US3244796A - Mineral-insulated cable connector - Google Patents

Description

April 5, 1966 F. B. STARK ETAL 3,244,796

MINERAL-INSULATED CABLE CONNECTOR Filed Sept. 12, 1965 Sheets-Sheet l 2 is: W

INVENTORS r/m/m a 577%? flan 4.40 6. 1400/6 19 7' TOR/YE Y5 April 5, 1966 F. B. STARK ETAL MINERAL-INSULATED CABLE CONNECTOR 2 BMW 1 054 e T. m W56 w WW W 5 Filed Sept. 12, 1963 14 T TOR/V5 Y5 United States Patent 3,244,796 MINERAL-INSULATED CABLE CONNECTOR Frank B. Stark, Harrisburg, and Ronald C. Laudig, Camp Hill, Pa., assignors to AMP Incorporated,

Harrisburg, Pa.

Filed Sept. 12, 1963, Ser. No. 308,567 Claims. (Cl. 174-77) This invention relates generally to electrical connectors, and in particular to electrical fittings for terminating and sealing the ends of metal-sheathed mineral-insulated cables.

The expression mineral-insulated cable, as used herein, denotes a type of electrical cable or conduit comprising a seamless tubular metallic sheath, usually copper, which houses one or more conductors, the latter being maintained in a spaced insulated relationship to each other and to the sheath by an especially electrically inert refractory mineral substance, such as powdered magnesium oxide. This type of cable is not only highly resistant to moisture and various fluids, but is also highly resistant to the effects of temperature changes.

These properties make this type of cable highly desirable for use under hazardous, corrosive, highly damp, or other conditions where its particular properties can be particularly utilized, e.g. in chemical plants or on board ships. Unfortunately this type of cable is very expensive relative to ordinary wiring, and most previous terminating connectors for this type of cable required extensive stripping back of the outer copper sheath and removal of the mineral-insulation to expose the conductors to serve as leads from the point of termination in to the switch on other apparatus which is within the cable box. The advantages of this type of cable are best realized when fluid tight fittings are used to terminate it to cable boxes, so prior connectors often were forced to use cumbersome potting procedures to effect tightly sealed fittings.

Consequently, it is an object of this invention to provide an electrical connector for mineral-insulated metalsheathed cable which requires only a minimal amount of insulation stripping to effect the termination, and advantageously this invention replaces the long bared cable conductors by inexpensive leads securely spliced thereto.

Another object is to provide such a connector which simply and effectively seals out fluids, e.g. moisture and combustible gases, from the mineral insulation and especially from the conductors therein, which also is tem perature resistant, and which resiliently supports the leads exiting from said connector against unduly localized and harmful flexing.

Still another object is to provide a termination connector which is simply and quickly applied without any potting and yet results in a strong, well-sealed connection.

Another advantage is that this connector is able to be easily and quickly applied, requires for application only tools which are readily available and are of the type normally found in an electricians kit, that it may come substantially preassembled ready for application, that it may provide a grounding path for the, cable sheath, and that it is readily adaptable to various use requirements.

Other objects and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings in which there "ice is shown and described a preferred embodiment of the invention; it is to be understood, however, that this embodiment is not intended to be exhaustive nor limiting of the invention, but is given for purposes of illustration in order that others skilled in the art may more fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify it in various forms, each as may be best suited to the conditions of a particular use.

In the drawings:

FIGURE 1 is a perspective view of our preferred embodiment, partially installed;

FIGURE 2 is an enlarged longitudinal section of the terminating connector of FIGURE 1, aligned as it should appear just prior to actual assembly to the prepared cable end;

FIGURE 3 is a partially sectioned longitudinal view similar to FIG. 2, showing the connector partially applied with the anti-burr bushing in place and with the leads spliced to the cables conductors;

FIGURE 4 is a view generally similar to FIGURE 3, but showing the completed connector prior to installation; and FIGURE 5 is a view generally similar to FIGURE 4, showing the completely installed connection within its protective collar afiixed therethrough to a cable box.

The preferred embodiment of the present invention as shown in FIGURES 1 to 5 is a terminating connector 10 for separately splicing leads 12 to corresponding conductors 14 of a mineral-insulated metal-sheathed cable 16 while sealing the end of cable and insulating the resulting splices.

As shown in FIGURE 2, in the preferred embodiment the terminating connector 10 includes the subcombination 17 of a resilient insulating spacer 18 with an outer shell 20 and with leads 12 threaded through longitudinal passages 24 therein, which leads 12 are advantageously vinyl insulated (according to common practice) and are each crimp-terminated beyond the neck portion 26 of shell 20 with a brass butt splice connector 28. This subcombination 17 is generally supplied to the customer in pre assembled form as illustrated at the right in FIGURE 2, together with a brass protective support collar 30, a split-ring wedge 32, and cap nut 34. As an added builtin safety feature a ceramic bushing 37 is included being shaped to force the customer during installation to expose and remove any conductive burrs resulting from stripping back the metal sheathing 36 which might otherwise cause a short between the conductors 14 and the sheathing 36.

In the preferred embodiment the application of the terminating connector 10 can best be described by the following example. First, the cable 16 is prepared by stripping back enough of the metal sheathing 36 and the mineral insulation 38 to expose a length of the solid copper conductors 14 sufi'icient to fit into the splice connectors 28. See FIGURE 2. This stripping back must be far enough to permit access of a crimping tool to the splice connectors 28. If the anti-burr bushing 37 is to be used, then the mineral insulation 38 should be removed from under the mineral sheathing 36 to a depth sufiicient to expose any potentially shorting metallic burrs which result from cutting the sheathing, thus enabling these burrs to he removed. For example, in a quarterof-an-inch mineral-sheathed cable the metal sheathing 36 would be stripped back about one-half inch and the mineral insulation 38 would be further removed from under the remaining sheathing to a depth of about an eighth of an inch as ilustrated in FIGURE 2. Second, with the cap nut 34, the split-ring wedge 32 and the collar 39 having been slipped onto the cable over a prepared end, oriented as illustrated in FIGURE 2, and with the ceramic bushing 37 pushed over the bared conductors 14 and pressed into the void left after the removal of the mineral insulation; thereafter, the splice connectors 28 are slipped over and securely crinrped to these bared conductors 14, as shown in FIGURE 3. Next, the shell 20 containing the resilent insulated spacer 18 is slid along the nowspliced leads 22 until the neck portion 26 of theshell 20 has been snugly positioned over the bushing 37 and the end of cable 16, with" the leading face ofthe resilient spacer 1 3 butted up against bushing- 37 and with the splices completely encased within the longitudinal passages 24 of spacer 18. With the sub-assembly 17 in this position, a double O-cri-mp is applied to the necl' portion 26 sealingly to gripthe shell 20 and the par carried therein to cable 16. Anotherdoiible O cri'ni p 1 a lied to the body portion 400i the shell 20 forcrbly'to s the resilient spacer 18 against thebu'shing'M and around splices 29 thereby sealing the 6nd or the Cable 16 and the splices 29. See FIGURE {1. Finally, as indicated by the arrows in FIGURE 4,-- the brass collar 3'0 issli'd over the c'rimpe'd shell until it's shoulder 41 butts against the corresponding shoulder 43 of the-shell, the Wedge 32 is pushed up against the narrow end 45 of the'colla'r 30 to engage an inwardly sloping cam surface 42 on the insidediameter ofthis narrow end portion 45-, anus then the cap nut 34 is drawn over this wedge 32 and screwed onto the threaded end of this narrow portion: 45 forcing the wedge against the cam surface 42 and therefore radially constricting this split-ringaround cable 1-6- until the split faces are drawn together into an air-"tight seal. anchoring the collar 30 to cable 16. The broader end portion- 44' of the collar 30 advantageously has a tapered self-sealing thread which is adapted to be screwed' into an appropriate hole in the cable box 46. Asillust'rated' the central portion of this collar 30 is formed into a hexagonal nut to facilitate screwing this collar ihto the cable box. Advantagcously' this collar 30' would be mounted on the cable box- 46 befofe the cap nut 34: and wedge 32 are applied to its other end.

The resilient insulating spacer 18 is shaped to" fit and be held snugly within the body portion 40 fv the shell- 20 and has longitudinal passages 24 running through it which equal in number, and align with respective conductors 14. These passages 24 are just large enough to accommodate leads 12. This spacer 18 might well be made from any elastomer having the propertiesset forth below. It has been found that silicone rubbers or neoprene rubber are particularly useful for this purpose. The particular ones of the properties below which determinet-he elastorner chosen for the jobwill, of course, depend upon the ens vironment' in which it is to be used; If extreme heat conditions are anticipated then naturally a rubber which preserves its elasticity without deterioration in= spite of thigh temperatures will be highly desirable.-- Furthermore, since this spacer 18 will be subjected to crimping it is important that the elastomer employed should retain its desirable properties after powerful squeezing.- It is desirable that the elastomer used should-have a compression set of under 20% of the original deflection. This will ensure that sufficient resiliency is retained by the spacer 18 after crimping to maintain an ifcctive seal. Related to this low compression set, i.e. resilient displacement with minimal permanent defo'rmati'om. is the ability of the material to resistcreep. If an eifective seal is to be maintained for an extended period, the tendency of the material to creep should be minimal. There are available on the market special w compression setsilicon'e rubbers which are recommended for use in the: tempera ture range of from -13() to +500 F. and even short 1 flashes of significantly higher temperature such as might be encountered under hazardous conditions; When this is combined with the added features of good moisture resistance, good electrical properties maintained over the entire operable temperature range, and good resistance to lubricating oils and hydraulic fluids; it can be appreciated that these special low compression set silicone rubbers are highly desirable for use in the spacer 18. Examples of commercially available low compression set organopolysiloxane rubbers include: Dow Corning Corporations Silastic 8-2096 U, 8-2097 U, and S2098 U, and General Electric Companys SIS-36 2, SE-372, SE+3701 and S-E-382. These silicone rubbers have the [following generalized formula: -(R SiO where the R-groups are" usually methyl, but in the low compression set silicone rubbers these R-groups are reputed to have a. vinyl form which encourages cross-linking in the actual polymer; The compression set test procedures have been well standardized, see ASTM vD 39 5-55, Method B. The general requirements tor H-igh- Temperature Resistant and Low Compression Set silicone rubbers have been thoroughly set forth in the military specification: Mil. R. 84-7 D; Class II B; I p The shell 20 is advantageously formed or a tube of r with one end rolled down to a neck portion 26 shoulder 48 and with the other end roll'e o-ve'r curved fet'aining lip 48, the latter for gripping and tent fling the spacer 18 between it and the shoulder 43 within the" body portion" 40 of this shell 261- As indi= eaten" earlier the neck portion 26 has an inside diameter slightly larger than the outside diameter of the cable 1*6 to enable a sealing O-crim'p to be effected therebetween. The access orifice 50 defined by lip 43 at the end oh the shell serves an important function in permitting the contrpres'sion of the spacer 18 while being c'rimped to remain withinthe safe lirn'its by acting as a safety valve such that any over-compression will be avoided by a: protrusion of the-elaston'ierout of the open end 50. This safety valve eifect important because it has been hound that. exc'essive compression of elastomers generally reduces their expectancy severely, particularly at elevated temperatures Itis a well known fact that silicone rubber when completely sealed from the air will tend to revert tov powder or paste at relatively low temperature elevations. Fr"- completely sealed at 300 F., such reversion will result; while even slight ventilation will norm-ally eliminate reversion up to 500 F. Thus, this access orifice permitsbreatlring necessary at high temperatures; For the foregoing reasons, the lip 48 should be' only just large enough to contain the spacer within the shell. Another advantage or having this opening 50 a generous size is so that the leads 12, if subject to' substantial flexing, areresiliently supported by the spacer and are not subject to chafing against the metallic lip 48.

The spacer =l'8' should be sufliciently wide such that the compression due to crimping will not be excessive at the point. or crimp; This is to avoid spreading this dielectric too thin and to avoidlocalized deterioration resulting from excessive com ression as was mentioned above This invention can be adapted for use with a tninerah insulated cable having any number or conductors and with any size of such cable. Also the metal collar 3'0 may be constructed to conform to safety specifications to ensure an explosion-proof termination for use in hazardous conditions.

Changes in construction will occur to those skilled in the art andvar-ious apparently different modifications and embodiments may be made without departing from the scope ofthe invention. The matter set forth in the foregoing description and accompanying drawings is offered byway of illustration only.- The actual scope of the invent-ion isintended tobe defined in the foliowingclaims when viewed in their proper'perspective against the prior art.

having a generous access orifice at its opposite We claim:

1. A device for terminating at a cable box and the like, a mineral-insulated metal-sheath cable having at least one conductor, which device comprises a lead for each conductor spliced onto a short bared portion of the corresponding conductor, a resilient insulating spacer individually enclosing, mechanically supporting, and dielectrically separating within longitudinal passages said spliced connections from each other and any further adjacent conducting material, a copper shell formed with a cylindrical neck portion extending back over said cable and sealingly crimped thereto and with a cylindrical body portion having its free end cur bed inwardly sufli-cient to contain said resilient spacer Within said body portion while leaving a generous access orifice for said leads and tfurther said body portion being crimped to form the resilient spacer into any substantial remaining voids with the shell.

2. A device for terminating leads to a mineral-insulated metal-sheath cable having at least one conductor, which device comprises a resilient insulating spacer having at least one passage therethrough, each such passage positioned to align with a respective conductor of said cable and shaped to enclose and insulate a splice made between one of said leads and a bared end portion of the corresponding conductor; a shell having said spacer held therein and having means adapted to fix one end of said shell in a sealing relation to said cable, said shell further end, whereby crimping said shell with it positioned with said resilient spacer insulating around said splices and adjacent to said cable and with it securely sealed to said cable forms the spacer into any substantial remaining voids within the shell.

3. A device as described in claim 2 wherein said resilient insulating spacer is composed of a temperature and creep resistant rubber.

4. A device for terminating leads to a mineral-insulated metal sheath cable having at least one conductor, which device comprises a resilient insulating spacer having at least one passage therethrough, each such passage positioned to align with a respective conductor of said cable and shaped to enclose and insulate a splice made between one of said leads and a bared end portion of the corre sponding conductor; a shell formed with a neck portion being shaped to fit over said cable whereby a crimp applied thereto seals said shell to said cable and with a body portion containing said spacer therein and having its free end curved inwardly sufficient to retain said spacer While leaving a generous access orifice, said body portion being adapted to receive a crimp after said shell and its spacer have been positioned over leads crimped to said conductors and said shell has been securely crimped to said cable in order thereby to form the spacer into any substantial remaining voids with the shell.

5. A device for terminating at a cable box and the like, a mineral-insulated metal-sheath cable having at least one conductor, which device comprises a lead for each conductor spliced onto a short bared portion of the corresponding conductor, a resilient insulating spacer individually enclosing, mechanically supporting, and dielectrically separating within longitudinal passages said spliced connections from each other and any further adjacent conducting material, a copper shell formed with a cylindrical neck portion extending back over said cable and sealingly crimped thereto and with a cylindrical body portion having its free end curved inwardly sufiicient to contain said resilient spacer within said body portion while leaving a generous access orifice for said leads and further said body portion being crimped to form the resilient spacer into any substantial remaining voids with the shell, having a portion of its conductors stripped bare, additionally has some mineral insulation removed from under the metal-sheath of a predetermined depth suflicient to ensure that any burr remaining after the stripping of the metal-sheath is exposed and removed, and a solid dielectric bushing having longitudinal passages passing the bared conductors therethrough and spaced at least to plug the void left by said removed mineral insulation and providing a face for said resilient spacer to butt up against.

6. A device for terminating a mineral-insulated metalsheath cable having at least one conductor through a hole in a rigid metal member such as a control panel, cable boxes and the like which device comprises a lead for each conductor spliced onto a short bared portion of the corresponding conductor, a resilient insulating spacer individually enclosing, mechanically supporting, and dielectrically separating within longitudinal passages said spliced connections from each other and any further adjacent conducting material, a copper shell formed with a cylindrical neck portion extending back over said cable and sealingly crimped thereto and with a cylindrical body portion having its free end curved inwardly sufiicient to contain said resilient spacer within said body portion while leaving a generous access orifice for said leads and further said body portion being crimped to form the resilient spacer into any substantial remaining voids with the shell, metal collar means protectively enclosing said crimped shell and secured to said rigid metal member, and means anchoring said cable to said member through said collar means thereby to protect said splices from undue tensile strain.

7. A terminating device for mineral-insulated metalsheath cable having at least one conductor which comprises an insulated lead for each conductor, a splice connector crimped to one end of each lead wire with the free end of the connector adapted to receive a crimp onto a short bared portion of the corresponding conductor of the cable to be terminated, a resilient insulating spacer having longitudinal passages for accommodating said respective leads and adapted to slip over said splice connectors after the latter have been crimped to said bared conductors thereby to enclose and insulate the resulting splices, a shell formed with a neck portion adapted to accommodate said cable and to receive a sealing crimp onto said cable and with a body portion having its free end curved inwardly sufiicient to contain said resilient spacer within said body portion while leaving a generous access orifice for said leads, said body portion being adapted to receive a crimp after said shell has been positioned with said resilient spacer insulating around said splices and adjacent to said cable and with its neck portion securely crimped to said cable in order thereby to form the spacer into any substantial remaining voids within the shell said spacer being positioned within said shell and carrying said leads within its longitudinal passages.

8. A device as described in claim '7 wherein said resilient insulating spacer is composed of a rubber chosen from the group consisting of silicone rubber and neoprene rubber and which is temperature and moisture resistant and has a compression set of less than 20% of the original deflection.

9. A device for terminating at a cable box and the like, a mineral-insulated metal-sheath cable having at least one conductor, which device comprises an insulated lead for each conductor, a solderless connector crimp-splicing each lead wire onto a short bared portion of the corresponding conductor, a resilient insulating spacer individually enclosing, mechanically supporting, and dielectrically separating within longitudinal passages said splice connectors and any attached bare wire from each other and any further adjacent conducting material, a copper shell formed with a cylindrical neck portion extending back over said cable and sealingly crimped thereto and with a cylindical body portion having its free end curved inwardly suflicient to contain said resilient spacer within said body portion while leaving a generous access orifice for said leads and further said body portion being crimped to form the re- 7 sili'enf spacer into any substantial remaining voids with the shell.

10. A device as described in claim 9 wherein said resilient insulating spacer is composed of a rubber chosen from the group consisting of silicone rubber and neoprene rubber and which is temperature resistant and has a compression set of less than 20% of the original defiection.

Iieferences Cite d the Examiner UNITED STATES PATENTS Q iN AT M 11/1950 (311661 31115111. 12/19 52 Great Qritairi. 11/1961 Great Britain.

RQBERT K. SCHAEFER, iri'hidzj 6x11511267.

LARAMIE E. ASKIN, Examiner. w. B. FREDRICKS, Assist dni Exdmini.

Claims (1)

1. A DEVICE FOR TERMINATING AT A CABLE BOX AND THE LIKE, A MINERAL-INSULATED METAL-SHEATH CABLE HAVING AT LEAST ONE CONDUCTOR, WHICH DEVICE COMPRISES A LEAD FOR EACH CONDUCTOR SPLICED ONTO A SHORT BARED PORTION OF THE CORRESPONDING CONDUCTOR, A RESILIENT INSULATING SPACER INDIVIDUALLY ENCLOSING, MECHANICALLY SUPPORTING, AND DIELECTRICALLY SEPARATING WITHIN LONGITUDINAL PASSAGES SAID SPLICED CONNECTIONS FROM EACH OTHER AND ANY FURTHER ADJACENT CONDUCTING MATERIAL, A COPPER SHELL FORMED WITH A CYLINDRICAL NECK PORTION EXTENDING BACK OVER SAID CABLE AND SEALINGLY CRIMPED THERETO AND WITH A CYLINDRICAL BODY PORTION HAVING ITS FREE END CURBED INWARDLY SUFFICIENT TO CONTAIN SAID RESILIENT SPACER WITHIN SAID BODY PORTION WHILE LEAVING A GENEROUS ACCESS ORIFICE FOR SAID LEADS AND FURTHER SAID BODY PORTION BEING CRIMPED TO FORM THE RESILIENT SPACER INTO ANY SUBSTANTIAL REMAINING VOIDS WITH THE SHELL.

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