Understanding what functions are needed in your motor control circuit is critical when selecting motor control devices.
Engineers benefit from the standards and codes established to ensure safety and protection to personnel and equipment.
Engineers benefit from the standards and codes established to ensure safety and protection to personnel and equipment.
In measuring electric motors and motor controls, there are two standards in use: the National Electrical Manufacturers Association (NEMA) and the International Electrotechnical Commission (IEC). Basically, NEMA vs IEC.
NEMA is mostly used in North America while IEC is used in most parts of the world. But that doesn’t mean the motors used are different. In fact, NEMA and IEC motors have the same output power, efficiency, and size.
When choosing between NEMA vs IEC, the pros and cons of each can guide you. Read on to understand the differences between NEMA vs IEC and how each can suit your intended application.
For a long time, many clients have preferred to use NEMA ratings over all others. This is because the ratings pertain to electric motors, enclosures, and motor controllers. Most American-based companies require that electrical components and enclosures adhere to NEMA standards.
Recently, IEC has found its way into the market, covering almost the same categories as NEMA codes. The ratings were originally more specific to the Asian and European markets. As the world continued to move towards globalization, electrical designers and engineers have had to conform to IEC standards.
It’s imperative that the engineering, maintenance, and service personnel are familiar with these standards. Most production equipment finding its way to the U.S. market from overseas must meet the IEC standards.
NEMA is the National Electrical Manufacturers Association. It’s the largest trade association of electrical equipment manufacturers in the U.S. It was founded in 1926, to urge manufacturers to use a standard frame size for motor control and lighting applications.
This would allow the standardization of parts from different manufacturers. It also sees to it that manufacturers design components that meet the safety factors of the design ratings. The association also dictates the configuration and performance parameters of electrical components.
Those used in power generation, distribution, control, transmission, and end use must comply with NEMA standards. This has been a daunting responsibility, but one which NEMA has carried out with distinction all through.
The advantages of NEMA ratings are that they’re better at withstanding short circuits. They’re also versatile and highly suitable for a wide range of applications.
IEC is the International Electro-technical Commission that oversees the standards for the European electrical communities. It was formed in 1906 and mainly focused on the European market until after World War II.
IEC-certified components are now widely being used by a growing number of companies in North America and the U.S.
The benefits of IEC-rated products are that they’re low cost, compact, and inherently safe to the users.
The two standards of rating have a significant similarity. This lies in the solid-state overload relay, which has evolved rapidly over the past decade. The relays have replaced both eutectic and bimetal trip mechanisms in many applications.
However, bimetal mechanical overload devices are still widely in use today. The difference between the solid-state overload relays used in NEMA vs IEC ratings is minimal. Both ratings can be used on the same application, making the main difference be the contactors and enclosure.
The advantages of using either NEMA or IEC controls are:
However, there are instances when each type of classification has advantages over the other. For example, IEC is less expensive if the operating conditions are clearly defined.
NEMA and IEC electromechanical products differ, but in today’s business environment, flexibility is essential. If users can apply IEC or NEMA-style products, they’ve got the flexibility to adapt to product supply and local requirements.
In so doing, they’ve got the benefit of local availability and expertise, which is a competitive edge. However, to adequately apply this flexibility, you need to understand the differences between NEMA and IEC designs.
The philosophy upheld by NEMA emphasizes on robust designs for applicability on a broader scope. The two primary fundamental mainstays within the philosophy are ease of selection and range of application.
The design of NEMA motor control devices is governed by the NEMA Industrial Control Standard (ICS-2). This is a formal document that contains detailed information about the electromechanical design of NEMA motor control.
On the other hand, the IEC philosophy revolves around performance and application. IEC devices require a sophisticated level of knowledge about the equipment in question. For example, you must understand the duty cycle, motor load, and full load current functions.
This requirement may be a drawback in some segments. In some others, it’s a considerable advantage, especially in the Original Equipment Manufacturer sector. For example, an HP-rated IEC device may be substantially smaller than a similar one from NEMA.
This is one significant advantage for OEM designers. Besides, IEC products are less expensive.
The design of NEMA products gives them the advantage of the ease of selection. The most essential features to know when choosing a NEMA product are voltage and horsepower.
Most importantly, it’s essential to check the serviceability of devices in the NEMA market. Most of the products are easy to service as they provide access to internal parts. Apart from cases where total replacement is required; coils and contacts can be repaired with the device still on the panel.
Another consideration in the features is reserve capacity. Most of NEMA products are robust and broadly applicable. They’re also more general purpose than their IEC counterparts.
NEMA devices have interchangeable heater elements, with a range of units available for the overload. This is a characteristic that makes NEMA products more desirable on most construction jobs.
The Enclosed Package Solution or Motor Control Center is a well-known NEMA tradition. Most products are sold as starters, either in open-style or enclosed versions.
Most IEC contactor sizes allow you to match the contactor to the application conveniently. This contrasts NEMA, where the sizes are standard across the industry. With IEC, the contactor size ratings vary by manufacturer.
Normally, an IEC starter is almost half the size of a similar NEMA starter. However, above 100A, the physical differences are negligible.
IEC products are more flexible and modular in nature and can snap on DIN rails up to 75mm. This removes the need to drill holes for mounting each component individually. Putting them into a panel becomes relatively easy.
IEC starters are sold as components comprising a contactor, an auxiliary block and overload relay block. This way, you can assemble the parts yourself. You do this by selecting the accessories you need and snapping them together without the use of tools.
IEC-style thermal overload relays come with fixed thermal elements. Their adjustment range may call for the complete overload when there are changes in the application requirements.
NEC sec. 430-53 deals with contactors that need to be applied in group applications. However, this isn’t unique to IEC only since other starters can be installed this way.
Type 2 Coordination
This is an IEC standard that applies to NEMA products as well. It’s afforded by the use of a contactor or starter. The protection type requires the starter to be reusable after short-circuit conditions. The IEC standards allow no significant changes in the operating time-current features of the overload relay.
Since this is a coordinated protection standard, it applies to both NEMA and IEC. However, NEMA has a greater selection of short-circuit protective devices. The selection of fuses with IEC-style products is limited.
It’s also worth noting that IEC products are more disposable than serviceable. Most of them below 100A can’t be serviced; they are required to be removed from a DIN rail, for replacement with a new component.
Self-protected starters are the representation of a new category of combination starters. This kind of starter has a contactor, overload relay, and short-circuit protection. They also undergo a unique testing procedure that goes beyond the conventional combination of motor controls.
One of the biggest differences between IEC and NEMA products is training. The design of IEC products is more application-specific. The products also require a higher level of knowledge in the selection process.
You may not need intensive training to be able to select an IEC product, but the training has to be very specific. It calls for more time and knowledge upfront, to match the selection to the application.
2. The State of the Market
NEMA largely has its base in North America, with some presence in some parts of the world. The presence is mostly in areas with large U.S. influences, like U.S. companies based in the Middle East.
Over several years, many companies have shifted from NEMA-style contactors and starters to IEC ones. The conversion has leveled off by market segments. Those in commercial and light industries have nearly completed the transition to IEC.
Those in process industries have proactively remained with NEMA-style devices. In terms of the number of products sold, IEC-style ones outsell NEMA-style ones. In dollar value, NEMA-style devices outsell IEC products.
The primary difference between the two contactors is that NEMA provides for up to 25% service factor. IEC, on the other hand, focuses on space and cost-savings. It tests components to their exact design IP rating, using utilization categories to rate items according to their intended use.
As such, devices that operate below 100A or 50HP are going to be much larger for NEMA and more expensive. IEC will also have more options for a power rating, making it more critical than the NEMA ratings. This is where the contention lies in the United States regarding the IEC system.
It’s also worth noting that NEMA addresses matters to do with the construction of electrical elements. The standards are all about minimum design requirements for enclosures. IEC is more inclined towards IP ratings.
NEMA addresses corrosion, something amiss with the IEC classifications. NEMA also incorporates some level of protection enclosures against corrosion. Sometimes, NEMA ratings and IEC’s IP ratings don’t directly correspond, since they cover different protections.
When choosing between NEMA vs IEC, there are some key differences to note.
Despite these significant differences, there are still some common misunderstandings that need to be debunked. One of them is concerning the NEMA starter. Although it looks larger than the IEC starter, some people think it makes more robust devices.
In actuality, it merely looks more extensive because of its design. As a result, the wrong IEC classification will be used instead of the accurate NEMA classification. This will lead to blame on the IEC system when the rating fails to perform as expected.
In reality, the Underwriters Laboratories testing applies across the board for both IEC and NEMA applications. In essence, the differences are not merely about the sizes or cost-effectiveness. There’s a need to gain a deeper understanding of how each system works.
The NEMA ratings of a starter depends largely on the maximum horsepower ratings given in the National Electrical Manufacturers Association ISCS2 standard. The selection of the NEMA starters is done on the basis of their NEMA size, which varies from Size 00 to Size 9.
The NEMA starter, at its stated rating, can be used for a wide range of applications, ranging from simple on and off applications to plugging and jogging applications, which are more demanding. It is necessary to know the voltage and horsepower of the motor when selecting the proper NEMA motor starter. In the case where there is a considerable amount of plugging and jogging involved, then derating a NEMA-rated device will be required.
The International Electrotechnical Commission (IEC) has specified the operational and performance characteristics for IEC devices in the publication IEC 60947. Standard sizes are not specified by the IEC. The typical duty cycle of IEC devices are defined by utilization categories. As far as general motor starting applications are concerned, AC3 and AC4 are the most common utilization categories.
Unlike NEMA sizes, they are typically rated by their maximum operating current, thermal current, HP and/or kW rating.
There are other parameters that are important to consider, while selecting motor starters, such as time-limit acceleration, current-line acceleration, control voltage, number of poles, and operating temperature.
Mechanical and electrical, industrial applications must be tested for safety before their release into the market. The Ingress Protection mark differs from one rating company to the other. However, the two primary outstanding standards are by NEMA and IEC.
NEMA standards have been more popular than the IEC one. Currently, they’re becoming more acceptable in the global market, especially for compact devices. IEC-rated devices are less expensive than NEMA-rated ones.
When choosing between NEMA and IEC rated-devices, it’s essential to understand what the rating represents. The industry has made efforts to standardize the ratings; hence, you shouldn’t expect any impactful differences.
One key aspect of the ratings is that they’ve helped eliminate vagueness in some commonly used terms like “waterproof.” The ratings give you a clear explanation of what you can expect with each device. If you’ve got challenges interpreting the ratings depending on a devices application, seek professional help.
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