US3148926A - Dead-back grounding outlet with reinforced cover - Google Patents

Description

P H. WINTER Sept. 15, 1964 DEAD-BACK GROUNDING OUTLET .WITH REINFORCED COVER w 2 i w I l 5 4 Q H N 6 @Q E 6 2 1.8 H g 3 H. M 03 6 w 53% 6 o 6 2 1 AI/MWS 7 1 H3 3 J 2 2 H W x M 8 w w E 4 4 Ill ll PAUL H. WINTER IN VENTOR Z/ ATTORNEKL United States Patent 3,1433% DEAD-EACK GRQUNDING OUTLET WETH REEJFGRCED CDVER Paul H. Winter, Syracuse, N.Y., assignor to Pass 81 Seyincur, Inc, Syracuse, N.Y., a corporation of New York Filed Aug. 2th, 1962, Ser. No. 217,813 12 Claims. (Ci. 339-14) This invention relates to duplex convenience outlets and more particularly to improvements in the so-called dead-back style of convenience outlet.

It is a general object of the present invention to provide a novel and improved duplex convenience outlet of the dead-back type in which the top face plate or cover and the mounting strap are integrated for mutual reinforcement.

More particularly, it is an object of the invention to use the metal mounting strap to reinforce the relatively thin plastic cover or top half of the outlet housing required in dead-back constructions.

Another object of the invention consists in the use of the mounting strap to support and ground more effective contacts for the third or grounding prong of each receivable attachment plug.

Still another object of the invention resides in the unique arrangement wherein the screws for securing the housing parts together and retaining the assembly unitized are threaded into metal instead of the usual plastic thereby materially strengthening the assembly.

A further feature of the invention resides in the gripping of each end of the plastic top cover between the widened end portion of the mounting strap and ears thereon to provide added rigidity for the top and strap assembly, firmer mounting for the whole outlet in a wall box and more secure anchorage for the housing assembly screws. Other and further features and objects of the present 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 ciaims without departing from the spirit of the invention.

In said drawings:

FIGURE 1 is a top plan or face view of a dead-back grounding outlet with a reinforced cover constructed in accordance with the present invention;

FIGURE 2 is a bottom or rear elevation of the reinforced cover and mounting strap assembly;

FIGURE 3 is a side or edge elevation of the assembly of FIGURE 2, superimposed on a longitudinal central section through the base part of the insulation housing;

FIGURE 4 is a transverse section on line 44 of FIGURE 1 shown on a much enlarged scale; and

FIGURE 5 is a top plan view of the base section of the insulation housing, complete with its contacts and terminals and shown on the same scale as FIGURES 1 to 3, inclusive.

When an effort is made to improve the quality and capacity of a duplex convenience outlet the designer is confronted with certain problems presented by the rigid size controls fixed by the now accepted standards of plug blade size and spacing, single gang wall box size, underwriters requirements for insulation barriers and spacing between contacts of opposite polarity, together with the requirement in many cases for a third or grounding contact for the grounding prong on certain plugs. All of these standards, as they may be termed, hamper and hamstring the designers efforts to increase the current carrying capacity and improve the mechanical strength of such a wiring device for here six stationary contacts must be maintained insulated from each other and yet all in such close proximity that they tend to interfere with the means used for mounting the device in a wall or switch box. This then contributes difficult problems in assembly and in securing the housing parts together and mounting them securely to the wall box. If the contacts are made sutficiently strong to effect high contact pressures for high current carrying then the mechanical problems presented, bythe extra forces needed to introduce the prongs or remove the plug, require increased strength in the mounting mechanism and the means for attaching the insulation parts to the mounting strap.

Up to now, there have been two general types of duplex receptacle mounting strap constructions, it being understood that each receptacle is usually made from two connected insulating parts, which envelop the contacts, and to which the strap is attached and carries ears extending beyond the ends of the insulation to rest either on the wall in which the box is mounted or on outturned tabs from the forward edges of the end walls of the box which are threaded to receive the screws which attach the ends of the mounting strap to the box.

The first type of strap, made from heavy sheet metal, may be defined as generally U-shaped, a long flat shallow U in which the strap passes fully along the ends and back of the insulation parts, being fully exposed on the outside thereof and creating a potential short-circuit hazard with the wires which may be mounted against the strap in a close fitting box.

The second construction is the so-called dead-back design in which the strap passes between the two insulating halves of the insulation body, i.e. the bottom or contact holding portion and the cover, the assembly screws then being run through the bottom of the body, through clearance holes in the strap, which extends between the two body parts, and plastic material of the body top or cover. This embeds all but the ends of the strap in insulation and eliminates the electrical short circuit hazard, but creates mechanical problems since the assembly screws for holding the two parts of the insulation body together and to the mounting strap are threaded only into the thin plastic material of the cover which does not provide as dependable holding as threading into metal. This construction, however, does provide for a secure threading of the screw, which mounts the cover plate for the receptacle for it is received into a threaded hole in the strap which is near the upper surface of the outlet, but the cover plate has but little mechanical stress in use, Whereas the mounting strap must resist the thrust of inserting the plugs and the pull of removing them and with high grade reinforced contact springs these forces become quite large and are exerted as a bending effort on the strap which tends to separate the two portion of the insulation body between which its main section is clamped.

The present invention combines the advantages of both constructions by securely attaching the strap to the body cover by means of a central plate at the front and a hollow rivet extending through the mounting strap and further by means of locking tabs overlying the ends of the cover and which extend integrally from the widened mounting strap ends. Thus, a mechanically strong as sembly is secured by passing the assembly screws through the thick plastic back or main portion of the body and into the metal of the strap, providing a solid metal-to metal connection, but without exposing the strap on the back of the receptacle. In addition, the plate on the front of the cover and through which the hollow rivet passes reinforces the cover and provides an extremely rigid integrated structure therefor.

Reference should now be had to the drawings for a beta ter' understanding of the invention. In these drawings FIGURES 1 to 4, inclusive, show the assembly of the insulation cover It and the mounting strap 11 for a high grade grounding outlet. FIGURES 3 and 5 illustrate the base or contact carrying portion of the outlet. The cover itself comprises a relatively thin plate 13 of molded insulating material having two raised face portions 14 and 14', spaced apart from each other and comprising the usual non-circular faces which extend through the cover or wall plate (not shown) having appropriate apertures for passing them. Their thickness, as seen in FIGURE 3, is such as to cause their front surfaces to be substantially flush with the cover plate when mounted. The two raised portions are spaced apart by a gap 15 through which that section of the cover plate passes which is perforated to receive the central mounting screw therefor.

The front of each face 1 2 and 14' is appropriately contoured as shown to guide the main prongs of an attachment plug into the pair of main contact plug blade openings 16 and 17 which are spaced apart the conventional distance required by the usually accepted standards, and on the center line or axis of the outlet, each of the faces is provided with an opening 18 and 19 to receive the now conventional grounding prong as provided on many attachment plugs which is generally a sheet of heavy metal bent to a U -shaped cross-section.

Below the level of the protruding face portions 14, M the cover or front It is formed as the thin plate 13, previously referred to, which on the underside of its edges has the reinforcing thickened sections 26 and the inclined ramp portions 21 on the upper side and longitudinally beyond and only partially overlapping the thickened portions 26). The ramp-like configurations lead up to the surfaces 22 which define those front faces of the cover plate which serve to limit the wall plate in its movement over the faces l4, 14'. The ends of the reinforcements 20 are shouldered as a 2.3 at their ends to cooperate with corresponding shoulders 23 on the base section 24 which serve to locate the cover longitudinally in respect to the base section. There are also corresponding interlocking shoulders to determine the lateral positioning of the cover in respect to the base.

Viewed from the rear as in FIGUREZ the mounting strap 11 is seen to comprise substantially identical end sections 25 of substantial width which project well beyond the ends of the cover plate, as seen in FIGURES 1, 2 and 3, and are substantially fiat, having holes 26 to receive the mounting screws for attaching the outlet to outturned lips from the end wall of a switch box. Plaster ears 27 are provided in duplicate on each end section and are shown in the form of break away washers which can be removed and used beneath the mounting screws to build up a solid support for the strap ends in case the box is somewhat below the surface of the Wall. The intermediate section of the mounting strap merges with the upper end section 25 by means of the tapered portion 28 and then is narrowed at 29, to fit between the barriers 3d of insulation which separate the ports 16 and 17 for the plug blades. The recesses 32 surrounding these ports accommodate the outer ends of the contacts 32. for the blades, which are mounted in separate compartments in the bottom section 24 as seen in FIGURE 5. Beyond the narrowedsection 29 the center portion 33 of the mounting strap widens, again narrows at 34 for the reasons explained in connection with 29, and then merges into the triangular portion 28', which joins it to the widened lower end 25.

The end sections 25, it will be seen, are raised above and parallel to the level of the intermediate and center sections of the mounting strap by virtue of the double bends 35 just beyond the ends of the housing sections. Tabs or holding lugs 36 are partially severed by two longitudinal slots 37 which extend into each end section 25 as shown in FIGURES 1 and 2. The inner ends of opposite tabs are spaced apart a distance less than the overall length of the plastic cover section, as seen in FIGURES l,

2 and 3 and this cover section has at each corner of its upper face a depressed portion 38, the surface of which is engaged by the under face of the'corresponding tab as est seen in FZGURE 3. Since the center section of the mounting strap up to the deflections 35 rests in the bottom of the channel between the walls such as 36, and others on the under face of the cover section, the tabs 36 engaging the upper surface thereof, as just explained, clamp the cover section, which is of plastic material, rigidly against the strap, and reinforcing it throughout its full length and most of its width, particularly at the ends. It will be appreciated that in order to effect the assembly the tabs 36 must be bent upwardly almost at right angles to the surfaces of the end sections 25 while the cover section is inserted between the tabs which are then bent downwardly to clamp the parts together rigidly.

To complete and strengthen the assembly just described the area 15 between the faces of the outlets is provided with a shallow depression 4% extending out to nearly the full width of the faces 14, 14, and is fitted with a metal plate 41 which closely fits against the bottom of the recess.

This plate is securely attached to the wide center section.

33 of the strap by means of a hollow rivet having the head 42 seen in FIGURE 2 bearing on this strap, a hollow stem passing through the cover and plate 14 and is headed over as shown at 43 in FIGURES l and 3. The interior of the hollow rivet is threaded to accept the customary screw for securing the wall plate in position. The small protrusions 44 on plate'l, seen in FIGURE 1, serve to support the center portion of the cover plate so that excess tightening of the screw mounting the same will not bend the narrow section of the plate and break it. The turned over portion of the rivet 43 is also sufiiciently high to accomplish this purpose fairly well of itself.

The lower end of the mounting strap is somewhat different from the upper since immediately above the ends of tabs 36 it has opposite lateral arms 46, provided with down turned tabs 47 with edge lugs 4-8. Each tab 47 accommodates a grounding screw 49, preferably having a hexagon head and painted green, as required. By hav ing one on either side the grounding conductor can be continued through the outlet if desired, and is at times a great help to wiremen.

Since the main or lower section 24 insulation block, forming a portion of the housing of the duplex receptacle, must accommodate four contacts to accept the two pairs of main plug blades and also provide terminals for connection to them, and it is preferred to have duplicate terminals either for feed through, or, that separate lines can be led to each receptacle, the base section is relieved of carrying the contacts for the grounding prongs of the plugs by mounting them directly on the cover. This also relieves the connection screws for the two sections of the housing from at least a portion of the strain resulting from introducing the grounding prongs. This result is achieved by fastening a springy conductor strip 59 over the back face of a portion of the mounting strap. This has an intermediate widened section over which the square head 42 of the rivet fits, to secure it in position and grounded to the mounting strap. It also has a short narrow strap 51 extending upwardly as viewed in FIG- URE 2, and a longer narrow strap 52 extending in the opposite direction. At the end of each of these straps is a contact assembly positioned beneath opening 18 or 19 to receive the plug grounding blade. To achieve this strap 51 and 52 are each bent downwardly as seen at 52' in both FIGURES 3 and 4. After a right angle bend 53' the strap is widened laterally sufficiently to provide the flat bottom 53 and material for the upturned arms 54 which are bent close to each other at the top and have flared ends to accept the prong. Each of these assemblies is somewhat flimsy because of the length and narrowness of the straps 51 and 52 and, hence, is received into a recess 55 in the lower housing part, having a fiat bottom wall 56 and a side wall 57 supporting the strap 52 and holding it rigid against movement in any direction. The upper tips of arms 54 engage beneath the mounting strap when the grounding prong is withdrawn to prevent strain on 52.

The strap 50 is preferably of Phosphor-bronze to have springiness and good conductivity but each of the arms 54- and bottom 53 is reinforced by a U-shaped steel spring having arm 58 closely fitting the outside of the arms 54 and a connecting bottom portion 59 engaging beneath the bottom portion 53 of the bronze contact. This supplemental spring is merely slipped into position since it cannot move relative to the bronze spring, which it encases, because of the close fit of the walls of the two recesses 55 in the base referred to above.

It will be remembered that earlier in the specification it was pointed out that screws for fastening the bottom or main portion of the outlet housing extended into threaded engagement with the walls of apertures in the metal mounting strap and such apertures are shown at 69 and 61 in areas where the strap widens out, at 28 to join the large upper end 25 and at 63 to join the wide central section 33. These areas are close either to the attachment of the wide end to the front and back faces of the plastic as at the upper portion, or close to the attachment of the wide strap center to the plate on the front of the cover by means of the hollow rivet, Whereby they will stand the exertion of considerable tension, are a result of tightening the assembly screws 65, without bending. FIGURE 3 shows how these screws extend through the main section of the insulation body and enter the strap, which, as previously described, is rigidly secured to the cover in at least five places.

It will be appreciated that the cover and strap assembly as described above is extremely strong and rigid and has no areas of weakness to fail from rough usage. The main contacts as shown at 32' in FIGURE 5 can be reinforced similarly to the grounding contacts and the extra effort of insertion and removal of the plugs, because of the added contact friction does not endanger any of the mounting and assembly components of the outlet.

I claim:

1. A duplex convenience outlet having in combination a two part insulating housing including a back section mounting main contacts and terminals therefor and a thin cover section having raised spaced, front faces perforated for at least parallel plug blade entry; a mounting strap for supporting said outlet in a wall box and having wide ends perforated for attachment to a box, a connecting part having narrow sections adapted to be straddled by plug blade pairs, and a widened center section; means permanently attaching said strap to and to bear on the under side of said cover with the wide ends extending beyond the ends of the cover; and headed fastening screws extending through said back section and threaded directly into said strap for joining the housing parts.

2. The convenience outlet of claim 1 in which the wide ends of the mounting strap have integral tongues overlying adjacent front surfaces of the cover section to attach the strap to and reinforce the cover section.

3. The convenience outlet of claim 1 in which a metal plate is positioned between said raised front faces and bears on the main portion of the cover therebetween, a hollow rivet extending through said plate, said main portion of the cover and the widened center portion of said mounting strap to attach the strap to and reinforce the cover section, said rivet being internally threaded to receive a wall plate fastening screw.

4. The convenience outlet of claim 2 in which a metal plate is positioned between said raised front faces and bears on the main portion of the cover therebetween, a hollow rivet extending through said plate, said main portion of the cover and the widened center portion of said mounting strap to provide central reinforcing of the cover section intermediate its end attachments to the mounting strap, and an internal thread in said rivet to receive a wall plate fastening screw.

5. The convenience outlet of claim 3 in which each front face is also perforated on the outlet center line for a U-shaped grounding prong, said strap being correspondingly perforated, a grounding conductor of flat resilient metal of good conductivity secured against said mounting strap by said hollow rivet, and each end of said conductor being formed into a spring socket aligned'below one of said grounding perforations.

6. The convenience outlet of claim 5 in which each spring socket comprises a portion extending downwardly from said conductor, a bottom portion integral therewith and two wings extending upwardly from the bottom and opposing and bent toward each other to engage the plug grounding prong on opposite sides.

7. The device of claim 6 in which a steel spring corresponding generally in shape to said bottom portion and wings surrounds these parts, and a socket in the back section of the insulating housing receiving said bottom and wings and the reinforcing steel spring to hold them assembled together and in position to resist the insertion thrust of a grounding prong.

8. A cover and mounting strap assembly for a duplex convenience outlet of the box mounting type comprising in combination, a relatively thin cover section of molded insulation having spaced, raised, front faces each perforated for entry of at least two plug blades, a mounting strap for supporting said outlet in a wall box and having wide ends each extending beyond one end of said cover section, a channel in the under surface of said cover section having a wide center section and two narrow sections toward the ends thereof adapted to be straddled by said blade pairs, strap means integrally joining said wide ends and generally conforming to said channel, a tongue on each wide end of said strap extending over and engaging the upper face of said cover to hold the strap in said channel and to the cover, a metal plate on the upper surface of said cover between said faces and a rivet extending through the widened portion of said strap, through the cover and through said plate and securing them rigidly together.

9. The cover and mounting strap assembly as claimed in claim 8 in which the said rivet is hollow, internally threaded and positioned to receive the mounting screw for a wall plate.

10. The cover and mounting strap as claimed in claim 8 in which each front face and the mounting strap behind it has a perforation for the passage of a grounding prong, a conductor strip mounted beneath the strap and secured by said rivet, each end of said strip being formed into a pair of opposed contact springs each aligned beneath one of said perforations.

11. The cover and mounting strap as defined in claim 10 in which each pair of contact springs is connected to the conductor strip by an integral suspension piece, and a generally U-shaped steel helper spring embracing each pair of opposed contact springs to more tightly hold them against a grounding prong. I

12. The cover and mounting strap as claimed in claim 8 in which said mounting strap is perforated and threaded to receive screws from beneath to secure a body part containing main contacts beneath said cover, i

No references cited.

Claims (1)

1. A DUPLEX CONVENIENCE OUTLET HAVING IN COMBINATION A TWO PART INSULATING HOUSING INCLUDING A BACK SECTION MOUNTING MAIN CONTACTS AND TERMINALS THEREFOR AND A THIN COVER SECTION HAVING RAISED SPACED, FRONT FACES PERFORATED FOR AT LEAST PARALLEL PLUG BLADE ENTRY; A MOUNTING STRAP FOR SUPPORTING SAID OUTLET IN A WALL BOX AND HAVING WIDE ENDS PERFORATED FOR ATTACHMENT TO A BOX, A CONNECTING PART HAVING NARROW SECTIONS ADAPTED TO BE STRADDLED BY PLUG BLADE PAIRS, AND A WIDENED CENTER SECTION; MEANS PERMANENTLY ATTACHING SAID STRAP TO AND TO BEAR ON THE UNDER SIDE OF SAID COVER WITH THE WIDE ENDS EXTENDING BEYOND THE ENDS OF THE COVER; AND HEADED FASTENING SCREWS EXTENDING THROUGH SAID BACK SECTION AND THREADED DIRECTLY INTO SAID STRAP FOR JOINING THE HOUSING PARTS.

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