Principal types. Electric drives may be classified according to design characteristics into three types: single-motor, group, and multimotor. Single-motor electric drives are used in power tools, simple metalworking and woodworking machine tools, and household appliances. Group electric drives are almost never used in modern industry. Multimotor electric drives are used in multioperation metalworking machine tools and as individual electric traction drives for railroad transportation equipment. Electric drives may also be divided into reversible and nonreversible types (seeREVERSIBLE ELECTRIC DRIVE) and, depending on the possibility of controlling the flux of the converted mechanical energy, into uncontrolled and controlled-velocity types (including automated types with programmed control).