US3391374A - Electric receptacle - Google Patents

Description

y 2. 1968 H. E. SCHLEICHER ELECTRIC RECEPTACLE Filed April 27, 1966 INVENTOIF. Harold ESCh/E/Chl BY h/s otffimeys Ill/II w RM km United States Patent 3,391,374 ELECTRIC RECEPTACLE Harold E. Schleicher, West Hartford, Conn., assignor to The Arrow-Hart & Hegeman Electric Company, Hartford, Conn., a corporation of Connecticut Filed Apr. 27, 1966, Ser. No. 545,759 7 Claims. (Cl. 339-44) ABSTRACT OF THE DISCLOSURE An attachment plug receptacle having a ground contact stamped in one piece from sheet metal with a one-piece mounting strap of U-shape, with a strut extending lengthwise of the base engaging the strap to hold it from spreading. The line contact and terminal members being of the clamp type, each have a compression spring pressing the clamping plate toward the terminal portion of said members retaining the plates in position and preventing them from getting lost in the receptacle base.

This invention relates to electric attachment plug receptacles and more particularly to such receptacles having grounding prong contacts for engagement by the ground prong of an attachment plug connector.

In both domestic and industrial use, the provision of ground connections is becoming more and more necessary to meet the standards of the underwriters for detachable connections of electric equipment such as power tools, air conditioners and portable electric devices of all kinds to attachment plug receptacles.

The provision of grounding connections and contacts in electric attachment plug receptacles has heretofore been known, but such prior devices have been difficult to assemble. They required separate parts which had to be connected to the supporting bridge or strap of the receptacle. They afforded poor or inadequate ground connections at times. They had parts riveted or connected to the supporting bridge which loosened in use causing increase in resistance in the path to ground. They were not as rugged, nor as reliable and satisfactory when subjected to long and hard usage as the present invention.

The general objective of this invention is to provide an improved attachment plug receptacle with grounding contacts, wherein the receptacle parts may be easily fabricated and assembled and to afford optimum conductivity both to the ground contacts and to the line contacts and great reliability over long periods of hard usage.

The many advantages of the invention will appear and be mentioned as the various means employed in the invention are described in connection with the drawings.

In the drawings:

FIG. 1 is a top plan view of an attachment plug receptacle embodying the invention, with one-half of the cover of the receptacle body broken away.

FIG. 2 is a detail view, partly broken away, showing in plan the mounting strap and associated strut as used in the embodiment of FIG. 1.

FIG. 3 is a side elevation view, partly in section, of the parts in FIG. 2.

FIG. 4 is an end view of the embodiment of FIG. 1.

FIG. 5 is a fragmentary sectional detail view of one of the ground contacts in relaxed condition before the insertion of the ground prong.

FIG. 6 is a view similar to FIG. 5, but with the ground prong inserted.

FIG. 7 is a fragmentary detail view showing in perspective the spring clip and receptacle line contact assembly.

The invention will be described as applied to a duplex attachment plug receptacle.

Referring to the drawings, the receptacle comprises ice a two-part insulating body of molded insulating material. The base part 10 is hollowed out and recessed to provide separate compartments on opposite sides of a longitudinally extending central partition or spine 12. If desired, a central transverse partition 14 may be provided which with the longitudinal partition divides the interior of the receptacle base into four compartments such as 16 in the four quarters of the base. Each compartment receives a combined one-piece terminal and contact member stamped from sheet metal having a pair of facing contact fingers or prongs (21, 22) connected by a U-shaped connecting portion 23a. The bottom half of the contacts 21 are connected by a rectangularly bent portion 23b with a terminal plate portion 24 lying across an opening in the side of the base. The terminal plate portion 24 is slotted from the top to freely receive the shank of a terminal screw 25. The terminal screw threads into a tapped hole in a rectangular clamp 26 in the form of a sheet metal plate positioned behind the terminal plate 24. When the screw is threaded part way into the tapped hole in the clamp, both may be dropped into place in the base with the shank of the terminal screw slipping down the slot in the terminal plate. Adjacent terminal plates 24 on the same side of the base are preferably connected by break-off bridging or connection portions 27 as in Shenton Patent 2,262,712.

In the floor of the base 10 are two small wire holes 26h beneath the terminal portion 24 and the clamp 26 so that the bared ends of wires may be inserted therethrough and between the clamp 26 and the terminal plate 24 to be gripped thereby as the screw 25 is tightened.

Preferably the wire gripping faces of the clamp 26 are knurled for firmer frictional gripping of the wires. For a similar purpose, the inner faces of the outer contact fingers 21 are knurled; and to further enhance gripping and retaining the prongs of the attachment plug, the inner faces of the inner contact fingers 22 have a small centrally located bump.

Clamp type terminals of the type described have given difiiculty heretofore because if the terminal screw was backed out too far, the clamp would become detached from the screw. It would then become very difficult to reengage them and start the screw into the tapped hole in the clamp. To overcome this difficulty, a coiled compression spring 28 is provided behind the clamp with one end pressing against the longitudinal partition 12 and with its other end pressing against the clamp, thus pressing the clamp against the terminal portion 24.

To support the receptacle across the open front of a conventional wall box, there is a U-shaped stamped sheet metal supporting strap 30 having conventional plaster ears 31, 32 out-turned from the parallel arms 33, 34 which are connected by a longitudinal connecting part 35 upon which the base 10 seats.

In order to keep the arms 33, 34 in parallel, resisting tendency to spread when tensile stresses are applied, a narrow sheet metal strut or bridge 36, preferably of metal having good conductivity and strength such as bronze, is positioned across the space between the arms 33, 34 over the top of the base part 10. The ends 36', 36" of the strut 36 are bent at right angles to the plane of the strut in the same direction and are adapted, respectively, to enter apertures 31a, 32a formed in the bends at the juncture of the plaster ears 31, 32 and arms 33, 34. The bent ends, hooking over the arms 33, 34, hold the arms from moving apart or spreading when tensile stress is applied as by pulling of an attachment plug away from the receptacle. On the other hand, the base 10 prevents movement of the arms toward each other when pressure is applied to the base such as while an attachment plug is being engaged with the receptacle.

Heretofore connections of the grounding contacts of attachment plug receptacles to the supporting strap or bridge of the receptacle by which the receptacle body is mounted across the opening of a conventional wall or outlet box have often been separate stamped metal pieces riveted or bent to be frictionally held on the strap or supporting bridge. Due to manufacturing inaccuracies or variations or due to usage, these connections have loosened and dirt and grime could work into them, increasing the resistance or substantially reducing the effectiveness of the connection.

According to this invention, these disadvantages are entirely avoided and at the same time assembly of the receptacle parts is simplified and assembly costs are re duced.

Each of the outlets of the duplex receptacle is provided with a grounding contact 37, 38 consisting of two facing parallel contact fingers 37, 37" and 38, 38" which are integral with the connecting portion 35 of the supporting strap. One 37 of these contacts is positioned adjacent the strap arm 33 while the other 38 is located midway along the connecting part 35 about one-third the distance between the strap arms 33, 34 from the arm 34.

The contact fingers are formed initially as extensions extending in opposite directions from the connecting part of the supporting strap when it is stamped out. Then the fingers 37, 37 and 38', 38" are bent up substantially perpendicular to the transverse part 35 and are formed into usual contact shape as shown in dotted lines in FIG. 4.

The insulating base 19 is molded with a square passageway 17 from rear to front in the longitudinal partition to receive the contact fingers 38', 38". Likewise, in the end wall of the base a recess 19 is formed extending from rear to front for the contact fingers 37', 37".

To provide a wire terminal connection to the supporting bridge, conveniently accessible from both sides of the receptacle, two terminals 39, 39 are provided, one on each side of the receptacle extending obliquely from the strap arm 33. These terminals (like the contact fingers just described) are initially formed as unitary opposite extensions from the arm 33 when the strap is stamped. They are subsequently bent obliquely to the arm 33, as best shown in FIGS. 2 and 3. The insulating base 19 is shaped at one end so that the oblique terminals 39', 39" Will lie along it with the shanks of conventional terminal screws entering slots in the walls of the base behind the terminals.

The parts as heretofore described are assembled in the base 10 which is then covered over by a molded insulating cover 40, one-half of which is broken away in FIG. 1. The cover is conventionally formed with parallel slots (such as 41, 42) at each end in alignment with the receptacle contacts beneath. Similar semi-circular openings (such as 44) are in alignment with the grounding contacts 37, 38. Conventional three-pronged caps and connectors may thus have their prongs inserted and connections made with the opposite line wire contact fingers 21, 22 and grounding contact 37 or 38.

To permit passage of the grounding contact prongs of the connector (not shown) through the strut 36 to the ground contacts 37, 38, apertures such as 36a are provided in the strut 36 in the mid-portion and near one end in alignment with the ground contacts 37, 38 and their respective openings in the cover 40. The apertures are only slightly larger than the ground prong G, so that if the ground prong is tilted slightly, as is usual, the ground prong will first engage the periphery of the strut aperture causing immediate grounding, before the current-carrying contacts are engaged by their prongs. When the strut is of bronze, the conductivity of the ground connection is improved.

So that the spring contact fingers of the ground contacts 37, 38 will not be over-stressed, they are backed up by contouring the walls of the recesses in which the con- 4 tacts are located as shown in FIGS. 5 and 6. FIG. 5 shows the contacts in relaxed condition with the ground prong not inserted; while FIG. 6 shows the ground prong inserted and the fingers backed-up and supported by the walls.

To improve the pressure of the current-carrying contact fingers 21, 22 against the prongs of the plug, and to continue to maintain their spring pressure against the prongs, and to avoid over-stressing and permanently deteriorating the pressure grip of the fingers against the prongs, U-shaped clips 52 of spring metal embrace the fingers 21, 22 as best shown in FIG. 7. Since the clips do not have to be relied upon to carry current, they are conductive and can be made of metal having known long life, springiness and possessing the desired stress characteristics to give the desired degree of pressure.

From the foregoing, it will be apparent that the receptacle can be easily and quickly assembled by placing each line contact and its connected terminal member in its recess on one side or the other of the base; then the clamp plates 26, with terminal screws already threaded partway therein, can be dropped into the base with the shanks of the screws sliding vertically into the slots of the terminal plate portions 24. Then the backup springs 28 can be quickly put in place. The whole base assembly is then ready to be fitted between the strap arms 33, 34 on the longitudinal part 35, after which the strut 36 is easily pressed into place and the cover 40 applied. The cover is secured by a central hollow rivet 46 and its end spun over. To prevent cracking or chipping the molded insulation cover as the rivet is spun over, a thin metal plate 50 is laid on top of the cover around the rivet hole and the rivet head is spun over on it.

To insulate the rivet from the current-carrying parts within the receptacle body, a protuberance on the under side of the cover surrounds the rivet shank and fits into a large central hole 360 in the strut 36.

Thus, a strong rugged easily assembled construction is provided.

Modifications within the scope of the invention will occur to those skilled in the art. Therefore, the invention is not limited to the specific details of the form illustrated and described.

What is claimed is:

1. An attachment plug receptacle comprising a molded insulation base, a plurality of line contact and terminal members in said base, a one-piece mounting strap for supporting said base, grounding contact means stamped as a one-piece unit with said strap, said ground contact means comprising a pair of fingers bent perpendicularly to said strap and adapted to be engaged by the grounding prong of an attachment plug connector, and a wire terminal stamped as a one-piece unit with said strap and lying adjacent one wall of said base.

2. An attachment plug receptacle as claimed in claim 1 wherein the strap is U-shaped with parallel side arms connected by a transverse part and having apertures in said arms, and a strut extending lengthwise of and over said base and having ends with perpendicular portions passing through said apertures engaging said arms to hold them from spreading.

3. An attachment plug receptacle as claimed in claim 2 having wire clamping members within said base adjacent the terminal portions of said terminal members, terminal screws passing freely through openings in said terminal portions and threading into tapped openings in said clamp members, and compression springs pressing against said base and said clamp members pressing them toward said terminal portions, said base having openings in its side walls giving access to said terminal screws and terminal portions.

4. An attachment plug receptacle comprising a molded recessed insulation base, a plurality of line contact and terminal members in said base, a one-piece mounting strap for supporting said base, wire clamping members within said base adjacent the terminal portions of said terminal members, terminal screws passing freely through openings in said terminal portions and threading into tapped openings in said clamp members, said base having openings in its side walls giving access to said terminal screws and terminal portions, compression springs pressing against said base and said clamping members, said springs holding said clamping members against said terminal portions after removal of said screws and maintaining said clamping members in position for reinsertion of said screws.

5. A duplex attachment plug receptacle comprising a molded insulation base, a plurality of line contact and terminal members in said base, a U-shaped mounting strap for supporting said base having parallel side arms connected by a transverse part and having apertures in said arms, and a strut extending lengthwise of and over said base and having ends with perpendicular portions passing through said apertures engaging said arms to hold them from spreading.

6. An attachment plug receptacle as claimed in claim 2 in which said strut is conductive and overlies and is spaced from said ground contact, and has an aperture shaped like a transverse section of the ground prong and overlies said ground contact whereby the ground prong on insertion through said aperture may engage the side of the latter and be grounded to said strut and strap prior to engagement with the ground contact.

7. An attachment plug receptacle as claimed in claim 1 wherein said ground contact means comprise bent flexible fingers facing one another between which the ground prong of an attachment plug may be inserted to be engaged thereby, said base having recesses in which said ground contact means are located, the sides of said recesses being adjacent said fingers and engaged thereby to prevent over-stressing thereof when a ground prong is inserted between and presses apart said fingers.

References Cited UNITED STATES PATENTS 1,817,441 8/1931 Madigan 339-164 1,909,270 5/1933 Guett 339-133 1,990,087 2/ 1935 Nichols et al 339-259 1,998,353 4/1935 Bennett 339-133 2,105,884 1/1938 Hanser et al. 339-259 XR 2,262,712 11/1941 Shenton 339-263 XR 3,126,239 3/1964 Winter et al. 339-164 XR FOREIGN PATENTS 379,828 9/1932 Great Britain. 620,951 5/1961 Italy.

MARVIN A. CHAMPION, Primary Exmnincr.

PATRICK A. CLIFFORD, Examiner.

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