New Nema Rerating of AC Motors

The motor and generator section of the National Electrical Manufacturers Association (NEMA) has adopted new suggested standards for future design which assign higher horsepower rating to a given motor frame size. The rerating will make available standard 1-to 50-hp ac motors smaller by two frames than those motors produced in the past; this will, later, affect ratings to 200 hp. Per rating reductions of 50 percent of volume and 75 percent of weight are shown to be typical. Development of improved and new materials plus advancements in the art of polyphase induction motor design, are given as factors that make the revision possible.