Square DSquare D
Square D was originally known as the Detroit Fuse and Manufacturing Co. The letter 'D' for Detroit was stamped inside a square on all of their electrical products, and technicians referred to these products as "Square D". Schneider Electric acquired the company in 1991.
Under the Square D brand, Schneider Electric markets limit switches, motor starters, circuit breakers, servo drives, speed switches, signal conditioners, rotary cam switches, Smart Motor Controls, and PLCs.