A general misunderstanding of NEMA 250 types and IEC 60529 ratings has led to them being used interchangeably. However, after taking a closer look at what the two rating systems test and account for, we find that the interchangeable use may have been slightly frivolous. Read on for a short history lesson on the rating systems, what they account for, and how to use them.
Who is NEMA?
NEMA stands for National Electrical Manufacturers Association. They're a North American organization of business leaders, scientists, engineers, experts, and technicians developing standards, application guides, white papers, and technical papers for various industries and supporting and recommending policies for industry at all levels of government.
Who is IEC?
IEC stands for International Electrotechnical Commission. They're a global organization that develops the basis of the design, manufacturing, testing, and certification parameters of electrical technologies. Founded in 1906, the IEC now works with 170 countries and over 20,000 global experts to provide international standards for safe and reliable products.
What are NEMA 250 Types and IEC 60529 Ratings, and Why do We Need Them?
To keep things simple, NEMA types and IEC ratings are classification systems for electrical enclosures. At their most basic, they measure the ability of an electronic equipment's enclosure to protect internal electrical components from liquid and solid contaminants.
Why do we need to protect the internal electrical components of an electric motor from contaminants?
Water and condensation can build up inside a motor, causing issues like rust build-up on internal components. When rust builds up on electric components, it interrupts the normal flow of voltage, creating a higher load and eventual overheating of components. This overheating can cause bearing damage, winding failure, and several other issues. On the other hand, a liquid contaminant could be a corrosive agent, which would corrode wire and winding insulation, causing voltage drops and load issues that would also result in overheating.
Solid contaminants like dust particles cause many of the same issues, just in different ways. A build-up of dust or other particles can significantly reduce the motor's ability to circulate air that helps offload heat, causing overheating issues that can damage many different motor components. Dust and other particles can wreak havoc on the voltage within the motor. These particles can develop an electrostatic charge causing strange voltages in the motor. Alternatively, they can create a high-resistance layer on stator windings, causing a critical drop in voltage.
As such, you can see why one would want to prevent the ingress of contaminants through an electric motor's enclosure. The damages it can cause directly result in high repair costs, energy efficiency issues that cost, and increase your equipment's downtime. NEMA and the IEC began rating and classifying enclosures to mitigate the problems end-users faced. The motor purchaser can now acquire a motor enclosure that's the perfect fit (has the appropriately rated enclosure for the application setting) for the job, avoiding unexpected damages due to contamination and saving on time and maintenance costs.
NEMA 250 Types
NEMA 250 types classify enclosures based on several tests; ability to prevent human access, prevent the ingress of solids, prevent the ingress of liquids, construction requirements, door and cover securement, corrosion resistance, effects of ice, gasket ageing and oil resistance, and cooling effectiveness. Please see the tables below for ratings and their specific non-hazardous applications.
IEC 60529 Ratings
IEC 60529 ratings are based on only three types of tests; protection of people from hazardous internals, preventing solid objects from entering, and preventing water from entering (please note, this is specifically water and doesn't cover coolants or other corrosive agents). The ratings are stated with an IP Code. "IP" stands for "international protection" but is often expressed as "ingress protection" as that is what the rating is based on. The IP code is written as "IP" and followed by two numbers; the first number is the protection against solids rating, and the second number is the protection against water rating. Please see the table below for ratings and their applications.
NEMA 250 and IEC 60529 Differences
Are the two rating standards interchangeable? To put it quite simply, no. While the two systems are similar in that they test for prevention of access by humans, solids, and water, the NEMA 250 Types cover many more details. As such, there's no exact match between the two systems. However, since NEMA 250 Types cover more testing parameters, these ratings can often meet or exceed the IEC 60529 Rating. A NEMA rating can be used in place of an IP Code, but the inverse is not true as IP does not specify protection against oils, coolants, corrosive agents, or ice.
Having a solid understanding of your intended application is the absolute best way to choose an electric motor enclosure with the correct rating, no matter if it is NEMA or IEC.
Comparison Cheat Sheet
NEMA 250 Types and IEC 60529 Ratings are systems of standardization for electrical equipment enclosures. Both testing for human access, ingress of solids, or ingress of liquids through the enclosure to the internal electrical components. However, as noted above, since NEMA 250 Types test for additional protections, the two rating systems are not interchangeable. The best way to choose your motor's correct enclosure is to understand the intended application and operating environment. Our experts here at eMotors Direct are ready to answer any questions you have should you have any issues with choosing your electric motor enclosure.
Information and tables sourced from NEMA documentation: