IEC and NEMA motor starters: understanding the differences

After a historical review of the IEC (International Electrotechnical Commission), NEMA (National Electrical Manufacturers' Association), and UL (Underwriters Laboratories) and their goals, a description is given of how differences in market forces and conditions in Europe caused IEC-type contactors to develop differently from NEMA-type contactors. These dissimilarities also caused IEC-type overloads to evolve differently. Since the introduction of IEC-type overload relays in the North American market has caused problems for U S engineers, a detailed review of operational and feature differences of IEC- and NEMA-type specified devices is given. Eight issues that should be considered when making a choice between IEC-type and NEMA-type starters are discussed: starter size; starter price; contactor performance; contactor application; overload relay trip characteristics; overload relay reset mechanism characteristics; and fault-withstand capability.<>