US3688247A

US3688247A - Cable connectors

Info

Publication number: US3688247A
Application number: US66409A
Authority: US
Inventors: Marcel Desire Prodel
Original assignee: Societe Industrielle de Construction dAppareils et de Materiel Electriques SICAME SAS
Current assignee: Societe Industrielle de Construction dAppareils et de Materiel Electriques SICAME SAS
Priority date: 1969-09-04
Filing date: 1970-08-24
Publication date: 1972-08-29
Anticipated expiration: 1989-08-29
Also published as: GB1320022A; BE754938A; DE2042692A1; FR2058441A5

Abstract

A cable connector for making a branch connection to a main cable comprises a clamp spanning the cable fitted with a closing member traversed by a screw and with an intermediate part resting on the base of the clamp. The screw carries a shoe and by tightening the screw the cable is gripped between the intermediate part and the shoe which have teeth which penetrate to the core of the cable through its insulation. Simultaneously the spread-out, bared end of a branch cable is gripped between the intermediate part and the base of the clamp.

Description

Patented Aug. 29, 1972 ZShQetS-Sheet 1 F/GZ vllllllfill'la all! III 7! I'll til vlla Awzh rwe Patented Aug. 29, 1972 2 Sheets-Sheet z FIGS Ava r05 CABLE CONNECTORS BACKGROUND OF THE INVENTION There are known several types of connectors for making branch tappings on distribution systems with preassembled insulated cables, notably those supplying service leads.

One of the characteristics common to all connectors is that before placing them into position it is necessary to strip the main cable for an exact length; it is on this part of the cable, which thus has its metal core exposed,

The operation of stripping a main cable, which forms part of a preassembled twisted group of several cables, is long and troublesome as well as being delicate, for the following reasons:

1. The stripping, which depends on the dimensions of the connector, has to be performed to a precise length. Also, the safety regulations require that after this has been done the whole branch connection be enclosed in protective insulating cover; hence it is important that the length of cable which is stripped shall not exceed the dimensions of the protective cover.

2. Even though special pliers are used it is very awkward to strip one of the conductors which can only be separated with difficulty from the twisted group of which it forms a part. More often, in order to carry out this operation, use is made of wooden wedges which are inserted in the group on each side of the location to be stripped, thus permitting relative freeing of the cable to be worked on. Obviously the use of procedures of this nature is not always without serious risk to the insulation, for it must be emphasized that these cables have only one thin layer of insulation.

3. The preliminary stripping of the main cable can be carried out, in spite of the above-mentioned drawbacks, on a system which is electrically dead if precautions are taken; it becomes practically unthinkable, in view of the danger incurred, if the system is in service, that is to say if it is live; this defect constitutes a very serious handicap at a time when it is increasingly urgent to maintain a continuous service of electrical energy and to carry out as much work as possible on the system without cutting off the current.

There is a connector, which has still only just been put into commercial use, with which it is possible to connect branch lines to an overhead group of preassembled insulated cables without preliminary stripping, and the use of this connector is spreading very rapidly, particularly in connection with aluminum core cables. This connector consists of two solid parts, each drawn from a section, which are assembled by being hooked in in dovetail formation. The lower part, in the shape of a cradle, has two sharp projections which, under pressure, are thrust against the metal core of the cable,

passing through the insulation; a hole formed in this lower part receives the branch cable which is fixed there by means of an ordinary set screw.

The upper part is substantially in the form of an inverted V, the back of which provides a passage for a milling screw which is nothing more than an ordinary screw, the flat end of which has a fairly wide and fairly deep slot. As has already been stated, this part interlocks with the lower part by dove-tail grooves.

that the branch cable is joined by means of the connec- The method of operation of the equipment is simple. The stripped end of the branch cable is inserted in the passage formed for the purpose in the lower part of the connector and the tightening screw is locked. Then the two parts of the connector are assembled on the main cable, which is not stripped, by interlocking them by the dovetails, after which the milling screw is tightened. At first the screw comes into contact with the insulation which breaks up by the combined action of the pressure of the screw and its rotation, permitting the sharp edges of the screw slot to act like two knives which, as they turn, out shavings from the insulation. As the screwing action continues the edges of the slot in the screw produce an identical effect on the metal core of the cable which is thus brought into contact with the milling screw and so with the upper part of the connector, then with its lower part, through the interlocking dovetails, then, finally, with the branch cable. During the period of exertion of pressure the two sharp projections, running transversely to the main cable, carried by the lower part of the connector pass through the insulation and then rest firmly on the metal core of the cable, thus preventing any inadvertent loosening of the connector which might lead to flowing, owing to softening through heating of the insulating sheath.

This connector has serious disadvantages:

Being composed of solid parts it lacks the tightening elasticity which is essential to ensure permanence of contact.

Because of the curvature of the cable which is accentuated locally by the fact that it consists of strands of small diameter, the braking action of the screw which is situated in one plane can only give the markedly convex metal core a lineof contact or possibly a small surface of contact if the rotation of the milling screw is continued sufficiently, while it must be noted that this rotation, which produces metal shavings, reduces the section of the metal core locally, with consequences which such action entails, both as regards the electrical aspect and also the mechanical performance aspect in the case of cables subjected to mechanical stress, as follows:

The passage of current in the connector is unnecessarily long and, which is serious, it traverses an additional contact in the joint grooves.

The insulation shavings accumulate in the slot of the milling screw and clog it up. Furthermore since the cutting system is not perfect what happens is more of a paring down of the insulation, with the result that burrs or scrap from the insulating material can very easily become lodged between the screw and the metal core, thereby reducing their area of contact without the possibility of any control.

Finally it is awkward to put the connector into position because it is not a monolithic construction.

The present invention provides a one-piece connector which is free from the disadvantages of earlier connectors and permits the fixing in a very convenient manner of a branch connection to an insulated main cable without stripping the main cable.

SUMMARY The invention provides a connector for joining electrical conductors, including a capping element which at least partially surrounds an insulated cable and a bared portion of a branch conductor. An intermediate part of electrically conductive material is positioned between the insulated main cable and the bared portion of conductor, which intermediate part has teeth on its side which is facing the cable. Pressure means are provided to press the main cable, intermediate part and bared portion of branch conductor, against one another so that the teeth penetrate through the insulating layer of the main cable and contact the metal core of the main cable. Electrical contact with the core of the insulated cable is thus effected by the penetration of the teeth of the intermediate part through the insulating layer, without removal of insulation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation of the front face of a connector according to the invention,

FIG. 2 is a sectional view of the closed connector of FIG. 1 across its width,

FIG. 3 is an elevation of the rear face of FIGS. 1 and a FIG. 4 shows, in elevation in the direction of width, the open connector with the intermediate part removed,

FIG. 5 is a perspective view of the intermediate part,

FIG. 6 represents a variant of the intermediate part of FIG. 5,

FIG. 7 represents, in section in the direction of width another method of construction of a connector in accordance with the invention, and

FIG. 8 shows the embodiment of FIG. 7 in longitudinal elevation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description, the word cable will designate according to the applications, either a solid core conductor or a conductor with a stranded core or composed of several metal strands.

In the embodiment illustrated in FIGS. 1 to 5 a connector in accordance with the invention comprises a clamp 5 of sheet metal, such as bronze, which cut out and shaped with two arms, and the base of which is pierced by a hole 21 through which the bared end of a branch cable is introduced. The strands 22 of the core of the branch cable are spread out and distributed evenly on both sides of the hole.

The base of the clamp 5 is bent, as shown at 26, to provide a certain amount of play in relation to the parts to be gripped, so that when pressure is applied a substantial elastic deformation of the bends 26 is possible.

The clamp 5 has on one of its arms two lugs 6, each pierced by a pivot hole 7. On the opposite arm two rectangular openings 8 are formed. The lugs 6 receive a hinge pin 12 of a closing latch consisting of a brass or bronze profile. On the side opposite the hinge pin 12 this latch 10 has two lips 9 which are shaped to engage automatically at the time of closing of the clamp in the openings 8, due to the elasticity of the arms of the clamp 5. In practice the hinge-mounting of the latch 10 is effected by forcing the pin 12 into the hole 11 in the latch while this pin 12 rotates freely in the holes 7 in the lugs 6. This pin is advantageously made from brass or bronze wire.

The latch 10 comprises in addition a tapped hole 13 in which a hexagonally headed screw 14 engages. A pressure shoe 15 consisting of a brass or bronze profile has sharp teeth 17 on its lower surface and over its entire length. In the center it is countersunk at 16 in which a tip of the screw 14 engages, this tip being crimped on the shoe with play so that the screw 14 can rotate freely within the shoe. The upper part of the shoe has chamfers 27 which, when the screw 14 is fully loosened, lodge in the latch 10 on complementary chamfers 25 on the slot formed over the entire length of the lower surface of the latch 10, so that the shoe is then immobilised as regards rotation in relation to the latch 10 and is thus oriented correctly in relation to the arms of the clamp 5 when the latch 10 is closing.

The lower surface of intermediate part 18, which is formed of a profile in brass or bronze, is shaped to match the shape of the base of the clamp so that when the connector is tightened up it can grip the spread strands 22 of the branch cable, even if they are of very small diameter. The upper surface of the intermediate part has teeth 19 of adequate height and well sharpened over its entire length. The intermediate part 18 is slightly bigger than the width of the arms so that retaining clips 20 can be fitted on the ends of the part 18 to fix it in the clamp 5 while still allowing it to slide along the arms of the said clamp.

The connector is used in the following manner. With the latch 10 open (as shown in FIG. 4) and the intermediate part 18 removed, the stripped end of the branch cable is introduced into the interior of the clamp 5, the strands 22 forming the cable are spread out on both sides of the hole 21 and the intermediate part 18 is replaced by inserting it through the top part of the arms of the clamp 5 and letting it slide until it contacts the strands 22 of the branch cable. Then, without stripping it, the distribution system main cable 24 is introduced into the interior of the clamp 5; this is easy to do, even though the cable 24 is part of a preassembled twisted group of several cables, because the very thin arm of the connector 5 can be inserted very easily between the cables of the group. The latch 10 is pivoted and as it rotates it carries with it the screw 14 which is fully loosened and the shoe 15 which is prevented from rotating, being immobilised in the chamfers 25 until the lips 9 of the latch 10 come into engagement with the openings 8, which thus automatically locks the latch on the clamp 5. So far all the operations described have been performed without touching the insulation of the distribution system cable and consequently without any risk of electrocution.

All that is needed now is to tighten up the set screw 14, preferably using an insulated spanner. The teeth 17 of the pressure shoe 15 pass through the insulation 24 of the main cable 23 and come to rest firmly, independently of the plasticity of the sheath 24, on the metal core of the cable. At the same time the teeth 19 of the intermediate part 18 also pass through the insulating sheath 24, gripping tightly the strands 22 of the branch cable which are imprisoned between the intermediate part 18 and the bottom of the clamp 5. As soon as the teeth 19 touch the metal core of the cable, electrical contact is established between the main cable 23 and the branch cable by way of the intermediate part 18.

As can be seen from FIGS. 2 and 5, the teeth 19 are rectilinear and parallel to the axis of the distribution system cable and their cutting edges are on a cylindrical surface of diameter substantially equal to the diameter of the core of that cable, which enables contact to be established with the latter along several generatrices.

In the same way, the teeth 17 of the pressure shoe advantageously have rectilinear edges parallel to the main cable.

In the modification shown in FIG,. 6 the two outer teeth 19 or the intermediate part 18 have a straight cutting edge, whereas the two central teeth 19 have a serrated cutting edge with triangular indentations 32 between which there remain sharp portions 33 which form a succession of almost pin-point zones of contact with the core of the cable covered by an insulation. In the case of an aluminum core these pin-point contacts facilitate the breakdown of the non-conducting layer of aluminum oxide which develops on the surface of the aluminum. Further they assist perforation of the thin, but resistant tape, known as terphane tape, which is often disposed between the metal conducting core and the insulating sheath in dry systems.

Furthermore, in this same figure the lower surface of the small plate 18 is provided with shallow longitudinal ridges 34 with sharp edges, which are either straight or serrated, for rupturing the film of aluminum oxide on the strands of the branch conductor, when the core of this conductor is of aluminum.

It is convenient if each of the zones of contact 33 extends over a length from 0.5 mm. to 1.5 mm.

The embodiment shown in FIG. 7 and 8 is especially convenient for making branch tappings from underground dry-insulated cables and, more particularly, in the case of those requiring the joining of conductors with a solid sector-shape core, often consisting of a solid aluminum profile in the form of a sector of a circle, in place of conductors composed of strands which are apt to spread out at the base of the clamp. This embodiment also facilitates the so-called tangent tappings where the branch cable emerges from the conductor parallel to the main cable and with which it is possible to reduce the dimensions of the metal boxes in which the whole tapping is enclosed, which then comprises as many connectors as phases in addition to that of the neutral conductor.

ln FIGS. 7 and 8, in which the parts corresponding to those in FIGS. 1 to 5 have the same reference numbers, the edges 21' delimiting the hole 21 formed in the base 5 of the clamp 5 are curved upwardly. The base 5' is V-shaped and resting on the two arms of the V are the two plane faces of a main cable in the form of a sector of a circle. The latter may be of variable dimensions and may, for example, have one of the two

profiles

30, 31 illustrated by chain-dotted lines, or any intermediate profile, a clearance being left between this cable and the elbowed inner faces 5" of the clamp. The intermediate part 18 has on its lower surface a series of teeth disposed parallel to the axis of the

cable

30 or 31 and having their cutting edges pointing downwardly. The upper surface of the part 18 is hollowed out into a V-shaped groove which forms a seating for the bared portion of a branch cable 28 which is round in shape.

As a variant, the two faces 18' of this groove can act as supporting surfaces for the two plane faces of a branch cable 29 which has a sector shape. The shoe 15 has on its lower surface a concave portion 15' with a rounded off shape, adapted to facilitate close contact between the shoe and the

branch cable

28 or 29. The screw 14 is provided with a lock nut 14.

The device illustrated in FIG. 7 and 8 is operated by bringing the latch 10 into the open position, spanning the main

insulated cable

30, 31 with the clamp S, sliding the part 18 from top to bottom along the two arms of the clamp so that it rests on the main cable, placing in the V-shaped groove of that part the bared portion of the

branch cable

28 or 29, situated parallel to the

cable

30, 31, then bringing the latch into the closing position and turning the screw .14 so as to grip the electrically conductive intermediate part 18 between the main cable and the branch cable, causing the teeth 19 to penetrate through the insulating layer of the main cable until their cutting edges make contact with the metal core of that cable. The tightening also has the effect of causing the upturned edges 21 of the opening 21 to penetrate through this same insulation layer, which assists the stability of the joint. Advantageously some, at least, of the teeth 19 have serrated cutting edges of the above-described type and the contact surfaces of these

parts

15 and 18 with the branch cable comprise ridges (not illustrated and disposed parallel to the

conductor

28 or 29, for example), the function of which is to rupture the non-conductive layer of aluminum oxide in cases where the branch cables have an aluminum core. In a general way this device is applicable both to main cables with solid core and also to those with a stranded metal core.

In the connectors according to the invention it is advisable to take special precautions to prevent the phenomenon of ageing of the electrical contact, which is likely to be caused by repeated cycles of heating and cooling. It has been found that when the volume of insulation of the main cable is excessively compressed into the grooves between blades when the connector is fixed, this insulation may tend to flow, as a consequence of the heating which causes a passage of current, which entails a drop, which may be considerable, in the clamping pressure and as a result a lowering in the quality of the electrical contact.

To obviate this the contact teeth assembly is preferably so dimensioned that the ratio of the average width of grooves between blades the average width of blades has a value of at least 2.5 l. The ratio of height of the teeth thickness of insulation layer is advantageously at least equal to 2 1. Thus, teeth 4 mm. in height, with an average width or thickness of 1 mm. and separated by grooves with an average width of 2.5 mm. are suitable for cables up to 14 mm. in diameter covered with an insulating sheath 1 to 2 mm. thick of PRC (reticulated polythene) or PVC (polyvinyl chloride).

1 claim:

1. A connector for making electrical connection between a main cable having a core which is covered with an insulating layer and a bared part of a branch cable, comprising:

a U-shaped cradle having a base and two arms for receiving said cables therebetween;

said base having a hole for passing therethrough the strands of a branch cable and spreading said strands on inner surface-of said base;

a closing member having an end hingedly assembled to one said arm and another end resiliently engageable with the other said arm for closing the connector;

an electrically conductive component between said strands and main cable and slidable along said arms and having spaced blades with rectilinear cutting edges pointing toward said main cable and parallel to the axis thereof;

means for exerting pressure against the base through the main cable, said component and said strands, comprising a screw passing through said closing member;

a shoe on one end of the screw and freely rotatable about the axis thereof and having spaced blades pointing toward said main cable and parallel to the axis thereof when the connector is closed, the ratio of the average width of the interval between blades to the average thickness of the blades being at least 2.5:1;

whereby closing of the connector followed by movement of the screw toward the cradle base causes each blade to make a straight cut through the layer and bear by its cutting edge against the outer surface of the main cable core whereby said core is firmly held by direct contact with a plurality of said cutting edges on opposite sides thereof.

2. A connector for making electrical connection between a main cable having a core which is covered with an insulating layer and a bared part of a branch cable, comprising:

a U-shaped cradle having a base and two arms for receiving said cables therebetween; said base having a hole for passing therethough the strands of a branch cable and spreading said strands on inner surface of said base;

a shoe on one end of the screw and freely rotatable about the axis thereof and having spaced blades pointing toward said main cable and parallel to the axis thereof when the connector is closed, at least some of the blades having a serrated cutting edge;

whereby closing of the connector followed by movement of the screw toward the cradle base causes each blade to make a straight cut thought the layer and bear by its cutting edge against the outer surface of the main cable core whereby said core is firmly held by direct contact with a plurality of said cutting edges on opposite sides thereof.

Claims

1. A connector for making electrical connection between a main cable having a core which is covered with an insulating layer and a bared part of a branch cable, comprising: a U-shaped cradle having a base and two arms for receiving said cables therebetween; said base having a hole for passing therethrough the strands of a branch cable and spreading said strands on inner surface of said base; a closing member having an end hingedly assembled to one said arm and another end resiliently engageable with the other said arm for closing the connector; an electrically conductive component between said strands and main cable and slidable along said arms and having spaced blades with rectilinear cutting edges pointing toward said main cable and parallel to the axis thereof; means for exerting pressure against the base through the main cable, said component and said strands, comprising a screw passing through said closing member; a shoe on one end of the screw and freely rotatable about the axis thereof and having spaced blades pointing toward said main cable and parallel to the axis thereof when the connector is closed, the ratio of the average width of the interval between blades to the average thickness of the blades being at least 2.5:1; whereby closing of the connector followed by movement of the screw toward the cradle base causes each blade to make a straight cut through the layer and bear by its cutting edge against the outer surface of the main cable core whereby said core is firmly held by direct contact with a plurality of said cutting edges on opposite sides thereof.

2. A connector for making electrical connection between a main cable having a core which is covered with an insulating layer and a bared part of a branch cable, comprising: a U-shaped cradle having a base and two arms for receiving said cables therebetween; said base having a hole for passing therethrough the strands of a branch cable and spreading said strands on inner surface of said base; a closing member having an end hingedly assembled to one said arm and another end resiliently engageable with the other said arm for closing the connector; an electrically conductive component between said strands and main cable and slidable along said arms and having spaced blades with rectilinear cutting edges pointing toward said main cable and parallel to the axis thereof; means for exerting pressure against the base through the main cable, said component and said strands, comprising a screw passing through said closing member; a shoe on one end of the screw and freely rotatable about the axis thereof and having spaced blades pointing toward said main cable and parallel to the axis thereof when the connector is closed, at least some of the blades having a serrated cutting edge; whereby closing of the connector followed by movement of the screw toward the cradle base causes each blade to make a straight cut through the layer and bear by its cutting edge against the outer surface of the main cable core whereby said corE is firmly held by direct contact with a plurality of said cutting edges on opposite sides thereof.