US1673752A - Nonmetallic sheathed multiple-conductor cable - Google Patents

Description

June 12. 1928. 1,673,752

E. H. LEWIS ET AL NONMETALLIC SHEATHED MULTIPLE CONDUCTOR CABLE Filed June 28, 1927 Ru lab 61" IYM/QntOrsl Edward H. Lew i s.

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Patented June 12, 1928.

UNITED STATES PATENT OFFICE.

EDWARD H. LEWIS; OF BRIDGEPORT, AND CLIFFORD O. HULL, OF NEW IBRIDGEPORT, CONNECTICUT, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A CORPORATION OF N EW YORK.

NONMETALLIO SHEATHED MULTIPLE-CONDUCTOR CABLE.

Application filed June 28, 1927. Serial No. 202,135.

The present invention relates to multiple conductor cables for conveying electric current for various purposes at the potentials commonly employed in buildings -f usual construction. These cables must be of such a character that they can be installed in all sorts of places, some of which may be dry and others damp. The insulation must be of such a character that the conductors are well insulated from each other and from any metal or grounded part with which the cable may come in contact. Further, the insulation must be as nearly fire proof as possible so as to withstand heating due to .heavy currents, as short circuits for example, or external heating due to any cause.

Desirable qualities of the cable are that it be capable of being bent at rather sharp angles without injury to the conductors or their insulation; that the insulation, especially the outer coating, be highly resistant to injury whenthe cable is being installed by being drawn over rough beams,-etc.;' that the cable shall have high tensile strength so as to prevent stretching of the insulation with the result of weakening it; and that the various parts of the insulation be so arranged or assembled that they may readily be removed from the conductors by the wireman preparatory to making electrical connections of the usual character.

The object of our invention is the provision of a noneme'tallic sheathed multiple conductor cable of improved construction which will have among other things all of the necessary and desirable qualities above enumerated.

For a consideration of what we believe to be novel and our invention, attention is directed to the accompanying description and the claims appended thereto.

In the attached drawing which is illustrative of ourinvention, Fig. 1 is a view on an enlarged scale of a two conductor cable, partlyin section; Fig. 2 is an end view of the same, and Fig. 3 is an end view of a three conductor cable, also on an enlarged scale.

In Figs. 1 and 2, 5 and 6 are tinned copper conductors, each of which is surrounded by an insulating body 7 made of suitable rubber or rubber compound. The rubber covering should be of a character to Withstand high voltage, say of the order of 1500 volts, for a limited time when the conductor and its covering 'is immersed in water. Surrounding the rubber body is a cotton braid covering 8. The braid coverings on the two conductors differ in color polarity of the conductors may be determined by the wireman and the proper con-' .nections made. For example, the braid covering for conductor 5 may be White and that for conductor 6 black. Where a third conductor is employed, as in Fig. 3, it has a still diflerent colored braid as red for example. The braid covering in each instance is given a thin protective coating of wax. For the white braid we use zinc oxide and Wax 9 and wipe it smooth, the color of the protective coating in each case corresponding generally to the color of the braid. The purpose of the wax is threefoldit prevents the saturating compound used on the next outer insulating layers from penetrating the braid and causing it to lose its distinguishing color, it water-proofs the braid, and finally, it revents the next outer layer of insulation rom adhering so closely to the braid that it can only be removed with difficulty. The last mentioned feature is of material advantage to the wireman who has to strip the conductors of their insulation before electrical connections can be made.

Over the braid and its protective wax coating is spirally wound two layers of jute 10 and 11, one layer being applied right handedly and the other left. These layers are applied simultaneously and each comprises a plurality of separate cords or elements, eight in the present instance, which are wound in multiple. When so applied the turns in. each layer are in contact with each other so as to form a complete covering Without intervening spaces. Due to the fact that the outer layer is of larger diameter because it surrounds the first, to the fact that the two layers are Wound simultaneously, and to the fact that the turns must be in side-wise contact to form a complete covering, the cord used in the second or outer layer is made of slightly larger cord. The weights of the Wraps may be of the order of six-pound dry jute for the inso that the nor wrap and eight-pound dry jute for the outerwrap. The cord wrapping is made of jute because of its good insulating properties, but it has one disadvantage; namely, that a large number of small fibers will project outwardly therefrom in all directions beyond the diameter of the cord and overlie the adjacent cords or turns on both sides. These projecting fibers while individually small form in the aggregate a substantial body and after the cords have been treated with a binder or compound will unite the cords quite firmly. This particular union is a distinct disadvantage from the standpoint of the wireman because it makes it so much more difficult to' -emove'the cords and other insulation prior to making an electrical connection. To avoid this the conductor afterv receiving its two jute wrappings or ribbons is-passed through a gas flame to singe off the loose projecting fibers above referred to, and in this'manner the objectionable binding of cord-to-cord is obviated. The singeing operation is chiefly confined to the outer layer but this sufiices for the purpose. With the fibers removed the wireman can easily unwind the cords or he may to a large degree remove them by an endwise pull,- after which the inner ends ,of

those portions can be cut with a knife.

After the jute wraps are applied and singed they are treated with a flame-proof compound or saturator 12 of a characterv having an asphalt base. The compound or saturator is applied at high temperature, say of the order of 500 F. after which the surface of the jute wrapping is closely wiped to remove any excess material and also to render the surface as smooth as possible. This treatment is of such a nature that the outer jute layer is thoroughly impregnated and the inner layer to a lesser extent so as not to seriously interfere with the stripping operation by the wireman. The wax coating on the braidbelow the inner jute covering softens during the singeing and slightly penetrates the immediately surrounding jute with the result of assisting to prevent the compound from completely impregnating it. The wax as previously stated also prevents the compound from discoloring the identifying braid on the conductor and facilitates stripping the jute insulation from the conductor. Due to the fact that there is less compound on the inner jute layer than on the outer the small fibers projecting therefrom do not adhere as strongly as would otherwise be the case. After the'jute Wrappings have been treated as above outlined they are given a thin protective coating of crude scale wax 13 and then wiped to remove the excess, care being exercised, how-. ever, to see that a substantial film of wax is permitted to remain. The melting point of this crude scale wax which has a parafiine base is substantially lower than that of the compound or saturator, and is applied at a lower temperature, say of the order of 120 F. After the two conductors have been insulated as above described they areassembled side by side and in close contact. In the spaces on each side of the region of contact of the conductors are located longitudinal members 14: and 15 also made of twine or jute and which have been treated with crude scale wax. These form fillers to round out the outer surface of the cable and by making them relatively hard they also prevent the cable, including of course the insulation, from kinking "when sharply bent. As previously stated these cables when being installed are subjected to considerable longitudinal strain due to the pulling operations. .Therefore,,in order, to add strength to the cablethe fillersare made of substantial strength, say of the order of one Of the metal conductors. The fillers may advantageously be made of what is known as Nassau twine for the smaller sizes and of dry jute for the larger sizes.

' As above stated, the jute wrappings are given a thin coat of wax which acts to prevent the] outside or over-all braid from sticking too closely thereto. For this purpose the material known as scale wax may be advantageously employed. It is a form of paraffin wax and has a lower melting temperature than the compound with which the cable is treated. Only a small amount of scale or other wax should be used because it is relatively inflammable. After being assembled the parts previously described are passed through a machine which applies to them the over-all cotton braid coating or covering 16. This covering tightly holds the various parts in place.

The cable with its over-all braid is then saturated with a hot compound similar to that used for the jute wrappings, which is flame-proof in character and which completely penetrates the fibers of the over-all braid 16 and alsov of the longitudinal jute fillers 14 to a greater or less degree.

This compound or saturant has an asphalt base and also has a higher melting point than that of the protective coating of scale wax on the jute wrappings and is applied at about 500 F. with the result that when the wax melts it somewhat increases thefluidity of that portion of the saturant which finds it way through the over-all braid into the interstices between the various elements of the cable. I After the saturant is applied to the cable it is run through a heated steel. wiping die which forces the mate rial through the fibers of the braid, sizes the cable and also smooths its outer surface. When the saturant hardens it renders all the material inside of the over-all braid or non-metallic sheath practically solid. Mention has been made of the specially strong fillers or members 14 and 15 to give increased tensile strength to the cable. They also have another and very useful purpose,

i. e., they are or may be used to split the over-all braid or sheath when necessary to remove the same. In some cases-the wireman has to remove ten to twelve inches of insulating covering in making a connection and in other cases as much as three feet. With the fillers arranged as described, as soon as the end of a filler is made accessible it can be easily removed.

After the saturator has set the cable is further treated b being given a coating of finishing wax which was a high melting point, say of the order of 380 F. To make the cable as smooth as possible to facilitate drawing into building partitions, etc. the cable may be given a coating of mica dust, which has a slight lubricating effect. After receiving the coating of mica dust the cable is passed through ironing rolls, after which it may be reeled.- After being cooled the cable may be again run through ironing rolls to give it the final finish. A so called slick finish may be given to the cable by using scale wax after the finishing compound, but it should be used sparingly because inflammable.

In Fig. 3 we have shown on a large scale three conductors 5, 6 and 17 arranged in multiple with insulation and fillers between the various parts constructed and arranged as described in connection with the other figures. sonably flexible the several conductors are spiraled or laid up like the strands of a rope before the over-all braid is applied.

As stated at the beginning of this specification one of the prime requisites of a cable is its ability to withstand use in damp places. A cable constructed in accordance with our invention maybe completely submerged in water for twenty-four hours and will not gain more than 10% moisture. As regards being-flame-proof, the cable will withstand being subjected to the heat of a five-inch unsen burner for five periods of fifteen seconds'each with similar periods between and will not flame more than fifteen seconds after the last period in the Bunsen flame.

What We claim as new and desire to secure by Letters Patent of the United States, is, I 1. A cable comprising multiple conductors,

In order to render such a cable reaeach conductor being enclosed in a body of insulating material, a double wrapping of cords surrounding the material, one of said Wrappings being heavier than the other, a compound with which both wrappings are treated, the compound more fully entering the fibers of the outer than of the inner wrapping, a protective coating between the said body and the inner wrapping to prevent the compound from affecting said body, fillers which also form strong tension members and sheath cutters, a braided over-all sheath, a protective coating between the sheath and the cord wrappings, and a flameproofing compound with which the sheath is impregnated.

2. A cable comprising multiple conductors, each conductor. being enclosed in a body of rubber, an identifying braid covering for the rubber, a double wrapping of jute cords around the braid, said cords bemg wrapped right and left handed, the cords of the outer layer being singed, a protective coating of wax between the braid covering and the inner cord wrapping, a compound with which the cords are treated, the inner cords having less compound than the outer cords, a protective coating for the outer cord wrapping, longitudinal fillers adjacent the cords, an over-all protective braid which holds the conductors and fillers in their respective positions, and a flame proof compound with which the over-all braid and the fillers are impregnated.

3. A cable comprising multiple conductors, each conductor being covered by a Water-proof body of insulation, a braided covering for the body, a protective coating for the braid, a double wrapping of jute cords, the wraps being wound right and left handed, a compound which fully impreg nates the outer wrap and partially enters the inner Wrap, the outer surface of the cords of the outer wrap being singed, a protective coatin for each of said outer wra in s longitudinal fillers which occupy spaces on opposite sides of the conductors and form strong tension members to increase the tensile strength of the cable, a braided overall covering of textile material which binds the conductors, their respective insulations and fillers into a compact mass, and a flame proof compound which saturates the braided covering and mixes with the protective coatings of the jute wraps to fill the small spaces between the jute wraps, the fillers and the braided over-all covering.

In witness whereof, we have hereunto set our hands this 17th day of June, 1927.

EDWARD H. LEWIS. CLIFFORD O. HULL.

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