Square D

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Square D
Industry Electrical equipment
  • McBride Manufacturing (1902-1908)
  • Detroit Fuse and Manufacturing (1908-1917)
  • Square D (1917-present)
Founder Bryson Dexter Horton
Headquarters Andover, MA, United States
Area served
  • North America, South America
Products electrical equipment
Brands Square D, QO, Homeline
Number of employees
20,000 (es. 2016)
Parent Schneider Electric
Website www.schneider-electric.com/us

Square D is an American manufacturer of electrical equipment headquartered in Andover, MA. Square D is a flagship brand of Schneider Electric, which acquired Square D in 1991.

The company was listed on the NYSE for 55 years prior to its acquisition without reporting financial loss in any calendar quarter, paying out 220 consecutive quarterly dividends to shareholders.


The Square D plant on Rivard Street in Detroit, 1920.


The classic "Square D" logo can be found on their products. Adopted circa 1910.
A 1917 Square D enclosed safety switch.

The company was founded on December 15, 1902 by Bryson Dexter Horton and James B. McCarthy. In 1903 they incorporated as the McBride Manufacturing Company. During the first decade of business, the company expanded into various other electrical products. In 1908, the company was renamed Detroit Fuse and Manufacturing. Bryson Dexter Horton, an 1895 electrical engineer graduate of the University of Michigan, was 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.[1] Their first enclosed safety switch was introduced in 1909.

Soon after their renaming to Detroit Fuse and Manufacturing, the company adopted their famous logo: a capital letter D for Detroit enclosed in a square. The logo was stamped on all Square D's switches and products. The combination of an easily remembered monogram logo and their great popularity resulted in customers referring their products as "Square D". Consequently, the company trademarked the logo and in 1917 they renamed the company to Square D. Horton served as Square D's president until 1928


In the early 1920s Square D sold the majority of their fuse business in order to focus more on their safety switches and other safety products. The company began an aggressive marketing campaign to promote their safety switches. Their ads, which became to be known as "Jones is Dead!", directed public attention onto the safety hazards of exposed electrical switches in factories. Square D hoped to capitalize on the growing concern of factory safety. One such fully working Square D safety switch from 1922 was donated in November 2003 to the Smithsonian's National Museum of American History.[2]

By 1929, Square D merged with a Milwaukee-based industrial controller company and began producing Westinghouse-licensed circuit breakers. In 1935 Square D began producing its own range of circuit breakers for both commercial and residential uses.[3]



In 1991, the company was acquired and became a subsidiary of Schneider Electric.[4] In 2003, the Square D by Schneider Electric brand celebrated its 100th anniversary.

Product lines[edit]

A 20-AMP double-pole Square D breaker.

Introduced in 1955,[3] their "QO" line of 3/4-inch circuit breakers may be their best-known product line, used in the electrical distribution boards 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. The 1960s Square D introduced the Safety Line distribution centers for large industrial electrical power loads. This design had solid or tubular busing with each large fused switch clamping onto the busing. The company also sold the B line 277-480 volt panels generally used for lighting in the 1970s and 1980s. The QO and QOB are by far their most popular commercial products. The QO standing for "quick open", and QOB for "quick open bolted" breaker. The QOB was usually specified for buildings with lots of vibration, or in industrial settings where a higher degree of reliability was desired. A QO breaker could easily be clipped into a QOB panel, but the chance that it could be popped out accidentally when an adjacent breaker was being changed made bolting the breaker in a nice feature.

Another well-known Square D product line is the Powerlink circuit breaker, created for lighting control, sold for bigger buildings/skyscrapers. B Line and D Line were the breaker panels in which power line breakers were used. Eventually the company branded Powerline and Powerlink panels and breakers. Powerlink was a heavy duty 277 volt lighting breaker used in large buildings with 277 volt lighting loads. These were also favored for their robust design, and functional reliability. Using Ohm's Law, a 277 volt lighting circuit can run over 2x the wattage of a 120 volt circuit. This means less panel space, and less wire. This is why high rises frequently have higher voltage lighting for general task lighting.

The I-Line series of distribution panelboards is favored by many electricians for its ease and safety of adding new breakers. The panel uses a stacked bus system that protects the energized bus from accidental contact and the breaker can be easily installed using a flat head screwdriver contacting only de-energized parts of the backplane of the panel. The design of the breakers and panel require that extra attention be paid to phase rotation as the right (even numbered) side of the panel will have the phases in a C-B-A configuration whereas the left (odd numbered) side of the panel will have a more standard A-B-C arrangement.

Square D also made disconnect switches, both fused, and unfused, as well as HACR (Heating Air Conditioning and Refrigeration) rated switch boxes that held an HACR breaker for use as a disconnect. The QO type breaker fits this disconnect box. These were popular with food service, grocers, and other cold storage users.

Other companies used terms like "Quick Lag" and similar brand name letter coding on their circuit breakers e.g.: QL, QLRB, etc. No one knows who started the brand coding for sure. QO is an industry recognized standard, like "Kleenex" is used to refer to a tissue regardless of brand. These brand specific letter codes had nothing to do with NEMA specifications or coding though it looks like they were intended to emulate NEMA codes.


  1. ^ Clarence Monroe Burton, William Stocking, Gordon K. Miller (1922). The City of Detroit, Michigan, 1701-1922, Volume 5. S.J. Clarke Publishing Company. p. 187. Retrieved 20 April 2014. 
  2. ^ "1920S SAFETY SWITCH DONATED TO SMITHSONIAN". EWWEB. December 1, 2003. Retrieved 20 April 2014. 
  3. ^ a b "The Square D key dates" (PDF). Schneider Electric. Retrieved 21 April 2014. 
  4. ^ http://www.schneider-electric.us/about-us/company-profile/history/

External links[edit]