US2305431A - Electric cable - Google Patents

Description

ELECTRIC CABLE Filed Nov. 8, 1.959

FlaRous WEATHERPROOF FIBROUS MATERIAL COMPOUND TAPE CONDUCTOR MATERIAL CONDUCTOR TAPE c511. ULOSE RUBBER DERIVATIVE Inventors: Siam"; bigger, dramas D. Lojl ve, fa :%d//// Pj0fi4M Ti'aehr Atto'r rwgyo Patented Dec. 15, 1942 ELECTRIC CABLE Glenn Koger and James D. Lowe, Bridgeport, Conn., assignors to General Electric Company, a, corporation of New York- Application November 8, 1939, Serial No. 303,348

2 Claims.

This invention relates to electric cables, and more particularly to armored cables for outdoor use.

It is customary in providing an electric main for the conduction of current from a pole to a house-wiring system to employ for part of the main an armored cable having sufficient conductors for a two-wire or three-wire system, and one which is heavily armored and weatherproofed to discourage malicious tampering therewith and to be bent on edge in view of the heavy overlying armor and insulating wraps which closely engage the conductors and hinder them from moving relatively to each other.

It is an object of the invention to provide an improved electric cabl of the type described which may be easily bent in any direction without difficulty and without injury to the conductors thereof.

In the accompanying drawing Fig.' 1 is a vie of the cable stripped back to show the elements thereof; Fig. 2 is a similar view of a modified form of cable; Fig. 3 is a sectional view through the cable of Fig. 1; and Fig. 4 is a sectional view through the cable of Fig. 2.

Referring to the drawing, th electric cable is formed with a plurality of conductors l each provided with a heavy insulating covering ll of rubber, or the like, which, in turn, is overlaid with a fibrous covering I2, for example, a cotton braid. In order to moisture proof the individual conductors, the braids are impregnated with an be applied in th form of a spiral, or it may be longitudinally wrapped around the insulatedconductor. By this arrangement the saturant in the braid and the pitch filler are retained be- ,1

hind a relatively impervious layer so that they cannot become mixed with the coloring com--. pound of the other conductor. This means that the conductors may always be easily identified.

In addition, the layer of regenerated cellulose being an excellent insulating material greatly increases the dielectric strength between the individual conductors l0 and the concentric outer conductor l3 thereby reducing the chances of breakdown of the cable.

When in cabled position the individual conductors are closely gripped by the overlying strands i3 of the conductor inasmuch as the fibrous insulating material, such as the impregnated braid [2, forms a relatively rough sticky surface giving a high frictional contact with the strands. This means that edgewise bending of the oblong-shaped cable assembly is resisted due to the inability of the conductors to move relatively to the outer conductor in those cases where the smooth layer of regenerated cellulose is omitted. In such cases, slight longitudinal movement of the insulated conductors relative to one another is likewise retarded due to the frictional engagement of the impregnated braids l2 causing further resistance to bending of the cable. Cases have been known in which edgewise bending of the cable has caused buckling and kinking of the conductor on the inner side of the bend with consequent failure of the insulation. However, by providing a layer of regenerated cellulose around one of the conductorsy it is possible to greatly reduce the frictional re sistance to sliding between the conductors as well as that between the strands l3 and the braids I2. The smooth finish of this layer facilitates relative sliding movement between the insulated conductors and the strands l3 to such an extent that edgewise bends of the cable may.

slightly relative to the outer strands l3 and the other conductor. Very little movement takes place between the latter elements so that the cable assembly is not distorted. While it is preferred to make the layer ll of regenerated cellulose, other materials may be used, for example, cellulose acetate or a smooth material such as varnished cambric. cellulosic'derivative are that it is smooth and tough and will stand hard usage; it is a good insulator; it is relatively thin and does'not appreciably increase the overall dimensions of the cable; it is transparent permitting the use of a colored paint beneath it, or it may itself be colored for polarity identification of the conductors.

' Over the stranded conductor II is placed a rubber'taced tape 15, a layer of asphalt compound II and another rubber raced tape II. This arrangement provides an efiective weatherproof covering for the assembled conductors. The tapes prevent the asphaltic layer from coming in contact with the stranded conductor, so that the latter may be easily handled and the cable stripped without difliculty. An overall braid l8 surrounds the tape i1 and provides mechanical protection for the assembly; it is saturated with moisture-resisting and flameretarding compounds, for example, asphalt and stearine pitch, to further protect the cable. The saturated cover may be painted to provide a smooth dry finish and one which presents a pleasing appearance and is easy to handle.

In those cases where the cable is connected to a three-wire system the strands II are connected to form the third or neutral conductor while in a two-wire system the strands may form simply an armor which may or may not be grounded. In both cases, however, the strands protect the inner conductors from blows, and make it dimcult for one to tamper with the cable or tap the inner conductors. Should the outer covering and armor become damaged the inner live conductors are nevertheless protected by the heavy insulating layer of rubber and the individual coverings or weatherprooted braid. This means that the cable is well adapted for use in exposed positions.

In those cases where extra protection for the The advantages oi! using as cable is desirable a fiat band armor may be ap plied directly over the stranded conductor II beneath the tape II, as shown at It, in Fig. 2. The advantages of such a construction are that the stranded conductor is protected from damage and unwarranted tampering with the cable is made especially dimcult.

What we claim as new and desire to secure by Letters Patent 01' the United States, is:

1. An electric cable comprising a plurality of conductors, insulation for each 01 said conductors including a layer of fibrous insulating material having a rough surface, a wrap 01' smooth insulating sheet material surrounding and completely enclosing the fibrous insulating material on at least one of said conductors, the conductors thus insulated being assembled together in side by side parallel relationship, a conductor comprising individual strands spirally wrapped around the assembled conductors and an overall insulating covering over said stranded conductor, said smooth insulating material providing for slippage between the individual insulated conductors and the stranded conductor upon edgewise bending of the cable;

2. An electric cable comprising a plurality of conductors, insulation for each of said conductors including a layer of fibrous insulating material having a rough surface, a wrap of sheet material comprising regenerated cellulose having a smooth outer surface surrounding and completely enclosing the fibrous insulating material on at least one of said conductors, the conductors thus insulated being assembled together in side by side parallel relationship, a conductor comprising individual strands wrapped spirally around the assembled conductors, and an overall insulating covering over said stranded conductor, said wrap of regenerated cellulose providing a smooth surface for slippage between the insulated conductors and the stranded conductor upon edgewise bending of the cable.

GLENN KOGER. JAMES D. LOWE.

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