T his pape r desc ribe s the physical co nstruc tion, basic principles o f o pe ratio n, a serie s of compariso n tests co nducted o n an adjustable speed coupling syste m ( A SCS) , and a low-vo ltage variable-freque ncy drive ( V FD ). T hese syste ms have been te sted at three diOEe re nt ratings ' ( 50 hp, 100 hp, 200 hp) driving load pro le s re prese nting both fans and pumps. T he A SCS emplo ys high e nergy-product neodymium/iro n/bo ro n (Ne FeB ) pe rmane nt magnets, which ac t on stee l-backed copper discs to pro vide to rque transfer from moto r to load witho ut mec hanical contac t. T he slip that occurs between the moto r and load shafts can be c hanged by adjustment o f the mechanical c learance of the magne ts and the co ppe r disc s. T hus, a form of speed co ntro l fo r the load is aOEec ted fo r a syste m drive n by a constant freque ncy inductio n moto r. T he te st results co mpare the e nergy savings pote ntials o f the V FD and the A SCS and the merits and disadvantages o f the two system s re lated to motor o peratio n and powe r syste m connec tio n issue s.