMA uses an enclosure description that is of a similar standard.

Insulation Class

The highest temperature in the motor’s hottest spot has a serious impact on the life of the electric motor. The temperature that occurs at that spot is a combination of motor design temperature and the ambient temperature. The insulation class shows the motor’s ability to withstand temperatures over time.

The motors have different insulation capabilities. The insulation codes show their thermal tolerance or ability to survive at a specified temperature for a period of time. The higher the designated code letter, the greater the heat capability.

It is based on the highest temperature the material can withstand continuously without degrading or reducing motor life. IES specify 5 different types of insulation classes:

    Class A – 105c
    Class E -120c
    Class B – 130c
    Class F – 155c
    Class H – 180c

Temperature Rise

Each class of insulation has a maximum motor winding temperature rise and a maximum temperature rating. In addition, a hot spot temperature rise is specified which pertains to motor windings that are surrounded by other windings.

Frequency (Hz)

This shows the input electricity frequency that the motor is designed to operate at. Usually for motors, the input frequency is 50 or 60 Hz. If more than one frequency is marked on the nameplate (like our example), then other parameters that will differ at different input frequencies have to be indicated on the nameplate as well.

Motor Rated Power

kW is an expression of the motor’s mechanical output rating – its ability to deliver the torque needed for the load at rated speed.

Full Load Speed (RPM)

Full-load speed is the speed at which rated full-load torque is delivered at rated power output, this speed is sometimes called slip-speed or actual rotor speed.

Rated Operating Current

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

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.

Ambient Temperature

The maximum ambient temperature (AMB) lists the temperature at which the motor can operate and still be within the tolerance of the insulation class at the maximum temperature rise.

Service Factor

This Indicates the amount of overload a motor can handle. Electrical motors are often designed to handle a temporary increase in demand, the ability of the motor to handle these demands are represented by the service factor.

For example, a motor with 1.0 service factor cannot be expected to handle more than its nameplate kW. A motor with service factor 1.15 can be expected to safely handle infrequent loads to 15% past it’s rated kW.

In general, it is bad practice to size motors to operate continuously above rated load in the service factor area. Operating a motor at overloads allowed by the service factor for extended periods can result in reduced speed, overheating, decreased efficiency, decreased power factor all of which affects the overall life span of the motor.


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. Below this altitude, the motor may run cooler. Above this temperature, the motor may run hotter.

Serial Number

This shows the serial number of the motor. As it is unique to the motor, knowing this number can help when liaising with manufacturers or M&E companies about the type of motor you have.

Motor Nameplate FAQs

What Is On a Motor Nameplate?

A motor nameplate is a panel which is affixed to electric motors. The nameplate contains information about the construction characteristics and performance of the motor. The types of information that are shown include the number of phases, rated operating voltage, service duty, efficiency code, frame size, IP rating, insulation class and more.

How Do You Read a Nameplate on an Electric Motor?

As a lot of information is condensed into a small amount of space, motor nameplates can be difficult to understand without the right expertise. In most cases, each piece of information will be preceded by a number, letter or symbol which indicates the meaning of the field. The layout of a motor nameplate may change based on the manufacturer but generally, the same information is given. Therefore, once you can understand one motor nameplate, it’s much easier to understand others.

What is the Function of a Nameplate?

The function of a motor nameplate is to provide precise information about the characteristics of a motor. This information means those who work on or maintain the motor can easily recognise the type of motor and its characteristics without having to perform thorough analysis of the unit. As the language is standardised and largely numerical, the same nameplate could be understood by operators from around the world.

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