US 3126239 A
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March 1964 P. A. WINTER ETAL THIRD PRONG CONTACT AND GROUNDING MEANS FOR OUTLETS OF THREE-WIRE TYPE Filed May 25, 1961 m R m m n MW A WA H 0 w mm F D MM m 2 m 7F A m w uw an a; ksamu m United States Patent TERI-D PRONG CONTACT AND GROUNDING MEANS FUR OUTLETS 0F THREE-WEE TYPE Paul A. Winter and David C. Amsier, both of Syracuse, N.Y., assignors to Pass & Seymour, Inc., Syracuse, N.Y., a corporation of New York Filed May 23, 1961, Ser. No. 112,054 6 Claims. (Cl. 339-14) This invention relates to electrical outlets of the type adapted to receive and make electrical connection with the blades or prongs of attachment plugs such as are used at the end of flexible cables to supply current to portable devices, and more particularly to such outlets adapted to accommodate a third or grounding prong on each attachment plug.
It is a general object of the present invention to provide in an outlet novel means to engage a plug grounding prong and to electrically connect it to the outlet mounting strap and to a grounding terminal.
More specifically, it is an object of the invention to provide simple means in a duplex outlet for engaging the grounding prongs of attachment plugs received in said outlet and to electrically connect them to the outlet mounting strap and to a grounding terminal integral therewith.
An important object of the invention consists in forming the receptacle grounding contacts from straight lengths of resilient conducting wire mounted between the two insulating body parts of the receptacle and spaced apart slightly less than the distance across a plug grounding prong.
Another important object of the invention consists in clamping both the grounding contact wires and the mounting strap for the receptacle between the two body parts thereof and held thereby into contact with each other whereby a grounding terminal can be integrated with the mounting strap.
Other and further features and objects of the invention will be more apparent to those skilled in the art upon a consideration of the following specification and the accompanying drawing wherein is disclosed a single exemplary embodiment of the invention with the understanding that such changes and modifications may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.
In said drawings:
FIGURE -1 is an exploded view of a duplex outlet including third prong contact and grounding means constructed in accordance with the present invention, the two upper parts of the figure being in perspective and the lower one in plan; and
FIGURE 2 is a transverse section taken on line 2-2 of FIGURE 1 and illustrating a plug and its grounding prong in position to cooperate with the grounding cont-act wires.
In addition to being the approved and prudent practice, the electrical codes in many areas require the grounding of the frames or other conducting portions of portable electric devices and those of a semi-permanent character, any of which are connected by flexible cable to electrical outlets. This calls for a third conductor in the cable connected to the conducting frame or casing of the portable electrical device, a third prong on the attachment plug, and some means for connecting this prong to ground within or adjacent the electrical outlet supplying the power through the cable to the portable device.
For most circuits of 110 volts and 220 volts, the industry has practically standardized on an attachment plug using parallel prongs or blades for connecting the two live conductors of the cable to the electric circuit at what are commonly known as convenience outlets, together 3,126,239 Patented Mar. 24, 1964 with a third prong of relatively rigid metal bent into a U-shape cross-section and positioned on a center line passing between the parallel prongs, but sufliciently remote therefrom to form the apices of a substantially equilateral triangle with them.
Various means have been adapted in convenience outlets or receptacles for making connection with this grounding prong, but because of its large size and proximity to the current-carrying blades, some difficulty has been experienced in finding adequate room for such contacts and their terminals. The present invention provides a simplified contact system which does not occupy any of the space desired for the principal power conducting contacts, which, in the best practice, must engage not only two faces of each blade, but also at least one of its edges.
Referring now to the drawing for a better understanding of the invention, there is illustrated a dual convenience outlet '10 having a two-part housing formed of molded plastic material including the lower or contact carrying body portion 12 and the cover 14 adapted to be attached thereto by a pair of screws, one shown in FIGURE 1, which are introduced through the openings 15 in the body part and threaded into corresponding openings 16 in the cover, the heads of the screws being deeply counter sunk in the bottom.
The cover plate 14 has the usual front face, not shown, providing the two disc-like portions 17 slabbed ed at the ends and :at the facing parts, as is customary, to project through the usual face of a wall plate and each provided with a pair of parallel slots 18 to receive the parallel blades of the conventional attachment plug. Each also has the larger aperture 20, that to the right near the cover end and the one to the left near the center of the cover in order to accommodate two plugs facing in the same manner. These apertures 20 are each of a size to receive the third prong for grounding purposes and are on the longitudinal center line of the face plate, the side walls of the apertures being parallel to each other to accommodate the parallel sides of the prongs. Such a prong may be seen in dot-and dash iines at 19 in FIG- URE 2.
The undersurface of the cover plate has a longitudinal central channel therethrough defined near the ends by the spaced parallel walls 21, 21 and at the center by the wider spaced parallel walls 22, between which there may be seated the intermediate portions 23-, 24 and 25 of the substantially flat mounting strap by which the receptacle or outlet is mounted in a wall or junction box. The strap has ends 26 for this purpose, incorporating plaster ears 27 which may be broken off if not required through the weakened are-as illustrated, and the elongated transverse apertures 28 for mounting screws which are adapted to be engaged in tongues extending outwardly from the end walls of the box. This mounting strap is apertured as at 29 to pass the screws 29" which secure the two parts of the housing about it and is apertured at 20 in alignment with the openings 20 for passage of grounding contacts. Each section 23 and 25 of the strap is sufliciently narrow to pass freely between a pair of apertures 18 for the plug contact blades from which they are separated by the walls 21, 21'.
The body portion 12 is provided with four separate chambers 30 and 31, one for each slot 18. They accommodate contacts, not shown, to engage the plug prongs entering through the slots. These contacts are arranged in pairs, one in a chamber 3% and one in a chamber 31 and those of each pair are connected together by an integral portion which has a terminal thereon for attaching a conductor, the terminal being available in side opening 33 above cut-down wall 34 of the body to facilitate making connections.
The contact chambers 30 and 31 on opopsite sides of the longitudinal center of the body are separated from each other by full height walls molded integral with the body. As seen at 35, the central portions of these Walls, between the solid parts through which the fastening screw apertures 15 are formed, are sufiiciently widely spaced laterally to freely receive the grounding prong which passes through the left cover aperture 20, and the walls are again widely spaced at 36 to receive between them the prong passing through the right aperture 20' in the cover. Between these widely spaced portions, the walls are brought toward each other to enlarge the compartments 30 and 31 and for other purposes, and these portions are numbered 37.
Contact is made with both sides of each grounding prong on the attachment plugs by means of a pair of parallel lengths of stnaight spring wire or rod 40 placed apart somewhat less than the width across the prongs or the openings 20 and having their right ends fitted in notches 41 in the right end wall of the body. The rods extend along over the widely spaced walls 36, then rest on the upper edges of portions 37, and pass beside the boss for opening 15, the top of which extends above the level of the edges of walls 37 just slightly less than the diameter :of a wire 40. The rods then pass inside the planes of the inner surfaces of walls 35 and then alongside of boss 43 through which the left aperture 15 for a fastening screw passes, this boss being out down to the height of the walls 37 as far as walls 44 which locate the wires against longitudinal movement as do the ends of notches 41.
The portions of the wires or rods in the areas beneath openings 20 and 20' are unsupported and unrestrained against lateral movement to facilitate the passage of the prongs between and in contact with them. However, lateral movement is limited by locating lugs 46 extending upwardly from walls 35 an amount just slightly less than the diameter of the wires. This shortens the length of wire which must be forced aside to permit entrance of the left prong and insures close engagement electrically therewith.
It will be remembered that walls 21, 21' on the cover were referred to as barriers between plug blades and the mounting strap, and they are spaced apart just sufliciently to pass over the outer edges of walls 37, wires 40, and enter into chambers 30 and 31 thereby preventing the wires from being sprung apart at these positions. This plus the restraints 41 and 46 assures adequate wire pressure on the grounding prongs when inserted in through the cover apertures.
In assembling the convenience outlet, the combined contacts and terminals are arranged in compartments 30 and 31 and in the intervening areas where the terminals are exposed, the wires 40 are then dropped into the respective holding slots and grooves as illustrated in FIGURE 1 and the mounting strap positioned above these wires. It should be remembered that the wire diameter is such that they everywhere project slightly above the upper surfaces of the bosses, Walls, etc. surrounding them so that the flat central portions 23, 24 and 25 of the mounting strap rest on and make good electrical contact with the wires throughout most of their length assuring their electrioal continuity with the mounting strap. The portions of the strap indicated by the reference characters 50' and 51 are received in notches 52 and 53 in the end walls of the housing body to prevent relative lateral movement of the strap and housing and then the widened portions 54 and S engage against the outer ends of these walls at 56 to prevent longitudinal movement of the strap. The screws 29' also maintain strap alignment and position.
As seen in FIGURE 1, the strap has a tab 60 turned down at right angles from a lateral extension 61 and this tab has edge lugs 63 and is fitted with terminal screw 64 whereby a conductor may be attached thereto forming part of the electrical circuit and grounding the mounting strap, and thus the wires 40 independently of any ground which may exist by virtue of the strap being attached to a grounded conduit system. This makes the unit available for use with non-metallic sheath threewire cables which are legal in many jurisdictions.
The cover is next placed in position so that walls 21, 21' pass along the sides of narrowed portions 23 and 25 of the mounting strap and of the wires beneath it and hold everything properly in position. The bottom of the long central channel throughout the length of the cover plate rests in appropriate positions on the strap, both at its ends and in areas adjacent the openings 15 through the strap whereby a secure and rigid mounting is effected which is completed by passing screws up through openings 15, through strap holes 29 and threading them into the blind holes 16 in the cover plate. The large rectangular aperture 70 in the center of the cover exposes the center portion of the mounting strap and its internally threaded aperture 71 which is adapted to receive the screw which passes through the covering wall plate, apertured for the faces 17 in the customary manner, and secures it in position on the outlet assembly.
The device described above comprises an extremely simple, sturdy and foolproof assembly which automatically insures adequate grounding of the prongs of one or two attachment plugs by their insertion into appropriate openings therefor in the receptacle. Dual contact is made with each grounding prong of the attachment plug by wires which are immediately in contact with the mounting strap, carrying the grounding terminal 60, 64 which also grounds the prong to the junction box within which the receptacle is mounted.
1. In an electric outlet for receiving an attachment plug having a grounding prong in combination, a body formed of insulating material, an insulating cover for said body having a grounding prong passage therethro ugh, a metal mounting strap extending between said body and cover, projecting beyond the ends thereof, having an opening registering with said passage and having a grounding terminal, a straight, cylindrical resilient metal rod supported by said body and extending longitudinally under one face of and separate from said strap, in electrical contact there with and positioned to be engaged and deflected laterally by a prong entering said passage, and abutrnents on said body part laterally engaging and positioning said rod remote from the passage whereby the rod may flex for prong entry.
2. In a three-wire grounding outlet, in combination, a body part formed of insulating material and having contact receiving chambers therein, an insulating cover part for said body having access openings leading to said chambers, a mounting strap extending between and beyond said body and cover parts and having a grounding terminal, a grounding plug prong passage extending through said cover part and strap and into said body part, a straight, cylindrical resilient metal rod extending over and engaging one face of said strap, separate therefrom and extending within a border of said plug prong passage and means on one of said parts engaging said rod at remote points on both sides of said passage to hold it resiliently within said border.
3. The outlet as defined in claim 2 in which said body and cover parts are secured together and against portions of said strap by fasteners extending through said strap remote from said passage to permit lateral flexing of said rod at the passage area while insuring good electrical contact between rod and strap adjacent the fastening areas.
4. The outlet as defined in claim 2 in which there are two resilient rods arranged within opposite borders of said passage and similarly supported and laterally engaged.
5. The outlet as defined in claim 4 which is duplex and has two longitudinally spaced grounding plug prong passages, each passing through the strap and the straight resilient rods extend longitudinally of the strap for sub- 5 stantially the full length of the body part to be engageable by the two grounding prongs.
6. A three-wire grounding outlet having in combination, a body part having a chamber therein, a longitudinal partition Wall dividing the chamber and having a recess therein to receive a plug grounding prong, a cover part for said body having an entnance aperture for said prong, a metal mounting and grounding strap part extending over said partition wall, beyond the ends of the body and covered and engaged by said cover part, a registering prong aperture in said strap, a pair of straight, round, resilient conductive rods spaced apart less than the width of said prong aperture extending along the top of and supported solely by said partition wall and independent of but engaged by the undersurface of said strap, means integral with one of said parts restraining lateral separating movement of said rods only in areas remote from said plug prong aperture and means securing said parts together and thereby establishing and maintaining an electrically conductive path between said rods and said mounting strap, and abutments at the end of said body part engaging the ends of said rods to prevent longitudinal movement thereof.
References Cited in the file of this patent UNITED STATES PATENTS 2,001,990 Tregoning May 21, 1935 2,297,449 Baumbach Sept. 29, 1942 2,686,297 Hutt Aug. 10, 1954 2,969,456 Rayrnaley Jan. 24, 1961 3,064,224 Wiley Nov. 13, 1962 FOREIGN PATENTS 768,352 Great Britain Feb. 13, 1957