Shallow Electrical Receptacle With Surge Suppression and Isolated Ground

This invention relates to electrical receptacles and particularly to receptacles with a shallow housing also provided with surge suppressor and isolated ground features.

Most duplex electrical receptacles used for residential and commercial applications have a housing, including an insulating base and cover, with a depth dimension for the base of about 1 inch or more to house the contacts and any other internal components. Some receptacles for such applications have a more shallow depth dimension. One such receptacle is the Bryant T-82 receptacle with a maximum base depth of only about 0.7 inch and only about 0.5 inch over most of the base. These receptacles are easily installed in construction boxes having a total depth of only about 1.5 inches. While the basic features for a satisfactory duplex receptacle have thus been provided in a shallow enclosure, the shallowness of the enclosure minimizes the internal volume available for additional features or functional components.

There has recently been a growing interest in providing receptacles with surge suppression. In Misencik et al. U.S. Pat. No. 4,912,590, Mar. 27, 1990, there is disclosed an electrical surge suppressor and dual indicator apparatus for incorporation within receptacles. The surge suppressor of the patent is one example of surge suppressor apparatus that may be utilized in accordance with the present invention within shallow receptacles.

One object of the present invention is to provide receptacle configurations, with surge suppressors, that are suitable even for compact, shallow receptacles.

Grounding is an important feature of most receptacles. Receptacles as. commonly used have an insulating housing with a metal mounting yoke. For duplex receptacles in which each part has three contacts for the pair of line conductors and the ground conductor, it is commonly the case that the ground contacts within the receptacle are conductively related to the metal mounting yoke. A grounding path may exist through the metal mounting yoke to the wall box in which the receptacle is mounted, as well as through a ground conductor connected to the ground contacts. As is well known, it is sometimes preferred that the internal grounding contacts are conductively connected only with a grounding path apart from the metal yoke and wall box. Such an isolated ground has been achieved by providing an insulating barrier between the ground contacts and the yoke. Shallow receptacles, such as the above-mentioned Bryant type SP52L, present a need for isolated ground features that is uniquely satisfied in accordance with a further aspect of the present invention.

The foregoing aspects of the invention, relating to (1) mounting a surge suppressor and (2) the provision of an isolated ground, may of course be used independently of each other as well as in combination. They are described together in the specific embodiment of applicant's invention hereinafter.

Briefly, the invention succeeds in mounting surge suppressor circuits in receptacles, even if they are shallow, by use of an insulating circuit board on which components of the circuit are mounted with board portions that fit in close relation to insulating walls of the receptacle base so it is secure in use while also being easily assembled in the receptacle.

In an embodiment of the invention, the circuit board is centrally located between the two contact areas of the duplex receptacle and on its top surface facing the front cover of the device are mounted the indicator element or elements of the surge suppressor which are viewable from the front of the device when the cover is on. The other components of the suppressor circuit are located on the back side of the circuit board within a pocket of the base. The circuit board is mounted on respective notched wall portions in which elements such as first and second lateral ears of the circuit board fit to avoid movement of the board. Further, there is provided support under the board by part of the insulating wall portion and the cover may assist in clamping the board in place.

The circuit board may be configured to have most of its working elements closely bonded to the circuit board itself while one or more metal oxide varistors, which provide the key surge suppression functions in the circuit, are physically located spaced from the circuit board, attached thereto by conductors to complete the circuit, in the volume located below the circuit board and its more closely mounted components.

To provide the isolated ground of a receptacle, which may be shallow in its housing configuration, the two sets of contacts each include a pair of power contacts and a ground contact in which the ground contact has a length that extends into a bottom projection of the base. Ground contacts are normally longer in extent than power contacts because the mating plug has a longer ground prong. In shallow receptacles, it may not be possible to configure the housing to provide the ground contact within the depth that accommodates the power contacts Thus, the base of a device such as the Bryant SP52L is provided with two bottom projections that each provide a cavity for each ground contact. According to this invention, each such bottom projection has an opening allowing external access to the ground contact contained therein and a ground conductor is connected to each such ground contact. Each ground contact is free of any connection to the mounting yoke.

In one embodiment, the ground conductor is a metal bar or strap to which each of the ground contacts is directly fastened such as by a rivet. The metal bar slides in place through a slot defined by parts of the insulating housing of one housing projection and into a pocket of the other housing projection. A flexible conductor is bonded to the metal bar for joining to a separate conductor to ground.

In a further embodiment, the housing and metal ground bar as described above are provided in combination with an insulating cover that shields the ground bar against inadvertent contact with other grounds. The cover for the ground bar is configured, in one form, so it also serves as a strain relief protecting against breakage of the connection of the flexible ground conductor with the ground bar.

The cover may be used with or without the ground bar as a way to provide an assembly with an increase space for varistors of the surge suppressor circuit. In the latter case, the use of the back cover allows the bottom wall of the housing to have an opening so components of the surge suppressor can occupy more space. This is especially helpful for allowing use of more varistors in the surge suppressor, even though the back cover extends substantially only to the depth of the housing projections that accommodate the ground contacts.

These and other aspects of the present invention will become more apparent with reference to the following description and drawings.

FIG. 1 is a front view of a receptacle in accordance with an embodiment of the present invention showing a cover and mounting yoke but not intended to show internal components through the openings in the front cover;

FIG. 2 is a side elevation view of a receptacle in accordance with an embodiment of the present invention showing contact components within the base housing with the cover and mounting yoke, as shown in FIG. 1, removed;

FIG. 3 is a view of an insulating base portion of a housing of a receptacle in accordance with the embodiment of the previous views showing the internal configuration of insulating housing walls and their relation to a circuit board that may be associated therewith;

FIG. 4 is a view like that of FIG. 4 further including the internal contact elements and surge suppressor elements of a specific embodiment of the invention;

FIG. 5 is a bottom view of a receptacle in accordance with the present invention showing the base portion and isolated ground;

FIG. 6 is a side elevation view of a receptacle similar to that of FIG. 2 but with the addition of an insulating cover for the isolated ground and also with an aperture in the base bottom wall to allow increased space for varistor elements of a surge suppressor circuit;

FIG. 7 is a bottom view of a receptacle in accordance with FIG. 5 with the addition of an insulating cover for the isolated ground;

FIG. 8 is a circuit schematic of an embodiment of surge suppressor circuit that may be provided within a shallow receptacle in accordance with the present invention; and

FIG. 9 is a partial view similar to FIG. 7 but modified to show a further variation of the invention.

Referring to the drawings, FIG. 1 shows a front view of a duplex receptacle 10 in accordance with the present invention. The example receptacle of the drawing is similar to Bryant Type T-82 modified to incorporate surge suppression and isolated ground features. In FIG. 1, there is an insulating front cover 12a of device housing 12 which also includes an insulating base 12b as shown in FIGS. 2-5. A metal mounting yoke 14 is held in place between the front cover 12a and the housing base 12b when they are secured together by fastener extending upward from the bottom of the base at locations 16. The cover 12a is provided with two areas 18 and 20 with apertures to the internal contacts. The apertures include a pair in each area (18a and 18b; 20a and 20b) to the internal power contacts plus an additional aperture in each area (18c; 20c) to the internal ground contact. For simplicity of illustration, no part of the internal contacts is shown in FIG. 1 and also certain normally used graphic indicia identifying the receptacle as equipped with surge suppression and isolated ground features have been omitted.

The front cover 12a is also provided with apertures 22 for viewing one or more indicator devices associated with an internal surge suppressor circuit. In the embodiment shown, two such indicators are employed.

The mounting yoke 14 is apertured at each end for conventional mounting of the receptacle in an outlet box or similar installation such as by fasteners 24. Because the intent is to illustrate a receptacle with isolated ground, the mounting yoke has a notched portion 14a that assures a gap from the location of the upper-most ground contact. Also, the yoke has another notched portion 14b fit with a metal spring clip 14c that forces the mounting screw 24 into contact with mounting screw 24, a feature that has been previously used in isolated ground receptacles.

FIG. 1 also illustrates a laterally extending isolated ground wire 26 associated with a conductor on the underside of the device as will be subsequently described.

FIG. 2 shows a side view of the base 12b of the device 10, absent the front cover and the mounting yoke, but with some of the key interior components shown. The base is a unitary, molded, insulating member configured to have internal walls defining compartments for locating internal elements. The base 12b without components in place is shown in plan view in FIG. 3.

In the receptacle as made, the internal depth of the base is only about 0.4 in. (dimension.times.in FIG. 2) and the extra space afforded by the cover is less than about 0.2 in. Therefore the need is to provide surge suppression within a space whose depth is merely about 0.6 in. or less.

The contact apertures 18a, b and c and 20a, b and c of the cover 12a of FIG. 1 each access a contact shown in FIGS. 2 and 4 having a reference numeral higher than that of its corresponding aperture by 10. In FIG. 2 is shown one of the power contacts 28b and 30b in each set of contacts 28 and 30, the other power contact being behind that shown, and a ground contact 28c and 30c for each set. Between the sets of contacts, there is a central portion or volume 32 of the base 12b that in this embodiment is configured to be provided with a suppressor circuit 34 mounted in accordance with the present invention. The suppressor circuit includes an insulating circuit board 35 on the underside of which are mounted various components of the suppressor circuit interconnected in circuit relationship. These components include, for example, a fuse 36 and one or more metal oxide varistor devices 37, and additional components 38 that are not detailed herein; for further description of the circuit, see above mentioned U.S. Pat. No. 4,912,590, the description of which is incorporated herein by reference. The suppressor circuit 34 is readily assembled as a subassembly outside of the receptacle base 12b and is put in location with the varistor 37 on the underside and the circuit board 35 fit in place with elements of the base housing walls so as to be secured in place. Once the subassembled surge suppressor 34 is in place, appropriate interconnections with the internal device contacts are made. Dual indicators 22', viewable through openings 22 of the front cover, are provided in accordance with the patent.

The power contacts of the two sets of contacts 28 and 30 are interconnected as shown by the interconnections 29a and 29b in the view of FIG. 4. In FIG. 2, a flexible lead 42 to one pair of power conductors (28b and 30b) is illustrated; a flexible lead 43 to the other pair of power contacts of the two sets of contacts would be located behind the one shown in the view of FIG. 2 but is shown in FIG. 5.

Referring to FIGS. 3 and 4 in conjunction with the view of FIG. 2, a more complete understanding of the mounting of the surge suppressor circuit 34 may be obtained. FIG. 3 shows the housing base 12b without the components and other contacts all illustrated. For orientation with the other drawings there are shown in FIG. 3, the locations of the apertures 42a and 43a for entrance of the conductive leads 42 and 43 to the power contacts as well as the openings 16 for the fasteners that join the housing cover 12a and base 12b together. Compartments 45, 46, 47 and 48 illustrated in FIG. 3 accommodate the power contacts 28a, 28b, 30a, and 30b, respectively, as illustrated in FIG. 4 and the ground contacts 28c and 30c are located in respective compartments 49 and 50. FIG. 3 also shows in outline form the location of the circuit board 35 as illustrated in FIG. 2 and more fully shown in FIG. 4. Circuit board 34 may be interlocked with base housing wall portions in various ways. In this example, the circuit board 35 has a pair 35a and 35b of lateral ears that fit within notches 53 of a portion of an insulating wall 54 on or in the top portion of the view of FIG. 4. In the lower portion of the view of FIG. 3, the board is shown resting on top of a portion of an insulating wall 55.

Referring now to FIG. 4, the elements as shown in FIG. 3 are shown with the sets of internal contacts 28 and 30 and surge suppressor circuit 34 in place.

The fuse 36 as shown in FIG. 2 aids in mounting the circuit 34 as it limits movement of the board 35 to the left in the view shown in FIG. 2 by its close location next to base wall 55.

In FIG. 4, it is shown how the suppressor circuit 34 is interconnected with the power contacts and their respective power leads 42 and 43 by conductors 57 and 58. Circuit 34 is also connected to ground contact 30c by conductor 59 which passes through a gap 55a in the wall 55 on which the circuit board 35 rests.

Circuit board 35 is shown as a printed circuit board as is preferred.

The ears 35a and 35b of the board 35 fit in the notches 53 of wall 54; a glue may be used if desired but is not considered necessary. The opposite edge of the board rests on wall 55 and horizontal movement is restricted by the location of fuse 36 near the wall and also by the indicators extending through apertures 22 in the cover. The cover 12 does not directly clamp down on the board 35 when secured to the base in the illustrative embodiment. Alternate designs may employ other internal housing features to secure a surge suppressor circuit board in place.

It is therefore seen that duplex receptacles of the shallow configuration necessary to fit within construction boxes having a total box depth of only about 1 1/2 inches can be configured to include surge suppressor circuits.

FIGS. 2 and 5 also show portions 60 and 62 of the housing base 12b that project below the major portion of the base and accommodate the internal ground contacts 30c and 28c that have a greater length (e.g., about 0.8 in overall) than the base otherwise accommodates. A ground strap 64 connects the two ground contacts and is joined by rivets 61 and 63 to them. Flexible conductor 26 is joined to the metal ground strap 64 by soldering, for example.

As seen in the bottom view of FIG. 5, the bottom of the base 12b has fastener apertures for locating fasteners 17 to hold the base and cover together. Additionally, there are shown in FIG. 3 the power leads 42 and 43 to the internal conductors. The insulating base 12b has integrally molded with it the projections 60 and 62 for accommodating the ground contacts. These projections have broken away portions to leave openings to allow the ground strap to be inserted by sliding from the left as FIG. 5 is oriented through a slot within the insulating material of projection 60 and into a pocket of the projection 62 of the other contact. Once the strap is in place, the internal ground contacts are riveted to it.

Referring to FIGS. 6 and 7, an embodiment of the invention is shown in which most of the elements correspond to those of FIGS. 2 and 5, respectively with the addition of an insulating back cover 70. Back cover 70 is of a piece of molded insulating material secured to the housing base 12b by fasteners 71. It has walls 72 extending upward to the base 12b from a floor 73 that is at substantially the same depth (only slightly greater in the example shown by an amount of about 0.1 in., including screw heads) as the base projections 60 and 62 that accommodate the ground contacts 30c and 28c. The back cover in the form shown has a total depth of, for example, about 0.25 in. and is a shallow tray-like element.

The back cover 70 has as one purpose the shielding of the isolated ground bar 64 against inadvertent contact with other grounds or contacts but it also has advantages even if the isolated ground bar is not used in a particular device. In either case, the cover 70 as shown interfits with the projections 60 and 62. Indents 74 that fit over each side of base projection 60 while an intermediate portion 75 fits in the gap between. Also, an extended portion 76 at the right end (at a region of the cover where walls 72 have a gap), fits within the opening of projection 62. Elements 75 and 76 come closed to the rivets 61 and 63 securing the ground contacts 30c and 28c to the bar 64.

In addition, in the isolated ground device, back cover 70 serves as a strain relief element for flexible ground lead 26 because the ground lead 26 extends through an aperture 77 in the floor 73 that restricts motion of the lead that could disturb or break the soldered connection 78 of the lead to the bar 64.

Another advantage of the back cover 70 is it allows the housing base wall to be open such as at aperture 79. This has the principal virtue of allowing extra components, or extra component size, in the surge suppressor 34, as will be described. It happens also to be the case that a lead 80 from the surge suppressor 34 can make direct connection, through aperture 79, to ground bar 64. A small indentation 81 in cover 70 accommodates an end of lead 80 which extends through a hole in, and is soldered to, the bar 64.

In contrast to FIG. 2 which shows a device having a varistor package 37 confined within the base 12b, the device of FIG. 6 has a varistor package 37' that can extend through the base aperture 79 into the space enclosed by the cover 70.

Referring to FIG. 8, varistor unit 37 could have a pair of varistor disks 37a and 37b connected as shown between the hot (H), neutral (N) and ground (G) conductors; see the above referred to patent for details of the construction. Now, however, the additional space allows a varistor unit 37' with three disks 37'a, 37'b, 37'c similarly arranged but with the outer surfaces of 37'a and 37'c interconnected by lead 82; this provides further surge suppression between N and G.

Moreover, it is now practical within the shallow configuration of the example device to have a device without isolated ground (structure like that of FIGS. 6 and 7 without bar 64 and leads 26 and 80 connected to it) but with both varistor packages 37 and 37' as schematically shown in FIG. 8. This is achieved by the compact configuration of the varistor packages and by the slight extra volume afforded by removal of the bar. The partial view of FIG. 9 shows the basic physical arrangement.

In any device without an isolated ground, or in addition to an isolated ground, a ground can be made by a conductor (not shown) which is welded to the mounting yoke 14 within base 12b and extends out through hole 83.

It is therefore seen that the several features of FIGS. 6-9 provide additional versatility in achieving surge suppression in shallow receptacles, an isolated ground in shallow receptacles, or both.

It will be apparent that the invention may be modified from the specifics of the embodiment illustrated consistent with the more general aspects of the present invention.