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Publication numberUS3710287 A
Publication typeGrant
Publication dateJan 9, 1973
Filing dateJul 1, 1971
Priority dateJul 1, 1971
Publication numberUS 3710287 A, US 3710287A, US-A-3710287, US3710287 A, US3710287A
InventorsEckert W
Original AssigneeEckert W
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Insulated plug
US 3710287 A
An electrical plug of the type used with convenience outlet receptacles, but improved by having insulation integral with and effectively faired-in with the prong structure adjacent the plug body so that the conductive portions of the prongs can never be exposed while the plug is carrying current; in various embodiments the prongs are undercut to receive and retain the insulation, are fitted with insulative sleeves of effectively zero obstruction thickness, and have divided portions to receive and retain molded-in-place insulation.
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Description  (OCR text may contain errors)

United States Patent 1 Eckert 1 Jan. 9, 1973 [54] INSULATED PLUG FOREIGN PATENTS OR APPLICATIONS [76] Inventor: William F. Eckert, 729 Milyer Lane, 1,048,309 l/ 1959 Germany ..339/196 R Baltimore, Md, 21229 1,181,370 2/1970 Great Britain ..339/196 M Primary Examiner-James A. Leppink V Assistant ExaminerLawrence J. Staab Attorney-John F. McClellan, Sr.

[57] ABSTRACT An electrical plug of the type used with convenience outlet receptacles, but improved by having insulation integral with and effectively faired-in with the prong structure adjacent the plug body so that the conductive portions of the prongs can never be exposed while the plug is carrying current; in various embodiments the prongs are undercut to receive and retain the insulation, are fitted with insulative sleeves of effectively zero obstruction thickness, and have divided portions to receive and retain molded-in-place insulation.

1 Claim, 6 Drawing Figures PATENTEDJAN 9 I975 3,710,2 7


ATTORNEY INSULATED PLUG can be made by means of paperclips, knife blades, portions of toys, or even in some cases, by direct contact with a portion of the body of the user, particularly when the plug is being inserted or withdrawn.

The problem would arise less often if it were not for the necessity of connecting receptacles and prongs in a positively retentive manner, to avoid too-easy disconnection by dislodging the plug.

Some plugs are provided with cam-locking devices which secure them in place, but in most cases the spring-action of the parts is relied on. in ordinary spring-action plugs, considerable overlap between conductive parts of the plug and of the receptacle is provided, so that when the plug is pushed all the way into the receptacle, substantial friction can be applied.

sures have been made which involve loose or working.

parts, such as, for example, those which can be found in military multi-prong insulators which involve the use of springdoaded precision blocks of insulation sliding on the prongs of the connector or sliding on special ways provided for the purpose.

Some fixed-insulation prongs have been used in the past ,as in jacks, but it is believed that prior to the present invention no flush-insulated convenience outlet plug prongs have been known or used.

Accordingly, it is a principal object of this invention to provide as a new and useful article of commercea safety plug having prongs with continuous, effectively flush insulation fixed along the base portions of the prongs to such extent that contact with the conductor of a receptacle is made only after a portion of the insulated length of the prong is inside the receptacle, and this object comprises also a brief summary of the invention.

The above and other objects and advantages of the invention will become more readily apparent upon examination of the following description, including .the drawings to which reference is now made as follows:

FIG. 1 is a face view and FIG. 2 is a side view of a plug according to this invention;

FlG. 3 is a face view and FIG. 4 is a side view of another embodiment of a plug according to this inven tion; and

FIG. 6 is a side view of yet another embodiment. of a plug according to this invention.

In the Figures, like reference numerals designate like parts.

Referring in detail to FIGS. 1 and 2, there is shown at 10 a two prong electrical plug of the type supplied for use with ordinary household electrical convenience outlets. Each of the flat-shaped metallic prongs, l2 and 14, is reduced in section, at 16 and 18 respectively, in the mannerof undercuts.

The reduced section portion of each prong extends from the insulative base 20 about halfway the length of the prong and includes reductions in both length and breadth of the section. The terminal half including the free end of the prong remains the standard size provided in present electrical practice, as does the electricallead'22 connective portion (not shown) in the base.

An insulator 24, 26 covers each reduced-section portion of the prongs l2, 14, extending from the base 20 to the full-size terminal portion of the prongs. The insulators are made of such dimension as to fill out the undercut portions to the full size of the terminal portions of the prongs, fairing in smoothly with the prongs in both length and breadth.

In operation, the plug is used in the accepted manner, being inserted in the normal way into any ordinary convenience outlet and withdrawn to break the connection when desired. The insulation does not interfere in the leastwith the oper'ationof the plug, since there is no insulative protrusion to catch on the receptacle structure.

However, it will be noted that shook hazards arewith the exposed portions, and no danger of short circuiting. Even when an electrolyte such as salt-water is poured over a wall-outlet towhich a plug made according to this invention is connected, the chance of shorting the plug is very small.

Material for the insulators 24; 26 can be transparent polyvinyl chloride, as indicated in the drawings, or polyethylene, or any other suitable insulation.

The insulation ispreferably molded in place, but if it is rubber, or similarly elastic, it can be stretched over the full-sized ends of the prongs and slid into the recesses. i

With the molded construction, a positive fit'can be assured and danger of cutting the insulation on installation is eliminated,

In either case, the insulation is positively constrained by the width and thickness ledges at the end of the reduced section so thatit cannot be dragged over the prong ends, and abut the plug body in a tight fit at the other end. The tight fit assures that even a knife blade cannot be inserted between the plug body and the insulation without forcing it, in the elastic slip-on insulation version of the invention. In the molded insulation version of the" invention, the insulation flows into all minute irregularities of the reduced section, throughout the length and breadth of the reduced section, so that the insulation cannot be resiliently collapsed on itself, and cannot be displaced without using force sufficient to rip the insulation.

FIGS. 3 and 4 illustrate a molded insulation construction, installed on a plug 300 which is even more tenacious in gripping to retain itself and in protecting the prongs gripped, than the FIG. 1 and 2 embodiment.

In FIGS. 3 and 4, the reduced sections 316, 318 of the prongs 312, 314, extend the same distances along the prongs as in the previous embodiment, but the prongs themselves are divided into plural lengthsjoined at one end at the plug base and at the other end at the full size terminal portion of the prongs.

As shown these lengths may be in four parts, 316a, b, c (d not shown) and 318a, b, c (d not shown).

Insulation 324, 326 is molded on the respective prongs as before, but in this embodiment the insulation also flows into and around the spaces between the plural portions of the prongs. The result is that even though the insulation may be torn loose from the underlying prong structure, it cannot slip off. The insulation can even be slit lengthwise without any possibility of coming loose from the prongs.

The prongs are made to have the divided structure described by punching-out sections of the prong blanks during manufacture, or by any other suitable means. Even though this reduces the theoretical current carrying capacity of the prongs, no conductive problem arises practically since the remaining section is easily left heavier than the cross-section of the wiring 322 used with it. Wear problems are confined to the terminal portion of the prongs, which are full size as noted. Bending stiffness and strength are sufficiently bolstered by application of the plastic reinforcement to prevent distortion in normal use. If desired, rigid porcelain insulation or semi-rigid insulation such as solid Nylon can be molded in place to assure exceptional rigidity.

FIGS. 5, a side view with the near prong removed for exposition, illustrates a version 500 of the invention in which a resilient clip of insulation 524 is snapped in place around each recessed prong base to achieve the same result of insulating it safely. Material for the resilient clip can be insulatively coated spring steel, or merely resilient plastic as shown. The clip is in the form ofa squared C in section, and the ends of the C" do not necessarily abut on installation, but preferably should. If the ends fail to meet, due to individual variation in prong size to which the clip is applied, the line of conductor exposed between the ends of the C should be on the inside of the prong, facing the other prong. This location is least accessible for accidental contact. In addition, there is less chance of opening the ends of the C by accidental contact with external structure when the seam is between the prongs.

It will be appreciated that instead of being merely clipped to the prongs, the squared C structures may be cemented in place.

Taking advantage of extremely thin, tenacious, wearresistant films such as high density polyethylene and the like, it has become possible to provide a plug which has such thin insulation extending along the prongs that, particularly for seldom removed plugs, protection can be provided without recessing the prongs to receive the insulation.

FIG. 6, a side view, shows this embodiment 600 in which the film is preferably thermoplastically applied directly to the base portions of the prongs 614, 612 (not shown). The film can also be applied as a pullover sleeve, as previously described.

This arrangement IS the cheapest n that it can be apthe scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by United States Letters Patent is:

1. In a plural prong insulated-base electrical plug of the type adapted for insertion into convenience outlet receptacles and the like, the improvement comprising: each prong having a uniform-depth recessed portion extending from said insulative base to a point intermediate the length of the prong and terminating in a shoulder at said point intermediate the length of the prong, each prong recessed portion being divided by slits into lengthwise extending strips spaced apart and joined at the ends, at least one said slit being through the thickness of each prong and another said slit being through the width of each prong, an insulative covering secured to each prong over said portion of'the prong extending from said insulated base to said point intermediate the length of the prong, the insulative covering extending integrally through and along all said slits between the lengthwise extending strips and being flush with the exterior of the prongs adjacent the recessed portions, thereby preventing the insulative coverings from coming loose from the prongs even when out lengthwise.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2226148 *Sep 28, 1939Dec 24, 1940Jack C LewisSafety wall socket connection and plug
US2537370 *Oct 12, 1948Jan 9, 1951Parnes Abraham DMale safety plug member
US3181102 *Jun 8, 1964Apr 27, 1965Gen ElectricElectrical busway apparatus
US3377613 *Feb 15, 1966Apr 9, 1968Andrew M. ArcherElectrical connector
US3533052 *Feb 12, 1968Oct 6, 1970Degaetano BenElectrical cord plugs
DE1048309B *Jan 21, 1956Jan 8, 1959Leonische Drahtwerke A GStecker mit Beruehrungsschutz
GB1181370A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3781913 *Jun 8, 1972Dec 25, 1973Liburdi FElectrical safety block
US4780088 *Aug 17, 1987Oct 25, 1988Means Eugene EConnecting plug for electrical switches and receptacles
US5083946 *Sep 7, 1990Jan 28, 1992Chester Jr Lyle FElectrical plug, light socket and receptacle apparatus
US5641311 *Nov 8, 1995Jun 24, 1997Chuang; Wen-PiaoElectric plug blade structure
US5897398 *Jun 2, 1997Apr 27, 1999Sony CorporationPower source plug
US6109977 *Aug 11, 1998Aug 29, 2000Motorola, Inc.Prong for adapter plug for international use
US6527596 *Feb 1, 2002Mar 4, 2003Tun Li SuPlug blade structure with a shallow recess and a reinforced guide slot for forming an insulating layer
US6753755 *Feb 28, 2002Jun 22, 2004Safer Home, Inc.Electrical safety connector fuse
US6863561 *Dec 19, 2001Mar 8, 2005ProtectconnectSafety electrical outlet and switch system
US6945826Apr 30, 2004Sep 20, 2005Charles Michael WiseMethod and apparatus for preventing electric shocking
US7081009Apr 20, 2005Jul 25, 2006ProtectconnectElectrical distribution functional module
US7321120Nov 26, 2005Jan 22, 2008Protectconnect, Inc.Motion detector module
US7332683Jul 25, 2006Feb 19, 2008Protectconnect, Inc.Dimmer switch module
US7367121Feb 14, 2006May 6, 2008ProtectconnectElectrical wiring method
US7544941Dec 20, 2007Jun 9, 2009Protectconnect, Inc.Motion detector module
US7718893Jul 21, 2008May 18, 2010ProtectconnectAdjustable plaster ring cover
US8028408May 14, 2010Oct 4, 2011ProtectconnectMethod of manufacturing a wiring module
US8105107May 5, 2008Jan 31, 2012Protectconnect, Inc.Safety electrical outlet and switch system
US8388371Jan 27, 2012Mar 5, 2013Protectconnect, Inc.Safety electrical outlet and switch system
US8678856Mar 1, 2013Mar 25, 2014ProtectconnectSafety electrical outlet and switch system
US8910377Oct 3, 2011Dec 16, 2014ProtectconnectMethod of manufacturing a wiring module
US20020052139 *Dec 19, 2001May 2, 2002Gorman Michael P.Safety electrical outlet and switch system
US20020142678 *Mar 27, 2002Oct 3, 2002Kang-Wen LiuBlade base for a plug
US20050225913 *Jun 13, 2005Oct 13, 2005Dell Products L.P.Progressive impedance connector
US20050250377 *Apr 20, 2005Nov 10, 2005Gorman Michael PElectrical distribution functional module
US20080020632 *Jul 24, 2007Jan 24, 2008Gorman Michael PUniversal electrical wiring component
US20080053698 *Jul 27, 2007Mar 6, 2008Steve PurvesPre-wired power distribution system
US20080093552 *Dec 20, 2007Apr 24, 2008ProtectconnectMotion detector module
US20080190640 *Apr 21, 2008Aug 14, 2008Protectconnect, Inc.Safety module electrical distribution system
US20080235943 *May 5, 2008Oct 2, 2008Protectconnect, Inc.Safety electrical outlet and switch system
US20080261420 *Apr 8, 2008Oct 23, 2008Charles Wayne RiddleSafety electric plug for preventing electric shock
US20090020306 *Jul 21, 2008Jan 22, 2009Protectconnect, Inc.Adjustable plaster ring cover
US20100218374 *May 14, 2010Sep 2, 2010ProtectconnectSafety module electrical distribution system
US20100218969 *Sep 2, 2010Protectconnect, Inc.Adjustable plaster ring cover
USRE44546Aug 11, 2011Oct 22, 2013Protectconnect, Inc.Universal electrical wiring component
USRE45430Oct 10, 2013Mar 24, 2015ProtectconnectUniversal electrical wiring component
EP0005983A1 *May 29, 1979Dec 12, 1979BICC Public Limited CompanyImprovements in or relating to electric plugs
WO2000010229A1 *Aug 10, 1999Feb 24, 2000Motorola Inc.Prong for adapter plug for international use
U.S. Classification439/693
International ClassificationH01R13/44
Cooperative ClassificationH01R13/44
European ClassificationH01R13/44