US3733522A

US3733522A - Arc-over protective device

Info

Publication number: US3733522A
Application number: US00107121A
Authority: US
Inventors: S Simovits; C Dumas
Original assignee: AMERICAN PLASTICRAFT Co
Current assignee: AMERICAN PLASTICRAFT Co
Priority date: 1971-01-18
Filing date: 1971-01-18
Publication date: 1973-05-15
Anticipated expiration: 1990-05-15

Abstract

An arc-over protective device is disclosed having a discrete gap whereby the initial arcing is initiated across contiguous edges of the arc gap, and the surfaces adjacent the gap are positioned such that the arc initiated across the contiguous edges moves and spreads along the adjacent surfaces, thereby improving the characteristics of the device.

Description

United States Patent 1 Simovits, Jr. et al.

11 3,733,522 1 May 15, 1973 [54] ARC-OVER PROTECTIVE DEVICE [75] Inventors: Stephen S. Simovits, Jr., Woodridge; Christ J. Dumas, Forest View, both of Ill.

[73] Assignee: American Chicago, Ill.

[22] Filed: Jan. 18, 1971 [21] Appl. No.: 107,121

Plasticraft Company,

[52] U.S. Cl. ..317/77, 339/143 T, 313/325, 339/111 [51] Int. Cl. ..H02h 9/06 [58] Field ofSearch ..317/61.5,61,71, 317/77; 313/325; 339/143 T, 194 R [5 6] References Cited UNITED STATES PATENTS 3,292,049 12/1966 Lucas ..3 1 7/77 3,251,016 5/1966 Manetti ..339/111 2,565,945 8/1951 Bockman ..317/77 3,227,910 l/l966 Pittman ..3l3/325 3,502,933 3/1970 Leimontas ..339/143 T Primary Examiner-Gerald Goldberg Assistant Examiner-Harvey Fendelman Attorney- Petherbridge, ONeill & Lindgren [5 7] ABSTRACT An arc-over protective device is disclosed having a discrete gap whereby the initial arcing is initiated across contiguous edges of the arc gap, and the surfaces adjacent the gap are positioned such that the arc initiated across the contiguous edges moves and spreads along the adjacent surfaces, thereby improving the characteristics of the device.

18 Claims, 11 Drawing Figures PATENTEB MAY 1 51975 SHEET 1 [1F 2 FIG. 3

TAE'WQ so 58 FIG. 4

. a 5 E T 5 m? m MM w EWVU f V D f w A MT fa/r F EM W SC 5 F m ARC-OVER PROTECTIVE DEVICE This invention relates to electronic tube sockets having arc-over protective devices and is directed to an improved construction of an arc gap assembly for such sockets, particularly adapted for use with television picture tubes. The invention generally relates to the type of structure disclosed and claimed in U.S. Pat. No. 3,377,612, issued Apr. 5, 1968, and assigned to the same assignee as the present invention.

It will be appreciated at the outset that, while the con-cept disclosed herein is specifically applicable for use with color television sets, the principal disclosed is generally applicable to any type of spark gap protective device in electronic equipment.

During the normal operating condition of a television picture tube, various factors may cause or develop undesirable arcing across the high voltage components within the tube. Also, television picture tubes of the type having narrow neck portions have their circumferentially spaced terminal pins so closely positioned that this often results in arcing. The high voltage resulting from either type of arcing may be conducted through the associated tube pins, socket terminals, and lead wires to the other components of the television set, which high voltage may cause damage to the components in the set.

Accordingly, the invention is generally concerned with the provision of a means which may be incorporated in the assembly of the tube socket to reduce or prevent objectionable high voltage disruptive discharge or arcing between the terminal pins or between the socket terminals.

More particularly, the socket of the present invention embodies a novel arc-over conductive means which includes a section thereof providing an arc gap assembly comprising an electrical path having a predetermined arc gap provided by two electrically spaced end portions. The edges of the two end portions are in spaced juxtaposed position to form the narrowest spacing between the end portions. The surfaces adjacent said edge portions are positioned in angled relation to enable an are which is initially developed across the edge portions to move or travel along said surfaces to dissipate the energy in said arc, as will be explained more fully hereinbelow.

It is a principal object of the present invention to provide a novelly constructed television picture tube socket with a novel high voltage arc-over protective means to dissipate high voltage disruptive discharges developed in said tube.

Another object of the invention is to provide a picture tube socket having a plurality of terminal pin connectors and an associated collector ring common to all or to some of said connectors and adapted to absorb high voltage current when arcing occurs.

It is still another object of the invention to provide an arc gap means constructed by shearing an elongated metallic member to provide an arc gap wherein the arc gap spacing is defined by contiguous edges across which an arc can be initiated, and the surfaces adjacent the edges form an area across which the arcing energy may be dissipated.

The structure by which the above-noted and other advantages of the invention are attained will be described in the following specification, taken in conjunction with the accompanying drawings, showing representative embodiments of the invention in which:

FIG. 1 is an approximately full-size perspective view of one embodiment of the tube socket embodying features of the invention;

FIG. 2 is a top view of the socket body of FIG. 1 inverted with respect to FIG. 1 and having a section which is partly cut away to show the arc gap assembly of the invention;

FIG. 2A is a sectional view taken along arrowed line 2A-2A of FIG. 2;

FIG. 3 is an enlarged view of the arc gap assembly shown in FIG. 2;

FIG. 4 is a view in cross section taken along the lines 4-4 of FIG. 3;

FIG. 5 is a cross sectional somewhat exaggerated view to show the relative position of the edges and surfaces of the arc gap;

FIG. 6 is an illustration useful in explaining the theory of operation of the invention;

FIG. 7 is a partial cross sectional view of another embodiment of a gap assembly according to the invention;

FIG. 8 is an enlarged view of the members shown in FIG. 7 and is useful in explaining the function or operation thereof;

FIG. 9 is a partial cross sectional view of a third embodiment of the invention; and

FIG. 10 is an enlarged view of the gap assembly shown in FIG. 9 and is useful in explaining the function or operation of the embodiment of FIG. 9.

Referring now to the accompanying drawings, the socket generally indicated as 11 is comprised of two relatively cylindrical sections comprising a body section 12 and a cover or cap 14. The socket 11 may be made of any thermosetting or thermoplastic material such as, for example, polyethylene, polypropylene, ceramic, Bakelite, or other material having dielectric properties and shape retaining characteristics.

As shown in FIG. 1, the body section 12 includes a base 13 on which a tube pin terminal or receiving socket assembly 17 is formed. The socket assembly 17 includes a plurality of contact means 18 for contacting the terminal pins of the associated television picture tube.

Referring now particularly to FIG. 2, which is inverted with respect to FIG. 1, each contact means 18 includes an inner end terminal which terminates in a bifurcated spring, a center support section, and an outer end labeled 24 connecting to a lead wire 26 which in turn connects to a respective resistor 27 positioned in the inner surface 16 of base 13. Each resistor 27 is connected to an associated circuit wire 28 which extends through respective channels 29 in section 12 to connect to the electronic circuitry, not shown, of the associated television receiver set. The subject matter of the contact means 18 is disclosed and claimed in patent application Ser. No. 82,414 now U.S. Pat. No. 3,636,412, and assigned to the same assignee as the present invention.

The body section 12 of socket 11 includes a plurality of holes or apertures 32 into which suitable studs 36 on cover 14 can be inserted for affixing the cover to the body section 12. j

A recess 38 comprising essentially a circular groove with radially extending spokes is formed on the outer surface 15 of base 13 for receiving a conductive metallic ring 39 of similar configuration and having radial inwardly extending members or arms 40. Studs 42 are formed in recess 38 and extend upwardly from the outer surface and conform in, or fit into, associated holes in the conductive ring 39 to affix the conductive ring in position in recess 38.

The innermost ends 43 of members 40 are connected through respective holes 53, see FIG. 2A, extending through base 13 and hole 54 in arm 40 as by spot welding a plug 51 through the base 13 to attach to the end 24 of contact means 18.

In the structure shown in, for example, US. Pat. No. 3,377,612, the conductive ring is positioned in spaced relation to the associated tube pins. As can be appreciated from the foregoing, in the present application, the radial members 40 of the conductive ring 39 are, in fact, connected to the terminal pin of contact means 18 and the arc gap assembly is established by forming a precise electrical spacing in the radial members 40 themselves, as will be explained hereinbelow.

In one method of assembly, the conductive ring 39 is mounted in recess 38 in the base 13 of body section 12. Next, the assembled conductive ring 39 and the body section 12 are placed in a shearing die which shears and forms an arc gap assembly 50, see FIGS. 2, 3 and 4. Venting holes 59 have previously been formed in the base 13 in the area adjacent the arc gap assembly 50, and the shearing dies may be extended through the holes 59.

The arc gap assembly 50 is formed in the elongated radial members 40 by shearing the elongated members across its width to form a gap 52 or opening, as best shown in FIG. 4. As the radial members 40 are sheared, the lower'edge 52 (as oriented in FIG. 4) of the righthand end portion of the gap assembly 50 is bent upwardly relative to the adjacent left-hand end portion such that the edge 56 is positioned contiguous to or ad-' jacent the upper edge 54 of the left-hand portion. The term contiguous herein is used in the dictionary meaning of near, though not in actual contact. Note the angled surface 58 which is an important aspect of the invention, as will be explained more fully hereinbelow.

One important advantage of the construction as shown herein is that the arc gap spacing between the

edges

54 and 56 can be precisely and conveniently formed and controlled to provide protection against undesired arcing across the terminal pins of the associated electron tube. More precisely, the arc gap assembly 50 provides a means of dissipating high voltage energy before it can produce arcing across the terminal pins of the associated electron tube.

An important principal of the invention is the provision of a graduated electrical spacing which disperses the are energy along selected path as a mathematical function. An initial arcing is developed across the gap 52 formed between the contiguous'edges 54 and 56 of the arc gap assembly to thereby provide a precise controllable point-to-point or. more correctly an edge-toedge spacing. The two spaced

edges

54 and 56, separated by air, are sufficiently close to each other such that an are or disruptive discharge will jump between them. This disruptive charge is usually accompanied by t a sharp, quick snap or crackle and the phenomenon may be explained by noting that the few ions which are always present in the air are hurled violently so that they produce other ions by collision; these latter ions.

in turn produce still more ions, and by this cumulative action the air causes a high-conduction almost instantly to provide the disruptive discharge or arcing.

The phenomenon may also be explained by noting that once the arcing starts, the space between the two edges function somewhat like a defined conduction chamber. Thus, when ionization occurs a low impedance is presented to the current flowing across the gap. The electrons stream from one edge encounter air or gas molecules on the way to the other edge; when an electron collides with a molecule the energy transmitted by the collision may cause the molecules to release an electron and become a positively charged ion.

Prior art devices cannot normally sustain heavy arcing currents and maintain gap integrity; that is, maintain a constant effective electrical spacing between the edges constant. In the prior art devices, the arcing current causes the spaced juxtaposed surface to be oxidized and pitted and the arc gap ignition voltage to be changed.

In contrast to the prior art, shear formed gap assembly of the invention enables the arcing or ignition voltage to initiate an arcing event; and, then, and very importantly, permits the arcing energy to be dissipated along the adjacent surfaces according to a mathematical function, apparently a logarithmic function. When arcing is initiated between

edges

54 and 56, see FIG. 4, the ionization phenomenon will spread in the space between the electrodes because of the decreased impedance across the air gap. After ionization has started, the action maintains itself and relatively large currents flow at a voltage considerably lower than the ignition or ionizing potential. For example, referring to FIG. 6, it has been found that after arcing is initiated, the arcing current is gradually dispersed away from the point-to-point or edge-to-edge gap (54,56) as indicated by the arrows and dashed lines, and dissipated throughout the large angular plane surfaces 58 and 60, thereby providing a large energy handling capability while retaining a structure having a precise controllable arc-over or ignition voltage.

The area of the dissipating surfaces may be theoretically or empirically determined with relation to the desired arc ignition voltage, distance or width of gap 52, the gauge or thickness and width of the member 40, and the angle of the surface 58.

A particular advantage of the construction of the invention is that gap integrity is maintained. For example, if the structure is designed to cause arcing at 1500 volts, arcing will still occur at 1500 volts, i a preselected tolerance, even after extensive arcing.

In the prior art, after arcing occurs the arcing point will over-heat and oxidize, and form a higher resistance and a passive barrier across the gap which will in turn increase the voltage required to initiate the next arcing event. Hence, in the prior art if a structure was designed to cause arcing at 1500 volts, after the initial arcing and because of oxidation, pitting and searing, the gap assembly might are at not less than 2000 volts, thereby changing the protection available to the associ ated circuit.

Another advantage of the invention includes the fact that'the arc gap spacing in the new configuration can be more accurately formed because there is no wear in the die area itself. And, also, importantly there is a minimum wear and oxidation of the

edges

54 and 56 such that the gap spacing is maintained constant due to the fact that

surfaces

58 and 60 dissipate the arcing current and prevent wear and oxidation of the edges.

In the showing of FIG. 4, perfectly smooth rectangular gap surfaces are indicated; however, the shearing operation results in a slight deformation of the ends of the metal to cause the edges of the members to be formed, as shown in FIG. 5. The shearing operation also desirably accentuates the formation of a gap assembly where the edges are the closest spaced surfaces and the

adjacent surfaces

58 and 60 are positioned at an angle. The angle at which surface 58 is positioned is predetermined by the forming die and, as shown in the FIGS. 4, 5 and 6, one embodiment discloses a surface forming an angle of approximately 30 relative to the plane of the member 40.

FIG. 7 shows a modification of the embodiment of FIGS. 1-6. The structure of FIG. 7 shows a sheared form wherein both

portions

70 and 71 of member 40 at the sides of the arc gap 52 are bent downwardly (as oriented in FIG. 7) at an angle with respect to the plane of the member 40. The upper edges 72 and 73 of

portions

70 and 71 are formed to be adjacent to each other. Referring now also to FIG. 8, the end surfaces 76 and 77 of

portions

70 and 71 form an increasingly Wider opening and form an acute angle with each other. Note that the upper surfaces 78 and 79 also form an acute, although relatively large angle, with each other. Note, of course, that

portions

70 and 71 could likewise be bent upwardly, as oriented in FIGS. 7 and 8, and obtain similar results.

The operation of the structure of FIG. 7 is substantially the same as that of the structure of FIGS. 1-6. That is, the arcing is initiated across

edges

72 and 73 and the arc spreads or moves in an increasing function across end surfaces 76 and 77. It has also been found that there is some tendency for the arcing phenomenon to spread along surfaces 78 and 79, as indicated by the dashed lines in FIG. 8.

FIGS. 9 & show a third embodiment of the arc gap structure of the invention wherein

portions

86 and 87 of the member 40 are sheared and bent with respect to each other such that the upper surface 91 of one portion 87 is positioned to be adjacent the lower surface 92 of the other portion 86 and the arcing phenomenon is initiated across gap 52 between the lower edge 84 of portion 86 and the upper edge 85 of portion 87. An acute angle is formed between end surface 89 of portion 86 and upper surface 91 of portion 87. Likewise, a substantially equal acute angle is formed between end surface 88 of portion 86 and the lower surface 92 of portion 86. It will be appreciated that the relative positions of

portions

86 and 87 could be reversed.

The structure of FIG. 9 also functions fundamentally the same as the previous two embodiments. However, in FIG. 9, there is an advantageous benefit derived in that there is a tendency for the arc which is initiated across

edges

84 and 85 to spread or move between the end surface 89 and upper surface 91, as well as across the second spacing and lower surface 92 which provides essentially equal conductive characteristics for this purpose. Therefore, the disruptive arcing energy is absorbed or dissipated more efficiently along a relatively larger area.

Note, that as described above with respect to FIG. 4, 5 and 6, the shearing operation will cause a slight deformation of gap 52, as shown in FIGS. 7-10; and, as discussed above, this appears to be desirable to the formation and function of the gap assembly.

Each of the embodiments of the arc-over protective device of the invention is based on the concept of providing a structure having a first means across which an arcing phenomena is initiated in combination with a second means for dissipating the energy resulting from the arcing. More particularly, a structure forming a defined edge or point in combination with a graduated electrical spacing operating somewhat as a so-called Jacobs ladder or horn gap," has been found to provide a means for initiating the arc at a preselected voltage level and then effectively dissipating the arcing energy to thereby afford a positive protection against arcing damage for the associated electronic components.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. An electron tube socket comprising, in combination, terminal means for contacting terminal pins of an associated electron tube, electrically conductive means coupled to said terminal means, said conductive means having at least one are gap assembly providing an variable electrical impedance including first means across which arcing may be initiated, and second means for dissipating the energy resulting from said arcing.

2. An electron tube socket as in claim 1 wherein said second means includes a graduated electrical spacing for dissipating the energy resulting from said arcing.

3. An electron tube socket as in claim 1 wherein said second means comprises angled means providing a graduated electrical spacing between said portions whereby an ignition are gap initiated across saidspacing and the energy resulted from said arcing can be dispersed and dissipated across said graduated electrical spacing.

4. An electron tube socket as in claim 1 wherein said arc gap assembly is defined between sheared edges of said conductive means to thereby provide an accentuated edge, for initiating an arcing, and an angled surface for providing a graduated electrical spacing.

5. An electron tube socket comprising,

terminal means for contacting terminal pins of an associated electron tube,

electrically conductive means coupled to said terminal means, said conductive means providing an arc gap assembly for dissipating high voltage energy comprising an electrical path interruption in said conductive means,

said electrical path interruption formed with electrically spaced end portions, one edge of one of said end portions being positioned to form the narrowest spacing between said end portions,

a surface adjacent said edge being positioned to provide a gradually increased space such that an arcing current initiated across said edge gradually disperses across said spacing to thereby dissipate the arcing currents.

6. An electron tube socket comprising,

terminal means for contacting terminal pins of an associated electron tube,

said electrical path interruption comprising an elongated member sheared at a selected point with the sheared portions being angled relative to one another.

7. An electron tube socket comprising,

terminal means for contacting terminal pins of an associated electron tube,

electrical conductive means coupled to said terminal means, said conductive means providing an arc gap assembly for dissipating high voltage energy comprising an electrical path interruption in said conductive means,

said electrical path interruption comprising an elongated member sheared at a selected point and portions thereof adjacent said shear being bent relative to the plane of said member.

8. An electron tube socket comprising terminal means for contacting terminal pins of an associated electron tube,

said electrical path interruption comprising an elongated member cut at a selected point and with the portions thereof adjacent said cut being bent relative to one another for forming a first means for initiating an arc and a second graduated electrical spacing for dissipating the energy resulting from said arcing.

9. An electron tube socket as in claim 8, wherein said portions are bent in opposite direction relative to the plane of said member whereby edges of the opposed surfaces of said cut portions are positioned adjacent each other, and wherein a pair of graduated electrical spacing are formed between the edge of one member and the surface of the'other member.

10. An electron tube socket comprising terminal receiving means for coupling to terminal pins of an electron tube, and

electrically conductive means coupled to said terminal receiving means having a variable impedance arc gap assembly including arc initiating means across which arcing is initiated and dissipating means across which the energy resulting from said arcing is dissipated,

said arc initiating means and said dissipating means being positioned within an open arc chamber to vent gases formed during an arcing event to prevent premature arc extinguishing.

11. The apparatus of claim 10 wherein said dissipating means across which the energy resulting from said arcing is dissipated includes a graduated electrical spacing.

12. The apparatus of claim 11 wherein said graduated electrical spacing comprises a variable spaced air dielectric formed between an accentuated edge of said conductive means and an angled surface thereof.

13. The apparatus of claim 10 wherein said are initiating means across which arcing is initiated comprises spaced end portions of said electrically conductive means wherein one edge of one end of said end portions is positioned to form the narrowest spacing between said end portions.

14. The apparatus of claim 13 wherein said dissipating means across which the arc energy is dissipated comprises a graduated electrical spacing formed between one edge of one end of said end portions and an angled surface of the other of said end portion.

15. The apparatus of claim 10 wherein said are initiating means and said dissipating means comprise an elongated member sheared at a selected point with the sheared portions being angled relative to one another.

16. The apparatus of claim 10 wherein said arc initiating means and said dissipating means comprise an elongated member sheared at a selected point and portions thereof adjacent said shear being bent relative to the plane of said member.

17. The apparatus of claim 10 wherein said are initiating means and said dissipating means comprise an elongated member cut at a selected point and with the portions thereof adjacent said cut being bent relative to one another for forming said are initiating means for initiating an arc and said dissipating means having a graduated electrical spacing for dissipating the energy resulting from said arcing.

18. The apparatus of claim 16 wherein said portions are bent in opposite directions relative to the plane of said member whereby edges of the opposed surfaces of said cut portions are positioned adjacent each other, and wherein a pair of graduated electrical spacings are formed between the ,edge of one member and the surface of the other member.

Claims

1. An electron tube socket comprising, in combination, terminal means for contacting terminal pins of an associated electron tube, electrically conductive means coupled to said terminal means, said conductive means having at least one arc gap assembly providing an variable electrical impedance including first means across which arcing may be initiated, and second means for dissipating the energy resulting from said arcing.

3. An electron tube socket as in claim 1 wherein said second means comprises angled means providing a graduated electrical spacing between said portions whereby an ignition arc gap initiated across said spacing and the energy resulted from said arcing can be dispersed and dissipated across said graduated electrical spacing.

5. An electron tube socket comprising, terminal means for contacting terminal pins of an associated electron tube, electrically conductive means coupled to said terminal means, said conductive means providing an arc gap assembly for dissipating high voltage energy comprising an electrical path interruption in said conductive means, said electrical path interruption formed with electrically spaced end portions, one edge of one of said end portions being positioned to form the narrowest spacing between said end portions, a surface adjacent said edge being positioned to provide a gradually increased space such that an arcing current initiated across said edge gradually disperses across said spacing to thereby dissipate the arcing currents.

6. An electron tube socket comprising, terminal means for contacting terminal pins of an associated electron tube, Electrically conductive means coupled to said terminal means, said conductive means providing an arc gap assembly for dissipating high voltage energy comprising an electrical path interruption in said conductive means, said electrical path interruption formed with electrically spaced end portions, one edge of one of said end portions being positioned to form the narrowest spacing between said end portions, said electrical path interruption comprising an elongated member sheared at a selected point with the sheared portions being angled relative to one another.

7. An electron tube socket comprising, terminal means for contacting terminal pins of an associated electron tube, electrical conductive means coupled to said terminal means, said conductive means providing an arc gap assembly for dissipating high voltage energy comprising an electrical path interruption in said conductive means, said electrical path interruption formed with electrically spaced end portions, one edge of one of said end portions being positioned to form the narrowest spacing between said end portions, said electrical path interruption comprising an elongated member sheared at a selected point and portions thereof adjacent said shear being bent relative to the plane of said member.

8. An electron tube socket comprising terminal means for contacting terminal pins of an associated electron tube, electrically conductive means coupled to said terminal means, said conductive means providing an arc gap assembly for dissipating high voltage energy comprising an electrical path interruption in said conductive means, said electrical path interruption formed with electrically spaced end portions, one edge of one of said end portions being positioned to form the narrowest spacing between said end portions, said electrical path interruption comprising an elongated member cut at a selected point and with the portions thereof adjacent said cut being bent relative to one another for forming a first means for initiating an arc and a second graduated electrical spacing for dissipating the energy resulting from said arcing.

9. An electron tube socket as in claim 8, wherein said portions are bent in opposite direction relative to the plane of said member whereby edges of the opposed surfaces of said cut portions are positioned adjacent each other, and wherein a pair of graduated electrical spacing are formed between the edge of one member and the surface of the other member.

10. An electron tube socket comprising terminal receiving means for coupling to terminal pins of an electron tube, and electrically conductive means coupled to said terminal receiving means having a variable impedance arc gap assembly including arc initiating means across which arcing is initiated and dissipating means across which the energy resulting from said arcing is dissipated, said arc initiating means and sAid dissipating means being positioned within an open arc chamber to vent gases formed during an arcing event to prevent premature arc extinguishing.

13. The apparatus of claim 10 wherein said arc initiating means across which arcing is initiated comprises spaced end portions of said electrically conductive means wherein one edge of one end of said end portions is positioned to form the narrowest spacing between said end portions.

15. The apparatus of claim 10 wherein said arc initiating means and said dissipating means comprise an elongated member sheared at a selected point with the sheared portions being angled relative to one another.

17. The apparatus of claim 10 wherein said arc initiating means and said dissipating means comprise an elongated member cut at a selected point and with the portions thereof adjacent said cut being bent relative to one another for forming said arc initiating means for initiating an arc and said dissipating means having a graduated electrical spacing for dissipating the energy resulting from said arcing.

18. The apparatus of claim 16 wherein said portions are bent in opposite directions relative to the plane of said member whereby edges of the opposed surfaces of said cut portions are positioned adjacent each other, and wherein a pair of graduated electrical spacings are formed between the edge of one member and the surface of the other member.