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What Does all of the Information on a Motor Nameplate Mean?

January 9, 2014
Typical NEMA Motor Nameplate

Typical NEMA Motor Nameplate

Every sanitary pump needs some kind of a motor. In previous posts, we’ve talked about some nuances of motors in sanitary applications (see our post on JM frame motors and motor efficiency/enclosure types), as well as 3 phase motor control. To kick off 2014 we’ll review all of the information you can get from a motor nameplate and how that information can help you to replace or specify a new motor.

To begin, motor standards can be grouped into two major categories: NEMA and IEC. Stateside, the National Electric Manufacturers set motor standards, including what information each manufacturer needs to include on their nameplate. In most other countries, the International Electrotechnical commission (IEC) sets the standards.

Despite our name, Holland Applied’s primary market is North America and this post will focus on NEMA nameplates. If you do have an IEC motor, however, don’t hesitate to reach out to us. NEMA specifies that every motor nameplate must show the following:

Manufacturer’s Type- while NEMA requires this, there is no industry standard motor types. Motors are sometimes referred ot as single or three phase (3-phase, 1-phase shaded pole, 1-phase permanent split capacitor, ect.) or classified by their purpose, general or special. General purpose motors are designed for mechanical loads and hard to start loads, such as conveyors, pumps and compressors. Special purpose motors are designed for certain applications. JM frame and C face motors are good examples of special purpose motors. Some manufacturers will simply add the model, date, and serial number hear to help with identification.

Rated Volts- This is a relatively straight forward one. The rated voltage is the voltage at which the motor is designed to operate at maximum efficiency. Other nameplate parameters, including power factor, torque, and FLA are at the rated voltage and frequency. Most industrial motors we see are 3 phase and dual rated for 230 or 460 V. Motors are designed with a 10% tolerance for voltage above and below the rated nameplate value. So a 230 V motor can run at 253 or 207 V. It won’t be at peak performance, but it will work.

Full Load Amps (FLA)- this is the amount of amperage the motor draws at full load torque and horsepower. This is important for selecting correct wire size, motor starters, and variable frequency drives. In fact, VFDs should be selected based on FLA, not horsepower (which is common practice).

Rated Frequency and Phases- this is the electrical frequency the motor is designed to operate on. In the US and Canada, this is 60 Hz. In other parts of the world, such as China, Singapore, and the EU, this is 50 Hz. Motors are either single or three phase.

Rated Full Load Speed- the full load RPM is the approximate speed under full load conditions. The actual speed is always lower than the synchronous speed and it drops off as the load increases. Typically, the full load speed is 96%-99% of the no-load or synchronous speed. The difference is known as slip.

Insulation System Class- this is the industry standard classification of the thermal tolerance of the motor winding. When motors spin, they generate heat. Insulation is responsible for dissipating this heat. Materials are classified as A, B, F, and H. The letter indicates the time a motor can survive at a certain temp. As most motors are totally enclosed and fan cooled, this is very important in variable frequency applications where running at reduced speeds can increase motor temperature. Increase in temperature and failure of motor insulation can lead to motor shorting.

Time Rating- time rating specifies the length of time the motor can operate at its rated load. Standard motors are rated for continuous (24/7) speed. This is shown as “CONT” on the nameplate.

Rated Horsepower- this is the measure of the motor’s mechanical output rating. A motor’s horsepower is the calculated by multiplying the motor speed by torque (lb-ft) and dividing by 5,250.

Torque- is the turning or twisting force supplied by a drive. Future posts will focus more on torque and its importance, especially in pumping applications.

Locked Rotor Indicating Code Letter- when AC motors are started with full voltage, they create an inrush current that’s usually many times great than the FLA. The high current can cause a system voltage dip that could affect other equipment. The start inrush current has been standardized and defined by NEMA in terms of kilovolt amperes. These values are important for selecting and sizing motor starters and proper branch circuit protection devices.

Power Factor- known as PF, the power factor is the ration of active power (W) to apparent power (VA) and is expressed as a percentage.

Service Factor- is the percentage of overloading a motor can handle for short periods of time. When the motor HP is multiplied by the motor SF, which gives the allowable HP loading that can be carried out by the motor for short periods of time. It is essentially a fudge factor. Most motors have a service factor of 1.0 or 1.15.

Efficiency- Efficiency is the ratio of the power output divided by the power input. Basically, this measures how well the motor converts electrical energy into mechanical energy. Large motors tend to be more efficient than small motors. Today’s 3-phase premium efficient motors range from 86.5% at 1 HP to 95.*” at 300%.

Frame Size- See our previous post about this topic. Dimensionally, this is extremely important and critical in identifying a drop in replacement motor for an existing application.

Enclosure Type- this classifies the motor as to its degree of protection from its environment and its method of cooling. Most motors we see are totally enclosed and fan cooled. Additional designations, such as wash down duty (for high pressure, direct spray applications) and explosion proof motors are called out here. Future posts will elaborate on this topic

 

To conclude, hopefully this serves as a quick overview of nameplate terminology for NEMA motors. Previous posts have discussed topics like motor frames size and future posts will elaborate on motor efficiency and torque. Stay tuned for new posts in 2014 and contact Holland today with any motor or pump questions you have today.

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