US3349196A

US3349196A - Wire contact device

Info

Publication number: US3349196A
Application number: US343576A
Authority: US
Inventors: Karl R Anderson
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-02-10
Filing date: 1964-02-10
Publication date: 1967-10-24
Anticipated expiration: 1984-10-24

Description

Oct. 24, 1967 K. R. ANDERSON 3,349,196

WIRE CONTACT DEVICE Filed Feb. 1o, 1964 2 sheets-'smet .1

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f 66 Z I INVENToR. KARL ANDERSON BY Eon/A20 D. 06E/AN Arran/EY Oct. 24, 1967 K. R. ANDERSON 3,349,196

WIRE CONTACT DEVICE Filed Feb. V1o, 1964 2 Sheets-Sheet 2 .F.7z'6. /mo

INVENTOR.

KAR/ ANDERSON Eon/A20 D. OBR/,4N

ATTaQA/EY United States Patent Ofice 3,349,196 Patented Oct. 24, 1967 3,349,196 WIRE CONTACT DEVICE Karl R. Anderson, 3536 Lacksley Drive, Pasadena, Calif. 91107 Filed Feb. 10, 1964, Ser. No. 343,576 6 Claims. (Cl. 179-175.25)

ABSTRACT F THE DISCLOSURE The wire contact device is characterized by a base plate with a face and a channel in the base plate interrupting the face. An abutment forms one side of the channel, on the side away from the main portion of the base plate. A hole extends through the base plate substantially tangent to the abutment. Spring contact is secured to the f-ace and extends across the face, unattached to the face a distance at least equal to the width of the channel. With this structure, insertion of a wire through the hole presses a spring out of the channel and retraction of the wire pulls the free end of the spring contact back into the channel to lock the wire with the end of the spring close to the juncture between the abutment and the bottom of the channel. This provides positive and firm electric contact between the wire and the spring contact.

Background In the telephone industry cables having 100 pairs of 'telephone wires therein are quite common. These cables are worked on by the linemen when new cables are added, when new services are installed, when the cables are damaged and for similar purposes. The 100 pairs of wires in the cables are color coded and each pair is twisted so that a pair is discernible. Furthermore in each pair the ground wire and the energized wire are distinguishable. These are normally called the ring wire and tip Wire, respectively, in conformity with the terminology of telephone jacks which were formerly used in great numbers in conjunction with telephone cables. Despite this identification it often becomes necessary to identify individual Wires or individual pairs with respect to the wires or pairs in another cable in electrical continuity with the rst cable. To accomplish this end, several varieties of test equipment permit detec- ,tion of continuity by laboriously investigating each wire or pair in a cable bundle. Lately, equipment has become available for use in Wire continuity testing which employs a plurality of selectable contacts or a plurality of lamps by means of which continuity is established. The failure of these devices rests in the inability to make quick, sure contacts with each of the plurality of Wire ends inserted in the test equipment and the inability to remove the Wire ends with speed and surety when continuity is found. In other cases it is desirable to handle a large number of pairs and to make temporary electrical connection therewith, and equipment has not been available to make quick, sure electrical contact for these purposes.

Accordingly it is an object of this invention to provide a wire contact device which quickly and surely makes electrical contact with the conductor in an insulated electric wire inserted therein, which device is useful over a wide range of wire sizes.

It is another object of this invention to provide a wire contact devce of such dimension as to permit a large plurality of such contact devices to be placed in test equipment of relatively small size and yet provide proper access to each contact device for ease of insertion of the wire therein, and ease of removal of the Wire therefrom.

It is another object of this invention to provide a continuity testing device for testing the continuity of wires in a telephone cable and for selecting the wire ends for which continuity occurs employing the wire contact device of this invention so that wires may be readily inserted therein and easily removed therefrom.

It is another object of this invention to provide an economic, sturdy, and useful piece of wire test equipment which determines continuity in telephone wire by selecting the correct wire of a group by multiple switching, with the equipment employing the wire contact device of this invention to provide rapid and sure use thereof.

It is another object of this invention to provide telephone wire continuity test equipment employing a plurality of lamps which are selectively lighted upon the appearance of continuity and to provide the wire contact device of this invention to permit quick, sure Contact.

It is another object of this invention to provide ternporary splice equipment having the wire contact device of this invention so that quick, sure contact can be made and temporary splices quickly achieved for rapid resumption of service.

Other objects and advantages of this invention will become apparent upon a study of the following portion of the specification, the claims and the atttched drawings in which:

FIG. 1 is a top plan view of a switching continuity selector employing the wire Contact device of this invention;

FIG. 2 is an enlarged bottom plan view of the right end of the selector shown in FIG. l;

FIG. 3 is an enlarged section taken along the line 3-3 of FIG. 2;

FIG. 4 is a section taken along the line 4-4 of FIG. 3;

FIG. 5 is a schematic diagram showing the selector of FIG. 1 in use;

FIG. 6 is a top plan View of a temporary splice bar employing the wire contact device of this invention;

FIG. 7 is an enlarged end elevation of the bar of FIG. 6;

FIG. 8 is an isometric view, partially in section, of a light continuity selector employing the wire contact device of this invention;

FIG. 9 is an enlarged partial section of the light continuity selector of FIG. 8; and

FIG. 10 is schematic showing the manner of use of the selector of FIG. 8.

As an aid to understanding this invention, it can be stated in essentially summary form that it is directed to a wire contact device. The Wire contact device comprises a conductive flexible wire contact finger, in the form of a leaf spring, operating in association with a wire guide means and a wire holding abutment. As the wire is inserted through the guide hole it deflects the contact finger so that the end of the wire can extend therepast. When the wire is forced in the withdrawing direction, the contact finger is bent to force the contact finger through the insulation surrounding the Wire and into contact with the wire conductor itself while the wire is against the abutment. The wire contact finger is so dimensioned and positioned with respect to the abutment and guide hole that when in the Wire contact position, force is continually applied by the finger to maintain electrical contact. Such contact device is proportioned in such a small size, and can be used in such small spaces that is particularly suited for use in situations where a large number of wires are commonly found. Particularly in the telephone industry where often pairs of wires must be sorted out for continuity, the Wire contact device of this invention finds particular suitability. Similarly, where a light is connected to each of a group of wires to be distinguished, the wire contact device of this invention finds ready applicability in connecting individual wires to the light. -In another particular application of the Wire contact device of this invention, it can be used to quickly and surely con- 3 nect each of a plurality of wires for in temporary splices used around damaged sections of formerly operative telef phone cable.

This invention will be understood in greater detail by f reference to the following portion of this specification wherein the drawings are described. Referringnow to FIGS. 1 through 5 a switchingcontinuity selector 10 is generally shown. The utility `of this switching continuity t selector ltlis indicated in FIG. 5. Cable 12 and cable 14 each contain 100 pairs of telephone wires. The remote ends of

cables

12 and 14 are connectedso that individual pairs are arranged in electrical continuity. This continuity sponding pairs with color is lost. Accordingly it becomes necessary to select the corresponding pairs by other means. Switching continuity selector is of particular value for this purpose. Selector 1()` contains wire contact means and selector means 16 with the selector incontact withcontact bar 18.

In order to use the selector 10 for determining pairs, a pair of wires from the lcable 10 .is placed in each contact device in selector 10, and contact bar 18 is connected by wire 20 through battery 22 to. lamp 24. The other side of lamp 24 is connected by testprobe 26 to one of the pairs in cable 12.. Sliding selector means 16 is then moved down the contact bar 18 until the lamp 24 lights to indicate continuity. Thereupon the wire indicated by the selector means 16 is cut from selector 10 and joined to the wire in contact with test probe 26. Thus, the corresponding pair is selected.` The test probe 26 is moved to another pair in cable 12 and slider 16 has again traversed along contact bar 18 to determine the corresponding pair in cable 14. When lamp 24 lights the cor-` responding pair is found. Since the remote ends of

cable

12 and 14 are connected in electrical continuity in terms of pairs, the wires in each of these cables can be handled either individually or as pairs when correspondence is being determined.

Selector 10, see FIG. 3,`primarily comprises base plate 28 of high dielectric strength material. As can be seen from FIG. 1, base plate 28 is relativelyy long and narrow as is required by the hereinafter described features, The central portion of base plate 28 terminates in face 30 and along side face 30, closer tothe longitudinal edges of base plate 28 are

channels

32 and 34 which are undercut below face 30. The outside edge of

channels

32 and 34 are deiined

bywire retaining abutments

36 and 38, respectively'. These abutments extend above vthe channels 32 and above the face 3G. In the widthwise direction `the

abutments

36 and 38 are suiciently thick for adequate structural strength. The row of holes 49 is drilled through top 44 into the .channel 32` in such a position as to be substantially tangent to abutment 36. Similarly, a row of holes, 42 is drilled through top 44 into channel 34 substantially tangent to abutment`38l Each of the holes in row 40 and each ofthe holes in row 42 is on equal centers down the length of base plate 28 and the holes in rows 49 and 42 are positioned across from each other in base plate 28. Each of the

holes

40 and 42 is suitably chamfered at top 44 for ease of entry of wire therethrough. In the illustratedswitching continuity selector 1t), which is designed to handle 100 pairs of wires there is provided 100

holes

40 and 100 holes 42 so that there is a hole corresponding to each Wire in a 100 pair cable. Of course a greater or lesser number of such holes could be provided depending on the number of pairs usually tested. However, it is not necessary to fill all of the holes so that a lesser number of pairs could be tested in a switching continunity selector 10 having 100 holes 40` and 100 holes 42. Furthermore, a larger number of pairs than can be tested by using two such switching continuity selectors 10 both connected to wire 20.

Inner and outer tapped holes 46 and 48 are provided for each hole 40 and inner and outer tapped holes 50 `and 52 are provided for each of the holes 42. Similarly, a spring contact 54 is provided for each of the holes 40 and a spring contact 56 is provided for each of the holes 42. The

spring contacts

54 and 56 are of conductive resilient material, preferably spring brass or the like. Spring contact 54 is retained in position by short screws 58 and 60 each passing through appropriate holesin spring Contact 54 and respectively engaging in tapped holes 48 and 46. Screws 58 and 60 are considered short for they do not approach the top 44 ofv base plate 28. Similarly, spring contact 56 is secured in position by means of short screw 62 passing .through a hole therein and engaging in tapped hole 5t) and long screw 64 passing through a hole therein and engaging in tappedhole 52. Screw 64 is considered long for it approaches the top 44 of base plate 28 for a purpose which is hereinafter described.

Spring contacts

54 and 56 are thus secured at their inner ends against face 30 by means of the previously described screws. The outerends of the springs are not secured and pass outwardly over the face 30 and thence over

channels

32 and 34 to have their ends form a termination just short of the

wire retaining abutments

36 and 38. The ends adjacent the abutments may be formed,

square, as by stamping the springs, or sharpened with a knife edge, or may be formed with serrations or points along the length of the end. Square stamped ends are satisfactory 4to cut through the insulation on telephone wires, but the other end formations may be useful with insulation of a different character. These

springs

54 and 56 may be entirely of flat metal stock, but preferably have their edges adjacent the terminal ends turned slightly toward the corresponding wire guide holes, as is shown in the figures. This structure provides means which are very useful for making quick, sure electrical contact.

As is seen in FIG. 3,.wires carrying insulation are thrust downward through

holes

40 and 42. It isunderstood that one wire is thrust into each hole. As` the end of the Wire engages with the closest side of the spring contact, the spring contact is bent away from the channel until there is suicient space between the end of the spring contact and the abutment for the wire to pass through. Such passage is relatively free, and can be easily determined by the feel of the wire as it moves into the hole. After the end of the wire is past the spring contact, lthe wire is pulled back. Due to the fact that the wire is resting t against the abutment, and the spring contact is resting against the wire, pulling of the wire causes bending of the spring contact together with the biting of the spring contact through the insulation on the wire. Continued pulling draws the spring contact down to the bottom of the channel so that a double bend occurs in the spring contact, see lthe right portion of FIG. 3, when .the end of the spring contact is at the bottom of the channel so that the contact cuts `through the insulation and resiliently engages against the conductor in the wire. Thus substantial resilient force of the spring contact upon the conductor of the wire prevent movementtof vthe wire in either direction through its hole and maintain the spring contact in excellent electrical contact relationship with the conductorin the wire.

This arrangement is of special utility for it can readily accept and make contact with a wide range of Wire sizes both with and without insulation. The wires are quickly removed from engagement by the spring contact by cutting them olf adjacent the top 44 of base plate 28 and withdrawing the cut off, short end of wire inthe direction it was originally inserted through the hole.

In order to determine which of the wires inserted in the holes is in electrical continuity with contact wire 18, it is necessary for the selector meansv 16 to selectively make contact therebetween. The selector means 16 is in the'form of a slider which slides along contact bar 18. The slider has a handle 66 which has a slot 68 cut therethrough in the direction of contact bar 18. Sprin-gs 70, in the form of a relatively thin, bent, resilient bar lies in slot 68 and has its end in contact with contact bar 18. Secured to handle 66 by means of screws 72 and 74 are

slider retainers

76 and 78 which engage beneath contact bar 18 adjacent its edge.

Slider retainers

76 and 78 are appropriately formed so that the slider is constrained to a linear path along the contact bar 18.

Slider retainers

76 and 78 carry slots 80 and 82 which carry indicator spring 84. Indicator spring 84 is secured to contact spring 70 by means of rivet I36 for electical and mechanical securement.

Holes

88 and 90 in

slider retainers

76 and 78 beneath slots S0 and 82 carry

contact balls

92 and 94. These balls are of such dimension that the balls slightly enter the tapped holes 48 and 52 which do not contain ldlat head screws 64, which are preferably chamfered at their top edges, to act as a detent. Further, the balls roll overthe fiat heads of screws 64 to provide selective electrical continuity. Screws 64 are alternately positioned in outer tapped holes 43 and 52 so that electrical contact is alternately obtained between the contact spring 56 on one side of base plate 28 and contact spring 514 on the other side thereof. Indication of which contact spring is in electrical continuity is made by a suitable dot 96 adjacent to the holes corresponding .to long screws 64.

Since pairs in the cable are easily determined, as is previously noted, for they are twisted together and the ring Wire can be distinguished from the tip wire therein by color coding, tip wires are placed in holes without any fiat head screw 64 and thus without any electrical contact, for the tip wires are unimportant in determining continuity. The ring wires are placed in holes having dots -96 and corresponding to the at head screws 64 and thus it is the ring wires are selected for continuity. The corresponding tip wire is in the hole adjacent thereto and is simply retained for mechanical purposes. Thus it can be seen that the switching continuity selector described v4above can be used to quickly make temporary electric contact with the pertinent wires in the cable and to select which of these Wires is in electrical continuity with a particular wire of another cable. Quick and sure establishment of electrical contact and ease of removal of the cut end of the wire make this switching continuity selector of significant Value.

The wire contact device described with respect to FIGS. 1 through 5 has considerable more utility than -merely with continuity selectors. Occasionally a cable which is in service becomes parted. This can happen in the case of a storm tearing down a tree through an elevated cable, or a storm tearing down a pole carrying the cable to thus part the overhead cable. Cable parting can also occur from a tire in a manhole or by excavators inadvertently digging up and parting a cable. In the circumstances it is extremely important to the continuity of the system to have the cable back in service, even on a temporary basis, as soon as possible. When such a temporary splice is completed, a permanent splice can be installed without haste While the cable is in service. The temporary splice equipment 100 of FIGS. 6 and 7 is particularly suited to such use.

Temporary splice bar 100 has a base plate 102. Base plate 102 has a face 104 which terminates in channels 106 and 108 which are depressed below face 104. The channels 106 and 10S terminate at

abutments

110 and 112. A row of holes 114 is drilledrthrough the base plate 102 so that they enter channel 106 substantially tangent with abutment 110. A similar row of holes 116 is drilled through base plate 102 into channel 108 to be substantially tangent to abutment 112. A sulcient number of holes is drilled, preferably 100 in each row to accept each wire from the destroyed end of a pair telephone y cable. One spring contact 118 is associated with each of the holes 114 and one spring contact 120 is associated with each of the holes 116.

Spring contacts

118 and 120 are identical in structure and function to the spring contacts 54 and S6 and their related abutments and structures. Thus springs 118 and 120 act as a quick and sure means of making electrical contact between the spring contacts and the conductor in a telephone

wire Spring contacts

118 and 120 are suitably secured to base plate 102 by means of screws or rivets 122 and 124. Such additional securing means as required are also furnished.

Mounted on

spacers

126 and 128 above face 104 is connector plate 130. Base plate 102,

spacers

126 and 128 and connector plate 130 are preferably made of high dielectric material. Openings in connector plate 130 accept standard 25 pair receptacles 132. Each of these standard receptacles 132 contain 5() contacts and each of the contacts is electrically connected by means of connecting wires 134 to one of the spring contacts. Since four 25 pair receptacles are provided, as is seen in FIG. 6, each wire of a 100 pair cable can be associated with a contact in the receptacle.

In use, the temporary splice bar 100 is of advantage as follows. Assuming that a 100 pair cable has been parted, two temporary splice bars 100 are brought to the scene. Two men are required, and each one takes one temporary splice bar 100 and strips back the end of the cable where it was parted so that the pairs therein are accessible. Working together, from color coding, ea`ch of the men inserts the corresponding pairs by color identification in successive and corresponding holes in his temporary splice bar 100. When all pairs are installed, the two temporary splice bars 100 are plugged to-gether by means of 25 pair cables carrying appropriate standard plugs for plugging into the receptacles 132. Thus, continuity is again established. It can be seen that if the 25 pair cables with their associated plugs are inserted in Vthe receptacles 132, each line is in service again as it is connected into the temporary splice bars, as above described. The

spring contacts

118 and 120 provide sure contact with each of the wires so that a sure, temporary splice ensues.

The wire contact device of this invention is of particu.- lar utility in the telephone linemans work, as has been noted above, for a plurality of wires and cables must often be connected in such work. The connections must be quick and sure, and easily removableso that Work may proceed swiftly and without diculty caused by poor contact. Another piece of telephone test equipment for which the wire contact device of this invention is particularly suited is the light continuity selector shown in FIGS. 8, 9 and 10. This selector is generally indicated by the numeral 140. Selector is functionally used as is indicated in the schematic of FIG. 10. Here it is desired to select matching pairs in cables 142 and l144. The remote ends of these cables have corresponding pairs connected in electrical continuity, perhaps through central oce equipment. Color coding no longer indicates corresponding pairs because of the intermediate central oceequipment. If cables 142 and 144 are standard 100 pair cables, two selectors 140 are used for each has 50 lamps. The end of cable 140 is opened and one pair is electrically connected to one side of each of the lamps in selector 140. The other side of each of these lamps is connected to a common line which is connected to wire 146. Wire 146 is connected to battery 148 which in turn is connected to test probe 150. When test probe 150 is 'touched to one of the pairs in the end of cable 144, one of the lamps light because of the electrical continuity. This lamp corresponds in position to the pair in cable 142 which is being probed by probe 150. These pairs are immediately connected in permanent relationship. This selector 140 quickly and accurately establishes corresponding pairs.

In FIGS. 8 and 9 more detailed structure of selector 140 is shown to indicate the manner in which the pairs are quickly and surely placed in electrical contact with the individual lamps. The structure comprises rst and second

symmetrical lamp bars

152 and 154. These are secured in back to back relationship with spacer 156 therebetween. A plurality of bores 158 are provided in each lamp bar and each bore contains one lamp 160.

Spring lamp contacts

162 and 164 are provided adjacent the base of each lamp 160 and are secured in yposition by means of insulation and fastening means generally indicated at 166. Thus each ,lamp `is in electrical contact with its

own lamp contacts

162 and 164.

Common buses

168 and 170 are `in contact with each lamp contact 162 so as to form a common line for one side of each of the lamps 160. The two

common busses

168 and 170 are connected together to wire 146 to serve as electrical energization for one side of each lamp.

Spacers

172 and 174 are respectively secured to

lamp bars

152 and 154. Secured to

spacers

172 and 174 are

base plates

176 and 178, respectively. These base plates are symmetrical, so`

only base plate 178 will be described in detail. Base plate 178 has a face 180 at one edge of which is formed channelr 182 which terminates in abutment 184.Wire holes 186 are drilled through base plate 178 in such a position as to be substantially tangent to abutment 184. Wire` holes 186 are chamfered on the outside of base plate 178,l opposite channel 182 and there is one such hole for each lamp `160, with'the positions of the hole corresponding along the length of base plate 178 to the positions of the lamps 160 along lamp bar 154. Spring contacts 188 are secured to face180 by means of screws 190 which are received in appropriate channels in spacer 174. One spring contact 188 is provided adjacent each hole 186. Similarly to the earlier described springv contacts, each spring contact 188 terminates just short of abutment 184 and has its edges turned downwardly toward holes 186 adjacent their terminal ends. The other end of each spring Contact 188 is bent upwardly by rib 192 to make contact with lamp `contact 164.

Thus, as has been described with respect to the previous structure wires may be inserted individually or in pairs to holes 186 to thrustback spring contact 188 until the ends of the wire are past the end of the spring. Then, the Wire is pulled and the spring contact 188 is bent downwardly into the juncture of hole 168, channel 182 and abutment 184 to cut through the wire insulation and make electrical contact with the conductor therein and to firmly retain the wire in place. Thus electrical continuity is established between the wires inserted in holes 186 and the corresponding lamp 160. The light continuity selector 140 is ready for use as has been described with respect to FIG. 10.k

This invention has been described in its preferred embodiment and it is clear that numerous modifications and changes may be made therein aswell as application of the inventive concept to other varieties of equipment without the exercise of the inventive faculty. Accordingly this invention is defined by the scope of the rfollowing claims.

I claim:

1. A wire contact device comprising a base plate having a face, a channel in said base plate interrupting said face and positioned below said face, said channel terminating in abutment, said abutment defining a plane at `substantially right angles to the plane of said face, said abutment extending on both sides of said plane of saidface where said plane intercepts said abutment, a hole through said base plate from the side opposite said face into said channel substantially tangent to said abutment, and a spring contact secured against said face and extending freely along said face for a distance at least equal to the Width of said channel, and ,extending substantially to said abutment, said channel, the lengthof said face along which said spring contact freely extends and said spring contact being so dimensioned that when a wire is inserted through said hole into said channel and is partially withdrawn, the

portion of said spring contact extending freely along said face is positioned away from said face and the end of said a base plate, said base plate being of high dielectric` strength material and being of generally rectangular configuration and bounded by a face, a top, edges and ends, a channel in said base plate, said face terminating at said channel, said channel having a bottom closer to said top than said face, said channel terminating in an abutment of substantially planar form, a plane defined by said face, said plane being at substantially right angles to the plane formed by said abutment, said abutment extending on both sides of said plane of said face where said plane intersects with said abutment;

a hole in said base plate, said hole having an axis, said axis being aty substantially right angles to said plane of said face, said hole extending through'said base plate from said top into said channel and being positioned so that said hole is substantially tangent to said abutment;

a spring contact positioned adjacent saidv face, said spring contact being of resilient electrically conduc said spring contacteagainst said face, said spring con-z tact extending freely along said face from said securing means to said channel a distance at least equal to the width of said channel, said second end terminating adjacent to said abutment, said first end of said spring remote from said abutment being in contact with telephone equipment, the length of said face between said springcontact securing` means and said channel, the width of said channel, the depth of vsaid channel and said spring contact being so dimensioned so that when a wire is thrust through said hole past said springcontact and when the wire is partially withdrawn, said spring contact is positioned away from said face between said securing means and said channel and said second end of said spring contact is positioned adjacent the juncture of said abutment and the bottom of said channel so that said spring contact resiliently urges the wire towards the juncture between said abutment and the bottom of said channel whereby electrical contact is made between the Wire and said spring contact.

6. The wire 4contact device of claim 5 wherein said securing means includes at least one contact member, said contact member dening a contact on said top of said base plate and extending through said base plate into electrical contact wit-l1 said spring contact, movable contact means being selectively movable into electrical contact with said contact on said top of said base plate.

References Cited UNITED STATES PATENTS 3,167,252 1/1965 Smith 339--95 12/.1925 McDonough 179-175.25

Claims

1. A WIRE CONTACT DEVICE COMPRISING A BASE PLATE HAVING A FACE, A CHANNEL IN SAID BASE PLATE INTERRUPTING SAID FACE AND POSITIONED BELOW AND FACE, SAID CHANNEL TERMINATING IN ABUTMENT, SAID ABUTMENT DEFINING A PLANE AT SUBSTANTIALLY RIGHT ANGLES TO THE PLANE OF SAID FACE, SAID ABUTMENT EXTENDING ON BOTH SIDES OF SAID PLANE OF SAID FACE WHERE SAID PLANE INTERCEPTS SAID ABUTMENT, A HOLE THROUGH SAID BASE PLATE FROM THE SIDE OPPOSITE SAID FACE INTO SAID CHANNEL SUBSTANTIALLY TANGENT TO SAID ABUTMENT, AND A SPRING CONTACT SECURED AGAINST SAID FACE AND EXTENDING FREELY ALONG SAID FACE FOR A DISTANCE AT LEAST EQUAL TO THE WIDTH OF SAID CHANNEL, AND EXTENDING SUBSTANTIALLY TO SAID ABUTMENT, SAID CHANNEL, THE LENGTH OF SAID FACE ALONG WHICH SAID SPRING CONTACT FREELY EXTENDS AND SAID SPRING CONTACT BEING SO DIMENSIONED THAT WHEN A WIRE IS INSERTED THROUGH SAID HOLE INTO SAID CHANNEL AND IS PARTIALLY WITHDRAWN, THE PORTION OF SAID SPRING CONTACT EXTENDING FREELY ALONG SAID FACE IS POSITIONED AWAY FROM SAID FACE AND THE END OF SAID SPRING CONTACT IS POSITIONED SUBSTANTIALLY AT THE JUNCTURE OF SAID ABUTMENT, SAID CHANNEL AND SAID HOLE.