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Considerations for Purchasing a Large Electric Motor



For some reason, you've found yourself in a position where you need to purchase a large electric motor -- as in a motor that is not a standard "NEMA" electric motor. It may be that some new equipment is being installed at your location, you may be in search of a surplus motor, or the time has come to replace one. Regardless of why you need a large electric motor, there are some key things to keep in mind. But first, let's define what we mean by large.

Large Electric Motors

These are not your everyday, on-the-shelf motors that every PT (Power Train) house and motor shop has in stock.

The kind of motors under discussion here are typically built specifically for your application and although some large motors may provide hundreds of horsepower (400+ hp), the kind I'm talking provide thousands of horsepower. These are typically referred to Above-NEMA or A-NEMA motors and they can be far more challenging to purchase than a standard motor.

The Basics of Bidding Out an ANEMA Motor

First, start with the basics which include information such as ...

  • Horsepower
  • Speed
  • Voltage
  • Full load amps
  • Enclosure
  • Frame
  • Mounting
  • Bearing type
  • NEMA design
  • KVA code
  • and quite a few more!

You also want to include any other information you have about the original motor and its application. This can include frame dimensions, speed vs. torque curves, data packets, and schematics.

AC Induction Electric Motor Retrofit Guideline


There are not many new plants being built these days. Yes, there are some but most of what takes place today is retrofitting of older, existing equipment in plants that already exist. This process of retrofitting older equipment to new, modern, technology can be complex. We see many instances where someone replaces without considering all of the aspects of a replacement and the motor ends up not working. This article should serve as a guide for doing retrofits on large electric motors, focusing on AC Induction motors. We also want to give credit for a lot of this information from our friends at Siemens. They do many retrofits every year with us as well as their other channel partners.

Apples, Oranges, and Above-NEMA (A-NEMA) Large Electric Motors


A-NEMA_electric_motors-apples_or_oranges.jpgLarge electric motors, those of 400HP or more, are typically referred to as Above-NEMA or A-NEMA electric motors. When it comes time to purchase one (either new or previously owned), it’s vitally important that when bidding manufacturer to manufacturer, they are all given the same parameters.

There is tremendous value in saying “This is what I want.” Without specifying, “what you want” you will simply get what each manufacturer builds. It’s like the old saying “apples vs. oranges”. If you don’t specify that everybody quote an “apple” and you just say you want a piece of fruit, you might get an apple, an orange, or even a banana!

By specifying exactly what you want, you will have leveled the playing field and stand a much better chance of getting precisely the right motor for the job.

What A-NEMA Large Electric Motor is Best for You?



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 – 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?

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