US2364071A

US2364071A - Terminator

Info

Publication number: US2364071A
Application number: US381010A
Authority: US
Inventors: Weldon O Hampton
Original assignee: DELTA STAR ELECTRIC CO
Current assignee: DELTA STAR ELECTRIC Co
Priority date: 1941-02-28
Filing date: 1941-02-28
Publication date: 1944-12-05
Anticipated expiration: 1961-12-05

Description

Dec. 5, 1944. w. o. HAMPTON n 2,364,071

TERMINATOR Filed Feb. 28, 1941 da i 7 J9 :iff M 570 Z' ,Za/072 BY INVENTOR. am 6217/ Patented Dec. 5, 1944 2,364,071 TERMINATOR Weldon 0. Hampton,

Chicago, Ill., assignor toThe Delta, Star Electric Company, Chicago, Ill., a corporation of Illinois Application February 28, 1941, Serial No. 381,010

7 Claims.

This invention relates to potheads or termina- `tors and more particularly to sealed potheads and the manner of sealing the same.

A pothead or terminator is a structure used for terminating the end of an electric cable, particularly where connections are made between an underground cable and an overhead or aerial conductor. Such potheads, when used on medium or high voltages, must be maintained sealed against the entrance of air or moisture thereinto and against the escape of insulating compound therefrom. Any air or moisture that may enter the pothead may result-in a rapid deterioration of the insulation therein and consequent breakdown of the pothead. It is one of the objects of the present invention to provide a pothead wherein most, if not all, of the joints are soldered. It is a further objectief the present invention to provide a structure wherein most, if not all, of the soldered joints can be made at the factory under factory manufacturing conditions, as distinguished from the conditions prevailing in the eld where the pothead is ultimately to be located. In accordance with one of the principles of the present invention the pothead terminal to which the aerial conductor is to be connected consists cfa tube into which the bared end of the cablelconductor may be inserted. This tube is sealed to the end of the insulator first by a gasketed seal and then by an outer soldered joint.

Under normal conditions the outer soldered joint maintains the air-tight and liquid-tight condition of the terminator. However, should that factory soldered joint fail, the seal is still maintained by the gasketed joint.

It is a still further object of the present invention to provide a pothead of the above mentioned character, having a soldered joint between the terminal and the insulator, with an expansion joint between the cable conductor and the terminal stud so that the terminal stud is not subjected to alternate push and pull as the cable conductor expands or contracts under-changing thermal conditions.

It is a still further object of the present invention to provide an improved means for securing the base o f the insulator to its support in a manner which will provide a liquid-tight, airtight seal. The support or pothead base consists of a casting made preferably of aluminum. A thin copper tube isembedded in the cast aluminum and extends outwardly therefrom. This tube is embedded in the 'aluminum during the initial casting of the aluminum case by positioning the tube-in the mold and pouring the molten aluminum around the tube. The aluminum has a higher thermal coefficient of expansion and contraction than does the copper tube. Therefore, as the aluminum solidifies it shrinks tightly around the tube and thus forms a liquid-tight, air-tight seal between the tube and the aluminum casting. The copper tube is quite thin and yielding. The lower end of the pothead insulator has a skirt that fits very loosely into the copper tube, the space between the skirt and the tube being then filled with solder and a wiped soldered joint made between the outside of the tube and the insulator. The opposite end of the mounting case may have a similar copper tube similarly mounted therein and shaped for receiving a lead sheathed cable to which a wiped joint may be made.

It is a lstill further object of the present invention to provide an improved insulator and terminal stud assembly such as is adapted for potheads, transformer bushings, circuit breaker bushings, or the like, and which will be free of any air spaces in regions where an electrostatic field may be set up. This is particularly important in high voltage structures, since an air space which is subject to ionization or electric discharge causes considerable interference with radio reception. By providing a construction wherein the air spaces are reduced to a minimum and, where they do exist, are not' subjected to electric stress, I eliminate the electrostatic dis charges and ionization which is a source of radio interference.

The lattainment of the above and further objects of the present invention will be apparent from the following specification taken in conjunction with the accompanying drawing forming a part thereof.

In the drawing:

Figure 1 is an elevational view, in partial section, of a single conductor pothead constructed in accordance with the present invention;

Figure 2 is an enlarged View of a portion of the pothead of Figure 1;

Figure 3 is an elevational view of a three conductor pothead embodying the present invention;

Figure 4 is an end View of the pothead of Figure 3;

Figure 5 is an enlarged fragmentary sectional view taken along the line 5 5 of Figure 3;

Figure 6 is an elevational view, in partial section, showing a modied construction; and

Figure 7 is a fragmentary'sectional view illustratlng another type of mounting for the porcelain insulator.

Reference may now be had more particularly to the construction illustrated in Figures 1 and 2. The pothead includes a mounting casing I having integrally formed apertured mounting ears, or other mounting means, for mounting the pothead on a stationary structure. A tubular pot casing 2 extends from the bottom of the mounting casing I and is tapered at its lower end 3 for facilitating the making of a solder joint 4 between the po-t casing and the outer lead sheath of a sheathed cable 5. A circular tube 6 extends upwardly from the top of the mounting casing I. The tube B and the pot casing 2 are, preferably, thin spun copper tubes, cadmium plated. The lower end of the tube 6 is spun inwardly toV form an inwardly extending lip 'I around the periphery of the tube. The edge of the lip is rounded along smooth curves so that there are no sharp corners. The mounting casing I is, preferably, an

aluminum alloy, the preferred co-mposition being,

Per cent Silico-n .25 Manganese .50 Iron .60 Magnesium 3.75-4 Aluminum 1 94-95 1 Remainder.

The casing I is shrunk around the

tubes

2 and 6. To accomplish this result the

tubes

2 and 6 are mounted in the mold wherein the mounting casing I is poured so that the aluminum allo-y being poured comes into contact with the tube 2 and the tube 6. The material of the mounting casing has a higher thermal coefcient of expansion and contraction than do the

copper tubes

2 and 6 so that upon cooling of the cast metal of the mounting casing I, in the mold, the aluminum alloy shrinks tightly around the

tubes

2 and 6 whereby the tubes are firmly secured within the casing I to make a liquid-tight, air-tight seal between the tubes and the mounting casing. If desired, the

tubes

2 and 6 may constitute one continuous tube.

A pothead insulator 8, preferably of wet process porcelain, has a cylindrical skirt 9 at the bottom thereof which extends into the tube 6. Before the insulator is mounted in the tube 6 a terminal stud is to be assembled at the other end of the insulator. The terminal stud extends through an opening in the insulator. It is desirable that it make a snug fit in the bore through which it extends.` In molding insulators of this type it is exceedingly difficult to maintain a high degree of precision in the diameter of the hole. Usually there is a wide Variation in the hole diameters in different insulators. To overcome this difficulty it has heretofore been proposed to make the diameter of the hole in the insulator undersized and enlarge it to the exact diameter requiredr by roaming or the like. This is an expensive operation. To overcome this diiculty the bore or hole in the insulator is intentionally made oversized. It is then mounted in a moldl or die and a ring I of lead or other suitable soft bearing metal is cast in the interior of the bore of the insulator. The molded insulator is initially provided with a peripheral notch I0 in the bore thereof, which is filled by the cast metal I0 to key the ring I0 in place. The metal ring I0 is cast to exactly the requisite diameter for making a snug fit with the terminal stud to be thereafterinserted through the ring. 'I hel ring I0 terminates flush with the adjacent top surface of the insulator at the bore thereof, to constitute a seat at the inner peripheries of the gasket to be used, as will be presently explained.

At its lower end the cast metal ring I0 extends along the inner surface of the top of the insulator and continues downwardly along the peripheral wall of the insulator, as indicated at Ib. The lower edge of the metal Ib is smoothly curved to be free of any sharp corners. The portion IUb is cast integrally with the ring I0 so that there is no possible air space between the metal portion Ib and the adjacent insulator. The purpose of this extension will be more fully explained as thisy description proceeds.

The terminal stud for the pothead comprises a tube II of reduced diameter at its lower end, indicated at i2, to form a shoulder I3. A hooded disc washer I4 is fitted over the reduced end I2 of the terminal stud tube until the shoulder I3 rests against the top of the hooded dise washer. The washer makes a sealing f1t with the tube II. This may be accomplished either byl providing a shrink fit between the Washer and the tube, as by heating the hooded disc washer to expand the same and then sliding it into position on the tube, or it may be brazed or soldered on the tube at the shoulder I3. Thereafter an asbestos or the like sealing gasket I5 is placed on the top of the insulator 3 and then the end I2 of the tube II is lowered into the top opening of the insulator, passing through the lead liner IU with which it makes a snug fit. After the stud has been positioned on the insulator, a gasket I6,y a ring Il and a gasket I8 are strung on the lower end ofthe tube II. Thereafter the lower end I2- of the stud II is spun outwardly to form a flange 20 to retain the stud against Withdrawal. During the spinning operation the stud, tube II is pressed firmly towards the insulator to place the gasket I5 under high compression, and the` spun flange 2U is also forced towards the insulator to place the gaskets I6 and I8 under high compression. Thereafter the portion I2 of the stud II is permanently under tension and maintains gaskets I5, I6, and I8 under compression, thusl providing a liquid-tight, air-tight seal against the entry of air or moisture into the insulator by creepage along the outer top surface of the insulator.y The ring Il prevents outward spreading of the tube I2 above the part that is to constitute the ilange 2D as the tube flange is spun outwardly, so that the portion 2U forms a flange at, substantially right angles to the tube.

The hooded disc washer I4 includesL a downwardly extending flange 2I which loosely embraces the top of the insulator. The adiacent surface of the insulator is treated to render it receptive to solder as by forming a thin metallic glaze on the surface of the insulator. This metallic glaze is exceedingly thin and may comprise silver, platinum, or any other suitable exceedingly thin metal. Thereafter a soldered sealing' joint 22 is formed around the entire periphery of the flange 2I, between the flange and the metallic glaze at the top. of the insulator, securing the hooded washer I4 to the insulator. This maintains a liquid-tight, air-tight seal to prevent the entrance of air or moisture by creepage along the top of the insulator. However, .if the soldered joint 22 should ultimately commence to leak, the sealwill still be maintained by the compression of the gaskets I5, I6 and I8.

Prior to the operation of spinning the ange 20, or after that operation, if desired, a wedgeshaped ring 24 is secured inthe lower end of the ,tube I2, in any convenient manner as, for instance, by brazing.

The lower end 9 of the insulator 8 is then to be mounted in the tube 6. Before the insulator is mounted in the tube, a graphited asbestos gasket 2S is positioned at the bottom of the tube 6 resting on the inturned peripherally extending lip I. This gasket may be positioned in the tube 6 before or after the'metal I is cast around the tube. The outer surface of the lower end 9 of the insulator is metal glazed to render it receptive to solder. This metal glaze consists of an exceedingly thin lm of metal united to the glaze on the porcelain. The lower endrof the insulator 9 is then inserted into the tube 6 until the in- 'sulator comes to rest upon the graphited asbestos gasket.A The gasket thus serves to center the in sulator in the tube 6. Thereafter liquid solder 29 is poured into the space above the gasket 28. The solder unites with the metal glaze on the insulator and with the tube 6 to form a liquidtight, air-tight permanent seal between the tube and the insulator. To facilitate pouring of the solder the top inner edge of the tube 6 is beveled to act as a funnel. The top surface of the solder is smoothed off along a smooth curve extending between the top of the tube 6 and the metallic glazed surface of the insulator.

The structure comprising the mounting casing I, pot casing 2, tube 6, insulator 9, solder joint 29, terminal stud II, spun over the insulator, at 29 constitutes a factory assembled unit ready for use in the eld.

When the pothead is to be used in the field it isV mounted in place' and the bared end of the conductor of the cable is inserted through the opening at the lower end 3 of the pot casing 2 and pushed forward until the cable conductor 36 extends through and above the top of the terminal stud tube II. At this time the cable insulation has been bared to 3|, which is below the wedge-shaped ring 24. The lead sheath extends into the pot casing 2. Thereafter the wiped soldered joint II maybe made and then the upper end of the cable conductor 30 cut off flush with the top of the terminal stud tube II. The space between the conductor 30 and the inner periphery of the terminal stud tube II is then packed with silver wool or copper wool 32. The copper or silver wool is packed tight, resting on the wedge-'shaped ring 24 which ts fairly snugly, but not too snugly, around the conductor 30. A second wedge-shaped ring 33, which fits snugly in the terminal stud tube II, is then placed into the tube and around the end of the conductor 3U. This ring is to be used for compressing the silver or copper wool longitudinally and thus force it into firm pressure' engagement with the stranded conductor 30 and withthe stud I I. The

pothead is then lled with insulating oil or hot.

insulating compound in the usual manner, as through a pouring opening' in the pot casing 2, which opening is closedby a threaded plug 34. After the pothead has been filled with the insulating compound the clamping wedge ring 33 is forced downwardly by the threaded shank 36 of a cap 31, which threaded shank threads into the threaded terminal stud tube I I. The cap is forced into thetube until its square shoulder 38 seats on the topflat surface of the tube II. Thereafter a soldered sealing joint 39 is formed around the seating surface between-the cap 31 and the terminal stud tube.

The terminal stud tube I I is adapted to receive thelug of an aerial conductor. The aerial conductor may be connected to the tube I I in any desired well known manner. If desired a portion of the tube II below the top thereof may be of enlarged diameter and externally threaded to receive clamping means for clamping an aerial lug to the tube I I. However, the connection between the aerial conductor and the tube II is not a part of the present invention and may be made in any desired manner.

From the above descrip-tion it is apparent that the pothead of the present invention may be installed in the eld in a simple and reliable manner. -Only two soldered joints need be made in the eld, namely, the wiped joint 4 and the joint 39. The other soldered joints are all'made in the factory.

As the :pothead and the cable undergo thermal changes resulting in expansion and contraction of the cable conductor, the conductor 30 is free to slide in the pothead while maintaining firm electric Contact with the silver or copper wool 32. The electrical connection between the conductor 30 and the tube II thus constitutes a sliding or expansion joint. As a result of this arrangement the expansion or contraction of the cable does not produce an appreciable strain upon the tube II and the pothead. Since there are no appreciable alternating strains produced on thestud II by the cable conductor, the gaskets I5, I6 and I 8, and the wiped joint 22, are therefore not as likely to develop leaks as would be the case if the stud II were subjected to alternate substantial push and pull by the conductor. Should the soldered joint 22 develop a leak the gaskets I5, I6 and I8, being maintained under compression by the ange 20, would prevent leakage of air or moisture into the pothead.

When the pothead is filled with insulating compound it is not possible to vent the space above the flange 29. The metal portion Iilb is provided to prevent ionization or corona discharge in said space, since the metal portion Ib is vat exactly the same potential as is the terminal stud II. There can be no corona discharge in the air space between the metal portion Ib and the flange 28 or the ring I'I. This substantially reduces any radio interference. Furthermore, even aside from radio interference, corona discharge is productive of ozone which rapidly deteriorates the gasket material. By providing the shielding vportion Ib, which preventscorona discharge, I

thereby eliminate the possibility of production of ozone in the adjacent air space and consequent rapid deterioration of the gasket material. While I have shown the metal portion Ib as part of the cast metal ring I0, this portion may, if desired, consist of 'a thin metallic glaze or lm formed on the corresponding part of the insulator and in electric connection with the botto-m o-f the ring I0 and, therefore, in electrical connection with the terminal II, It is also to be noted that the solder at 22 is curved along a smooth curve and that the hooded disc 2| is also free of sharp corners. This eliminates the formation of streamers or electric discharge at the top of the insulator.

If any air becomes trapped between the bottom 9l of the insulator and the tube 6 this can be of no harmful consequence since here again opposite sides of the air space would be at the same electric potential and therefore there would Ibe no possibility for streamer or corona discharge through such air space.

In Figures 3 through 5 I have shown the present invention applied to a three conductor pothead. This pothead includes anvinverted, almost coni- 'cal housing 45 and a cover 46 both made, preferably, of an aluminum alloy such as the alloy of the mounting casing I. The housing 45 may have mounting ears. or other mounting means cast integrally therewith or may be mounted in place in any desired manner. The pot casing 2 is of a construction the same as the kpot casing 2 and adapted to receive a three conductor lead sheath cable 5 with which a wiped soldered joint 4 is made. The housing 45 is shrunk about the pot casing 2 by casting the metal of the housing 45 around the tube 2 which is placed in the mold previous to the casting operation, the same as the casing 2 is placed in the mold preparatory to the casting of the mounting casing I.

The housing 45 has a flat upper seating surface 41 for receiving the cover 46, a sealing gasket 48 beingV interposed between the cover and the housing. `The cast housing 45 is provided with indentations-IIS for receiving bolts 56 that thread into f tapped holes in a thickened portion 5I at the base of the cover 46, The bolts 50 are drawn exceedingly tight to secure the cover to the housing -45 and compress the gasket 48 suiiciently to maintain a liquid-tight, air-tight seal.

The cover 46 has a number of tubes 6', in this instance three, o-f copper or the like, identical with the tubes 6 of Figure 1, formed therein. The metal of the cover 46 is shrunk around the tubes 6- during the casting operation, the tubes being mounted in the mold and the metal of the cover 46 cast around the `tubes in the sam-e manner as the mounting casing I of Figure 1 is cast around the tube 6, Three insulators 8, of the same construction as the insulator of Figure l, extend into the tube 6 and are soldered thereto in the same manner as is illustrated in Figure 1. The insula- -tor 8 o'-v Figure 3 is of the same construction as .the insulator of Figure l and has a terminal stud tube II of the same construction and assembled together in the same manner as in Figure l. Insofar as these constructions are identical, similar reference numerals have been used and a repetition of the description is unnecessary at this point.

The cover 46 with the three insulators 8 mounted thereon each by a soldered joint 29 and each having a tubular terminal II secured in place at its opposite end, as illustrated in Figure l, constitutes a factory assembled unit. When the pothead is to be used the end of the cable is stripped of its sheath and the three conductors of the cable are fanned out, and the ends of thecon- Yductors bared of insulation the same as in Figure l. The end of the conducto-r is inserted through the housing 45 and the three ends of the conductors are passed through the respective insulatorsv and through the respective terminal tubes I I until the ends of the'conductors extend above the terminal tubes I I. ed to the casing 45. Thereafter the ends of the conductors are cut on flush with the tops of the A tubes I I and the electrical connections completed in the same manner as was previoush7 described in connection with the pothead of Figure 1, and

'the pothead is then filled with insulating oil or Then the cover is tightly boltin the same manner as the conductor 30 of the pothead previously described extends through the tube. In this construction the wedge-shaped ring 24 is located appreciably higher than in the construction previously described, but is otherwise of the same construction. Before insertion of the conductor through the insulator 8 the conductor 63 is wrapped with a number of turns 6.4 of asbestos thread to form a temporary seal between the conductor 63 and the ring 24. Thereafter the electrical connection between the conductor 63 and the tube II is effected by pouring hot solder 61 into the tube. Upon solidication the solder maintains the electrical connection between the conductor 63 and the tube. The expansion joint V6I is preferably of a construction such as illustrated in Figure 4 of my co-pending application, Serial No. 375,135, to which reference maybe had for a more complete description of this expansion joint. However, it is suicient for this purpose to state that the expansion joint consists of a conducting lug 'I0 bolted 0r otherwise secured in conducting relationship to the end of the cable conductor 60, which lug I0 has a flange 'Ii slotted for receiving flexible laminated conductors "I2, the opposite ends of which extend into slots in a flange I3 similar to the flange 1I, which flange has a conductor stud 63 extending therefrom as an integral part thereof instead of being bolted thereto as the cable conductor is bolted to the lug 10. As the cable conductor expands or contracts the lug I0 moves towards or way from the lug I4 but does not exert any appreciable push or pull on the lug '14, since the flexible laminations I2 bow to permit the iianges 'II-'I3 to approach or recede from one another. In this construction the mounting casing I is made in two ring parts, bolted together in the same manner as are the parts 45-46 of the pothead of Figure 3, with a suitable sealing gasket, such as the gasket 48, interposed. It is, however,` to be understood that any other means may be provided for bolting a pot casing 2 to a mounting casing or mounting ange that is cast around the tube 6. A bolted connection is used in order to permit positioning of the expansion joint in the insulator. A suitable type of bolted connection between thecasing I that is molded around the tube 6 of the pothead of Figure 6 and the pot casing 2 is shown in my pending application previously referred to, to which reference may be had.

Figure 'I shows an alternate means for securing the insulator in the tube 6. In this construction the lower end of the skirt 9 of the insulator is of slightly reduced diameter, as indicated at 80. This portion 80 together with the adjacent portion 8| of the insulator is metal glazed in the same manner as was previously described. A

Vwrapping of asbestos thread 82 is wrapped around the lower part of the insulator. Thereafter the insulator is inserted into the tube 6. The thread .82 is compressed by the tube and thus forms a temporary seal or stop for the lling of solder 2-9, which is thereafter poured into the space between the insulator and the tube 6. The solder unites the tube 6 with the metal glaze on the insulator 9. The space between the part 86 of the. insulator and the tube 6 will necessarily contain some air. This air is, however, free of any electric. potential difference since the metal glaze at 80 is at the same potential as is the adjacent surface of the tube 6. There is thus no possibility of corona or streamer formation in this air space. The lower end of the tube 6 is .curved along a smooth curve, as indicated at 84, to avoid any sharp corners and corresponding concentration of electric stresses at such places. It is thus apparent that when the insulator is mounted in its tube in the manner illustrated in Figure 7, there is no possibility of corona discharge.

In compliance with the requirements of the patent statutes I have here shown and described a few preferred embodiments of my invention. It is, however, to be understood that the invention is not limited to the precise constructions here shown, the same being merely illustrative of the principles of the invention. What I consider new and desire to secure by Letters Patent is:

1. In combination, a hollow insulator having a.

` stud receiving opening, a metal member overlying the insulator and surrounding the opening, a tubular stud extending through the member into the insulator and having a shoulder bearing against the outer side of the member, and a sealing joint between the member and the shoulder, the inner end of the stud being ared and held by the inner side of the insulator to secure the stud against retraction from the insulator.

2. In combination, a hollow insulator having a stud receiving opening, a metal member overlying the insulator and surrounding the opening, a tubular stud extending through the member into the insulator and bearing against the outer side of the member, the inner end of the stud being ilared to a diameter greater than that of the insulator opening to secure the stud against retraction from the insulator, and a soldered sealing `connection between the metal member and the insulator.

3. Electric apparatus comprising a hollow insulator having an opening therein, a terminal stud extending into said opening, a metal disc surrounding and making a shrunk sealing fit around the stud on the outside of the insulator, said stud having an outward projection on the part thereof inside of the insulator, and means cooperating with said projection for holding the stud against retraction from within the insulator, and a fused metal sealing joint between the outer periphery of the disc and the insulator.

4. Electrical apparatus comprising a hollow insulator open at both ends, a hollow terminal stud closing one end of the insulator, a metallic seal joining the stud to the insulator and fused to the insulator, a cable conductor extending into the insulator at the opposite end thereof and secured thereto and subject to alternate forces tending to move the cable conductor longitudinally in the insulator, electric connecting means between the conductor and interior of the terminal stud, said connecting means including an expansion joint for taking up expansion and contraction of the conductor and thus preventing the forces on the cable from producing alternate stresses in the fused metal joint, and means at that end of the stud which is on the outside of the insulator for obtaining access to the interior of the hollow stud to facilitate making of -the electric connections between the stud and the cable conductor.

5. A pothead comprising a hollow insulator, a

tubular terminal extending through the insula-` tor at one end thereof and sealed thereto by a fused metal seal, a conductor extending'through the insulator from the opposite end thereof and into the tubular terminal, and a lling of compacted conducting filaments between the conductor and the inside of the terminal, said conductor being longitudinally slidablein said lling, and means operable from outside of the pothead for maintaining said filling material under axial compression to expand the same radially into pressure contact with the conductor and with the tubular terminal.

6. Electric apparatus including a tubular terminal stud, a disc through which the stud extends, said disc making a sealing t with the stud, a supporting structure for the stud and disc, a fused metallic seal between the outer periphery of the disc and the supporting structure, a conductor terminating in the stud and subject to alternate forces tending to move it lengthwise of the stud, a filling of compacted conducting 1a` ments between the conductor and the stud for maintaining electrical connections between the two whilev permitting relative movement thereby preventing transmission of said alternate forces from the conductor through the stud and disc to the metallic seal between the disc and the support, and means operable from the side of the stud on the outside of the structure for compacting the conducting filaments.

7. Electric apparatus including a conducting tube open at both ends, a stationary support upon which the tube is immovably mounted, a cable conductor the end of which extends into one end of the tube and terminates in the tube and is of substantially smaller effective outside diameter than the inside diameter of the tube, a packed mass of intertwined conducting metallic laments in the space between the conductor and the tube and means operable from the opposite open end of the tube for compressing the conducting filaments axially to force them into pressure contact with the tube and with the conductor, said conductor and tube being relatively slidable while both are in pressure engagement with the conducting filament packing whereby thermal expansion and contraction of the cable conductor results in sliding of the end of the cable in the tube while the tube remains stationary on the support.

WELDON 0. HAMPTON.