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GB2212009A - Termination of mineral insulated electric cable - Google Patents

Termination of mineral insulated electric cable Download PDF

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Publication number
GB2212009A
GB2212009A GB8829840A GB8829840A GB2212009A GB 2212009 A GB2212009 A GB 2212009A GB 8829840 A GB8829840 A GB 8829840A GB 8829840 A GB8829840 A GB 8829840A GB 2212009 A GB2212009 A GB 2212009A
Authority
GB
United Kingdom
Prior art keywords
tube
button
sealing pot
disc
assembled sealing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB8829840A
Other versions
GB2212009B (en
GB8829840D0 (en
Inventor
Alan Postill
Tobias Furman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Balfour Beatty PLC
Original Assignee
BICC PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by BICC PLC filed Critical BICC PLC
Publication of GB8829840D0 publication Critical patent/GB8829840D0/en
Publication of GB2212009A publication Critical patent/GB2212009A/en
Application granted granted Critical
Publication of GB2212009B publication Critical patent/GB2212009B/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02GINSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
    • H02G15/00Cable fittings
    • H02G15/02Cable terminations
    • H02G15/04Cable-end sealings

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  • Insulating Bodies (AREA)

Abstract

A pre-assembled sealing pot 1, readily secured to a cut-back end of a mineral insulated electric cable 20, comprises a rigid metal tube 2 closed by an insulating ceramic or vitreous button 3 having throughbores 4 for passage of the conductors 21 of the cable. At the other end 7, the tube 2 fits closely over the cut-back sheath 22 of the cable 20. The tube 2 contains waterproof electrically insulating sealing compound 14 in a semi-liquid or jelly-like state. The button 3 has bonded to its end face a disc 8 of flexible electrically insulating material which has throughbores 9 in axial alignment with the throughbores 4 of the button and integral flexible sleeves 10 in axial alignment with the throughbores 9. <IMAGE>

Description

TERMINATION OF MINERAL INSULATED ELECTRIC CABLE This invention relates to the termination of mineral insulated electric cables, that is to say cables of the kind comprising at least one conductor insulated from a surrounding metal sheath, and where there is more than one conductor from the other conductor or conductors, by compacted mineral insulating powder, usually but not necessarily magnesium oxide.
Compacted mineral insulating powder is particularly vulnerable to water penetration and it is the general practice to protect an end of a mineral insulated cable against the ingress of moisture by a metal sealing pot which is screwed or otherwise secured to the cable sheath and which is filled with waterproof sealing compound. Assembly of a sealing pot on an end of a mineral insulated electric cable in such a way as to provide an effective waterproof termination requires a degree of skill and the time taken to terminate mineral insulated electric cables of a mineral insulated electric cable installation contributes to a substantial proportion of the overall cost of the installation.
It is an object of the present invention to provide an improved pre-assembled sealing pot for sealing a cut-back end of a mineral insulated electric cable, which pre-assembled sealing pot is simple and inexpensive and can be readily secured to an end of a mineral insulated electric cable by semi-skilled or unskilled personnel.
According to the invention, the improved pre-assembled sealing pot comprises a substantially rigid tube of metal or metal alloy which at one end is closed by a button of ceramic or vitreous insulating material secured within said end of the tube and having a throughbore or two or more throughbores for passage of the conductor or conductors of the cable, which at the other end is open and of such an internal diameter that said open end of the tube will fit closely over the cut-back sheath of the cable and which, between its closed and open ends, contains waterproof electrically insulating sealing compound in a semi-liquid or jelly-like state, wherein the button has bonded or otherwise permanently secured to its end face remote from said open end of the tube over substantially the whole of its surface area a disc of flexible electrically insulating material which has a throughbore or two or more throughbores in substantially axial alignment with the throughbore or throughbores of the button and which has integral with and upstanding from the exposed end face of the disc a flexible sleeve or flexible sleeves in substantially axial alignment with the throughbore or throughbores of the disc.
When an end of a mineral insulated electric cable is to be terminated by the improved pre-assembled sealing pot, the cable sheath is cut back and the exposed mineral insulation is removed to reveal a bare length of the or each conductor. The bare length of the or each conductor is introduced into the open end of the tube of the pre-assembled sealing pow and is passed through aligned throughbores of the button and disc so that the conductor protrudes from the aligned flexible sleeve and the open end of the tube is fitted closely over the cut-back sheath of the cable.
The tube of the pre-assembled sealing pot may be secured to the cut-back sheath of a mineral insulated electric cable by any co,venient technique which will ensure sound mechanical and electrical connection between the tube and the cable sheath. In one suitable technique that may be employed, the tube may have, at or near its open end, a circumferentially continuous groove for the reception of a circlip by means of which the pot can be secured to the cut-back cable sheath; in another suitable method that may be employed, the tube may be welded or brazed to the cut-back cable sheath.
Preferably, however, the part of the tube fitted over the cut-back sheath is so swaged or otherwise radially inwardly distorted throughout the whole or over parts of its periphery that the tube makes a sound mechanical and electrical connection with the sheath.
Where the cable has two or more conductors, by virtue of the fact that the sleeves of the disc of the pre-assembled sealing pot are flexible, it is a simple matter to ensure that the conductors of the cable protruding from the sealing pot are transversely spaced apart by an adequate distance.
Preferably, the button of ceramic or vitreous electrically insulating material and/or the tube of the improved pre-assembled sealing pot has means for positively preventing movement of the button with respect to the tube in a direction towards the open end of the tube. The button may have at its end remote from the open end of the tube an outwardly extending circumferentially continuous flange which bears against the end face of the tube but, preferably, the button throughout its axial length fits in the bore of the tube and the wall of the tube has an inwardly extending circumferentially continuous shoulder against which the button abuts. The inwardly extending shoulder may be inclined at an acute angle to the axis of the tube, e.g.
300, and the button may have a circumferentially continuous surface of complementary shape which will abut the shoulder.
To facilitate the introduction of the or each conductor of a mineral insulated cable into the or a throughbore of the button, over at least a part of the length of the or each throughbore nearer the open end of the tube, the internal diameter of the throughbore increases smoothly in a direction towards the open end of the tube to form, in effect, a throat into which a conductor can be readily guided.
The button of ceramic or vitreous material preferably is permanently secured within the bore of the tube by an appropriate cement or by crimping of the tube.
Preferably, the flexible disc throughout its axial length also fits in the bore of the tube so that the exposed end face of the disc and the end face of the tube lie in substantially the same plane. Bonding of the flexible disc to the exposed end face of the button may be effected by an appropriate cement or the flexible disc may be directly moulded on to said face of the button.
Preferably, also, the or each flexible sleeve of the flexible disc, has at or near its end remote from the disc, a circumferential wall which extends radially inwardly into the bore of the sleeve, the wall being of such an internal diameter that it will effect a wiping action on the or a conductor of the cable when the conductor is fed therethrough.
Between the button and the open end of the tube, preferably the wall of the tube has an inwardly extending circumferentially continuous shoulder against which the end face of the cut-back sheath of a mineral insulated cable will abut to limit the extent to which the tube can be fitted closely over the end of the cable.
Where it is desired to provide an earth conductor or tail electrically connected to the sheath of a mineral insulated cable, preferably the flexible disc has in its peripheral edge a recess which is in substantially axial alignment with a similar recess in the peripheral edge of the button and an elongate electric conductor is brazed or otherwise permanently electrically connected to the inner surface of the tube wall and extends through and protrudes from the aligned recesses in the button and disc. Alternatively, an elongate electric conductor suitable for use as an earth conductor is brazed or otherwise permanently electrically connected to the outer surface of the tube wall and extends lengthwise beyond the button and disc.
Any suitable waterproof electrically insulating sealing compound may be employed in the improved pre-assembled sealing pot but, where the sealing pot is required to pass the same tests with regard to its resistance to fire as a mineral insulated electric cable to which it is to be secured, preferably the sealing compound comprises a carrier liquid containing a filler, an anti-oxidant and a copper inhibitor.
Preferably, the button is made of a ceramic material such as alumina. The disc is preferably made of rubber or synthetic rubber or a high temperature elastomer, silicone rubber being preferred.
If desired, the open end of the tube of the improved pre-assembled sealing pot may be temporarily sealed by a thin disc of paper or plastics material which is so sealed to the open end of the tube that it can be readily peeled away when it is desired to use the pre-assembled sealing pot to terminate a mineral insulated electric cable.
The invention also includes a mineral insulated electric cable having an end terminated by the improved pre-assembled sealing pot hereinbefore described.
The invention is further illustrated by a description, by way of example, of a preferred pre-assembled sealing pot secured to an end of a mineral insulated electric cable with reference to the accompanying drawing, in which: Figure 1 is a sectional side view of the preferred pre-assembled sealing pot secured to an end of the cable, and Figure 2 is an end view, drawn on a larger scale, of the pre-assembled sealing pot shown in Figure 1 showing the position of the earth tail.
Referring to the drawing, the preferred pre-assembled sealing pot 1 comprises a rigid copper tube 2 which at one end is closed by a button 3 of alumina which abuts a circumferentially continuous inclined shoulder 13 extending inwardly of the tube 2 and which is permanently secured within the bore of the tube by an appropriate cement. The other end 7 of the tube 2 is open. The button 3 has four uniformly circumferentially spaced throughbores 4 for passage of the four conductors 21 of a mineral insulated electric cable 20. Over a part of the length of each throughbore 4 of the button 3 nearer the open end 7 of the tube 2, the internal diameter of the throughbore increases smoothly in a direction towards the open end of the tube to form, in effect, a throat 5.
The button 3 has bonded to its end face remote from the open end 7 of the tube 2 over the whole of its surface area a disc 8 of silicone rubber which has four throughbores 9 in axial alignment with the throughbores 4 of the button and which throughout its axial length also fits in the bore of the tube so that the exposed end face of the disc and the end face of the tube lie in the same plane. Integral with and upstanding from the exposed end face of the disc 8 are four flexible sleeves 10 in axial alignment with the throughbores 4 of the button 3. Each flexible sleeve 10 has, at its end remote from the button 3, a circumferential wall 12 which extends radially inwardly into the bore of the sleeve, the wall being of such an internal diameter that it will effect a wiping action on a conductor of the cable when the conductor is fed through the sleeve.The flexible disc 8 has in its peripheral edge a recess 16 which is in axial alignment with a similar recess (not shown) in the peripheral edge of the button 3 and an elongate electric conductor 17 is brazed to the inner surface of the wall of the tube 2 and extends through and protrudes from the aligned recesses in the button and disc to provide an earth tail. The tube 2, between the end closed by the button 3 and disc 8 and the open end 7, contains waterproof electrically insulating sealing compound 14 in a semi-liquid or jelly-like state. At the extremity of the open end 7 of the tube 2, the wall of the tube is folded outwardly back upon itself to form, in effect, a shoulder 17 against which a swaging tool (not shown) can be positioned.The internal diameter of the shoulder 17 increases smoothly in a direction towards the open end 7 to form, in effect, a throat 18 which facilitates fitting of the tube on to the cut-back end of a mineral insulated cable. The open end 7 of the tube 2 may be temporarily sealed by a thin disc of paper or plastics material (not shown) which is so sealed to the open end of the tube that it can be readily peeled away.
When it is desired to apply the pre-assembled sealing pot to the cut-back end of a mineral insulated electric cable 20 having four conductors 21 electrically insulated from a surrounding copper sheath 22 by compacted mineral insulating powder 23, the thin disc of paper or plastics material (if present) temporarily closing the open end 7 of the tube 2 is removed and the protruding cable conductors 21 are inserted into the open end of the tube and into the throats 5 of the throughbores 4 of the button 3 and through the throughbores 9 of the disc 8 and the sleeves 10, the radially inwardly extending circumferential wall 12 of each sleeve wiping any waterproof electrically insulating sealing compound from the conductor as it passes therethrough.Insertion of the cut-back end of the cable 20 into the tube 2 is continued until the end face of the cable sheath 22 abuts a radially inwardly extending shoulder 15 in the wall of the tube. The tube 2 is then secured to the cut-back cable sheath 22 of the cable by means of a swaging tool (not shown) which is positioned against the shoulder 17 and which is used to distort the tube radially inwardly over parts 19 of its periphery to make a sound mechanical and electrical connection with the cable sheath 22.
The improved pre-assembled sealing pot of the present invention has several important advantages. It can be easily mass produced and can be readily secured to an end of a mineral insulated electric cable by semi-skilled or unskilled personnel. It is of slim, attractive appearance and can be pre-packed in a strip or bag of, say, cellophane. The flexible sleeves of the flexible disc bonded to the button of ceramic or vitreous material provide for further sleeving and/or bending of the cable conductors, as required.

Claims (21)

CLAIMS:
1. A pre-assembled sealing pot for sealing a cut-back end of a mineral insulated electric cable, which sealing pot comprises a substantially rigid tube of metal or metal alloy which at one end is closed by a button of ceramic or vitreous insulating material secured within said end of the tube and having a throughbore or two or more throughbores for passage of the conductor or conductors of the cable, which at the other end is open and of such an internal diameter that said open end of the tube will fit closely over the cut-back sheath of the cable and which, between its closed and open ends, contains waterproof electrically insulating sealing compound in a semi-liquid or jelly-like state, wherein the button has bonded or otherwise permanently secured to its end face remote from said open end of the tube over substantially the whole of its surface area a disc of flexible electrically insulating material which has a throughbore or two or more throughbores in substantially axial alignment with the throughbore or throughbores of the button and which has integral with and upstanding from the exposed end face of the disc a flexible sleeve or flexible sleeves in substantially axial alignment with the throughbore or throughbores of the disc.
2. A pre-assembled sealing pot as claimed in Claim 1, wherein the button of ceramic or vitreous electrically insulating material and/or the tube of the sealing pot has means for positively preventing movement of the button with respect to the tube in a direction towards the open end of the tube.
3. A pre-assembled sealing pot as claimed in Claim 2, wherein the button throughout its axial length fits in the bore of the tube and the wall of the tube has an inwardly extending circumferentially continuous shoulder against which the button abuts.
4. A pre-assembled sealing pot as claimed in Claim 3, wherein the inwardly extending shoulder is inclined at an acute angle to the axis of the tube and the button has a circumferentially continuous surface of complementary shape which will abut the shoulder.
5. A pre-assembled sealing pot as claimed in Claim 2, wherein the button has at its end remote from the open end of the tube an outwardly extending circumferentially continuous flange which bears against the end face of the tube.
6. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein, over at least a part of the length of the or each throughbore of the button nearer the open end of the tube, the internal diameter of the throughbore increases smoothly in a direction towards the open end of the tube to form, in effect, a throat.
7. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein the button is permanently secured within the bore of the tube by an appropriate cement or by crimping of the tube.
8. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein the flexible disc throughout its axial length also fits in the bore of the tube so that the exposed end face of the disc and the end face of the tube lie in substantially the same plane.
9. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein bonding of the flexible disc to the exposed end face of the button is effected by an appropriate cement.
10. A pre-assembled sealing pot as claimed in any one of Claims 1 to 8, wherein the flexible disc is directly moulded on to the exposed end face of the button.
11. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein the or each flexible sleeve of the flexible disc has, at or near its end remote from the disc, a circumferential wall which extends radially inwardly into the bore of the sleeve, the wall being of such an internal diameter that it will effect a wiping action on the or a conductor of the cable when the conductor is fed therethrough.
12. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein, between the button and the open end of the tube, the wall of the tube has an inwardly extending circumferentially continuous shoulder against which the end face of the cut-back sheath of the cable will abut to limit the extent to which the tube can be fitted closely over the end of the cable.
13. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein the flexible disc has in its peripheral edge a recess which is in substantially axial alignment with a similar recess in the peripheral edge of the button and an elongate electric conductor suitable for use as an earth conductor is brazed or otherwise permanently electrically connected to the inner surface of the tube wall and extends through and protrudes from the aligned recesses in the button and disc.
14. A pre-assembled sealing pot as claimed in any one of Claims 1 to 12, wherein an elongate electric conductor suitable for use as an earth conductor is brazed or otherwise permanently electrically connected to the outer surface of the tube wall and extends lengthwise beyond the button and disc.
15. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein the waterproof electrically insulating sealing compound comprises a carrier liquid containing a filler, an anti-oxidant and a copper inhibitor.
16. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein the button is made of alumina.
17. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein the disc is made of rubber or synthetic rubber or of a high temperature elastomer.
18. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein the open end of the tube of the sealing pot is temporarily sealed by a thin disc of paper or plastics material which is so sealed to the open end of the tube that it can be readily peeled away.
19. A pre-assembled sealing pot as claimed in any one of the preceding Claims, wherein, at the extremity of the open end of the tube, the wall of the tube is folded outwardly back upon itself to form a shoulder whose internal diameter increases smoothly in a direction towards the open end of the tube to form, in effect, a throat.
20. A pre-assembled sealing pot for sealing a cut-back end of a mineral insulated electric cable substantially as hereinbefore described with reference to and as shown in the accompanying drawing.
21. A mineral insulated electric cable having an end terminated by the pre-assembled sealing pot as claimed in any one of the preceding Claims.
GB8829840A 1987-12-21 1988-12-21 Termination of mineral insulated electric cable Expired - Lifetime GB2212009B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB878729700A GB8729700D0 (en) 1987-12-21 1987-12-21 Termination of mineral insulated electric cable

Publications (3)

Publication Number Publication Date
GB8829840D0 GB8829840D0 (en) 1989-02-15
GB2212009A true GB2212009A (en) 1989-07-12
GB2212009B GB2212009B (en) 1991-08-14

Family

ID=10628793

Family Applications (2)

Application Number Title Priority Date Filing Date
GB878729700A Pending GB8729700D0 (en) 1987-12-21 1987-12-21 Termination of mineral insulated electric cable
GB8829840A Expired - Lifetime GB2212009B (en) 1987-12-21 1988-12-21 Termination of mineral insulated electric cable

Family Applications Before (1)

Application Number Title Priority Date Filing Date
GB878729700A Pending GB8729700D0 (en) 1987-12-21 1987-12-21 Termination of mineral insulated electric cable

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GB (2) GB8729700D0 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0894353A4 (en) * 1996-04-16 2001-04-04 Boyd B Moore Underground well electrical cable transition, seal and method
US9705302B1 (en) * 2015-12-28 2017-07-11 X Development Llc Combined electrical and mechanical potted termination for a center strength member cable

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0894353A4 (en) * 1996-04-16 2001-04-04 Boyd B Moore Underground well electrical cable transition, seal and method
US9705302B1 (en) * 2015-12-28 2017-07-11 X Development Llc Combined electrical and mechanical potted termination for a center strength member cable

Also Published As

Publication number Publication date
GB8729700D0 (en) 1988-02-03
GB2212009B (en) 1991-08-14
GB8829840D0 (en) 1989-02-15

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Legal Events

Date Code Title Description
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19931221