US1861404A - Insulated electrical conductor - Google Patents

Description

May 31, A1932. H. o. ANDERSON INSULATED ELECTRICAL CONDUCTOR Original Filed June 19, 1928 ation'of the circuits in which Patented May 3l, 1932 HERBERT o. ANDERSON, or NEW HAVEN,

CONNECTICUT, A SSIGNOR TO ROCKBESTOS 4 PRODUCTS CORPORATION, 0F NEW HAVEN, CONNECTICUT INSULATED ELECTRICAL CONDUCTOR Original' application nled .Tune 19, 1928, Serial No. 286,637, Patent No. 1,840,282, dated January 5, 1932, and in Canada September 14, 1928. Divided and this application led August 22, 1930. Serial This application relates to insulated electrical conductors and is a division of my application Serial No. 286,687 iled June 19, 1928, which has resulted in Patent No. 1,840,282 of January 5, 1932.

The invention is especially directed to an improvement in insulated electrical conductors for Wiring switchboards, but conductors of my invention may be used or Wiring elevator control panels, car heating circuits, power and lighting circuits, resistance grids, rheostats, track signal systems, electric furnaces, and mining machinery, and for other service whereA an insulated conductor which is heat, moisture, acid, flame, oil and gas proof, is desirable.

The insulated conductors generally provided heretofore for switchboard and similar uses, have been provided with insulating sheaths which were likely to crack and open up so as to expose the conductor, especially when the conductor was sharply bent. Also, many of the coverings heretofore provided were not llame-proof, and would ignite and either burn or disintegrate upon the application for a short period of time, of a flame. These covers, therefore, did not insure permanence of insulation under eXtreme conditions, and could not berelied upon in emergencies that required a' continua-tion of the operthe Wires were located. y

One object of this inventionis to provide a thoroughly insulated and ireproof electrical conductor, which will have high mechanical strength and ruggedness.

Another object of this invention is to provide an insulated electrical conductor, hav ing an insulating covering of high dielectric strength, substantially fiameproof and moisture resistant, said covering being characterized by its permanence and great resistance to strains, produced by .bending of the conductor, that would destroy the insulating properties of ordinaryswitchboard Wire.

Still another object is toA provide an insulating covering for an electrical conductor, composed of a plurality of layers of different insulatin materials, the material of one or more of e layers being adapted to act as a protector for another against damage by mechanical strains or distortions, or destruction or damage by heat, moisture, gas

insulating material having somewhat less dielectric strength, but relatively'soft and iieX- ible, so as to preserve to a maximum degree the continuity of the first mentioned layer of insulation, should the covered conductor be subjected to mechanical strains by sharp bending.

A still further object is to provide an insulating sheath for an electrical conductor, wherein a layer of insulating material having a comparatively high dielectric strength, though ordinarily subject to the destroying or disintegrating effects of eXtreme heat or moisture respectively, is thoroughly protected by another layer of insulating material having somewhat less dielectric strength, but fiame-proof and relatively high in moisture resistance, so as to insure that the first mentioned layer of material will not be subjected to such elects.

Still another object of this invention is to provide switchboard or like Wire which is covered by such a combination of layers of insulating materials having different characteristics, that, should one of the insulating materials be damaged, disintegrated or destroyed, due to excessive strain, heat or'moisture, the material of another layer or layers of insulation will be of suiiicient dielectric strengthto continue to act as an effective insulation for the conductor, and thereby obviate the possibility of damage to adjacent circuits', controls or mechanisms.

To these and other ends, the invention consists in the'novel features and combinations of parts to be hereinafter described and claimed.

In the accompanying drawings:

1 is a side view of a switchboard wire `or to the action of moisture, gas, etc.

embodying the features of this invention, with the 4dlifferent layers of insulating material expose Fig. 2 is a greatly enlarged longitudinal section of the conductor shown in Fig. 1;

Fig. 3 is asection on line 3 3 of Fig. 2;

Fig. 4 is a diagrammatic view, showing one manner in which a part 4of the insulating covering may be applied to the conductor;

Fig. 5 shows a somewhat modified form of conductor;

Fig. 6 is a greatly enlarged longitudinal section of the conductor shown in Fig.` 5;

Fig. 7 is a section on line 7-7 of Fig. 6, and

Fig. 8 is a side view of a stranded conductor, having the arrangement of insulating material shown in Fig. 5.

The improved insulated electrical conducjtor of this invention comprises a cable strand or wire, having a covering comprising a plurality of layers of insulating materials of diderent characteristics. Insulating materials of comparatively high dielectric strength and which are relatively thin, are generally stid or unyielding in nature and readily torn, fractured or otherwise ruptured by sharply bending or otherwise straining the sam-e. An example of this type of insulating material is specially treated textile fabric such as varnished cambric, which is used to quite an extent as an insulating covering for electrical conductors, customarily by applyingto the conductor a plurality of layers of this material in strip or sheet form, which y are folded or wrapped about the wire, after which an outer textile cover is superposed on the cambric by a braiding or similar operation. Such a conductor cannot be bent abruptly without the danger of rupturing at least the outer layers, and in many instances all of the layers of insulation aswell as the outer cover, are cracked or opened up, when sharply bent, whereby the wire will be eX- posed. In any event, such damage will result in a loss of the insulating properties of the insulation at the bend and expose the lremaining covering to excessive electrical stIrain stherlthis kind of covering, although having,

initially, excellent electrical insulating properties, provides poor heat insulation, being in many instances totally destroyed when the conductor becomes overheated due to excessive overloads of electrical current, or

when the covering is exposed to the`action of v fiber, which when applied to a conductor according to the method described in Patent No. 1,789,882 of Beauford H. Reeves, dated January 20, 1931, is an excellent insulating and fireproong medium. However, when this material is used alone or as primary insulation in locations where very high dielectric strength is required, the covering necessarily has more bulk than would be required if a material of higher dielectric strength could be successfully used, such bulk resulting in a larger conductor diameter, and somewhat reducing Jfacility of manipulation.

The insulating covering of the improved electrical conductor of this invention, comprises a novel combination of materials ofA both of these classes, which materials are arranged upon the conductor in such a manner that the advantages of both will lbe obtained and the disadvantages of both will be obviated. The resulting insulating covering, therefore, is one which possesses a relatively high dielectric strength and is flame-proof, as Well as moisture-resistant, while being mechanically strong, durable and flexible.

In the form of my invention shown in Figs. 1, 2 and 3, the conductor 10 is first covered with a plurality of, in this instance two, layers of insulating fabric 11, such as varnished cambric. by winding narrow strips of this material directly upon the surface of the conductor, preferably staggering the layers or alternating the direction of winding the different layers (see Fig. 8) so that the overlaps or joints of one layer will be out of line with those of the other, and so that a uniform thickness of material will be secured. Upon this structure, a layer 12 of fibers of another insulating material, such as asbestos, is formed. This layer is preferably formed of interentangled asbestos fibers pressed into a compact mass. Preferably, the layer 12 is formed directly upon the surface of the outer layer of fabric, by felting the asbestos fibers gf.

into a homogeneous mass thereabout in a machine and by a method disclosed-in the above mentioned patent.

Fig. 4 illustrates diagrammatically one method of applying the librous material to the fabric covered conductor. In this figure, the numeral 13 indicates the fabric covered conductor, and 14 indicates a sliver orv roving preferably composed of a mass of asbestos fibers disposed about and adhering to a carrier element such .as a cotton thread 14a (Fig. 2). The fabric covered conductor 13 may have an adhesive applied thereto, if desired, by passing it through an adhesive bath 15 shown in dotted lines. After the sliver or slivers have been applied to the conductor (as by winding them thereon by means such as a rotary device 15a) ,the conductor is passed through a rotary device 16 which ,smooths the asbestos fibers about the conductor and These layers are applied 3 Ale more completelyinterentanglesthefiberswith each other, while partially compressing the mass. The conductor is then passed through a rotary device 17, which further condenses and compacts the fibrous mass', and thence it passes through a bath 18 of suitable flameproof and moisture resistant material whereby the fibers are thoroughly impregnated and firmly bound together. The impregnant may advantageously consist of asphaltic materlal in solution, having a suitable flameproofing agent such as lead carbonate added thereto. The impregnated structure is then passed through a polishin device 19, which further compacts the brous mass and smooths the outer surface thereof.

The conductor, as thus covered, is then passed through a machine wherein an outer covering is applied thereto, preferably .by braiding strands of cotton or other suitable material directly upon the outer surface of the felted fibrous mass, which results in the outer covering snugly engaging the cushioning layer of fibrous material. This outer covering is then treated with an impregnant containing fiameproof paint or other flameproofing agent, and is then permitted to dry. A conductor such as that above described is admirably adapted for use on switchboards and in similar locations. It has very high mechanical strength andit can be bent so as 'to present sharp turns or angles, as required for switchboard use, without danger of breaking the wire proper. This advantage arises in part from the cushioning effect of the relatively bulky and yielding layer of fibers, which permits the metallic element to take the form of a curve, evenv when the outer covering presents a sharp angle. This cushioning effect of the asbestos or other fibrous layer also `applies to the thin and somewhat frangible or fracturable layer of insulation, which is permitted to assume a gradual curve, in a similar manner, to such an extent as to prevent this thin layer from being fractured or ruptured by sharp bending of the exterior structure, or to reduce to a minimum the likelihood of the fabric layer being broken in this manner. When the conductor is sharply bent, the thin layer of insulation is placed under some strain at the outer curve of the bend, tending to pull it apart, but the yieldable covering of bers supports this layer, by being more tightly pressed against it at this point, and prevents this action. Should a fracture of the cambric layer occur, however, the insulating effect is preserved in ample measure by the relatively thick protective fiber layer, and the rupture, if any, of the cainbric layer is usually slight. Owing to the thinness of the inner textile layer, it is inherently more flexible than would be the case if a large number of superposed varnished cambric layers were employed, with the result that the flexibility of the conductor .as a whole is increased, as compared to those conductors having a large number of layers of varnished cambric, whereas, on the other hand, the dielectric strength is noticeably increased as compared to those conductors of the same size in which the main reliance for insulation is placed upon a layer of asbestos or like fibers.A

The conductors of my invention will Serve satisfactorily under conditions that would cause the early destruction of other types of wire. They present high dielectric strength, smooth appearance, have uniform diameter, and, in addition, are entirely resistant to exterior ignition whether the wire is straight or bent, owingto the complete envelopment of the cambric material by the fiexible exterior asbestos layer.

Under some conditions of use, especially in locations where the wiring is subjected to high temperatures due to overloading of the apparatus, or where there is danger from iuteriorly conducted heat, the thin layer of tex-l tile material may be heat-insulated from the inside as well as from the outside, in which case a layer of fireproof material is inserted between the cambric and the metallic element. In Figs. 5 to 8 inclusive, I have shown conductors in which this feature is incorporated. In the particular cases shown in Figs. 5 to 8, an inner layer of felted asbestos fibers directly7 surrounds the metal conductor element, as shown at 11a. Upon this layer of fireproof fibers is superposed a thin layer, 11b, of varnished cambric strips, and upon this latter layer is superposed a further layer, 11, of asbestos fibers. In the use of this form of conductor, both layers of felted asbestos, that is to say, the inner layer and the outer layer, act as cushions for the fabric layer, and the inner asbestos layer effectively protects the textile layer and insulates it against heat generated in or conducted by the metallic element.

These felte'd layers may be formed if desired by apparatus such as previously described.

In the form shown in Fig. 8, the metallic element is constituted by a plurality of strands instead of by a single wire.

In the forms shown inFigs. 5to 8, inclusive, also, the braided covering is formed of asbestos, whereas in the case of the wire shown in Figs. 1 to 3, the outer braid is preferably of cotton.

As an example of the relative thickness of the` various layers of insulating material applied as above described, it has been found preferable to apply upon a #8 A. W. G. wire, which is .128 of an inch in diameter. two layers of varnished cambric, each ap-v proximately .005 of an inch in thickness, one

ayer of felted asbestos fibers approximately 30 mils thick, and a braided covering approximately 20 mils thick. The diameter of a completely insulated #8 A. IV. G. wire will,l

therefore, be approximately .250 of an inch,

lll

which is the nominal diameter required of covered wire for use in switchboard wiring or for any of the above other uses.

While I prefer to use, as one of the insulating materials, cambric or like fabric having applied thereto a hard, lustrous coating of resinous material, such as varnish, such material being utilized in the form of a relatively small number of superposed strips, the relatively frangible layer of high dielectric strength may be formed of other material possessing equivalent or substantially equivalent insulating properties; and the cushioning and yielding protective layer for the first-mentioned layer, While preferably composed of interentangled and somewhat compacted asbestos fibers, need not in all cases be formed of this identical material, provided the protective layer is suiiiciently yielding and bulky, and possessed of the requisite dielectric strength to serve the purposes above explained. X

It will be obvious that where the sliver or roving is provided with a. carrying filament, such as the thread 14, the latter Will notl only serve to hold in place the asbestos or other mineral .fibers but will tend to secure and retain the fabric strips in the layer which is surrounded by such layer of asbestos fiber.

.It will be observed that the fabric strips of the high dielectric layer are separate from the metallic element of the conductor and are of such a nature that they can be readily removed from the conductor when access is had thereto by the removal of the surrounding layer or layers of material. As the high dielectric layer can be readily stripped from the Wire, the conductor can be more easily stripped or bared at the end for the purpose of makingsuch electrical connections as may be necessary. The strip or strips of the high dielectric layer While fracturable and ignitible, is or are protected from undue mechanical strain by thel surrounding somewhat yielding layer which also protects the high dielectric layer from chemical attack and moisture, as well as from ignition. The high dielectric .layer as thus protected serves Very satisfactorily, as it is of a permanent character and it will not break down, deteriorate or decompose or otherwise lose etliciency to an appreciable degree with the passage of time.

While I have shown and described preferred embodiments of my invention, it is understood that it is not to be limited to all of the details shown, but is capable of modiication and variation which will lie within the spirit of the invention and the scope of the appended claims. Y

What I claim is: a

1. In an insulated electrical conductor, a metallic conductor element, a relatively bulky and yielding protective layer of asbestos bers enveloping and compacted about said conductor element, an insulating layer of high dielectric strength surrounding the rst layer and composed of a number of supei-posed fabric strips coated with resinous material and Wound on the first layer, arelatively bulky and. yielding protective layer of asbestos fibers enveloping and compacted about said second layer, and including in its structure a carrier filament which holds in place the said fibers and also the aforesaid fabric strips, said last mentioned layer being treated with a suitable impregnant and presenting a body which permits relative movement with respect thereto of the metallic element and the second mentioned insulating layer when the electrical conductor i sharply bent.

2. In an insulated electrical conductor, a metallic conductor element, a relatively bulky and yielding protective layer of fibers enveloping and compacted about said conductor element andincluding in its structure a carrier filament which holds in place the said fibers upon the conductor element and in respect to each other, an insulating layer of high dielectricl strength surrounding said first layer and composed of superposed strips 'of textile material treated with insulating compound, a relatively bulky andyielding said electrical conductor is sharply bent.

i 3.l In an insulated electrical conductor, the combination of a metallic conductor element, an outer jacket, an inner inelastic high dielectric layer surrounding the metallic element, a flexible yielding felted cushioning layer of fibrous material interposed between the high dielectric layer and the outer jacket, and a second flexible yielding felted cushioning layer of fibrous material interposed between the high dielectric layer and the metallic element, said conductor being adapted to take sharp bends.

4. In an insulated electrical conductor, a metallic conductor element, an insulating layer of high dielectric strength surrounding said element and composediof a small number of varnished cambric strips in superposed relation Wound helicallyabout the conductor with their edges overlapping and With'the strips breaking joint with each other, another insulating layer interposed between said first layer and said metallic conductor element and forming a protecting cushionv for said first layer and preventing ignition thereof from overheating of ysaid conductor element and comprising a yielding tubular body ofv 'yielding felted tubular body of interentangled and compacted fibres of fireproof maferial, and an outer braided jacket snuglyV enveloping the previous-mentioned layers.

5. In an insulated electrical conductor, a

metallic conductor elementl` an insulating layer of high dielectric strength surrounding said element and composed of a small number of varnished cambric strips in superposed relation Wound helically about the conductor with their edges overlapping and with the strips breaking joint with each other, another insulating layer interposed between said first layer and said metallic conductor element and forming a protecting cushion for said first layer and preventing ignition thereof from overheating of said conductor element and comprising a yielding continuous felted tubular body of interentangled and compacted fibres of fireproof material, a further insulating layer disposed adjacent and exteriorly of said first layer and forming a further protecting cushion therefor andpreventing ignition thereof from an exterior source and comprising a tubular body of interentangled and compacted fibres of fireproof material, and an outer braided jacket snugly enveloping the previously-mentioned layers, said second and third mentioned layers each containing an impregnant which proofs it against moisture and is flame-proof and which leaves such layer flexible.

6. In an insulated electrical conductor, the combination of a metal conductor core, a surrounding layer of` inelastic frangible and inflammable material Which is a high dielectric, a yielding felted cushioning layer of fibrous material interposed between said first layer and said core, a layer of fibrous material surrounding saidv first layer, and a cover of fibrous material surrounding and snugly enveloping said third layer, said second and third layers and said cover beingflexible and being impregnated with moistureproofing materialwhich does not materially detract from the fiexibility thereof, and said second and third layers and cover being flameproof.

7. In' an .insulated electrical conductor, a conductor core, an insulating layer of mineral fibres surrounding said core, a layer of inelastic high dielectric material surrounding said first layer and composed of frangible strips Wound on the first layer so as to break joint with each other, an outer braided jacket and a flexible yielding bulky cushioning layer of fireproof interentangled felted fibres interposed between said jacket and said high dielectric layer and adapted to prevent ignition of the high dielectric material from the exterior and also adapted to cushion the layer of high dielectric material and to permit the completed conductor to be bent at sharp angles without rupturing the jacket or the high dielectric layer.

8. In an insulated electrical conductor, a conductor core, a yielding felted layer of interentangled and compacted asbestos bres immediately surrounding said core and forming a substantially homogeneous sleeve, a layer of inelastic high dielecticmaterial surrounding said sleeve, a layer of fireproof cushioning material surrounding said high dielectric material, and a braided flameproof outer jacket forming a coveringfor all of said layers.

9. lIn an insulated electrical conductor, a

'imA

conductor core, a yielding continuous layer as asbestos fibres felted thereon and impregnated with a moistureproofing material which does not materially detract from the fiexibility of said layer, a layer of varnished cambric tape surrounding said first lay-er, a fiexible flameproof cover, and a flexible fireproof and moistureproof 'cushioning layer interposed betweenv the varnished cambric layer and said cover.

l0. In an insulated electrical conductor, a conductor core, an outer braided jacket -of asbestos fibresimpregnated with a moistureproof fiameproof impregnant, a yielding jointless layer of interentangled and compacted felt-ed asbestos fibres located beneath said jacket, a layer of inelastic high dielectric material of a frangible and inflammable character located beneath said asbestos layer and cushioned thereby, and a fireproof protective layer for said high dielectric layer interposed between the latter and said core, said layer of interentangled fibres containing a non-hygroscopic impregnant which moistureproofs the same but -does not materially detractrfrom the flexibility thereof.

1l. In an insulated electrical conductor,.a

conductor core, an insulating layer of asbestos fibres surrounding said core, an insulating layer of high dielectric strength surrounding the rst layer and composed of a plurality of strips of inelastic frangible inflammable insulating material Wound so as to break joint with each other, a third layer located adjacent the second and exteriorly thereof and comprising a relatively soft and yielding sleeve of considerable bulk composed of asbestos fibres adapted t0 cushion and protect said high dielectric layer, said third layer containing an impregnant vvfhich proofs it against moisture and is flameproof,I said impregnant being of a character to preventV125 said layer from substantially stiffening or restricting the bending` of the structure, and a flexible flameproof :covering of fibrous material snugly enveloping said layers, said relatively soft and yielding sleeve being adapted to prevent the cracking of said covering of 13 said high dielectric layer upon the 'sharp bending of the conductor.

12. In an electrical conductor, a conductor core member, a flexible lameproof outer n cover, and a plurality of, layers of insulating material interposed between the corer member and cover and held in place by the latter, one of said layers comprising strips of inelastic fracturable and ignitible material laid 1o so as to break joint with one another, another of said layers comprising feltedf interentangled inherently reproof fibres forming a substantially,homogeneous yielding body, s'aid last-named layer containing a moistureproofing impregnant which does not materially detract from the flexibility thereof and being disposed adjacent and exteriorly of the first-mentioned layer to cushion the same and protect it against damage by heat from an exterior source, and another of said layers comprising inherently fireproof fibres and 'being located between the core member and the aforesaid strips to protect said strips against damage by heat fromthe conductor corev member.

13. An insulated electrical conductor for switchboard and similar use, adapted to take sharp bends without injury, comprising a metallic conductor core, a longitudinally and transversely continuous bulky sleeve of interentangled compacted asbestos libres surrounding sai-d core and presenting a yielding cushioning body, said body Containing a moistureproofing felting impregnant of a flexible nature so as not to interfere with the flexibility of said body, a layer of helically wound inelastic high dielectric tape surrounding said body and cushioned thereby, and an outer covering structure for said tape layer including a yielding and flexible layer of reproof material surrounding the same exteriorly.

In Witness whereof, I have hereunto set my hand this 14th day of August, 1930. HERBERT O. ANDERSON.

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