- 1902 Detroit Fuse and Manufacturing, a US supplier of electrical distribution and industrial control equipment, begins operations.
- 1917 The company changes its name to Square D, based on its trademark "D" appearing on conduit boxes and switches.
- 1926 Square D builds its first power distribution panelboard. Three years later it moves into the industrial controls market.
- 1935 The company launches its own range of circuit breakers and the first circuit breaker for residential use.
- 1940s Square D has 10 factories in North America, 43 regional offices and a workforce of 7000, manufacturing half of all the circuit breakers used in aviation.
- 1950s The company opens its first European subsidiary and introduces its iconic QO circuit breakers.
- 1970s Square D opens agencies in South Africa and Asia. It introduces the Symax PLC and Watchdog energy management system.
- 1980s After many years of growth and expansion, Square D focuses on electronics, through strategic acquisitions.
- 1991 Square D has 18,500 employees and operations in 23 countries when it joins Schneider Electric.