NEMA and IEC motor controls differ in size, ruggedness, and complexity. The solid-state overload relay is common to both NEMA and IEC motor controls. Keep the application in mind when choosing between NEMA and IEC. The more things change, the more they stay the same, it has been said. This statement could be applied to the ongoing debate about National Electrical Manufacturers Association (NEMA) vs. International Electrotechnical Commission (IEC) motor controls and protection. During the past decade, overload motor protection mechanisms have changed substantially and become similar between NEMA and IEC motor controls. However, contactors have changed very little.
Size, ruggedness, durability, complexity, perceived quality, and domestic vs. global markets are the primary differences between NEMA and IEC motor controls. Size is the most apparent outward difference between NEMA and IEC motor controls. The NEMA contactor is physically larger than the IEC contactor for a given current rating. The larger size implies that ruggedness and durability are inherent in the NEMA motor control. Traditionally, NEMA motor controls are perceived to be simpler than their IEC counterparts. Despite the perceptions about size and assumptions about motor control complexity, neither the NEMA nor the IEC is intrinsically better or safer.
Historically, NEMA motor controls have been sold primarily in U.S. markets, while IEC motor controls have been sold primarily in the European/global markets. In Europe, much emphasis is placed on small size and efficient use of materials. This statement is true in general – not only with motor controls. While Europe's emphasis on small size, effective use of materials, and the high priority given to international trade have led to the type of product that is designed to IEC standards, those criteria have not been given the same priority in the United States. The emphasis has been placed on reliability and maintainability. Also, the practice has been to provide performance in almost all applications without the need to go through a lengthy and complicated selection procedure. The U.S. has a high level of automation, requiring that equipment be maintained quickly, rather than having to buy a new product. The emphasis has been on easy installation with a high level of confidence in the integrity of the installation and the equipment.
Despite the differences between NEMA and IEC motor controls, the two types have a major similarity. This similarity – the solid-state overload relay – has evolved during the past decade. Solid-state overload relays have replaced both bimetal and eutectic trip mechanisms in many applications. However, it should be noted that both mechanical overload devices are still used – bimetal primarily. Solid-state overload relays are found in the majority of both NEMA and IEC motor controls. There is little difference between solid-state overload relays used for either type. In some applications, the same solid-state overload relay can be used in NEMA and in IEC units, leaving the contactor and enclosure the main differences between the two. Advantages of using a solid-state overload relay with either NEMA or IEC controls are:Increased adjustability Better motor protection Minimized nuisance tripping Jam protection.