If you think NEMA is the name of your long lost cousin, you’re reading the wrong article. NEMA is an acronym for The National Electrical Manufacturers Association.
Most often organizational ratings are confined to a single manufactured product, whereas NEMA offers standardization on a range of electrical products.
NEMA standards define motor frames, electrical enclosures & electrical power outlets just to name a few. NEMA publishes more than 600 standards, application guides, white papers, and technical papers.
I’m an advocate to the theory of; “The more you learn, the less you know”. The problem with descriptions such as “waterproof”, and “air-tight,” they only partially define a need.
For the purpose of this article I will discuss and offer insight into NEMA enclosure and motor standards.
NEMA Electrical Enclosures
Have you had an electrical disconnect or enclosure, and wanted to use it outdoors? However, you weren’t certain it would hold up to the outdoor conditions? There’s nothing worse than discovering that everything inside the enclosure was destroyed due to water leakage or contamination from dirt or chemicals.
If you wish to protect enclosed electrical components against a myriad of inside or outside environmental conditions, while keeping personnel from harming themselves, you must understand and abide by the appropriate NEMA Rating Standards.
To convolute the matter further, two types of enclosure standards exists. They are NEMA & IP.
The NEMA rating system (NEMA Standard 250) is primarily used in the United States and Canada, whereas the IP rating system (IEC Standard 60529) is used throughout the rest of the world.
While it is possible to compare NEMA ratings and IP ratings, any such comparison is only related to the protection provided against dust and moisture.
Indoor And Outdoor Protection – You would think there should be no more than two levels of protection with an enclosure, indoor and outdoor. Not so lucky… NEMA ratings come in thirteen flavors. Not only do the ratings provide a degree of protection against contact with hazardous parts, but also protect interior components from solid contaminants, and water in the form of rain, sleet or snow.
Two Definitions to Understand
Egress and Ingress are often synonymous with the description of NEMA standards.
According to Merriam-Webster…
Egress is: A way to get out of a place or the act of leaving a place—usage, synonyms, more. Synonyms – Exit, Issue, Outlet.
Ingress is: the act of entering. Synonyms – Access, Admission, Admittance, Door, Doorway, Entry, Gateway, Entrance.
NEMA Ratings for Motors
Is a motor, just a motor? No, not really, but if you want consistency, and the right motor for the right job, you better get up to date with the associated standards. NEMA offers three individual standards for motors: NEMA Insulation Classes, NEMA Frame Assignments, and NEMA Motor Enclosures.
NEMA Insulation Classes
Here NEMA defines a motor’s exposure to the environment when considering the overall operating temperature. By exposing motors to excessive heat, you can substantially reduce the life of the motor. This is most prevalent in motors controlled by Variable Frequency Drives (VFD). A VFD causes a motor to experience high operational temperatures when operating at very low speeds.
Therefore, matching motors properly, and adhering to the operational temperature is part of the equation which should not be overlooked.
NEMA Motor Frame Assignments
NEMA’s Motor Frame Assignments include the frame, motor and shaft dimensions. This is important to know. If any of these dimensions are customized without proper documentation and notice, problems could occur.
Recently we required a specific motor which our supplier placed on back-order. We discovered one of our other manufacturing plants had excess, and several of the motors were sent to our facility. The motors carried the same internal part number, yet they wouldn’t fit onto the motor mounts.
It turned out the original motor was a special design which did not adhere to NEMA’s standards. Therefore, only the original motor would work, or a redesign of the motor mount would be necessary.
Additionally, a change in the diameter or length of the shaft can cause additional redevelopment costs as well as belt & pulley issues. If the length of the shaft is too long, the pulley misalignment could cause the belt to fall off, or break due to excessive wear and heat. If the shaft diameter is different, it may require a special order pulley which increases production costs as well as complicate future replacement part research.
Two Standards Exists
Motor standards are grouped into two major categories: NEMA and IEC (and its derivatives). In North America, NEMA sets motor standards, including what should go on the nameplate (NEMA Standard MG 1-10.40). This publication assists users in the proper selection and application of motors and generators. It offers practical information concerning performance, safety, test, construction and manufacture of ac & dc motors, and generators.
In most of the rest of the world, the International Electrotechnical Commission (IEC) sets the standards.
NEMA Motor Enclosures
According To EEP (Electrical Engineering Portal); NEMA standards MG1-1.25 through 1.27 defines more than twenty different enclosures types under the categories of open machines, totally enclosed machines, and machines with encapsulated or sealed windings.
- Open Drip-Proof (OPD)
- Totally Enclosed Air Over (TEAO)
- Totally Enclosed Non-Ventilated (TENV)
- Totally Enclosed Fan Cooled (TEFC)
- Totally Enclosed Wash down (TEWD)
- Explosion-proof enclosures (EXPL)
- Hazardous Location (HAZ)
Some of the enclosure types are obvious. If you place the wrong motor into a chemical plant, a disastrous explosion could occur. However, other option types are not as obvious.
Be certain to analyze and define the environment & conditional requirements for each situation. In most cases, every available motor enclosure could work for a single scenario. However, each motor up the specialized ladder comes with a premium cost. Choosing the wrong enclosure type can be costly and dangerous.
Overlooking NEMA standards can result in an increase of product and/or field replacement costs, as well as a safety costs to equipment and personnel. NEMA Standards are primarily in place to allow you to get the full life out of each motor, and components within an enclosure by protecting them from moisture, chemicals and abrasion damage from dirt and grit.
Most motor & electrical component manufacturers retain staff experts who are more than happy to best fit the right motor or enclosure to each specific job. Utilize these experts and study their decisions. Always replace an motor with the same same NEMA and electrical motor specs. Understanding the NEMA standards & options will prevent you from creating a potentially dangerous, costly, and embarrassing error.