{"id":372,"date":"2018-05-22T18:26:29","date_gmt":"2018-05-22T18:26:29","guid":{"rendered":"http:\/\/jpelectricalcompany.com\/blog\/?p=372"},"modified":"2021-02-12T16:11:44","modified_gmt":"2021-02-12T16:11:44","slug":"the-electrical-outlet-and-how-it-got-that-way","status":"publish","type":"post","link":"https:\/\/www.jpelectricalcompany.com\/blog\/uncategorized\/the-electrical-outlet-and-how-it-got-that-way\/","title":{"rendered":"The Electrical Outlet and How It Got That Way"},"content":{"rendered":"
\n

Right now, if you happen to be in North America, chances are pretty good that there\u2019s at least one little face staring at you. Look around and you\u2019ll spy it, probably about 15 inches up from the floor on a nearby wall. It\u2019s the ubiquitous wall outlet, with three holes arranged in a way that can\u2019t help but stimulate the facial recognition firmware of our mammalian brain.<\/p>\n

No matter where you go you\u2019ll find those outlets and similar ones, all engineered for specific tasks. But why do they look the way they do? And what\u2019s going on electrically and mechanically behind that familiar plastic face? It\u2019s a topic we\u2019ve touched on before with Jenny List\u2019s take on international mains standards. Now it\u2019s time to take a look inside the common North American wall socket, and how it got that way.<\/p>\n

Hubbell\u2019s Plugs<\/h2>\n
Separable Attachment Plug, US Patent 774,250. Note the round, headphone-like prongs rather than flat blades.<\/figcaption><\/figure>\n
Consider the problems faced by engineers and designers in the early days of the electrical age. They were literally inventing an industry from the ground up, with very little to go on in terms of prior art. Not only did they have to invent the means of producing electricity, they had to come up with absolutely every component that would connect together to create useful circuits for paying customers, preferably without killing them.<\/figure>\n<\/div>\n
\n

One thing customers, particularly\u00a0residential customers, would need would be a means to temporarily attach electrical devices to the mains supply, without requiring a visit from an electrician to connect them to the fixed wiring of a house or office, which was typically dedicated to sockets for light bulbs. The requirements were simple: provide two contacts, one for the line conductor and one for the neutral, that could remain firmly connected but easily interrupted at need.<\/p>\n

Imaginative minds worked on this and similar problems in the late 19th and early 20th centuries, and various solutions were\u00a0adopted. But it wasn\u2019t until 1903 that Harvey Hubbell, an inventor from Bridgeport, Connecticut, patented his \u201cSeparable Attachment Plug,\u201d a device that we\u2019d recognize as a plug and socket. Hubbell\u2019s first pass at a design used round conductors that looked a bit like the plugs used in manual telephone exchanges to make connections, and might have been inspired by them. The detents at the tip of the pins were retained by the spring action of the contacts inside the socket.<\/p>\n

A Hubbell plug with flat blades, from the 1905 catalog.<\/figcaption><\/figure>\n

The device worked well, but the manufacturer and businessman in Harvey saw problems. Foremost was the costs behind those round pins, which would have required machining to achieve the tip and detent. Harvey would have known that parts stamped from sheet metal would be cheaper and easier to manufacture, and so he scrapped the round pins in favor of flat metal blades in 1904. Like the round prongs, the flat blades had a detent for retention, and were arranged in a line. Catalogs from the time list dozens of variants of the \u201cHubbell Attachment Plug,\u201d and the prices shown\u00a0for each device suggest that Hubbell\u2019s company fared well in the early 20th century.<\/p>\n

For reasons unknown, though, Hubbell altered his design in 1912. The two blades were no longer in a line; each blade was twisted 90\u00b0 to form the familiar parallel arrangement we see to this day. Hubbell continued to sell both styles of plugs and sockets, and by 1915 had sold something like 15 million units, enough to ensure that Hubbell\u2019s design would be adopted as a standard, even without the millions of units also sold by Hubbell\u2019s imitators.<\/p>\n

Standardization<\/h2>\n

The specifications for the standard wall outlet we know and love today in North America are determined by the National Electrical Manufacturers Association (NEMA). NEMA standards cover a bewildering range of electrical products; we\u2019ve covered their enclosure and weather-resistance standards before. The standard 120-volt, 15-amp outlet is a NEMA 5-15. The third conductor, the ground pin that completes the outlet\u2019s face, is a round or U-shaped prong. It was added to some outlets as early as the 1920s as a safety feature and is now required for all outlets by the National Electrical Code.<\/p>\n

The ground connection is interesting. You\u2019ll notice that on three-wire plugs, the ground pin extends further out from the insulated cord body by about 1\/8\u2033. The idea here is that the ground circuit will be completed before the line and neutral connections are made when plugging the cord into an outlet, and perhaps more importantly, will be disconnected last when unplugging. That ensures that there\u2019s a path to ground any time a circuit is plugged into the outlet.<\/p>\n

Note too that the NEMA standard says the ground pin is actually located above<\/em> the slots for the line and neutral pins, turning that frowning face upside down. There\u2019s some logic to that \u2014 if something conductive should drape across a partially unplugged cord, it\u2019s safer to have the line and neutral blades physically blocked by the ground pin. In practice, though, most outlets in residential and business settings are installed with the ground plug down. But look around the next time you\u2019re in a hospital; chances are, the outlets there are all installed the correct way.<\/p>\n

Behind the Face<\/h2>\n

The internals of a NEMA 5-15 outlet vary by manufacturer, of course, and even within a brand, there are different grades of outlet. The picture below shows two different grades of outlet taken apart. They\u2019re similar in that both the line and the neutral connections are formed brass bus bars, with screw connections on the outside for connection into a\u00a0building\u2019s wiring, and springy contacts to grip and retain the mating plug. The industrial-grade outlet<\/a> has thicker bus bars, better contacts, and stouter plastic in the body. You\u2019ll notice too that both grades have the ground pin directly connected to the metal frame of the outlet, which would also be in contact with a metal wall box, if it were mounted in one.<\/p>\n<\/div>\n

\n
EMA 5-15 outlet internals. Source: HandymanHowTo.com<\/p>\n<\/figcaption><\/figure>\n

Considering how much else has changed in the last century, it\u2019s pretty remarkable that Harvey Hubbell\u2019s original plug and socket designs have remained pretty much unchanged. They\u2019ve been tweaked, for sure, and the original idea has been extended to a panoply of configurations for every connection imaginable. There\u2019s no doubt that the design has some deficiencies, but in the end, Harvey\u2019s ideas seem to have won the day by addressing the basic needs.<\/p>\n

Original Source: https:\/\/hackaday.com\/2018\/05\/14\/the-electrical-outlet-and-how-it-got-that-way\/<\/a><\/p>\n

Original Date: May 14 2018<\/p>\n

Original Author: Dan Maloney<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

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