Square D is an American
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
manufacturer of equipment used to control and distribute electric power
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
headquartered in Palatine, Illinois
Palatine is a village in Cook County, Illinois, United States. It is a northwestern residential suburb of Chicago. As of the 2000 census, the village had a total population of 65,479, making it the sixth-largest community in Cook County and the 16th-largest in the state of Illinois at that time...
Square D was founded in 1903 in Detroit, Michigan
Detroit is the major city among the primary cultural, financial, and transportation centers in the Metro Detroit area, a region of 5.2 million people. As the seat of Wayne County, the city of Detroit is the largest city in the U.S. state of Michigan and serves as a major port on the Detroit River...
by Bryson Dexter Horton who is credited with the invention of the safety switch which encased high voltage switches and started the company's main line of business of circuit breakers and encased control panels. Horton served as Square D's president until 1928.
In 1991, the company was acquired and became a subsidiary of Schneider Electric
Schneider Electric is a French global company. It was founded in 1836 by two brothers, Eugène and Adolphe Schneider.In the first part of the 20th century, Schneider et Cie associated itself with Westinghouse Systems, a major international electrical group at the time. The group began manufacturing...
Product linesIntroduced in (either 1955 or) 1962/1963, their "QO" line of 3/4-inch circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
s may be their best-known product line, used in the electrical distribution board
A distribution board is a component of an electricity supply system which divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit, in a common enclosure...
s of many homes in North America.
A second product line is sold under the brand name Homeline. Different breaker connection design and lower list price is what distinguishes it from the QO series. Homeline devices are marked HOM while QO devices are marked QO.
Another well-known Square D product line is the Powerlink circuit breaker, created for lighting control, sold to bigger buildings/skyscrapers.