US3912853A - High dielectric strength cable connector - Google Patents

Abstract

A jointing clip of the insulation-piercing type. A U-shaped insulation-piercing metal channel is provided with a surrounding insulating layer which is both longitudinally and vertically larger than the metal channel. During crimping of insulated wires within the metal channel, the vertically-extending legs of the insulating layer are first pinched together, inwardly buckled into loops, and then pressed downwardly to be secured between the inwardly-crimped legs of the metal channel. Dielectric strength with this jointing clip is improved by increasing the length of all possible paths of dielectric breakdown.

Description

United States Patent [191 Wilkes 1 Oct. 14, 1975 HIGH DIELECTRIC STRENGTH CABLE CONNECTOR [75] Inventor: Donald F. Wilkes, Albuquerque, N.

Mex.

[73] Assignee: Plessey Incorporated, 'Melville, NY.

[22] Filed: Aug. 8, 1974 21 Appl. No.: 495,551

[52] U.S. Cl. 174/84 C; 29/628; 29/630 F; 174/90; 339/276 R; 339/98 [51] Int. Cl. HOZG 15/08 [58] Field of Search 174/84 C, 88 R, 90, 94 R; 339/276 T, 97 C, 98, 223 R, 99; 29/628, 630

[56] References Cited UNITED STATES PATENTS 3,048,650 8/1962 Allen et a1. 174/90 6/1970 Faulkner 174/84 C X 9/1973 Golden et a1. 174/84 C 6/1974 Neale, Sr. 174/84 C Primary ExaminerDarrell L. Clay Attorney, Agent, or Firm-James J. Burke, 11

[ 7] ABSTRACT 3 Claims, 9 Drawing Figures US. Patent Oct. 14, 1975 Sheet1 0f2 3,912,853

FIG. I

PRIOR ART FIG. 2

PRIOR ART US. Patent Oct.14,1975 Sheet2of2 3,912,853

HIGH DIELECTRIC STRENGTH CABLE CONNECTOR BACKGROUND OF THE INVENTION layer surrounding the channel are provided. When the side portions of the channel are crimped over onto insulated wires placed therein, electrical contact between the conductive cores of the wires is achieved without stripping insulation therefrom. Still more particularly, the present invention relates to jointing clips of the general type described wherein both the clip and the surrounding insulating layer are'configured to provide an electrically conductive joint having a higher dielectric strength than has heretofore been possible. The invention has particular application in the splicing of telephone cables.

Telephone communications are generally carried in standarized telephone cables, which are generally composed of pairs (or multiples thereof) of insulated, single-strand copper or aluminum wire packed inside an insulated sleeve. Such cables must be manufactured, transported and eventually strung out between poles or in underground conduits and must span very large distances. Practically, this calls for lengths of cable to be joined together. In order to provide a telephone network, these wire pairs ultimately must be deployed to different telephones and switching locations, and be capable of infinite variations in interconnection. This requires a very large number of joints in each activated telephone circuit. Because there are so many joints in series, each one must be extremely reliable if the telephone system itself is to operate reliably.

Eachsplice must provide a low resistance coupling over a period of many years. In addition, the splice must have sufficient mechanical strength to resist degradation with repeated thermal stressing caused by day and night temperature changes, seasonal changes, etc. It must also not be degraded'by repeated freezing and thawing in' the presence of water or condensate. Each I joint must also have a high dielectric strength so that it will not break down under a high peak surge potential applied between adjacent pairs, even though the normal maximum operating voltage on the wire pairs in only In addition, leakage resistance must remain high enoughove'r the life of the splice so that attenuation of the phone message by leakage will be negligible, even if there are hundreds of joints involved.-

Testcrit eria for acceptance of connectors varies, of course, in different regions and different countries, but theyare generally very stringent. The following tests are illustrativeof such criteria: Temperature cycling is carried out between 40 and +l40F. in 8-hour cycles for over 500 cycles and in 2-hour cycles for over 1000 cycles. Tests at 95 percent relative humidity are carried out at 40 and 120F., with /hr. temperature to failure at a cross-head speed of l-in/min., and compared to wire strength.

Dielectric strength of plastic insulated connectors is tested in several ways. Pair-to-pair dielectric strength must be at least 3.0 kV rms from a 60 Hz ac source for at least one minute. Connectors must also withstand an 8.0 kV peak dc surge, wherein the waveform has a rise time of 0-10 11. sec. and a decay time to 4 kV in 1000 [LS6C., i 10 percent.

Connectors may be tested in groups of 50 or more,

and allowable failures are'generally not more than 1 or While such tests are manifestly more severe than would be encountered in normal service, the long life span expected of such connectors raises the probability of extraordinary conditions. Overhead cables are subject to lightning strikes, falling power cablesand heavy ice and wind loads, and underground cables are subject to floods, electrical and other fires and the like.

-2. Prior Art Jointing clips of the type heretofore employed are described and claimed in U.S. Pat. Nos. 3,517,804 and 3,715,456, assigned to the parent corporation of Applicants assignee. For purposes of better understanding of the present invention, this patented clip is illustrated prior to use in FIG.-1 of the drawings herein, and after crimping with the insulated, wires in place in FIG. 2, and attention is directed thereto. I

Referring now to FIG. 1, the illustrated connector 10 comprises a clip constituted by a thin-walled channel 12 of suitably deformable metal, for example, Phosphor bronze or half-hard brass, having a bottom or web portion 14 and two upwardly-extending legs, side walls or flanges 16. The length of the clip substantially corresponds to that length of each wire which is to be employed to form the joint. The web 14 of the channel may include a plurality ,of inwardly-extending triangular tabs 18 spaced along its longitudinal plane of symmetry, and webs l4, l6areboth provided with a number of mutually staggered sharp-edged excrescences 20. When using the clip to join two insulated wires, the two wires to be jointed are respectively placed unstripped into the channels at the two sides of the tabs 18, which serve as separators, and a suitable tool is then applied to fold-over the two channel side walls 16 towards the center of the channel and to press them down onto the wires so as to hold each wire firmly in position. The application operation will at the same time force the excrescences 20 of the channel bottom and sides through the insulation of the wires into intimate contact with the metal core of each wire. The tabs 18 are desirable when making in-line, butt or tap splices involving two wires, but clips not having such tabs may be preferred when making bridge taps with three or four wires.

When the above-described metal clip has been formed and suitably placed, it is covered on its outer side with suitably flexible insulating material by inserting the metal clip into an extruded length or section of channel 22, made of rigid polyvinyl chloride or other suitable insulating material, having a suitable combination of resilience and malleability, whose flanges 24 are formed at their free edges with inwardly projecting secondary flanges 26. These secondary flanges, which constitute clip-retaining portions, are arranged to cooperate with the free edges of the side walls of flanges 16 of the metal clip to retain the latter inside the insulating channel 22, and the height of the flanges or sidwalls 16 of the metal channel 12 is so chosen that the secondary flanges 26 of the insulting channel 22 will approximately meet when the crimping operation has been completed, as shown in FIG. 2. Typically, the PVC insulating channel will be about 0.015 in. thick.

As shown in FIG. 1, the profile of the insulating channel 22 is generally U-shaped, with the bottom 28 slightly concave from the outer side and the side walls 30 leaning somewhat towards each other. The bottom 14 of the metal clip is preferably concave, similar to the bottom of the insulating channel; such profile of the bottom of metal jointing clips assists in giving to the channel profile sufficient resilience for the doubledback edges to snap into position upon the insertion of a metal clip, and provides some springback during crimping to assure a tightconnection, even with wires of varying size.

In addition to the triangular tabs 18 and excrescences 20, the bottom web portion 14 of the channel 12, as well as the bottom 28 ofinsulating channel 22, are provided with a centrally-located rectangular opening 32. This facilitates the automatic feeding of jointing clip in seriatim into a slicing jig where the crimping or splicing operations are carried out. I

I Other insulation-piercing connectors are disclosed in the following US. Pat. Nos. 3,064,072, 3,242,256, 3,303,266, 3,320,354, 3,406,247 and 3,514,528.

.OBJECTSOF'THE INVENTION A general object of the present invention is to provide an improved jointing clip of the insulation-piercing Another object of the present invention is to provide a jointing clip of the insulation-piercing type having improved dielectric strength.

A further object of the present invention is to provide a jointing clip of the insulation-piercing type which is simple and economic to manufacture, is adapted for use on automatic equipment and which provides an electrical connection of improved mechanical and electrical properties.

Variousother objects and advantages of the invention will become clear from the following description of embodiments thereof, and the novel features will be particularly pointed out in connection with the appended claims.

THE DRAWINGS Reference will herein be made to the accompanying drawings, wherein:

FIG. 1 is a perspective view, in partial section of a prior-art jointing clip in the open position;

FIG. 2 is a perspective view of the prior-art clip of FIG. 1 in the closed position, i.e. after splicing;

FIG. 3 is a perspective view of a jointing clip in accordance with the present invention in the open position;

FIG. 4 is a perspective view of the jointing clip of FIG. 3 in the closed position;

FIGS. 58 are schematic views showing, in simplified form, the steps of forming a connection with a jointing clip of the type shown in FIG. 3; and

FIG. 9 is a cross-sectional elevation view of a jointing clip of the type shown in FIG. 3, showing how clips of the present invention may be accomodated in automaticslicing equipment.

DESCRIPTION OF EMBODIMENTS Understanding of the present invention will be facilitated by further consideration of the connector illustrated in FIGS. 1 and 2, and the inherent advantages and disadvantages of this design.

As discussed hereinabove, the connector 10 comprises an elongated U-shaped type plated Phosphor bronze clip 12, 0.004 in. thick, which has been pierced l8 and perforated 20 so as to squeeze into the insulative coating on the wire and provide a strong, distributed mechanical attachment. The crimping also pierces the insulation and penetrates into the copper wire in a controlled way, which minimizes stress concentrations while still offering adequate electrical and mechanical redundancy. The connector has an inherent adaptability to accomodate a range of wire sizes, insulation materials and manufacturing tolerances, while still producing joints with high enough statistical reliability for the use intended. The design accomodates many combinations of wire sizes to be spliced and also variations in wire position and straightness which are inevitable under field conditions. The plastic P.V.C. insulator 22 surrounds the metal clip 12 and is nominally about 0.015 inch thick, it is held in place on the metal clip by flanges 24, 26 along the top edges of the U and optionally, localized raised crimps on the ends. After splicing, the plastic becomes mechanically captive between the two ends of the metal clip, as shown in FIG. 2.

Connectors of the type shown in FIGS. 1 and 2 have been tested at very high DC voltages to determine the mode of breakdown between the connector 10 and an adjacent pair of wires. It will be appreciated that, in service, these connectors may be substantially surrounded on all sides by closely adjacent pairs of wires, and breakdown under a momentary surge condition could occur in essentially any direction. The abovereferenced tests showed that breakdown may occur in any of three modes. With reference to FIG. 2, the most common mode of breakdown is between an end 34 of the connector and an adjacent pair. It is to be noted that FIG. 2 illustrates a butt-type connection but more commonly the wire pair 36, 38 will be connected in overlapping and end-wise relation, with one wire extending from either end of connection 10. This is called an in-line or straight connection. In this mode, breakdown may be from the exposed wire end or from the edge of metal clip 12. The second mode of breakdown is along the top seam 40. More particularly, breakdown can occur starting at the tip of triangular tab 18 (FIG. 1) between the crimped-together edges of flanges 24 to an adjacent pair of wires. Lastly, and least commonly, breakdown can occur through the opening 32 in the bottom of connector 10, initiating at an exposed edge therein of bottom web portion 14.

In accordance with the present invention, the possible modes of dielectric breakdown are not changed, but in each case they are raised to such higher levels as to essentially eliminate this possiblity, even at momentary peak loads of more than 8000 V dc required in the above-described performance criteria.

With reference to FIGS. 3 and 4, it will be immediately obvious that in the present invention the configuration of metal channel 12 is essentially identical to the prior art construction, except for the optional elimination of opening 32, and the same reference numerals have been used to identify the various portions thereof.

such connections could be made with simple hand tools.

'As shown in FIG. 5, an anvil 62 is provided with a slight depression 64 adapted to retain the connector longer in the longitudinal direction than clip 12, so that both ends 56, 58 thereof extend beyond the ends of clip 12. Lastly, channel 50 does not have an opening 32 in thebottom web thereof.

Insulating channel 50 may fabricated from any suitable extrudable plastic material, such as polyvinylchloride (PVC) or the like. However, certain of these materials have an inherently higher dielectric strength than others, and in order to obtain the advantages of the invention to the fullest possible extent, it is preferred to utilize the higher-strength materials. In particular, polyester materials of the type known as Mylar (TM) and polyimides of the type known as Kapton (TM) have both superior dielectric strengths and mechanical properties. Between the two, the polyester are generally less expensive (the polyimides exhibit remarkable hightemperature properties, but that isnt a significant criteria in the present application). Typically, Mylar 0.003 to'0.0l2 in. thick is satisfactory and clips may be retained therein with adhesive applied to the outer sur-' face of the clip during manufacture.

A completed connection between insulated wires 36, 38 in accordance with the present invention is illustrated in FIG. 4. The legs 52, 54 of insulating channel 50 extend above the inwardly-bent edges 16 of metal clip 12, and are mechanically locked thereby. The portions of legs 52, 54 within the connector form buckled loops 53 and are thus firmly locked therein. Wires 36, 38 are pierced and clamped within the connector in the same manner as described in connection with FIGS. 1 and 2 hereinabove. By employing the larger insulating channel 50, crimped and locked as shown in FIG. 4, the path of dielectric breakdown is substantially lengthened in any of the possible modes.

The overlapping ends 56, 58 increase the path of breakdown from the ends of the metal clip 12 or wires 36, 38 to an adjacent pair of wires by an amount sufficient to eliminate this possibility under momentary surge voltages.

The seam 60 between the pressed-together legs 52, 54 likewise presents a long path for breakdown between the tip of a triangular tab 18 (if present) and an adjacent wire.

Lastly, the lack of a free path from the edge of opening 32 in bottom web 14 to an adjacent wire inhibits breakdown in this mode.

Those skilled in the art will appreciate that the distances of overlap on ends 56, 58 and the distance the legs 52, 54 extend above the completed connector will depend on the desired dielectric strength, the size and type of materials employed, overall connector size and the like. Exemplary figures are set forth in connection with specific examples of the invention hereinbelow.

The steps required in forming a connection of the type shown in FIG. 4 from a connector blankof the type shown in FIG. 3 are schematically illustrated in FIGS. 5-8, and attention is directed thereto. It will be appreciated that these steps are examplary only of one automatic device for making rapid, reliable wire interconnection; other means could be employed, and/or comprising a metal clip 12 and surrounding insulating channel 50. Wires 36, 38 are laid into the clip 12 in desired juxtaposition. In FIG. 5, a pair of horizontallymovable jaws 66, 68 are shown in their retracted position above indentation 64, whereby the channel 50 can be inserted into indentation 64 without impediment. Jaws 66, 68 have curved recesses 70, 72 on the lower portion of opposed surfaces 74, 76. The latter surfaces are disposed to beat the same level as the upper ends of legs 52, 54-.

In the first step of the crimping operation (FIG. 6), the jaws 66, 68 move toward each other as indicated by the arrows c'atching legs 52, 54 therebetween. Next (FIG. 7), anvil 62 commences to move upwardly, forcing the secured legs 52, 54 through a buckling action into opposed S-shapes, the intermediate portions of which being forced down below the level of the ends of legs 16 of metal clip 12. As anvil 60 continues its upward movement (FIG. 8), recesses 70, 72 force legs 16 toward each other and into locking engagement with the looped and doubled back legs 52, 54 of channel 50.

As can be seen in FIG. 8, this action forms legs 52, 54

into buckled loops 53 secured within the crimped channelby legs 16. Thus, the edges of legs 16 are compressively retaining four thicknesses of the insulating material. Because the insulating channel 50 is longer than clip 12,.the free ends of the loops tend to flare out where not restrained by clip 12, thus providing an additional locking mechanism, one that is particularly resistant toward the clip 12 being pulled out of channel 50. During the entireoperation, jaws 66, 68 securely press the ends of legs 52,-54 firmly together. In hydraulicallyactuated automatic splicing equipment, it is convenient to carry out the FIG. 8 step until the hydraulic fluid reaches a predetermined maximum pressure, thus assuring a sound crimp. In the final step (not shown) jaws 66, 68 retract totheir open position, anvil 60 returns to its retracted (lower) position, and the completed connection is removed from indentation 64.

For use in automatic slicing equipment, it is preferred to provide connectors of the type herein described in seriatim to the splicing head. To do this, individual connectors maybe connected end-to-end by means of an extension of the bottom web 56 of insulating channel 50. With reference to FIG. 9, an extension 78 connects adjacent connectors, which may be fed from a magazine to the splicing head. As noted in connection with FIG. 1, the prior art connectors included an opening 32 in both members for engagement with the feed mechanism. Such a feed commonly involved a pawl 80 (FIG. 9) which can move into engagement with the forward edge of opening 32 and advance the connector into the splicing head. In the connector of the present invention, the same type of feeding may be carried out in substantially the same way: A notch 82 is provided on the trailing edge of insulating channel 50, and used as the point of engagement for the pawl 80. This totally eliminates the possibility of breakdown involving opening 32.

It will be appreciated that when strips of connectors are employed in such automatic equipment, the crimping mechanism includes a cutting edge (not shown) which severs the connector being crimped from the remainder of the strip.

A further desirable but not necessary feature of the invention is the provision of means for severing the free end of a wire so that the entire splice is contained within metal channel 12 regardless of how the wires are laid therein.

Generally, cutting edges can be mounted at desired positions on the crimping jaws so that wires can be severed during the crimping operation. With the present invention, it is preferred that wire cutting take place in the plane of the ends of insulating channel 50 and, as crimping proceeds, wire guides (not shown) on the splicing head move outwardly /8 inch or so, retracting the ends of the severed wires to a position within metal clip 12. The guides frictionally engage'the wires with only a small force, so only severed wires are effected. Wire cutting may also be accomplished with a cutting blade that will press the wire against the bottom 14 of clip 12 prior to crimping, or in other suitable ways.

Connectors of the type shown in FIG. 4 employed Mylar insulation 7 mils thick and overlapped the ends of the metal channel by one-eighth in. Wires with plastic insulation were crimped therein in the manner shown and described hereinabove. The dielectric strength of these connectors was tested on a 10 kV power pack equipped with an RC network designed to produce a voltage waveform of the type noted hereinabove in connection with the typical performance criteria. No dielectric breakdown occured during these tests.

Various changes in the details, steps, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as defined in the appended claims.

What is claimed is:

1. An insulated joint electrically connecting at least a pair of unstripped, insulated wires comprising:

a channel-type metal jointing clip having channel walls bent over a web portion in a mechanicallyinterlocking relation with said wires located therebetween;

said clip including inwardly-extending protrusions piercing said insulation and in electricallyconductive engagement with said wires; and

a channel of resiliently flexible insulating material wrapped around said clip, said insulating channel extending longitudinally beyond the ends of said clip, the upper side walls of said insulating channel being locked between the edges of the inwardlybent walls of said clip forming buckled loops within said joint with the free ends of said insulating channel sidewalls extending upwardly between the edges of said inwardly bent clip walls.

2. The insulated joint as claimed in, wherein said metal clip is adhesively bonded to said insulating channel.

3. The insulated joint as claimed in claim 1, wherein said insulating material is a polyimide in the range of 3 to 12 mils thick.

UNITED STATES PATENT CE'RIIFICATE OF; CORRECTIOIJ Patent No. 3,912,853 I ggDated fOctober 14. 1975 Inventor(s) DONALD WILKES It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, lines 1,2: "Sid-walls" should be sidewalls lines 24 and 68: "slicing" should be splicing 001-. 5,' lirfles 30 and 36;: "38" should be in bold-race type;ll ine 48: "54; should; be bold-face type Col. 6, line 45: "slicing" should be --splicing Col. 8, line 26: after "in" and before the comme,

--claim 1 should be inserted Bighcd fend Scaled this isixth of 'ilanuar; 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Patents and Trademarks UNITED STATES PATENT QFFIdE CER'EIFICATE 0 CORRECTION Patent No. 3,912,653 eiDated EOCtQBer 14. 1975 lnventor(s) DONALD WILKES It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, lines 1,2: "Sid-walls" should be -sidewalls lines 24 and 68: "slicing" should be eplicing Col. 5,' lines 30 and 36;: "38" should be in bold-face j:ype; line 48: "541 should be in bold-face t e Col. 6, line 45: "slicing" should be ---splic ing Col. 8, line 26 after "in" and before the comma,

--claim 1 should be inserted Signed and Scaled this sixth I. D of "January 1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uj'latems and Trademarks

Claims (3)

1. An insulated joint electrically connecting at least a pair of unstripped, insulated wires comprising: a channel-type metal jointing clip having channel walls bent over a web portion in a mechanically-interlOcking relation with said wires located therebetween; said clip including inwardly-extending protrusions piercing said insulation and in electrically-conductive engagement with said wires; and a channel of resiliently flexible insulating material wrapped around said clip, said insulating channel extending longitudinally beyond the ends of said clip, the upper side walls of said insulating channel being locked between the edges of the inwardly-bent walls of said clip forming buckled loops within said joint with the free ends of said insulating channel sidewalls extending upwardly between the edges of said inwardly bent clip walls.

2. The insulated joint as claimed in, wherein said metal clip is adhesively bonded to said insulating channel.

3. The insulated joint as claimed in claim 1, wherein said insulating material is a polyimide in the range of 3 to 12 mils thick.

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