nema VS iec: WHICH IS BEST?

As because so many different electrical contactors and straters to choose , you may be curious about the pros and cons of IEC vs NEMA rated devices. Let Nofuel power explain you about the two different standards organizations and which one might suit your intended application best!

What is NEMA?

The National Electrical Manufacturers Association (NEMA) is the largest trade association of electrical equipment manufacturers in the United States.  Founded in 1926, NEMA urged manufacturers to utilize a standard “frame” size to allow parts from different manufacturers to be standardized, and to design components with safety factors over and above their design ratings.

Benefits of NEMA-Rated Devices

· High withstand capability: suited to heavy-duty applications with little concern for derating

· Versatile and suitable for a broad range of application , very robust and broadly applicable.

· Ease of selection is the fundamental design advantage of a NEMA-style starter. To effectively select a NEMA-style product, you only need to know the horsepower and voltage.

· Serviceability: Easy to maintain,contacts are easily inspected; coils are quickly changed, all sizes can be repaired usually without removing the device from the panel

· The motor control center (MCC) Most NEMA products are sold as starters

What is IEC?

The International Electrotechnical Commission (IEC) is a non-profit, non-governmental international standards organization that prepares and publishes international standards for all electrical, electronic, and rated technologies, which are collectively referred to as “electrotechnical”.  This organization traces its roots back to 1881 and has been involved in developing and distributing many well-known units of measure like Hertz (frequency – cycles/second) and Gauss (magnetic flux density).

Benefits of IEC-Rated Devices

· Compact size: saves panel space. (30% to 80% smaller than NEMA).

· Reacts quickly to overloads

· Fingersafe terminals: safety for operating and maintenance personnel.35 mm DIN rail mounting: saves installation time.

· Lower cost with modular components

· Meet IEC standards: acceptable worldwide

The Difference Between IEC and NEMA

The difference between IEC vs NEMA is that a NEMA contactor, by design, may have up to 25% service factor while IEC is more focused on space and cost savings by testing components to their exact design rating, and using utilization categories to rate devices based on their intended use. For example, a utilization category of AC-1 is for purely resistive loads, or only slightly inductive loads, like a heater circuit. AC-3 is for routine starting and stopping of a squirrel cage motor and only occasional jogging. AC-4 is similar to AC-3 but includes “inching” and “plugging” (jogging and reversing at speed), which requires significant instantaneous control of the motor current.

As a result, particularly for devices below 100A or 50HP, the NEMA rated motor starters and contactors are going to be much larger and much more expensive. IEC will also have many more options for a particular current or power rating, which makes proper selection much more critical than with NEMA components. This is where many misunderstandings have arisen in the United States with respect to the IEC system.

Tips:

Common Misunderstandings Debunked

– Visually the NEMA starter looks larger than the comparable IEC starter and some think this makes it “more robust”. In actuality, it’s simply oversized by design.

– Often times, the wrong IEC classification for a given application will be utilized. As a result, the IEC system itself is blamed when it doesn’t perform as expected. The reality is that the UL testing is the same for both IEC and NEMA starters.

Knowing this, there are instances where each classification system has its merits. IEC is smaller and less expensive when the operating conditions are well defined. NEMA devices may be a better choice when operating conditions like load are not well defined. IEC starters include single phase detection, and faster reaction to overload conditions, while NEMA devices can more easily withstand short circuits. NEMA starters have an open design, so often safety covers are required, while IEC contactors and starters are inherently finger safe. IEC devices also have many more options to network components together into a distributed control system using open fieldbus standards, which can be important in modern plant control systems.

As you can see the differences are not as simple as we often try and make them. It’s not a question of “which is more robust” or “which is more cost effective”. It’s about understanding the application requirements, and the differences between the two systems and selecting the proper device for the job.

IEC features and benefits

The large number of IEC contactor sizes allows you to more closely match the contactor to the load or application. Unlike NEMA, where the available sizes are standard across the industry, the number of different contactor size ratings varies by manufacturer.

Generally, an IEC starter is about half the size of a comparable NEMA starter. Above 100A (NEMA Size 3), however, the physical differences between NEMA and IEC are negligible.

IEC products are more modular in nature; they can snap onto a 35-mm, or in larger sizes, a 75-mm DIN rail. This eliminates the need to drill holes and mount each component individually. Thus, putting them into a panel is relatively easy.

Unlike NEMA starters, which typically are sold fully assembled, IEC starters typically are sold as components (a contactor, an auxiliary block, an overload relay block) so that you can make your own assembly. You simply select the accessories needed for the application and snap them together, without the use of tools.

Also unlike NEMA starters, IEC-style thermal overload relays typically have fixed thermal elements, with an adjustment range that may require replacing the complete overload relay when significant motor FLC changes due to application requirements.

Compared with NEMA-style products, IEC-style products are more disposable than serviceable. In fact, IEC products below 100A typically are considered disposable; they can be removed from a DIN rail, thrown away, and replaced with a new product in a matter of minutes.

* * Compact size: saves panel space. (30% to 80% smaller than NEMA).

* 35 mm DIN rail mounting: saves installation time.

* 45 mm width and 45 x 60 mm mounting hole spacing on small contactors: interchangeability among manufacturers without panel modification.

* Fingersafe terminals: safety for operating and maintenance personnel.

* Ambient-compensated bimetallic overload relay: compensates for varying temperatures at the controller.

* Automatic reset, field-convertible: suitable for remote or inaccessible locations.