Here You Go.


What NEMA Standard Electric Motor is Best for You?


new-equipment2.jpgYOU NEED A MOTOR. NOW WHAT?

Maybe you need a new NEMA standard electric motor. Maybe you need a previously owned one. In either case, there are some important questions to ask before placing the order. If you make the wrong call, it can cost you — big time.

The following will give you some tips to help make sure you don’t make that costly mistake.


OK, you need another motor – Then you call your local electric motor sales office.  Did you ask yourself, "Why?"

This is the most important question of all. Exactly why do you need one?  Was there a failure with a current motor? Has this exact same failure or one very similar occurred before?  If so, maybe the motor was not the best available motor for the application. Here are some things to ask yourself in that regard:

  • Did the motor have the wrong enclosure?
  • Did the motor have the wrong horsepower?
  • Is the motor on a VFD?
  • What else? There are a variety of items that can be mishandled or misapplied. Go over them all to get a handle on the situation when the motor went down.

If you don’t figure out why it happened – how on earth can you prevent it from happening again?

You’ve decided on a motor. Sure it's the right one?

Before that piece of equipment arrives on your doorstep, it’s good to do some double-checking. Who is supplying the motor? To what spec? How has the motor been sized? How have you decided what features are required? Which manufacturer makes that motor? Is it is one-off motor or a stocked catalog motor?

These aren’t easy questions to answer. It all depends on your situation, your plant floor, your industry, your company.

So… where to start?


Hey, don’t worry. This isn’t complicated — especially for NEMA (National Electrical Manufacturers Association) regulated motors. For most ¼ HP through 400HP standard motors, there are already standards in place. Here is some information you should know to decide what makes sense for you:

Basic NEMA Enclosures:

  • Open Drip Proof (ODP): Open enclosures permit the free flow of cooling air. These motors have internal fans to assist air movement. ODP motors are designed to allow airflow, and prevent liquids and solids from entering the enclosure.
  • Totally Enclosed Fan Cooled (TEFC): Enclosed motors are designed for applications where contaminates are a factor, such as chemical plants, paper mills, and the outdoors. These motors are the most commonly used motor in ordinary industrial environments.
  • Other Enclosures: There are other enclosures that exist, but are not as common as ODP and TEFC in industrial environments. However, they definitely are needed in certain circumstances.
  • Other Totally Enclosed: Totally Enclosed Non-Vented (TENV), Totally Enclosed Air Over (TEAO), Totally Enclosed Air to Air Cooled (TEAAC), Totally Enclosed Blower Cooled (TEBC) Totally Enclosed Water to Air Cooled, (TEWAC),
  • Other Open: Weather Protected I (WPI), Weather Protected II (WPII)

Efficiency of NEMA motors

Since 2010, most standard NEMA motors manufactured in or shipped to the United States were required to be “premium efficient” designs. When comparing new motor manufacturers, remember that efficiencies are regulated so they are all required to meet certain levels.  If you go above these levels, you are typically going into high cost, specialty designed motors.

However, comparing a modern day motor to an older, less efficient motor, efficiency should most certainly come into play. It’s been said that a motor’s energy is 95% of its total lifetime operating cost, while maintenance and the initial purchase price is only 5%.

Basic Motor Configurations

  • Standard Duty or General Purpose Motors

Typical “general purpose” motors can be either ODP or TEFC, and are regulated to ensure they meet NEMA’s premium efficiency regulations. They typically have ball bearings (or roller bearings for high radial load belted applications). General purpose motors are used in a variety of everyday applications.

  • Severe Duty Motors

Severe duty motors only have TEFC enclosures. They are made for tougher applications and environments such as chemical processing, mining, foundry, pulp and paper, waste management and petro/chemical applications.

  • IEEE 841 Motors

These motors are made to the IEEE 841-2009 standard for demanding environments that require more than just a severe duty motor. This specification covers three-phase motors from 1 to 500 HP, 1800RPM, 3600RPM, 1200RPM, and 900RPM.

Although these motors were specifically designed for the petrochemical and chemical industry, their premium features are used in a variety of industries and applications where:

  • Ambient Temp ranges from -25C to +40C
  • Maximum altitude of 1000m
  • Indoor or outdoor, humid, chemical (corrosive), or salty atmospheres.
  • +10% of rated voltage @ rated frequency
  • +5% of rated frequency @ rated voltage
  • Combination of voltage and frequency variation of 10% within limits above.

One last note on NEMA motors

There a few failure trends in industry today that should be considered when replacing or sourcing an electric motor. You will want to know:

  • Is the motor on a variable frequency drive (VFD)?

Consider adding a shaft-grounding device, such as an AEGIS shaft-grounding ring. These devices divert these currents from the bearing to ground, saving the bearing and the motor from the damage they cause.

  • Is the motor on a belted application (pulley) or is it a direct drive (coupling)?

Motors on a belted application can experience excessive radial (side) loading.

So… what does all this mean?

With NEMA regulated motors (1/4 HP through 400HP) you can use some already in-place standards. If your company is a clean environment, maybe ODP General Purpose motors will work for you, if you are a harsh, dirty environment you may want to look at Severe Duty motors or even IEEE841 motors.

Understand what you need and then you can specify to your vendor what you require to ensure you will be getting a motor that will the best for the application.


Motor manufacturers sell on the fact that motors are getting smaller and smaller. Is this better for you? The simple fact is that motors were designed to last 25 to 35 years in the past, and were over-designed for what they were required to do. Modern-day, smaller, more efficient motors are designed to last 15-20 years. They are engineered with little to no leeway on what they are required to do.

The question: is it possible that you could purchase an older motor and have it re-manufactured in order to get that 25-35 years of life versus the 15-20 years out of a modern day motor? It may be possible, but it depends on the availability of an older motor, and the capability of a repair center to re-manufacture or re-engineer it for use in your application…. But it IS possible.


HECO can help you with any questions you may have about whether you should get a new or used motor, and which manufacturer offers the motor best suited to your needs. We’ll begin by asking “Why?”  Why do you need a motor? How will it be used? Where? Is it a replacement or an addition? What about spares?

Then we’ll use our problem solving and engineering expertise to keep your plant up and running. To learn more about what our “All Systems Go” approach can mean to you, please contact:

 Download How To Get The Righ Electric Motor


About the author:

Justin Hatfield is Vice President of Operations of HECO, Inc. He is responsible for Electric Motor & Drive Sales, Electric Motor & Generator Repairs, and Predictive Services. Justin was instrumental in developing HECO MAPPS (Motor And Powertrain Performance Systems) which focuses on “why” you have a motor problem instead of simply “What” product or service should be recommended.

Subscribe to Email Updates

Posts by Topic

see all

Recent Posts