| Classic straight blade plugs and sockets |  |  |
Classic material can still be found whenold homes are renovated. Examples are shown below.
Moreover radio outlets are added. They look like125V sockets, but had a very different use.
A few images of knob and tube wiring have beenadded also; a type of wiring that still can be found
old homes. The origin of US flat blade plugs is described on a separate page.
| Rating: Sockets and plugs may have twodifferent ratings foramperage and voltage: 15A- 125V and 10A - 250V. | Originally,domestic sockets were rated at 10A - 250V, because the NEC limitedlightingcircuits to 10 Amp. In 1923, the code changed to allow lightingcircuits to be fused at 15 Amp. However, the old rule (10 Amp) stillappliedto circuits over 125 volts. |
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| 1, 2 | Twoexamples ofclassicnon-grounded sockets with slots for plugs with two parallel bladesand for plugs that have blades in tandem orientation. Both typesof plugshavebeen designed by Harvey Hubbell. The tandem blade configuration waspatented in 1904, the parallel version eight years later. The page on origin of US plugs gives detailed information. For manyyears both types were available, but finally the parallel orientationbecame the standard US 15A - 125V plug. The coexistence of parallel and tandem blade plugs necessitated theconstruction of wall sockets that could accept both types. Manufacturers: General Electric (no. 1), and Hubbell Inc. (no. 2).Sockets became available duringrenovation of a 1937home in California. {BN}Leviton is the only company that still makes socket no.2 for repair use only (info given by Jan de Bondy, Canada). |
| 3 | Dual socket that accepts not earthed plugs witheither parallel or tandem blade plugs. Rating: 10A - 250V / 15A - 125V. Socket nos 3 and 4 have been found in a home build in 1905 in theprovinceof Québec, Canada,. Home was connected to mains later. {TH} Manufacturer: Canadian General Electric; the Canadian counterpart ofthe US-based General Electric. Both companies use the same logo (seetop inset). Socket has a Canadian Standards Association (CSA) mark, see bottominset. Because of the CSA mark, the socket must have been made afterthe introduction in 1953. |
| 4 note | Dualsocket for not earthed plugs with parallel blades. Rating: 15A - 125V. Manufacturer: former (1919 -1992) Canadian company Smith & StoneLtd. {TH} Dating: early 1940s - early 50s, because it doesn't have the CSA mark(see no. 3) that was introduced in 1953. The museum is grateful to Jan de Bondy for providing detailedinformation about manufacturer and dating. Thesocket is polarized. Left slots (hot = line) are 7.12 mm wide, rightwhile slots (White = neutral) are 8.72 mm wide, see inset.Socket nos 3 and 7 have similar polarized outlets. |
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| 5 | Standard flat blade plug and connector made of ebonite, avulcanized natural rubber. Arelative high sulfur content and prolonged times of vulcanizingresults in a solid product. Connector rating: 15A - 125V / 10A - 250V. Manufacturer: Arrow Electrical WiringDevices. Dating: ca. 1930s. {ChR} |
| 6 | Classicmodel of a not grounding socket, with switch, rated at 15A - 125V. Theswitchleft is an additional light switch. Nowadays onlygrounded sockets are allowed, but non-grounded plugs(NEMA 1-15P) are still permitted for appliances that don't require anequipment ground connection. Manufacturer: Leviton. US patent no. 2704832 was granted onMarch11, 1955. |
| 7 | Monolitequintet socket, rated at 15A-125V / 10A-250V. Manufacturer: Monowatt Electric Corporation, New York, Providence,Chicago. Socket dates back to late 1930s, when Monowatt was a divisionof General Electric. {RP} Socket nos. 7 and 8 came in their original carton. They are shownon a separate page. |
| 8 | 4-plugsocket,rated at 15A - 125V. The dual - duplex design probably dates back tothemid 1950s. Manufacturer: General Electric (wiring device department, Providence). {RP} |
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| 9 | US groundadapter for 15A - 125V two pole socket.The grounding clip of the adapter (green arrow) is connectedtoearth via the brass screw that is used to attach the wallplate to thebody of the socket (which have to be grounded !). These adapters arealso known as cheater plugs. In 2003 they were still available in somehardware stores. |
| 10, 11 | Obsoleteplug with two flat blades in T-configuration, rated at 10A - 250V. Theplug don't fitin socket no. 2 and is incompatible with NEMA2-20sockets, because of different pin spacing (see image no. 11).Manufacturer of the shown plug is notindicated; it could have been made in Australia, since a similar typehasbeen used also in Australia and New-Zealand in the 1930s -1950s. {ChR} |
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| 12 | Non-NEMAduplexsocket with angled slots for line (hot) and neutral (w). It is rated at15A - 125Vand 10A - 250V. Thetwo sockets are eachother'smirror image, an unusual orientation, but the top and bottom angledslots are correctly (crisscrossed) wired. Manufacturer: Hubbell Inc.(model 7051). |
| 13 | Hubbell10A-250V, 15A-125V plug that fits in socket no. 12. The type of plugwith angled power pins is described in more detail on the origin of US flat bladeplugs page. The plug has anUnderwriters Laboratories* certification mark. Dating; probably 1950s. * U.S. testingfacility and developer of safety standards. |
| 14 | Dualsocket with not earthed outlet for parallel and tandem plugs andearthed outlet for plugs with angled power pins, a now obsolete typedesigned in 1915 by George P. Knapp (Hubble Inc.). See images 12 and 13for details. Image of socket has been taken by Bryce Nesbittin a building slated for demolition in Berkeley CA. Manufacturer:Hubble Inc. Dating: 1930s. |
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| 15 | Tap-A-Line outlet with elongated slots toreceive the blades of multiple appliance plugs. Details are given on a separate page. |
| 16 | Pullchain mediumsize*light bulb socket with two non-grounded outlets. Only the lamp isswitchedon/off by the pull chain; outlets are continuously active. * medium refers to the diameter of the Edison screw base; medium = 26mm (U.S.), or 27 mm (Europe). Size are alsoindicated as E26 and E27. The adapter has been made in Colombia |
| 17 | Twomedium sizelight bulbadapters. Left: screw base to 2-pole outlet*. Right:non-grounded 15A - 125V plug to medium light bulb socket.Manufacturer:Leviton, Melville, New York. * screw base outlets date back to a 1904 Hubbell patent, see origin of US flat blade plugs for details. |
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| 18 | BothGeneral Electric Company and Academy Electrical Products Co. (laterpart of Eagle Electric and therafter Cooper Industries) have designedplugs and connectors with an automatic wiring method; tools are notneeded. Details about three automatic wiring methods are given on a separate page. These plugs date back tothe early 1950s; some are still available. |
↓ note | Nos. 19 and 20 have been made for theU.S.Army in Germany. They were for sale in Germany in the 1950s to ca. '80s. |
| 19 | Not earthed duplex socket withslots in parallel and in tandem position, rated at 15A - 250V (see alsono. 2). Slots accept also not earthedcontinental European2-pin plugs with 4.0 or 4.8 mm pins. Original wallplate is missing. Manufacturer: Busch-Jaeger in Lüdenscheid, Germany.The socket has a type of Busch-Jaeger logo that has been used from 1951until 1979. {FSE} |
| 20 | Adapter plug for NEMA 5-15 plugs (imageleft) that fits in Terko* sockets(image right).Note that NEMA 5-15 is a 120 Volt standard whereas the German Terkosystem is rated at 250 Volt. The adapter does not have a transformer. The adapter has a MPADmolding mark.No. 76 refers to the company that has produced the cast: Bezet-Werk,Herman Buchholz GmbH in Berlin-Lichtenrade. No. 131 stand for anurea-formaldehyde resin with cellulose as filling agent. It is notclear whether Bezet-Work also has assembled and sold the adapters. {FSE} * See Terko page fordetails. |
| Radiooutlets Inmany homes, build in the 1920s to '40s radio antenna coils wereinstalled at the attic. A wire connected the antenna to a groundedradio outlets in rooms downstairs. When homeantenna coils fell into disuse, radio outlets were often putout of sight by wall paper or layers of paint (see image No. 21). | Although radio plugs had a pin configuration that never has been usedfor 120 or 240 Volt power connections, it is confusing that often radiooutlets were part of a dualsocket; the other half was a standard 15A-120V outlet. |
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| 21 | Radio outlet made by Hart & Hegeman inHartford, Conn. H&H merged in 1928 with the Arrow Electrical Company to become theArrow-Hart & Hegeman Electrical Co. Photo has been sent by JoshuaHodges. The dual socket has a radio and NEMA 1-15 socket. |
| 22 | Radio outlet designed by Victor R.Despard. Patent application wasfiled in 1932 by Pass & Seymour Inc. in Syracuse, N.Y. Outlet hasbeen made also by Bryant Electrical Corporation in Bridgeport, CT. |
| 23 | Radio outlet found in a 1940 apartmentbuilding (a former hotel). The image is based on photos taken by JohnBardy, Los Angeles. The two parallel outlets resemble aregular 15A-125V socket and the copper strap indicates 10A-250V /15A-125V. However a NEMA 1-15 plug doesn't match because theGROUND outlet is smaller than the regular hot wire opening. The other end of the strap shows a diamond with character S. A similar logowas used by the Canadian electro-technical company Smith & StoneLtd (see image 4, above and manufacture details). The radio clock is eitherS&S made, or standard S&S straps have been used to mount anunknown radio outlet. |
| Knob and Tube wiring (K&T) Knob and tube wiring was an early standardized method of electricalwiring. It used individual wires supported by porcelain insulators(knobs) and run inside porcelain cylinders (tubes) when going throughwood beams. See image nos 23 - 26. Until the mid-1930s, knob-and-tube wiring was installed inmany U.S. homes and it can still be found in some older houses. | Whetheror not K&T has to be replaced isdiscussed on several websites. See forexample: httpsss://www.nachi.org/knob-and-tube.htmand https://diy.stackexchange.com/a/20279/5960 In short: knob and tube wiring, properlyinstalled and in good conditionis both reliable and safe, but it has no ground wire and is notappropriate for electrical equipment that requires grounding. K&T is not permitted in new constructions inthe US, except in a few industrial and agricultural related situationsspecifically listed in the US National Electrical Code. |
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| 24, 25 | Porcelainknobinsulator. This example consists of two pieces and has on each side ofthe nail a pass-through groove to guide the wire. Knobs are nailed intowall studs and floor joists.Usually hot and neutral wires are separated from one another, whichallows the wires to readily dissipate heat into free air. Thereforewires are capable of carrying higher currents than the same conductorsin close proximity. Another type of insulator (not shown) consists of asingle piece of porcelain. The wire loops in a circular groove runningaround the circumference. Also block-shaped ceramic cleats areoccasionally used. {BN} |
| 26 | Porcelaintube, used to keep wires from coming into contact with, or beingcompressed by wood framing parts of a building. {BN} |
| 27 | K&Twiring inside a 1930 Pittsburgh house. Part of a photo taken in 2006 byLaura Scudder and shown at the Wikipedia pageabout knob and tube wiring. |
