GB2233166A

GB2233166A - Compression connectors for electric cable conductors

Info

Publication number: GB2233166A
Application number: GB9004954A
Authority: GB
Inventors: Angelo Sala; Luigi Panzeri
Original assignee: Pirelli Cavi SpA; Cavi Pirelli SpA
Current assignee: Pirelli and C SpA
Priority date: 1989-03-08
Filing date: 1990-03-06
Publication date: 1991-01-02
Anticipated expiration: 2010-03-06
Also published as: GB9004954D0; BR9001178A; IT8919695A0; IT1229090B; GB2233166B; AR246137A1

Abstract

A compression ferrule 210 for interconnecting the end portions of respective cable conductors 312, 314 comprises an electrically conductive body provided with a through cavity. The body may have an electrical resistivity higher than that of the conductors, but must have a hardness which is markedly greater than the hardness of the conductors. The through cavity has a plurality of portions 220-228 each of which is provided with a respective circumferential groove means 230-238, the surface of the cavity between adjacent grooves being flat, chamfered or round. The ferrule may be used with a sleeve 260 in the case where the cable conductors are provided with respective central oil ducts. The sleeve 260 is also of a material which is markedly harder than the material of the conductors and is provided with external circumferential grooves 274, 276 and a through cavity 282. <IMAGE>

Description

COMPRESSION CONNECTORS FOR ELECTRIC CABLE CONDUCTORS This invention relates to compression connectors for electric cable conductors.

More particularly, although not exclusively, the invention relates to such connectors, often referred to as jointing ferrules, for electrically and mechanically interconnecting respective end portions of the conductors of two cable lengths, and furthermore the invention is especially applicable to such conductors which when compressed to make the interconnection have substantially the same outer diameter as the conductors.

High voltage electric cables, eg. 30 kV and above are subject during laying to tensile stresses which can be very high. This is particularly the case for submarine cables which are laid at depths of several hundreds of metres. Although such cables are provided with tensile resistant means disposed outwardly of the conductors thereof for carrying the tensile stresses which arise during laying, some tensile stress is still applied to the cable conductors.

Since tensile forces are exerted during a laying operation on the conductor of a cable, the connectors used for joining the conductors of adjacent lengths of cable should be able to bear these tensile stresses without fracturing, or separating or sliding with respect to the conductors. Any separation or sliding, even if minimal, of the connectors with respect to the conductors produces a jointing defect which will jeopardise or substantially reduce the current carrying capacity of the cable.

As with any cable, where it is not possible to exclude the presence of joints, it is very important to provide joints which are reliable and resistant to any type of stress, particularly tensile stress.

Connectors for connecting cable conductors are described in United Kingdom Patent Specification No.

1443578 to which reference is directed. The connectors disclosed in this specification are compression jointing ferrules comprising a hollow cylindrical sleeve provided with internal circumferential grooves suitable for receiving material from the cable conductors when the sleeve is radially compressed on the conductors to substantially the same diameter as that of the conductors.

Examination of these sleeves has shown that they may fracture, or separate or slide with respect to the conductors when subjected to particularly strong tensile stresses. We have concluded that this is primarily due to the material of the sleeves being selected on the basis of a perceived requirement for that material to have an electrical resistivity as near as possible to that of the cable conductors.

This has resulted in the sleeves being deformable to an extent of the same order of that of the cable conductors, so that when the sleeves are radially compressed on the conductors the sleeves suffer a deformation substantially of the same order as the cable core conductors with the result that in practice very little material of the conductors is deformed into the internal circumferential grooves of the sleeve and vice versa, very little deformation of the sleeve by the conductors occurs.

Further, in order to promote deformation of the sleeves and conductors it has been the practice to widen the circumferential grooves of the sleeves and to increase their spacing apart. However this reduces the number of anchoring zones between the sleeve and the conductors, worsening the tensile strength properties of joints made using such sleeves.

In order to overcome the above discussed drawbacks, we have found that it is necessary to select the material for the sleeves in a manner substantially contrary to that previously considered essential.

Specifically, instead of requiring a material for the sleeve to have an electrical resistivity as near as possible to that of the material of the electrical conductors, the present invention utilises materials which are selected because they have a hardness markedly higher than that of the conductor material, even though their electrical resistivity may be substantially higher than that of the conductor material. In this way deformation of the conductor material into the sleeve grooves and the regions of the sleeve between the grooves into the conductors is considerably improved.

As an indication of the relative hardness of the sleeve material to the conductor material, the hardness of the sleeve material may be measurable on a hardeness scale, for example Rockwell B, on which the hardness of the conductor materials is not measurable - ie. on a scale which is not suitable for providing an accurate measurement of the hardness of the conductor material.

By enabling the degree of deformation of the sleeve and conductors to be both reliable and substantial, it has been. possible to increase the number of internal circumferential grooves of the sleeves, increasing thus the number of anchoring zones between the sleeves and conductors.

Further, since the sleeves are markedly harder than the conductors and consequentially penetration of the regions of the sleeve between the grooves of the sleeve into the conductors is substantially guaranteed, it is possible for these regions to be round or flat thereby avoiding cutting of the surface of the conductors which would interrupt their crystalline structure and produce both a reduction of their tensile strength and an increase in their elongation. In fact, penetration of the sleeves into the conductors without causing cuts in the latter produces higher tensile strength joints made with this type of connector.

Whilst the background to the invention is concerned with the development of an improved compression jointing ferrule connector, it is to be understood that the invention is applicable to other forms of compression connectors for electric cable conductors. Thus, broadly stated the invention provides a compression connector for a cable conductor comprising an electrically conductive body having a cavity for receiving an end portion of the conductor, the cavity being provided with groove means in the surface thereof for receiving material from the conductor when the connector is compressed on to an end portion of a conductor received in said cavity so as to grip the conductor end portion to resist axial separation apart of the conductor end portion and connector, wherein the conductive body has a hardness which is markedly greater than the hardness of the conductor with which it is intended to be used.

Typically the surface of the cavity is generally cylindrical and said groove means extend circumferentially therearound.

The groove means may comprise a helical groove, the surface of the cavity between adjacent turns thereof being round or flat in axial cross-section, but as an alternative the groove means may comprise a plurality of annular grooves, the surface of the cavity between adjacent grooves being round or flat in axial cross-section.

As indicated above, the main consideration in selecting the material for the connector body is not as hitherto its electrical resistivity, and accordingly the electrical resistivity of the body may be higher than that of the conductors with which it is intended to be used.

In the embodiments of the invention described hereinafter, which take the form of compression jointing ferrules, the cavity extends through said body with respective openings at opposite ends thereof for receiving respective conductor end portions to be electrically and mechanically interconnected by said connector.

The cavity may comprise two outer cylindrical portions and a central cylindrical portion therebetween and coaxial thereto, the central portion having a smaller diameter than the outer portions and each portion being provided with a respective said groove means.

Further in this case, the cavity may comprise a respective intermediate cylindrical portion positioned between said central portion and each outer portion, each intermediate portion having a diameter greater than that of the central portion and smaller than that of the outer portions, and each of said intermediate portions being coaxial to said other portions and provided with a respective said groove means. This is the form of the cavity in the embodiments referred to above.

The invention also includes a sleeve for use with a compression jointing ferrule connector as defined in any one of the last three paragraphs for interconnecting respective end portions of two cable conductors each of which has a central oil duct, said sleeve having opposite ends which are insertable in the oil ducts of the respective conductors, the sleeve being formed with respective external groove means on each of its two end portions and having a hardness which is markedly greater than the hardness of the conductors with which it is intended to be used.

The invention also includes cable joints made with such a compression jointing ferrule connector and, in the case of conductors with central oil ducts, additionally with a sleeve as defined in the last preceding paragraph.

In order that the invention may be well understood, the above mentioned embodiments, which are given by way of example only, will now be described with reference to the accompanying drawings in which: Figure 1 is an axial section of a connector comprising a compression jointing ferrule embodying the invention; Figure 2 is an axial section of a sleeve for use with the ferrule of Figure 1 for joining cable conductors having central ducts; Figure 3 is an axial section through a joint between stranded conductors of two cable lengths utilising a known jointing ferrule, and showing the joint before compression of the ferrule; Figure 4 shows the joint of Figure 3, after compression of the ferrule;; Figure 5 is an axial section through a joint between stranded conductors of two cable lengths utilising the jointing ferrule shown in Figure 1, and showing the joints before compression of the ferrule; Figure 6 shows the joint of Figure 5, after compression of the ferrule; Figure 7 is an axial section through a joint between conductors having central ducts of two cable lengths utilising a known jointing ferrule and sleeve, and showing the joints before compression of the ferrule; Figure 8 shows the joint of Figure 7 after compression of the ferrule; Figure 9 is an axial section through a joint between conductors having central ducts of two cable lengths utilising the jointing ferrule shown in Figure 1 and the sleeve shown in Figure 2, and showing the joint before compression of the ferrule; and Figure 10 shows the joint of Figure 9 after compression of the ferrule.

Referring to Figure 1, there is shown a compression jointing ferrule 10 for use in interconnecting the respective end portions of the conductors of two cable lengths and is suitable for connecting conductors which are formed of stranded wires and also those which are formed with layers of keystone-shaped wires, wherein there are coaxial layers of wires.

The ferrule 10 comprises an electrically conductive cylindrical body 12 having a cavity which extends through the body with respective openings at opposite ends thereof for receiving respective conductor end portions. The body has two end portions 14 and 16 interconnected by a neck portion 18.

The cavity is formed by a series of cylindrical portions the diameters of which decrease from each end of the sleeve inwardly thereof. More, specifically, the cavity comprises two outer cylindrical portions 20, 22 and a central cylindrical portion 28 therebetween and co-axial thereto, the central portion having a smaller diameter than the outer portions.

Also, in the illustrated ferrule, the cavity comprises a respective intermediate cylindrical portion 24, 26 positioned between the central portion 28 and each outer portion 20, 22, each of the intermediate portions being coaxial to the other portions and having a diameter greater than that of the central portion and less than that of the outer portions.

Each of the cylindrical portions 20, 22, 24, 26 and 28, is provided with a respective groove means 30, 32, 34, 36 and 38 in the surface thereof. Each groove means extends substantially throughout the length of its respective cavity portion and the grooves thereof have a V-shape in axial cross-section.

Each groove means may comprise a plurality of annular grooves or a helical groove. In the former case, the surface of the cavity between adjacent grooves is round or flat in axial cross-section as indicated at 40, 42, 44, 46 and 48. In the latter case the surface of the cavity between adjacent turns of the helical grooves is round or flat in axial cross-section as also indicated at 40-48. The use of a helical groove for each groove means is preferred since such a groove can be formed more easily and accurately than a plurality of annular grooves and consequentially provides a more reliable jointing ferrule. It will be appreciated that each helical groove can be formed using a tap for machining a Vshaped thread in the cylindrical cavity portion and that thereafter a further tap or a turning tool can be used to remove the crests of the turns of the thread to render them flat or round to form the surface portions 40-48 between the turns.

Referring now to Figure 2, there is shown a sleeve 60 for use with the ferrule 10 when the latter is used for interconnecting respective end portions of two cable conductors each of which has a central oil duct. The sleeve, which is insertable in the oil ducts of the respective conductors comprises a cylindrical body 62 having two end portions 64 and 66 extending outwardly from a central collar portion 68 of larger diameter than the end portions. The free ends of the end portions 64 and 66 are of reduced diameter and chamfered as indicated at 70 and 72 respectively. Furthermore, each end portion 64 and 66 is provided with a respective groove means 74 and 76, which extends over the majority of the length thereof. As with the groove means of the ferrule, each groove means 74 and 76 may comprise a plurality of annular grooves or a helical groove.In the former case the outer surface of the end portion between adjacent grooves is round or flat in axial cross-section and in the latter case the outer surface of the end portion between adjacent turns of the helical groove is round or flat in axial crosssection.

The sleeve 60 is provided with a central cylindrical through cavity 82 for providing a communication between the oil ducts of the conductors of the cable lengths into which the end portions 64 and 66 are inserted.

Reference is now made to the composition and properties of the materials used for forming the jointing ferrule 10 and the sleeve 60 when that is used with the ferrule, because as indicated hereinbefore the improved performance of these items is achieved by the choice of materials for them.

These materials are not selected because they have the same electrical resistivity as the material forming the cable conductors, as previously, but rather because they have a hardness which is markedly harder than that of the conductors. The resistivity of the material for the ferrule and sleeve may be higher than the resistivity of the conductors but should be of the same order of magnitude.

As an indication of the relative hardness of the material for the ferrule 10 and sleeve 60 to the conductor material, the hardness of the ferrule 10 and sleeve 60 may be measurable on a hardeness scale on which the hardness of the conductor material is not measurable, ie. on a scale which is not suitable for providing an accurate measurement of the hardness of the conductor. Further the electrical resistivity of the material for the ferrule 10 and sleeve 60 may be between 1.2 and 2.5 times that of the conductor material.

By way of non-limiting example, some suitable materials for use in manufacturing the ferrule 10 and sleeve 60 for use in making joints with conductors formed with substantially pure copper are given in the following tables. It should however be understood that the properties of these exemplary materials can result in even greater advantage in the case where the cable conductor is formed from a material which is softer and which has a higher electrical resistivity than substantially pure copper.

The following tables show the electrical and mechanical properties of some materials usable for forming the ferrule 10 and the sleeve 60 compared with the same properties of substantially pure copper as used for forming the cable conductors. TABLE 1 MATSRIALS FOR CLAMPS EMPLOYED FOR JOINING CONDUCTORS

Materials Ultimate Ultimate Hardness Electrical State Modulus Tensile 0.2% alongation (HRB) resistivity of Stress Proof % Rockwell B microhm cm elastic Stress ity N/mm N/mm N/mm Cu-Cr 1 8 82 2-2.3 hardened 119630 chromium 627 598 and copper tempered Beryl- 125828 bronze A 716 500 24 92 3.6 treated Beryl- not 109828 bronze B 353 157 38 42-49 3.6 treated Hardened 125515 copper (chromium copper) 436 314 26 66 2.2 treated Tombac not 106885 90/10 303 294 16 50 4 treated TABLE 2

Ultimate Tensile 0.2% Ultimate Hardness Electrical State Modulus Materials Stress Proof elongation (HRB) resistivity of Stress microhm elastic N/mm N/mm % Rockwell B cm ity N/mm Hardened copper 431 412 12 73 2.2 treated 73545 (drawn) 444 422 12 73 77468 Hardened copper 392 294 18 70 2.2 treated 120614 (forged when rough) 400 303 18 68 127480 Beryl- 694 529 20 95 128460 bronze G 713 529 20 95 3.6 treated 131400 Cu ETP 215 70 8 (electro- a) 1.71 forged 117700 lytic copper) 370 345 45 TABLE 3 CHEMICAL COMPOSITION OF THE MATERIALS REFERRED TO IN THE PREVIOUSLY GIVEN TABLE

Material Cu Cr Be Co Zn Zr Al Cu-Cr 1 chromium copper 98.9 1 - - - 0.1 Berylbronze A 96 - 0.4 1.5 - - 98 0.8 3 Berylbronze B 96 - 0.4 1.5 - - - 98 0.8 3 Hardened copper 99 0.4 - - - - - (chromium copper) 1 Tombac 90/10 90 - - - 10 - Hardened copper 99 1 - - - - (drawn) 99.6 - 0.4 Hardened copper 99 1 - - - - - (forged when rough) 99.6 0.4 Berylbronze C 96 - 0.4 1.5 - - 98 0.8 3 Cu ETP 99.90 - - - - - (electrolytic copper) 99.95 Note: a) the hardness of the electrolytic coppers have not been indicated in the table, since these materials are markedly softer than the other materials and the Rockwell B hardness scale is not suitable for measuring them, instead they would be measured on a different hardness scale.

As shown in the foregoing tables, the electrical resistivities of the exemplary materials for the ferrule and sleeve are higher than those of the electrolytic coppers used for the conductors being from about 1.17 to 2.4 times those for the electrolytic coppers. More importantly, it is also to be noted that the hardness of the electrolytic coppers is not measurable in the hardness scale used for measuring the hardness of the materials for the ferrule and sleeve, so that from a practical point of view the relative hardness of these materials cannot be quantified.

The formation of a cable joint between stranded conductors using a ferrule as described above in connection with Figure 1 will now be described with reference to Figures 5 and 6 and compared with the formation of such a joint using the known ferrule which will be described with reference to Figures 3 and 4. Further the formation of the cable joint between conductors having coaxial keystone-shaped wires and provided with a central oil duct using a ferrule and sleeve as described above in connection with Figures 1 and 2 respectively will also be described with reference to Figures 9 and 10 and compared with the formation of such a joint using the known ferrule and sleeve which will be described with reference to Figures 7 and 8.

Referring first to Figures 3 and 4, there is shown a jointing ferrule 110 as disclosed in the above-mentioned United Kingdom Patent Specification No. 1443578. The ferrule 110 is illustrated being used for interconnecting the end portions of two stranded conductors 112 and 114. Each respective conductor 112 and 114 comprises an outer layer 116 and 118 of circular section conductor wires covering an intermediate layer 120 and 122 of such wires which in turn covers an inner layer 124 and 126 of conductor members, each of which is formed from stranded conductor wires.

As shown in Figure 3, the ferrule 110 has enlarged end portions 128 and 130 within which respective outer cylindrical portions 132 and 134 of a through cavity of the ferrule are disposed. The outer cylindrical portions 132 and 134 extend inwardly to respective intermediate cylindrical cavity portions 136 and 138 which in turn extend inwardly to a central cavity portion 140. The through cavity has a maximum diameter at its outer portions 132 and 134, an intermediate diameter at its intermediate portions 136 and 138 and a minimum diameter at its central portion 140. Each of the outer portions 132 and 134 has a respective circumferential groove 142 and 144, each of the intermediate portions 136 and 138 has a respective circumferential groove 146 and 148 and the central portion 144 has two circumferential grooves 150 and 152.

In order to arrive at the stage shown in Figure 3, the end portions of the two conductors are prepared by cutting back the wires in the outer and intermediate layers such that when the two end portions are inserted in opposite ends of the ferrule the inner layers are received in the central portion 140 of the through cavity, the intermediate layers are received in the intermediate portions 136 and 138 and the outer layers are received in the outer portions 132 and 134.

As disclosed in the above cited United Kingdom patent specification, radial compression of the ferrule 110, by means of a suitable press, deforms the ferrule as indicated at 110' in Figure 4 to substantially the same outer diameter as the conductors and connects the end portions of the conductors 112 and 114 which are gripped in the respective cavity portions 132' and 134'. 136' and 138' and 140' which derive from the deformation of the cavity portions 132, 134, 136, 138 and 140 of the ferrule 110. The deformation of the ferrule leads to a deformation of the wires of the end portions of the stranded conductors and to their material being received in the deformed circumferential grooves 142' and 144', 146' and 148', 150' and 152' of the ferrule.

This is the engagement between the ferrule and the conductor portions obtainable with the known ferrule.

Referring now to Figures 5 and 6, Figure 5 shows a ferrule 210, into which the prepared end portions 112 and 114 of two conductors as described above in connection with Figures 3 and 4 are inserted. In Figures 5 and 6 - and also in Figures 9 and 10 hereinafter - the circumferential grooves and the flat surface portions therebetween are shown in an exaggerated manner to more clearly illustrate their action.

The ferrule 210 is provided, in the same way as the ferrule 10 of Figure 1, with two end portions 214 and 216 interconnected by a neck portion 218 and has a through cavity comprising coaxial cylindrical portions 220, 222, 224, 226 and 228. Further, the end portions of the conductors are inserted into the ferrule such that the outer layers 116 and 118 engage the outer portions of the through cavity, the intermediate layers 120 and 122 engage the intermediate portions of the through cavity and the inner layers 124 and 126 engage the central portion as shown in Figure 5.

Further, as with ferrule 10 of Figure 1 each cavity portion 220, 222, 224, 226 and 228 is provided with a respective groove means 230-238, each of which comprises either a plurality of annular grooves or a helical groove, the surface of the cavity between adjacent grooves or turns being round or flat in axial cross-section as indicated at 240-248.

After the conductor end portions have been inserted into the ferrule 210, radial compression of the ferrule 210, by means of a suitable press, deforms the ferrule as indicated in 210' in Figure 6 to substantially the same diameter as the conductors.

During compression of the ferrule the material of the conductors is deformed into the deformed groove means 230'-238' primarily from those regions of the conductor engaged by the round or flat portions 240'248' of the cavity between adjacent grooves or turns of the groove means in view of the hardness of the material of the ferrule with respect to that of the conductors. This ensures close abutting engagement between the conductors and the deformed ferrule which provides the formation of a joint carrying an electrical resistance of the same order as that of the conductors and with excellent anchorage between the conductors and ferrule such that the joint can withstand higher tensile forces than the joint shown in Figure 4.

The above comments regarding the use of the ferrules 110 and 210 apply equally to the case where the conductors have coaxial keystone-shaped wires and are provided with a central oil duct.

Referring now to Figures 7 and 8 and Figures 9 and 10, it will be seen that in each case the keystone-shaped conductors are arranged in three layers or shells - i.e. each conductor comprises an outer layer or shell 316 and 318 of keystone-shape wires an intermediate layer or shell 320 and 322 of keystone-shaped wires and an inner layer or shell 324 and 326 of keystone-shaped wires. The inner layers 324 and 326 define respective inner ducts 328 and 330 for the flow of oil within the cable.

Referring to Figure 7, there is shown a sleeve 160, which like the sleeve 60 shown in Figure 2, has two end portions 164 and 166 extending outwardly from a central collar portion 168 of larger diameter than the end portions. The free ends of the end portions 164, 166 are of reduced diameter and chamfered as indicated at 170 and 172. Furthermore, each end portion is provided with a series of radially outwardly openipq circumferential grooves 174 and 176.

The grooves 174 and 176 are spaced apart along the length of the end portions and define projecting zones 178 and 180 respectively therebetween. The sleeve 160 is provided with a central cylindrical through cavity 182 for providing a communication between the oil ducts 328 and 330 of the conductors 312 and 314.

As already known from the above cited UK Patent Specification No. 1443578 the formation of a cable joint between the conductors 312 and 314 using the ferrule 110 and sleeve 160 is as follows.

The layers 316, 320 and 324 of the end portion of the conductor 312 are cut into a stepped configuration with the wires of the inner layer projecting outwardly with respect to the wires of the outer layer. The layers 318, 322 and 326 of the end portion of the conductor 314 are cut in the same manner. Thereafter the sleeve 160 is inserted into the oil duct of the prepared end portion of one of the conductors, for example duct 330 of conductor 314. Then the ferrule 110 is fitted onto that end portion such that the cavity portions 134, 138 and 140 receive the stepped layers 318, 322 and 326.

Thereafter, the prepared end portion of the other conductor 312 is inserted into the other end of the ferrule 110 and over the other end of the sleeve 160 such that the oil duct 328 receives the sleeve end portion and the stepped layers 316, 320 and 324 are received in the cavity portions 132, 136 and 140 of the ferrule.

The ferrule 110 is then radially compressed, by means of a suitable press, until it is deformed as indicated at 110' in Figure 8 to substantially the same outer diameter as the conductors. The deformed circumferential grooves 142'-152' which derive from the circumferential grooves 142-152 of the ferrule 110 receive material from the keystone-shaped wires of the respective conductor portions 312 and 314 which are deformed into those grooves.

Similarly, the circumferential grooves 174 and 176 of the sleeve 160 receive material from the inner layers 324 and 326 of the conductors.

Deformation of the material of the keys one shaped wires into the grooves of the deformed ferrule 110' and sleeve 160 provide the connection between the conductor end portions.

The joint formed in the manner illustrated in Figures 9 and 10 can withstand higher tensile forces than the above-described joint formed in the manner illustrated in Figures 7 and 8. The joint shown in Figures 9 and 10 utilises a ferrule 210, which corresponds to the ferrule 10 shown in Figure 1, and a sleeve 260, which corresponds to the sleeve 60 shown in Figure 2.

The ferrule 210 also corresponds with the ferrule of Figure 5 having each of its cavity portions 220-228 provided with a respective groove means 230-238, each of which comprises either a plurality of annular grooves or a helical groove, the surface of the cavity between adjacent grooves or turns being round or flat in axial cross-section as indicated at 240-248. The sleeve 260, like the sleeve 60 shown in Figure 2, has two end portions 264 and 266 which are each provided with a respective groove means 274 and 276, which extends over the majority of the length thereof and comprises either a plurality of annular grooves or a helical groove, the outer surface of the end portion between adjacent grooves or turns being round or flat in axial cross-section as indicated at 278 and 280.

Preparation of the joint is carried out in a similar manner to that described above in connection with Figures 7 and 8 except that in this case the ferrule 210 and sleeve 260 are utilised instead of the ferrule 110 and sleeve 160. Thus the stepped layers 316, 320 and 324 and 318, 322 and 326 of the conductors 312 and 314 respectively are inserted in opposite ends of the ferrule 210 with the sleeve 260 inserted in the oil ducts 328 and 330 of the conductors in the manner described hereinabove.

Thereafter, the ferrule 210 is radially compressed, by means of a suitable press, until it is deformed as indicated at 210' in Figure 10 to substantially the same outer diameter as the conductors. During compression of the ferrule 210, the material of the conductors is deformed into the deformed groove means provided in each cavity portion of the ferrule and vice versa the material of the ferrule at locations 240-248 penetrates into the keystone-shaped wires.

Similarly, the consequent radially inward deformation of the conductors compresses the inner layers 324 and 326 against the sleeve 260 causing the material of the sleeve at the locations 278 and 280 to penetrate into the material of the keystone-shaped conductors in those inner layers and vice versa the deformation of material from the conductors of those layers into the groove means 274 and 276 of the sleeve.

Consequentially, in view of the hardness of the material of the ferrule 210 and the sleeve 260 with respect to that of the keystone-shaped wires, the penetration of the material of the ferrule 210 and sleeve 260 into the conductors and the deformation of the material of the conductors into the groove means provides excellent anchorage between the conductors 312, 314 and the ferrule 210 and sleeve 260.

It is to be understood that whilst we have described with reference to Figures 5 and 6 and 9 and 10 two joints for joining cable conductors of two different types, modifications to the ferrule 210 can be made to cater for different conductor constructions by altering the number and size of the cylindrical cavity portions of the ferrule. Further, it is to be understood that the number of annular grooves or the number of turns of a helical groove constituting each groove means may be modified, as may the shape of the grooves and the surface therebetween on both the ferrule 210 and the sleeve 260.

Claims

CLAIMS:

1. A compression connector for a cable conductor comprising an electrically conductive body having a cavity for receiving an end portion of the conductor, the cavity being provided with groove means in the surface thereof for receiving material from the conductor when the connector is compressed on to an end portion of a conductor received in said cavity so as to grip the conductor end portion to resist axial separation apart of the conductor end portion and connector, wherein the conductive body has a hardness which is markedly greater than the hardness of the conductor with which it is intended to be used.

2. A connector as claimed in claim 1, wherein said conductive body has a hardness which is measurable on a hardness scale on which the hardness of the material of the conductor is not measurable.

3. A connector as claimed in claim 1 or 2, wherein the hardness of the conductive body is measurable on the Rockwell B scale.

4. A connector as claimed in any one of claims 1 to 3, wherein said surface of said cavity is generally cylindrical and said groove means extend circumferentially therearound.

5. A connector as claimed in claim 4, wherein said groove means comprises a helical groove, the surface of the cavity between adjacent turns thereof being round or flat in axial cross-section.

6. A connector as claimed in claim 4, wherein said groove means comprises a plurality of annular grooves, the surface of the cavity between adjacent grooves being round or flat in axial cross-section.

7. A connector as claimed in any one of the preceding claims, wherein the electrical resistivity of the body is higher than that of the conductor with which it is intended to be used.

8. A connector as claimed in any one of the preceding claims, wherein said cavity extends through said body with respective openings at opposite ends thereof for receiving respective conductor end portions to be electrically and mechanically interconnected by said connector.

9. A connector as claimed in claim 8, wherein said cavity comprises two outer cylindrical portions and a central cylindrical portion therebetween and coaxial thereto, the central portion having a smaller diameter than the outer portions and each portion being provided with a respective said groove means.

10. A connector as claimed in claim 9, wherein said cavity comprises a respective intermediate cylindrical portion positioned between said central portion and each outer portion, each intermediate portion having a diameter greater than that of the central portion and smaller than that of the outer portions, and each of said intermediate portions being coaxial to said other portions and provided with a respective said groove means.

11. A sleeve for use with a connector as claimed in any one of claims 8 to 10, for interconnecting respective end portions of two cable conductors each of which has a central oil duct, said sleeve having opposite ends which are insertable in the oil ducts of the respective conductors, the sleeve being formed with respective external groove means on each of its two end portions and having a hardness which is markedly greater than the hardness of the conductors with which it is intended to be used.

12. A sleeve as claimed in claim 11, wherein the sleeve has a hardness which is measurable on a hardness scale on which the hardness of the conductor core is not measurable.

13. A sleeve as claimed in claim 11 or 12, wherein the hardness of the sleeve is measurable on the Rockwell B scale.

14. A cable joint comprising respective end portions of two conductors received in the through cavity of a connector as claimed in any one of claims 8 to 10 the connector body being compressed to have substantially the same outer diameter as the conductors and such that material of the conductors is received in said groove means.

15. A joint as claimed in claim 14, wherein each of said conductors has a central oil duct, wherein opposite ends of a sleeve as claimed in claim 11, 12 or 13 are inserted in the respective ducts of the conductors, and wherein material of the conductors is received in said external groove means.

16. A method for manufacturing a jointing ferrule usable for joining cable conductors, said ferrule comprising at least one coaxial inner cavity provided with peripheral grooves turned inwards and separated by protuberandes, comprising employing for said ferrule a conductive metallic material having an electric resistivity which may be higher than that of the metallic material constituting the said cable core conductors, but showing a hardness, in a hardness scale, greater than that of said core materials, so as to ensure an unfailing penetration of the ferrule into the conductors whereby it is possible to increase the number of grooves and protuberances provided in said inner cavity of said ferrule to increase the number of the anchoring zones between ferrule and conductors.

17. A method as claimed in claim 16, wherein the protuberances separating the peripheral grooves inside the ferrule are rounded and/or flattened to avoid said protuberances cutting the surface of the conductors to interrupt their crystalline structure and lead thus to a weakening of their tensile strength and to an increase of their elongation.

18. A compression connector substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

19. A sleeve substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

20. A cable joint substantially as hereinbefore described with reference to Figure 6 or Figure 10 of the accompanying drawings.