Patent model
On July 31, 1790 inventor Samuel Hopkins of Pittsford, Vermont became the first person to be issued a patent in the United States. His patented invention was an improvement in the "making of Pot Ash by a new apparatus & process." These earliest patent law required that a working model of each invention be produced in miniature.
History of AC power plugs and sockets
The earliest American patent application for an earthed plug appears to be 11 January 1915 by George P. Knapp, on behalf of the Harvey Hubbell company. This patent covers the use of an earthing pin which extends further than the other two contacts to ensure that it is engaged first. Knapp's design was obsoleted in the US before the modern NEMA designations, but is still used in some other countries including China, Argentina and Australia. The configuration of the socket was not operable with existing two-contact unearthed plugs. Other earthed sockets that are widely used in the US today are operable with unearthed plugs. It is sometimes claimed (e.g., in Illumin) that the modern American version of the earthed plug, was invented by Philip F. Labre who was issued a US patent for an earthed socket and plug in 1928. However, Labre's design is no more similar to the modern version than Knapp's earlier design.