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When an original equipment manufacturer (OEM) or a service technician selects contactors for their applications, they expect them to be safe and durable.

When meeting specific safety standards, products may be labeled with logos of safety organizations that establish safety standards for products.  For example, products may have logos from Underwriters Laboratory (UL or the “backward” UR) or The CSA Group (formerly Canadian Standards Association) indicating that they comply with specific safety standards.  Contactors meeting UL requirements, for example, would carry the “backward” UR mark indicating that they are a recognized component under UL Standard 508.

Manufacturers may design their products to the durability and performance standards established by the Air Conditioning & Refrigeration Institute (ARI), National Electrical Manufacturers Association (NEMA), and International Electrotechnical Commission (IEC).  ARI 780/790 is an example of a design standard, establishing minimum performance characteristics for Definite Purpose Contactors.

NEMA contactors are considered general purpose contactors, in that they can be used in a variety of applications.  They are very robust with lots of material and wider gaps between the contacts.  This results in a bigger, longer lasting product.  These are the contactors that were used by the HVAC/R OEMs in the 1950’s.  The OEMs found that these contactors would last much longer than was required.  They would typically last longer than the equipment.  These contactors were very large, and very expensive.  In an effort to make the equipment smaller in size so that it would fit into more areas, as well as make it more affordable, the Definite Purpose contactor was designed.  This resulted in a smaller, quieter, less costly contactor, because the lighter load of an HVAC/R application did not require the same demands that a harsh industrial application might.

The IEC components were primarily focused on the European market until after World War II.  Products coming into the U.S. from Europe would typically be designed to the IEC standards.  Today, the IEC standards are seen globally.  More and more IEC products are being used in the U.S. in both HVAC/R manufacturing and the aftermarket.  The IEC contactor is typically matched more specifically to the application.  Like the Definite Purpose contactor, this could result in the IEC contactor being significantly smaller than the NEMA contactor, and consequently less costly, particularly for contactors below 100 Amps.

There is a place for each of these different designs.  But proper sizing is important.  When replacing a contactor always consider the application.  In HVAC/R applications, the Definite Purpose contactor not only provides excellent performance, but it is very cost effective.  It is selected based upon the full load amps (FLA) or inductive amp load, as well as the coil voltage.  The NEMA contactor is a true “general purpose” contactor.  It is very robust in its design and can be used for light duty as well as heavy duty applications.  This can result in a larger physical size when compared to the Definite Purpose and IEC contactors.  It is sized based upon horsepower and voltage.  When selecting the IEC contactor, it is selected more specifically to the application, which will typically result in a smaller physical size.  The application will determine the IEC Utilization Category of the contactor.  For most HVAC/R motors the Utilization Category is AC3, and for resistive loads AC1.  Using the appropriate IEC tables can then be used for appropriate sizing.  When in doubt, your wholesaler will be able to provide you with assistance.

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