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Is it TRUE that originally, before the invention of the 3-prong, (grounded outlets for homes) that the ground-pin was mounted at the TOP of the triangle, the TOP of the 3 "holes"?
Question Date: 2018-11-26
Answer 1:

It is true that the grounding prong was at the top of the triangle for some years; Philip Labre (US patent 1672067A) was the inventor of this particular type of grounded plug. Before Labre's patent, there was another patent by George Knapp (US1179728A) of a grounded outlet that had the grounding prong on the side. This design is still used in some parts of the world. As to the differentiation between consumer (for the home) and industrial or other usages of the grounded sockets, it is not clear that there was ever a socket that was NOT for consumers. If we don't see grounded outlets in American homes that have the grounding pin on top, that may be due to a lag between the invention/patenting of something and its commercial application, during which time the design may be improved and the old design rendered obsolete.

Answer 2:

Here's a link about the history of grounded outlets:
grounded receptacles. It is said in this link that grounded outlets were required in 1947 for laundry appliances.

Here's a picture of 3-prong vs 4-prong dryer outlets:
3 prong vs 4 prong outlet

modern outlet

Those pictures and the text below are from a site about power plugs and sockets. The grounded consumer plug has several claimants to its invention. The earliest patent for a grounded plug appears to be one applied for on January 11, 1915 by George P. Knapp, on behalf of the Harvey Hubbell company and granted on April 18, 1916.[7] This patent covers the use of a grounding pin which extends further than the other two contacts to ensure that it is engaged first. However, the suggested configuration of the pins was that found in the Australian plug used today primarily in Australasia and China, which was not interoperable with existing two-contact ungrounded plugs. Other grounded plugs that are widely used today were developed later by others so as to be interoperable with ungrounded plugs.

The Schuko-system plug was invented by Albert B├╝ttner, who patented it in 1926.[8] The current American version of the grounded plug, with two vertical blades and a round grounding pin was invented by Philip F. Labre, while he was attending the Milwaukee School of Engineering (MSOE). It is said that his landlady had a cat which would knock over her fan when it came in the window. When she plugged the fan back in, she would get an electric shock. Labre figured out that if the plug were grounded, the electricity would go to Earth through the plug rather than through his landlady. He applied a patent on May 12, 1927[9] and was issued a US patent for grounding receptacle and plug in June, 1928.[9] As the need for safer installations became apparent, earthed three-contact systems were made mandatory in most industrial countries.

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