US3180925A - Conductor strand - Google Patents

Description

April 27, 1965 s. EGE

CONDUCTOR STRAND Filed sept. 15, 1961 SIGMUND EGE Mwfk m um United States Patent O 3,136,925 CNDUCTGR STRAND ,Sigmund Ege, Hastings on Hudson, NY., assigner to Anaconda'Wirey and Cable Company Filed'Sept. 15, 1961, Ser. No. 138,372` 8 Claims. (El. 174-1tl2) My invention relates to-electrical conductors and particularly to compositel conductors with a molybdenum core.

In the manufacture of electric cables which are expected to maintain circuit integrity under severe conditions such as exposure to high temperatures or flame it is known to apply an inorganic insulation or an insulation comprising a large inorganic component over a stranded copper Wire and to cover the insulated core with a metallic sheath such as a copper braid. It is known to use silicone rubber for the aforementioned insulation and to cure the silicone at elevated temperatures before applying the braid.

In order to obtain the maximum conductivity for a given conductor size it is customary to use soft or annealed copper strands for the conductor. In any event the strands become annealed during the vulcanization of the silicone rubber insulation and this usually overcomes any work hardening of the copper in prior processing.

VSpecifications for iiame-proof cables of the type under consideration usually require that they should retain circuit integrity after a test involving ydirect exposure to a gas ame for a period such as one hour. Known cables have evidenced a high percentage of failures during this tiame test caused by short circuiting between the copper conductor and the metallic sheath and it is an object of my invention to produce a cable that will not short circuit during the ame test.

A stranded conductor is comprised of seven copper wires of equal diameter with six of the wires wrapped helically around a single wire core. I have discovered that a cable which invariably passes the ame test can be made by substituting a molybdenum wire for the center copper core while the six outer wires are not changed.

The practice of my invention involves an electrical conductor comprising a molybdenum core and a plurality of copper wires wrapped helically around it and preferably a round molybdenum core wire with six round copper wires wrapped around it, all the wires having the same diameter. It also involves the aforementioned conductor surrounded by a layer of incombustible insulation such as silicone rubber covered with a glass braid and a metallic sheath such as a braid over the glass.

A more thorough understanding of my invention may.

FIGURE 3 is a perspective View of a paired cabie made to my invention.

Referring to FIGURE 1 a conductor indicated generally by the numeral 11 has a central wire 12 of molybdenum which is wrapped with six copper wires 13. I prefer to employ molybdenum wire with a temper such that the tensile strength is no lessthan 145,000 p.s.i. and the elongation 5-l5% but I have found that molybdenum of other tempers is also eiective and I do not wish to be limited to the preferred values. do not wish to be limited to, copper wires 13 that are dead soft or fully annealed so as to yobtain maximum conductivity and tiexibility for my conductor. Y

In FIGURE 2 I have shown my conductor 1I insulated Similarly I prefer, butV glass braid Manda metallic braided sheath 17 to form a cable indicated generally by the numerall; It will be understood, however, that my invention is not limited toV silicone rubber, but will apply to any insulation capable ofl withstanding high temperatures. If the insulation is destroyed tothe degreethat itleaves no dielectric barriery around the conductor, the cable will, of course, lack utility, but the particular degree of temperature resistance required of the insulation will depend onfthe service andemergency conditions it is anticipated that the cable will` encounter. When silicone rubber burns it leaves an insulating residue and it is one of the functions of the glass braid 15 to retain this residue in place. Generally speaking, short circuits between conductors and sheaths due to increases in temperature insufficient to destroy the insulation do not constitute a problem at temperatures below 300 C. so that my invention will have utility when used with any insulation capable of maintaining a dielectric barrier at 300 C. or higher. Such insulations include the polyiiuorocarbons, asbestos, glass ber, inorganic powders such as magnesium oxide and blends or compounds of these materials.

In FIGURE 3 two of the conductors with glass braids but without any metallic sheath 17 have been twisted together, iillers 19 have been laid in the valleys and the braid sheath 17 has been applied over the twisted pair to form a cable indicated generally by the numeral 21. In this case the metallic sheath is applied over both of the insulated conductors so that short circuiting might occur between any one of the conductors 11 and the sheath 17 of the cable 21. It will be understood that a plurality of the cables 1S or 21 may be combined into a single multiconductor cable structure that will retain the advantages hereinbefore enumerated.

Example l Cables were constructed by stranding seven soft copper wires .0113 inch in diameter, six around one with a .44- inch lay. Silicone rubber insulation was extruded over these conductors to a diameter of .078 inch and cured at 250-500 F. for 23 hours. Braids of 150-1/0 glass ber were then applied over the insulation in l6carrier braiders. Two of the glass-braided conductors were twisted together and braided with a sheath of .005 soft copper in a l6carrier braider with 90% coverage.

Example 2 Cables were constructed identical to Example l except that a molybdenum center wire replaced the center one of the copper conductors.

Multipair cables were formed by stranding 12 of the pairs of Example l with appropriate iillers and covering. Multipair cables were also formed by stranding three of the pairs of Example 2 with appropriate fillers and covering. Six specimens of the multipair cable made with cables of Example 1 and three specimens of the multipair cable made with the cables of Example 2 were exposed over a 2-foot length for a period of one hour to an open gas iiame. Five of the multipair cables of Example 1 failed this test by short circuiting of conductor to shield, and none of the cables of Example 2 failed.

I have invented a new and useful article of manufacture for which I desire an award of Letters Patent.

I claim:

l. An electrical conductor comprising a molybdenum core and a plurality of copper wires wrapped helically around said core.

2. An electrical conductor comprising a round molybdenum core wire and six round copper wires wrapped helically around said core, all of said wires being equal in diameter.

3. Anelectric cable comprising a molybdenum core, a plurality of copper wires wrapped helically around said core, a layer of insulation capable of maintaining a dielectric barrier at 300"V C. surrounding said wires, and a metallic sheath over said insulation. v

4. The cable of claim 3 wherein said sheath is a braid.

5. An electric cable comprising a molybdenum core, a plurality of copper wires wrapped helically around said core, a layer of silicone rubber insulation surrounding said wires, a llame resistant brous braid over said insulation, and a metallic sheath over said fibrous braid.

6. The cable of claim 5 wherein said sheath is a braid.

7. An electric cable comprising a molybdenum core, a plurality of copper wires Wrapped helically around said core, a layer of insulation comprised of a composition selected from the group consisting of silicone rubber, poly- 4 uorocarbon, asbestos, glass fiber and magnesium oxide surrounding said'wires, and a metallic sheath over said insulation. Y

8. The cable of claim 7 wherein said sheath is a braid.

' References (Cited by the Examiner UNITED STATES PATENTS 990,040 4/11 Franke n 174-126 2,863,032 12/58 Morris 174-102 OTHER REFERENCES Advertisement by General Electric Co., General Elec-k tric Review, July 1955, vol. 58, No. 4, page 2.

Claims (1)

1. AN ELECTRICAL CONDUCTOR COMPRISING A MOLYBDENUM CORE AND A PLURALITY OF COPPER WIRES WRAPPED HELICALLY AROUND SAID CORE.

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