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Publication numberUS3760326 A
Publication typeGrant
Publication dateSep 18, 1973
Filing dateMay 3, 1971
Priority dateMay 16, 1969
Also published asUS3606155
Publication numberUS 3760326 A, US 3760326A, US-A-3760326, US3760326 A, US3760326A
InventorsWindsor L
Original AssigneeCarter Ltd J
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Three wire electrical plug
US 3760326 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United States Patent 1191 1111 3,760,326

Windsor [4 Sept. 18, 1973 541 TIIREE WIRE ELECTRICAL PLUG 3,021,503 2/1962 Hopkins et al 339/213 Inventor: Lynne Ewindsonwinnipeg 2,170,131 8/1939 .Doremus 339/59 R Manitoba, Canada FOREIGN PATENTS OR APPLICATIONS 7 A 3 142,780 7/1951 Australia 339/14 R 3] Sslgnee figifiig safiggg 1,074,111 1/1960 Germanym. 339/14 R 1,119,368 12/1961 Germany.... 339/14 R [22 Filed: May 3, 1971 483,067 7/1936 Great Britain 339/14 R 21 Appl. No.: 139,816

Related US. Application Data Division of Ser. No. 825,208, May 16, 1969, Pat. No. 3,606,155.

References Cited UNITED STATES PATENTS 9/1971 Windsor 339/14 R Primary Examiner-Marvin A. Champion Assistant ExaminerRobert A. Hafer Attorneyl(ent & Ade

[57] ABSTRACT An electrical plug with a ground wire connected to an angulated grounding strip moulded into the plug body between the two contacts and extending on each side of the body so that it grounds to the shroud normally shielding the pins of the heater and into which the plug normally engages.

2 Claims, 13 Drawing Figures THREEWIRE ELECTRICAL PLUG RELATED APPLICATION This application is a division of my copending application Ser. No. 825,208 filed May 16, 1969, now U.S. Pat. No. 3,606,155 dated Sept. 20, 1971.

This invention relates to new and useful improvements in three wire electrical plugs designed primarily for use with l Voltimmersion heaters for automobile engines. However, the foregoing is not to be construedas limiting as of course itwill be appreciated thatthe plug can be used for any form of electrical connectionwherein the plug-in portion engages within a socket having a grounded wall orportion therearound.

Conventionally, such heaters are plugged into an outside 110 Volt socket and connect to an immersion heater within the cylinder block.

At present such connections are not grounded or three wire connections but merely two wire COI'IIICC".


For reasons ofsafety, it is becoming desirable to insist upon all such immersion heaters and the like being grounded so that three wire extension cords and plugs will be necessary.

Inasmuch as the extension cord from the heater to the exterior of the car is detachable for manufacturing and other reasons, it is somewhat difficult to ensure a three wire connection without enlarging the plug-in receptacle on the heater plug.

These receptacles are relatively small due to the relatively small sizeof the plug and the present invention provides a three wire grounded connection without increasingthe size of the receptacle and in fact, without redesigning existingimmersion heaters.

C0nventionally,,said immersion heaters are provided withmale connecting posts'and theend of the line cord connecting to the immersion heater terminates in a female plug engageable over said posts. These posts are conventionally shrouded by ametallic shroud forming part of the body ofthe heater in order to prevent damage from'occurring to the pins and also in order to prevent inadvertentdisplacement of the plug from the heater so that this shroud provides a convenient ground contact for a three wire conduit.

The plug-in connector portion connected to the one endof the line cord is provided with an angulated.

grounding strip moulded into the connecting portion between the twosockets and having wings extending upon each side ofthe connecting portion so that when the connecting portion is engaged over the pins of the heater, the wings? engage the walls'of the shroud. This ground connector strip is electrically connected to a ground wire of-the conduit which in turn, of course, is connected to the ground of the source of electrical supply thus grounding the heater every time it is plugged Another object-of the invention is to provide a device of the character herewithin described in which the ground strip can be moulded into position without increasing the size of the connector portion of the plug.

A yet further object-of the invention is to provide a device of the character herewithin described which lends itself particularly to theuse of the flat three conductor cable presently used.

A still further object of the invention is to provide a device of the character herewithin described which is simple in construction,. economical in manufacture, and otherwise will suited to the purpose for which it is designed.

With the foregoing in view, and such other or further purposes, advantages or novel features as may become apparent from consideration of this disclosure and specification, the present invention consists of, and is hereby claimed to reside in, the inventive concept which is comprised, embodied, embraced, or included in the method, process, construction, composition; arrangement or combinationof parts, or new use of any of the foregoing, of which concept, one or more specific-embodiments of same are. herein exemplified as illustrative only of such concept, reference being had to the accompanying-FIGS. in which:

FIG. 1 is an isometric view of the plug secured to the end of a conductor cable.

FIG. 2 is a top plan view of FIG. 1 reduced in scale FIG. 3 is a view similar to FIG. 2 but showing an alternative embodiment.

FIG. 4 is an enlarged isometric view of one embodiment of the ground strip per-se.

FIG. 5 is a section along the line 55 of FIG. 1.

FIG. 6 is a front elevation of a heater plug showing the plug in position but sectioned for clarity.

FIG. 7 is a view similar to FIG. 4 but showing means to ensure angulation at'the desired locus.

FIG. 8 is a front elevation of a ground strip before angulation showing an alternative method of ensuring angulation at the desiredlocus.

FIG. 9 is a section along the line9-9 of FIG. 8.

FIG. a front elevation of a blank forming an alternative type of ground strip.

FIG. 11 isan isometric view. of the blank of FIG. 10 formed into the ground strip.

FIG. 12 is the ground strip of FIG. 11, shown in isometric form but with the plastic plug removed.

FIG. 13 is a side sectional elevation of the completed plug with the. ground strip of FIG. 11 incorporated therein.

In the drawings likecharacters of reference indicate corresponding partsof'the differentfigures.

Proceeding. thereforeto describe the invention in detail, reference character 10 illustrates the plug generally formed from moulded resilient material such as rubber or plastic.

This plug is moulded uponthe end of a three wire electrical conduit 11 which is covered with insulation 12 and includes an outer pair of wires 13 and a central ground wire 14. This particular conduit is relatively flat in configuration and therefore is suited for use with immersion heaters'and the like.

The plug 10 includes the conduit receiving portion 15 which in turn connects'to a main body portion 16. having a substantially rectangular connecting portion 17 moulded integrally therewith and extending substantially at right angles to the conduit receiving portion 15 as clearly shown.

A pair of sockets 18 are moulded integrally with the portion 17 and extend downwardly to be connected electrically with the wires 13 in-the usual manner, said connection not being shown in the accompanying drawings..

Also moulded integrally within the plug-in connecting portion 17- is a ground strip collectively designated 19. This is metallic and is angulated to the preferred shape shown in FIG. 4, and defined as Z-shaped. The

central plate portion 20 extends through the connecting portion 17 between the sockets 18 as clearly shown and is secured by the moulding process. The wings or outer panels 21 of this ground strip lie against each of the side walls 22 of the connecting portion 17 as shown in FIG. 2.

Alternatively, the ground strip 19 may be angulated to form a U-shaped member as shown in FIG. 3, once again with the central panel 20 passing through and being firmly secured within the connecting portion 17 between the wings 21 lying against the walls 22 of the connecting portion, but towards one of the sockets 18 as clearly illustrated.

FIG. 6 illustrates generally an immersion type heater collectively designated 23 having connector pins 24 extending therefrom, said connector pins being protected by substantially rectangular shaped shroud or shield 25 formed integrally with the heater 23 and extending from the outer face 26 thereof. The dimensions of the connector portion 22 are similar to the internal dimensions of the shield 25 so that this connector portion may be inserted within this shield with the sockets l8 engaging over the pins 24 thus making electrical contact with the immersion heater element (not illustrated).

The wings 21 of the ground strip therefore engage the inner surfaces of the walls 27 of the shield as clearly shown and as these walls are formed integrally with the body of the heater, ground contact is provided and maintained.

In order to ensure good ground contact, the wings preferably should stand slightly away from the walls 22 of the connecting portion and to ensure this, I may provide pads 28 as shown in FIG. formed integrally with the walls of the connecting portion 17 under the wings 21 thus forcing the wings to stand slightly proud of the surfaces of the walls and ensuring good electrical contact with the walls 27 of the shield 25.

Proceeding to describe FIGS. 7 to 13 inclusive, reference should first be made to FIG. 7. It is obviously desirable to ensure a relatively sharp angulation along the lines indicated by reference character 29. It is also desirable to ensure that these angulations occur when desired, after the ground strip 19 has been moulded into the plug body.

FIG. 7 shows one method in which small apertures 30 are stamped along the line of angulation thus weakening this line and ensuring angulation occurring at the point.

FIG. 8 shows an alternative method known as knifeedge coining and indicated by reference character 31. These are score marks as shown in FIG. 9 reducing the thickness of metal along the desired bending lines, once again ensuring clean angulation along the lines desired.

FIGS. to 13 inclusive show an alternative embodiment in which the ground strip is collectively designated by the reference character 32. It is preferably formed from a planar blank 33 stamped from spring bronze or brass material or similar suitable material. It comprises a substantially rectangular upper portion 34 and a bifurcated lower portion 35, said bifurcation being caused by a slit 36 extending from the lower end 37 to a circular cutout 38 which ensures that the material does not fracture beyond this point. The upper portion 34 is formed in a cylindrical configuration as indicated by reference character 34' in FIG. 11. This brings the two side wings or strips 29 in face to face relationship as clearly shown in FIG. 11. The end 40 of the ground conduit 41 is stripped and inserted within this cylindrical portion 34 which is then crimped into position as indicated by reference character 42 thus ensuring mechanical and electrical connection between the ground wire 41 and the ground strip 32.

The ground strip and conduit is then inserted within a mould (not illustrated) and plastic injected therearound thus forming the plug. It should be noted that the side wings or strips 39 extend beyond the mould and hence beyond the distal end 43 of the plug 44.

These wings or strips 39 are then bent around the distal end in opposite directions from one another to lie slightly spaced from the sides 45 of the plug 44 as clearly shown in FIG. 13.

In operation, of course, it may be inserted within the heater socket in the usual way with the wings 39 contacting the grounded walls of this socket.

Various modifications can be made within the scope of the inventive concept which is herein disclosed and- /or claimed.

What I claim as my invention is:

l. A grounded connector plug for use with an electrical appliance which has a pair of connector pins surrounded by a metallic shield, said connector plug comprising a block-shaped body of insulating material having an end surface and at least one pair of opposite side surfaces, a pair of spaced connector pin receiving sockets embedded in said body, and a metallic ground member comprising a substantially cylindrical and hollow ground wire receiving portion embedded in said body in the space between said sockets and extending in parallel with the sockets toward said end surface of the body, and a pair of strips integral with said cylindrical portion and projecting from said end surface of the body, said strips being reversely bent in relatively opposite directions at said end surface and being disposed at the respective opposite side surfaces of the body for contact with a pin surrounding shield of an applicance.

2. The device as defined in claim 1 which is further characterized in that said strips extend in divergent relation from the respective opposite side surfaces of said body but are resiliently pressabletoward the same.

t a: :r r: 4:

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2170131 *Jul 2, 1938Aug 22, 1939Cornelius W DoremusShielded telephone plug
US3021503 *Dec 5, 1960Feb 13, 1962Gen Motors CorpTerminal means
US3606155 *May 16, 1969Sep 20, 1971Carter James B LtdThree wire electrical plug
AU142780A * Title not available
DE1074111B * Title not available
DE1119368B *Oct 8, 1955Dec 14, 1961Kabelwerke Reinshagen G M B HSchutzkontakt-Steckvorrichtung
GB483067A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US6007384 *Mar 10, 1998Dec 28, 1999The Whitaker CorporationCasing for a plug for a cable having a drain wire
US7955101Oct 7, 2008Jun 7, 2011Hubbell IncorporatedModifiable electrical connector lug
US20100087106 *Oct 7, 2008Apr 8, 2010Fci Americas Technology, Inc.Modifiable electrical connector lug
DE19712810A1 *Mar 26, 1997Oct 1, 1998Whitaker CorpCable plug arrangement
U.S. Classification439/101, 439/607.8, 439/924.1, 439/825
International ClassificationH01R24/12, H01R13/648, H01R24/00
Cooperative ClassificationH01R13/648
European ClassificationH01R13/648