US3131987A - Electrical wiring device - Google Patents

Description

May 5, 1964 H. E. RADAcK ELECTRICAL WIRING DEVICE Filed Sep'b. 15, 1961 May 5, 1964 Filed sep'z. 15, 1981 H. E. RADACK ELECTRICAL WIRING DEVICE 2 Sheets-Sheet 2 INVENTOR. HARRY E. RADACK A'TTORNY 3,l3l,987 Patented May 5., 1964 United States Patent Ofitice 3,13=1,987 ELECTRHCA WERKNG DEVECE Harry E. Raacir, Trenton, NJ., assignor to Circle F Mfg. Co., Trenton, NJ., a corporation of New Jersey Filed Sept. 15, 1961, Ser. No. 138,447 Claims. (Cl. 339-164) This invention relates to duplex receptacles having the feature of optional contact separation.

Present-day duplex receptacles generally include parallel contact strips, each of which extends between corresponding plug-blade-receiving slots of the two outlets of the device. Connection of a wire to a strip thus provides a connection, either feed or return as the case may be, common to both outlets. Often, it is desired to Wire a receptacle with separate wire connections to the contacts at one side thereof, and with a common connection at the other side. In other cases, it may be desired to provide separate connect-ions at both sides so as to isolate one outlet from the other in the electrical sense.

Many duplex receptacles are accordingly made with an elongated contact strip having contacts respectively located below corresponding blade-receiving slots of the spaced outlets of the receptacle, and having between the contacts a break-off tab that normally provides an integral connection between the contacts. The tab is rocked back and forth with a screw driver or the like, until it eventually breaks off along weakened lines provided for this purpose.

Receptacles installed as permanent components of a building wiring system must now be polarized. When separate connections are to be made at one side only thereof, they are customarily made on the line or 'hot side. Therefore, if the wrong tab is inadvertently broken of, the receptacle must be discarded, or at least carried about until an occasion arises when the separation is to be effected at both sides.

A further deficiency in the present arrangement may be noted, in that the break-off tab must be rocked back and forth, usually vigorously and a number of times. This rocking force is transmitted directly to the contact strip over the full length thereof, due to the integral connection of the tab thereto. Since the contact strip is usually merely dropped into place in the initial assembly of 'the device, and may already be somewhat loose, the rocking action tends to loosen the same even move. This may cause it to rattle under vibratory conditions. More seriously, it may reduce its ability to exert a proper grip on inserted plug blades. t

The present invention aims to eliminate these objec-v tions to already known devices having the feature of contact separation, through the provision of a pair of longitudinally aligned contact strips at each side of the receptacle, having adjacent ends disposed in full contact with an electrically conductive Separator element. The separation element, in accordance with the present invention, is quickly removable to provide the desired contact separation, without exerting any loosening force upon the contacts, and may be reinserted when and if desired.

Other objects will appear from the following description, the clairns appended thereto, and from the annexed drawing, in which like reference characters designate like parts throughout the several views, and wherein:

` FIGURE 1 is an exploded perspective view of a duplex receptacle according to the present invention;

FIGURE 2 is a top plan view in which the cover is partly broken away;

`FIGURE 3 is a transverse section on line 3-3 of FIG- URE 2;

FIGURE 4 is a fragmentary longitudinal sectional view substantially on line 4-4 of FIGURE 3;

FIGURE 5 is a longitudinal sectional view substantially on line 5-5 of FIGURE 3;

FIGURE 6 is an enlarged, detail sectional view on the same cutting plane as FIGURE 3, showing one of the contact strip separation screws approaching its fully inserted, operative position;

FIGURE 7 is a View like FIGURE 6 in which the screw is fully inserted;

FIGURE 8 is a fragmentary transverse sectional view substantially on line 8-8, with a wire inserted;

FIGURE 9 is a top plan view of a modified form, the cover being partly broken away;

FIGURE 10 is a longitudinal sectional view substantially on line 10-10 of FIGURE 9;

FIGURE 11 is an enlarged detail sectional view similar to FIGURE 6 showing the separation screw of the modified device partly inserted; and

FIGURE 12 is la view similar to FIGURE 7, showing the modified screw fully inserted.

Referring to the drawing in detail, the receptacle comprising the present invention includes a hollow, one-piece, open-front body 10 of molded phenolic or other suitable electrically insulative material having a generally flat, approximately rectangular bottom wall 12 the end portions 14 of which are offset forwardly in respect to the central portion 15.

A continuous side wall 16 of body 10 is integral with the bottom wall 12, and is molded with laterally outward- 1y extending wire grip spring housings 18 medially between the opposite ends of the body.

The strap 20 (FIGURES 1 and 2) is formed with a raised or forwardly offset center part 22, merging at its opposite ends into inclined portions 24 which in turn merge into depressed portions 26 seated in the respective ends of the body 10. The depressed portions 26 are integral with forwardly projecting extensions 28 disposed exteriorly of the body in face-to-face contact with the end surfaces of the body. Extensions 28 are relatively narrow, corresponding in width to the portion of the mounting strap that is disposed in the body (see FIGURE 2).

Extensions 28 seat in end recesses 30'of body 10, the body having, at opposite sides of each recess, forwardly extended projections 32 providing, at the front ends thereof, Shoulders 34. Seating against the Shoulders 34 are wide portions 36 of the strap, having downwardly facing t Shoulders 38 in engagement with said Shoulders 34. The

l tensions 40 to receive the usual mounting screws, not

' shown, whereby the ends of the Strap are secured to an outlet box, also not shown.

For locating and seating the mounting Strap, I provide, as integral parts of the body 10, a pair of longitudinal partitions 46 (FIGURE 2) extending from end to end of the body 10 at opposite sides ofrand in parallel relation to the longitudinal center line of the body. The longitudinal partitions 46 are formed, medially between the opposite ends thereof, with inwardly offset, depressed, midlength portions 48 defining support ledges for the midlength part of the strap.

The provision of the longitudinal partitions 46 serves to define longitudinal, centrally disposed channel 50 in the body.

Referring to FIGURE 4, extending upwardly from the bottom wall 12, at the opposite ends of the body 10, are support bosses 52, respectively formed with through holes 54 receiving assembly drive screws 56. The drive screws 56 are ismooth-walledi for the major part of their lengths, with the smooth part of each drive screw extending through the associated hole 54 and through a registering aperture 58 of the mounting Strap. V

The threaded end portions of the drive screws 56, during assembly of the device, thread themselves into initialiy smooth-surfaced recesses 60 formed in cylindrical internal lugs 62 (FIGURES 1 and 4) formed on the underside of a molded phenolic cover 64.

Also referring to FIGURE 1, molded integrally upon the underside of the cover 64 is'a continuous, depending flange 82 in registration with the peripheral wall 16 of the body, so as to engage the same in the assembied condition of the parts, to completely close the phenolic housing through the entire periphery.

The invention includes electrically conductive contact strips 34, 86 housed within the body. As noted from FIGURE 1, there are two contact strips at each side of the longitudinal center line, each pair including a strip 84 in confronting, spaced relation to a strip 86.

Strips 84, (FIGURE 1) are formed with elongated flat, upstanding body portions 88, 90 respectively, terminating at the outer ends thereof in forwardly projecting eXtensions 92, 94 having at their forwardly projected ends transversely curved guide lips 96, 'extending in close proximity to the prong slots 68, 70 for the purpose of guiding the blades of an inserted plug into engagernent with rolled blade contacts 100, 102 respectively.

As will be noted, the blade contacts are rolled about aXes extending perpendicularly to the length of the contact strips, the arrangement being highly effective in producing, at minimum die costs, an effective, strong contact with the inserted plug blades.

As noted from FIGURE 1, confronting contact strips 84, 326 disposed at the same side of the body are provided with oppositely curved inner end portions 104, 106 respectively, which curve about a common center in the assembled relationship of the parts, each of said portions being curved through substantially 90 degrees, in diametrically opposed relation to one another. i

In the embodiment of the invention shown in FIG- URES 1-8, and referring particularly to FIGURES 1, 6 and 7, the end portions 104, 106 are formed with confronting, cooperating thread segments 108, 110.

As shown to particular advantage in FIGURES 2, 6, and 7, the body is molded vwith upstanding abutments 112, cooperating with the inwardly offset central portions 48 of longitudinal partitions 46, in locating therebetween the opposed, curved inner end portions, V104, 106 of the respective contact strips. In the space between each abutment 112 and its adjacent partition portion 48. the body is formed with an opening 114 (FIGURE 6) in the bottom wall 12 thereof, in concentric relation to the curved portions 104, 106 of the respective contact strips. The openings 114 extend into communication with receses 116-forrned in (FIGURE 1) flat, wide, opposite but identical thickened areas 117 of bottom wall 12. Recesses 116 are of greater diameter than the openings 11-1, thus defining circumferential shoulders 118 extending about said openings 114.

In accordance with the present invention, I provide electrically conductive bridging elements in the form of circuit separation screws 120 each of which (FIGURES 6 and 7) is formed, at the base of its head, with a deformable, shallowly dished collar 122, the concave face of which opens in a direction away from the screw head.

Openings 114 are lsmooth-Walled, so as to permit free passage of the screws therethrough, as shown in FIG- URES 6 and 7. On extension of the screws through the openings, the screws become threadedly engaged with the segmental threads 108, 110 of the opposed curved end portions 104, 106 of the respective contact strips, whereby to bridge the space between said end portions for the passage of electrical current.

When the screw is approaching its final, fully inserted position, as shown in FIGURE 6, the edge of the collar 122 engages the shoulder 118. Further turning of the screw in a direction to thread it into the end portions V1011, 106 of the contact strips is effective to deform the collar 122 into a substantially flat condition as shown in FIGURE 7, whereby to cause the sharpened edge of the collar to bite into `the surface of the body 10, to lock the screw in position. This is desirable, in order to prevent the screw from accidentally turning itself out of the threads, under vibration-producing conditions.

It will be apparent that this arrangernent is effective to perrnit the duplex receptacle to be utilized with a common feed for both plug outlets thereof, by disposition of the screws 120 in the FIGURE 7 positions thereof. In these circumstances, the circuits at opposite ends of the duplex receptacle are not separated, so that the receptacie is of the common feed, common return type.

If, however, it is desired to provide separate feeds,

the screw at the appropriate side of the receptacle can be removed swiftly and easily, so that the contact strips, 84, 86 at the feed side are now completely separated from one another, thereby requiring separate feeds for the respective plug outlets of the duplex receptacle. Of course, the other screw can be left in place to provide a common return. If separate returns are desired, the other screw is also removed, so that the circuits are now completely isolated both as to feed and as to return.

The construction not only permits the swift separation of the circuits, but also permits the circuits tobe restored, if necessary, as distinguished from conventional break-off arrangements prevalent in the art.

It is important, of course, to insure that the contact strips 34, 06 will remain firmly anchored against movement, both in the inserted and in the removed positions of the screws. To this end, I provide (see FIGURE 1) depending, substantially hemispherical spacer lugs 126 integrally formed upon the edges of short longitudinal flanges 124 rnolded upon the underside of cover 61. Lugs 126,v as shown to particular advantage in FIGURES 6 and 7, extend into the space between the curved portions 104, 106 of the respective contact strips, in such a manner as to insure that said strips are held apart, when the screw is removed.

Also serving to hold the contact strips in proper position are transverse abutment ribs 130, extending inwardly from the side wall of the body (see FIGURE 2). These cooperate with the longitudinal partitions 46 in holding the contact strips in their assigned positions Within the body. At the ends of the body, there are defined end stops 128,v said stops being defined through the provision of theiupwardly offset endportions 14 of the bottom wall. These are disposed to engage the adja'cent extremities of the contact strips 04, 86 to prevent endwise movement of saidfstrips in one direction. The spacer lugs 126, in Cooperation with the central partition portions 48 and abutments 112, are effective to prevent endwise movement of the contact strips'in the opposite direction.

Referring now to FIGURE 8, the means which I have provided for gripping an inserted Wire W includes, at each side of the receptacle, a pair of side-by-side, identical wire grip Springs 132. Each pair is mounted in a spring housing 13 of the body, with the Springs of each pair being located at opposite sides of the abutment 112, said abutment extending inwardly from the side wall of the spring housing'l as shown in FIGURE 2.

The Wire grip Springs 132 are formed with Vertical legs 134 disposed in contact with the inner surfaces of the side walls of the housings 18, and at their lower ends, legs 134 merge into upwardly crirnped portions 136 overlying locatingribs 138 formed upon the bottom surfaces of the spring housings 18 in juxtaposition to short slots 140. iThe slots 14-0 are disposed immediately below the respective Springs, so that should Vit be necessary to disengage a spring from a Wire W to permit removal of the Wire, one need me'rely insert the bit of a screw driver or the like, and press upwardly against the spring so as to flex it out of contact With the bared inner end of the Wire.

The free ends 142 of the leaf Springs are turned up- Wardly, in closely spaced relation to the adjacent portions V of the respective strips 84 or 86, and said free ends have their extremities located in position extending partially across the Wire insertion holes 144.

It Will be apparent that on stripping of the end of the Wire, the stripped end is inserted through the hole 144, so that on further inward movement of the Wire, the Wire Will come in contact With the extremity of the Wire grip spring, biasing said spring away from the contact strip. The spring is tensioned in such a manner as to exert a strong pressure against the Wire, holding it in face-to-face contact With the adjacent contact strip. When the Wire is fully inserted, further inWard movement of the same is prevented by the insulating sheath thereof, With the free end of the Wire coming to rest in a recess 146 provided in the underside of the cover above hole 144.

The modified form of the invention shown in FIG- URES 9-l2 Will noW be described, and it may be noted that this form of the receptacle is identical in every respect to the construction already described herein, With the exception of the circuit separation feature. Thus, in the modified form, instead of a smooth-Walled aperture 114 of body 10, I provide a threaded opening 114z, formed in the bottom Wall 12a of body 10a.

In this arrangement, the contact strips 84a, 86a differ from the strips 84, 86 respectively, in that the curved portions 104a, 10th; thereof are smooth-surfaced, instead of being formed With segmental threads. The screw 12th: of the modified form has a shank which is threaded as at 152 for part of its length, adjacent the head end of the screW. Thereafter, the shank of the screw is formed With a tapered outer end portion 148, tapering toward the other end of the screw as shown in FIGURE 11, said tapered portion having a longitudinal slot 150 disposed diametrically thereof, the slot extending to the threaded part 152 of the screw.

When the screw is partially inserted as in FIGURE 11,

the tapered portion moves into the space between the serted position of the screw.

In both forms of the invention, the same basic characteristics obtain, that is, the duplex receptacles can have a common feed and a common return, When the screws are inserted. Removal of either or both screws is permissible to separate circuits as necessary, and the screws can be returned to their inserted positions should this be desired at any time. In both cases, this is achieved quickly and With maximum facility, so that there is no necessity of rocking a tab until it breaks. The rocking action, of course, as mentioned previously herein, has been known to create pressuresupon the contact strips tending to loosen the same Within the body, this being an undesirable characteristic of the arrangement previously utilized in the art. In the illustrated example, however, the removal of the screW creates no pressures of this type upon the contact strips, and the contact strips Vremain firmly anchored in their assigned positions, Without regard to the insertion or removal of the circuit separaion screws. This is a desirable characteristic of the invention, which is of irnportance, not only to eiectricians, but also to the householder Who too often finds that plugs tend to become loose When inserted in duplex receptacles, due to the previous loosening of the contact strips resulting from the heavy rocking pressures exerted thereagainst when the circuits Were separated.

It is believed apparent that the invention is not necessarily confined to the specific use or uses thereof described above, since it may be utilized for any purpose to which it may be suited. Nor is the invention to be necessarily limited to the specific construction illstrated and described, since such construction is only intended to be illustrative of the principles of operation and the means presently devised to carry out said principles, it being considered that the invention comprehends any changes in construction that may be permitted Within the scope of the appended claims.

I claim:

1. In a duplex receptacle, the combination of an electrically i'nsulating case including spaced attachment plug seats each having at least two plug-receiving apertures; a pair of plug blade-contacting, electrically conductive, separate strips extending Within the case at each side thereof, the strips at each side hafving at one end bladegripping portions underlying corresponding apertures of the respective seats, the other ends of the strips being spaced apart and being curved about a common center, said case having a pair of holes spaced transversely thereof in underlying, concentric relation to the curved ends of the respective pairs of strips; and an electrically conductive ibridging means for each pair of strips, said means .being formed separately from the strip, each said means .including a shank of circ-ular cross-section removably mounted in a hole of the case in concentric relation to said other ends of the strips of the associated pair of the strips, said other ends of the strips of each pair embracing the shank of the associated means in contact therewith, to connect -thestrips of the pair electrically in a circuit common to both of them, the bridging means associated with each pair of strips extending out of the case through said hole so as to be accessible from Without the case for removal from the hole With consequent disengagement from the strips of the associated pair, thus to isolate each strip of a pair electrically from the other strip of the same pair.

2. In a duplex receptacle, the combination of an electrically insulating case including spaced attachment plug seats each having at least two plug blade-receiving apertures; a pair of plug blade-contacting, electrically conductive, separate strips extending Within the case at each side thereof, the strips a-t each side of the case having at one end blade-gripping portions -underlying corresponding apertures of the respective seats, the other ends of the strips being curved through substantially about a common center in diametrically opposed relation, said case having a pair of holes spaced transversely thereof in underlying, concentric relation to the curved ends of the respective pairs of strips; and an electrically conductive screw for each pair of strips, said screw being formed separately from the strips, each screW being removably mounted in a hole of the case in concentric relation to said other ends of the strips of the associated pair, said other ends of the strips of each pair embracing the screw associated therewith in contact With the screw, to connect the strips of 'the pair electrically in a circuit common to -both of them, the screw associated With each pair of strips extending out of the c-ase through said hole and having a head accessible from Without the case, for removal of the screw 'from its hole With consequent disengagement from the strips of the associated pair, thus -to isolate each strip of a pair electrically from the other strip of Ithe same pair.

3. In a duplex receptacle, the combination of an electrically insula-ting case including spaced attachment plug seats each having at least 'two plug blade-receiving ape-rtures; a pair of plug vblade-contacting, electrically conductive, separate strips ex-tending Within the case at each side thereof, the strips at each side of the case having `at one end blade-gripping portions underlying corlresponding aperztures of the |respective seats, the other ends of the strips being curved through substantially 90 about a common center in di-ametrically opposed relation, said case having a pair of holes spacedtransversely thereof in underlying, concentric relation to the curved endsof the respective pairs of strips; and an electrically conductive screwfor each pair of strips, said screw being formed separately 'from the strips, each screw being removably mounted in a hole of the case in concentric relation'to said other ends of the strips of the associated pair, said -other ends of the strips of each pair embracing the shank of the screw associated therewith in contact with said shank to connect the strips of the pair electrically in a circuit common to both of them, said case having counterbores opening to the eXterior thereof in concentric relation to the respective holes, the screw associated with each pair of strips extending out of the case through said hole and having a head disposed within the associated recess so as to -be accessible from 'without the case, for :removal of each screw from. -its hole with con-sequent disengagement of the same from the strips of the associatedpair, thus to isolate each strip of a pair electrically from the other strip of the same pair.

4. In a duplex receptacle, the combination of claim 3 fu-rther including a collar formed upon each screw at the base of the head thereof, said collar having an edge bitingly engaging the surface of the case for looking the screw in eng-agement with the strips of the associated pair.

5. In a duplex receptacle, the combination of claim 4, and said collar being of a deformable material shal-lowly dished in a direction away from the head, whereby to be deformed toward a flat condition responsive to movement of the screw inwardly of the body.

6. In -a duplex receptacle, the combination of claim 5, said hole of the case being threaded for engagement with the threads of the screw, the shanl of the screw having a part spaced axially of the screw from the threads thereo-f and 'Wedgingly engaged between said other ends of the associated strips in the inserted position lof the screw.

7. 'In a duplex receptacle, the combination of'clairn 5, said other ends of the stripsV being 'formed with segmental, cooperating threads engaging the threads of the screw in the inserted position of the screw.

8. In an electrical wiring device of the type having a provision ;for optional separation of normally electrically connected contacts, the combination of an electrically insulating case; at least two electrically conductive, spaced contact strips 'formed as separate pieces housed within said case, each strip including a flat body portion, the body portions 'of said strips lying in a common plane, a first end portion formed as a contact element, and a second end portion spaced from said first end portion, the second end portions of the strips having a space therebetween and said case having -an opening providing communication between the exterior thereof and said space, said second end portions being curved about a common aXis lying in said plane and being disposed diainetrically opposite each 'other about said axis; and an electrically conductive screw formed separately from the strips and threadedly mounted in the case -in coaXial alignment with said second end portions, said screw extending into the space between said second end portions of the strips and being exposed to the exterior of the case through said opening so as to -be -accessible tol a user, said screw being mounted in the case tor movement by the user through said opening along said axis into and out of said space to provide, at the users option, electrical connection and separation of the strips.

9. In an electrical wiring 'device of the type having a provision for optional scpar-ation of normally electrically connected contacts, the combination of an electrically insulating case; -at least two electrically conductive contacts formed as separate, spaced pieces housed within said case, said contacts having opposed, spaced portions curved 'about a common axis and said case including a spacer lug coaxial with said portions and extending partway through said space between said portions from one direction; and an electrically conductive shank removably mounted in said case and extending partway through the space between said portions from the opposite direction in engagement with said contact portions, said shank being in coaxial alignment with the spacer Vlug and being mounted in the case for rotational adjustment about said axis in -a direction away lfrom the lug out -of engagement with the curved contact portions to isolate the contacts electrically from each other, said lug being of a diameter approximately equal to the distance across said space, so'as to maintain the spacing between the contact portions `following disengagement of the shank -from the contact portions. i

10'. In an electrical wiring device of the type having a pro-vision for optional separation of normally electrically connected contacts, the combination of a hollow, electricallyl insulating case including a body having an open front and a cover secured to the body across said front, said cover including a spacer lug on the underside thereof projecting rearWa-rdly into the interior of the case, the body having a rear wall formed with an opening coaxially aligned with and spaced 'from said lug; a pair of electrically conductive contacts formed `as separate, spaced pieces wholly enclosed by the case and having contact portions disposed at opposite sides of said opelnng, said portions being curved in concentric relation to the spacer lug and to said opening, said cover and body clampably engaging the contacts therebetween to limit the same against deviation in forward and rearward directions respectively, said case including abutments thercin engaging said curved portions of the contacts to limit the same against movement in a direction radially out'wardly from said opening, the lug extending from the cover partway into the space between the contact portions; and an electrically conductive shank extending partway into said space from said rear wall in, engagement with the respective, curved contact portions, said shank being mounted in said opening for rotatable adjustment out of engagement with the contact portions to electrically isolate the same each from the other.

References Cited in the file of this patent UNITED STATES PTENTS

Claims (1)

1. IN A DUPLEX RECEPTACLE, THE COMBINATION OF AN ELECTRICALLY INSULATING CASE INCLUDING SPACED ATTACHMENT PLUG SEATS EACH HAVING AT LEAST TWO PLUG-RECEIVING APERTURES; A PAIR OF PLUG BLADE-CONTACTING, ELECTRICALLY CONDUCTIVE, SEPARATE STRIPS EXTENDING WITHIN THE CASE AT EACH SIDE THEREOF, THE STRIPS AT EACH SIDE HAVING AT ONE END BLADEGRIPPING PORTIONS UNDERLYING CORRESPONDING APERTURES OF THE RESPECTIVE SEATS, THE OTHER ENDS OF THE STRIPS BEING SPACED APART AND BEING CURVED ABOUT A COMMON CENTER, SAID CASE HAVING A PAIR OF HOLES SPACED TRANSVERSELY THEREOF IN UNDERLYING, CONCENTRIC RELATION TO THE CURVED ENDS OF THE RESPECTIVE PAIRS OF STRIPS; AND AN ELECTRICALLY CONDUCTIVE BRIDGING MEANS FOR EACH PAIR OF STRIPS, SAID MEANS BEING FORMED SEPARATELY FROM THE STRIP, EACH SAID MEANS INCLUDING A SHANK OF CIRCULAR CROSS-SECTION REMOVABLY MOUNTED IN A HOLE OF THE CASE IN CONCENTRIC RELATION TO SAID OTHER ENDS OF THE STIRPS OF THE ASSOCIATED PAIR OF THE STRIPS, SAID OTHER ENDS OF THE STRIPS OF EACH PAIR EMBRACING THE SHANK OF THE ASSOCIATED MEANS IN CONTACT THEREWITH, TO CONNECT THE STRIPS OF THE PAIR ELECTRICALLY IN A CIRCUIT COMMON TO BOTH OF THEM, THE BRIDGING MEANS ASSOCIATED WITH EACH PAIR OF STRIPS EXTENDING OUT OF THE CASE THROUGH SAID HOLE SO AS TO BE ACCESSIBLE FROM WITHOUT THE CASE FOR REMOVAL FROM THE HOLE WITH CONSEQUENT DISENGAGEMENT FROM THE STRIPS OF THE ASSOCIATED PAIR, THUS TO ISOLATE EACH STRIP OF A PAIR ELECTRICALLY FROM THE OTHER STRIP OF THE SAME PAIR.

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