United States Patent: 3602636

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United States Patent	3,602,636
Evans	August 31, 1971

WRAPPED SERVICE ENTRANCE CABLE

Abstract

A plurality of conductors are helically wrapped with at least one layer of moisture and thermal barrier tape made of open weave glass cloth partly embedded in a layer of fire retardant synthetic plastic electrical insulation material. An outer sheath of synthetic plastic material is preferably extruded onto the cable and bonds to the synthetic plastic material of the barrier tape.

Inventors:	Evans; Raymond D. (West Chester, PA)
Assignee:	Reynolds Metals Company (Richmond, VA)
Appl. No.:	04/874,466
Filed:	November 6, 1969

Current U.S. Class: 174/115 ; 174/110AR; 174/116; 174/121SR; 174/124GC

Current International Class: H01B 7/17 (20060101); H01B 7/285 (20060101); H01B 7/295 (20060101); H01b 003/00 ()

Field of Search: 174/115,124.1,124.2,121,121.1,121.3,113

References Cited [Referenced By]

U.S. Patent Documents


2658014	November 1953	Morrison
2718544	September 1955	Shepp

Primary Examiner: Goldberg; E. A.

Claims

I claim:

1. A service entrance cable comprising:

a. a plurality of electrically insulated electrical conductor strands and a neutral conductor, grouped to constitute a cable core;

b. a complete barrier layer about said cable core, said barrier layer being at least one helical wrap of a composite tape of open weave glass fiber cloth partly embodied in a coating of uncured, flame resistant synthetic rubber which closes the open spaces of the glass fiber cloth; and

c. a jacket of electrical insulation material extruded in place about said barrier layer and being fused thereto.

2. The service entrance cable of claim 1 wherein said flame resistant synthetic rubber coating is a skim coating of polychloroprene.

3. The service entrance cable of claim 1 wherein said glass fiber cloth essentially consists of woven glass fibers and is free of cotton and rayon fibers.

4. The service entrance cable of claim 1 wherein the glass fiber cloth consists of about 20 bundles of glass fibers per inch widthwise of the composite tape and about 10 bundles of glass fibers per inch lengthwise of the composite tape; and wherein said glass fiber cloth has a weight of about 1.6 ounces per square yard and a tensile strength of about 70 pounds per lineal inch both widthwise and lengthwise of the composite tape.

5. The service entrance cable of claim 4 wherein said coating of uncured, flame-resistant synthetic rubber comprises a skin coating of polychloroprene having a thickness of about 6-7 mils and wherein said composite tape has a finished weight of about 35-40 pounds per 100 yards.

6. The service entrance cable of claim 5 wherein glass fiber cloth of said composite tape faces outwardly of said cable core.

7. A service entrance cable comprising:

a. a plurality of electrically insulated electrical conductor strands and a neutral conductor, grouped to constitute a cable core;

b. a complete barrier layer about said cable core, said barrier layer being at least one helical wrap of a composite tape of open weave glass fiber cloth partly embedded in a coating of uncured, flame resistant synthetic rubber; the glass fiber cloth consisting of about 20 bundles of glass fibers per inch widthwise of the composite tape and about 10 bundles of glass fibers per inch lengthwise of the composite tape; said glass fiber cloth having a weight of about 1.6 ounces per square yard and a tensile strength of about 70 pounds per lineal inch both widthwise and lengthwise of the composite tape; said

glass fiber cloth of said composite tape facing outwardly of said cable core; said coating of uncured, flame resistant synthetic rubber comprising a skim coating of polychloroprene having a thickness of about 6-7 mils; said composite tape having a finished weight of about 35-40 pounds per 100 square yards; and

c. a jacket of electrical insulation material extruded in place about said barrier layer and being fused thereto;

said jacket comprising a layer of polyvinylchloride fused to said polychloroprene among the fiber bundles of said open weave glass fiber cloth.

8. A service entrance cable comprising:

a. a plurality of electrically insulated electrical conductor strands and a neutral conductor, grouped to constitute a cable core;

b. a complete barrier layer about said cable core, said barrier layer being at least one helical wrap of a composite tape of open weave glass fiber cloth partly embedded in a coating of uncured, flame resistant synthetic rubber; said complete barrier layer comprising two complete helical wraps of said composite tape, applied one over the other, with lateral edges in each wrap abutting to form butt joints, the butt joint of the outer of said wraps of composite tape being centered upon the inner of said wraps of composite tape; and

c. a jacket of electrical material extruded in place about said barrier layer and being fused thereto.

9. The service entrance cable of claim 8 wherein the said coating of the two wraps of composite tape face one another.

10. A service entrance cable comprising:

a. a plurality of electrically insulated electrical conductor strands and a neutral conductor, grouped to constitute a cable core;

b. a complete barrier layer about said cable core, said barrier layer being at least on helical wrap of a composite tape of open weave glass fiber cloth partly embedded in a coating of uncure, flame resistant synthetic rubber; said complete barrier layer comprising two complete helical wraps of said composite tape, applied with intercalation each with the other; and

c. a jacket of electrical insulation material extruded in place about said barrier layer and being fused thereto.

11. A service entrance cable comprising:

a. a plurality of electrically insulated electrical conductor strands and a neutral conductor, grouped to constitute a cable core;

b. a complete barrier layer about said cable core, said barrier layer being at least one helical wrap of a composite tape of open wave glass fiber cloth having an adherent coating thereon which closes the open spaces of the glass fiber cloth and is fusible with the following defined jacket; and

c. a jacket of electrical insulation material extruded in place about said barrier layer and being fused thereto.

Description

BACKGROUND OF THE INVENTION

Service entrance cables are a distinct kind of cable, usually used for transmitting electric power from the weatherhead or service equipment terminals of distribution lines (which usually follow streets) to individual customer's taps, service drops, meter boxes or load centers.

In many localities, one prerequisite to the use of cables of new or modified design is that approval of the design be obtained from Underwriters Laboratories, Inc. Approval requires subjection of the cables to standard tests by the testing agency. One such test for service entrance cables is entitled "Overload of Uninsulated Conductor in Type SE Cable." This test, commonly called the 300 amp. test, consists of the following:

"A Type SE cable with or without the metal tape mentioned in paragraphs 32-35 but containing either (1) two insulated No. 6 A.w.g. copper conductor and a No. 6 A.w.g. copper uninsulated conductor, or (2) two insulated No. 4 A.w.g. aluminum conductors and a No. 4 A.w.g. aluminum uninsulated conductor shall not warp excessively, flame, or rupture while a current of 300 amperes is flowing through the uninsulated conductor and the metal tape, if a tape is used, for one hour as described in paragraph 104. This requirement applies to cable with an uninsulated conductor regardless of how the conductor is assembled into the cable-- cabled in one of several sections, laid straight, or distributed helically.

One 11-foot specimen of finished cable is to be laid in a straight, open, 90.degree., V-shaped trough that is lined with asbestos. At each end of the specimen, connection is to be made between a source of alternating or direct current and (1) the uninsulated conductor or (2) the uninsulated conductor and metal tape in parallel, if both are used. A current of 300 amperes is to be maintained in the uninsulated conductor for one hour. Any cable from which a specimen warps excessively, flames, or ruptures during the hour is not acceptable."

In one conventional, approved design of service entrance cable in widespread use, the insulated and uninsulated conductors are wrapped with a layer of Mylar polyethylene terephthalate film (which may be coated with an adhesive waterproofing agent), which layer is in turn surrounded by a braided in situ glass, rayon cotton, or combination fiber sheath impregnated and covered with an asphaltic material and lacquered on the outside, usually with a gray-colored lacquer. The terephthalate film layers serves to hold the insulated and noninsulated conductors and ropes of paper filler together while the sheath braiding is being done.

The braiding process is relatively slow and therefore expensive. All glass fiber, although theoretically permissible in conventional, approved service entrance cable, has not been satisfactory because of the poor adherence of asphalt to glass fiber. In addition, all-glass fiber in such braided constructions tends to fare badly on abrasion tests, such as the standard joist pull-through test.

The slowness of the braiding operation, the desire to use all-glass fiber and the desire to produce cables of more flame or fire resistant or retardant materials has led to attempts at innovation in the design of service entrance cable.

However, even those skilled in the art encounter much difficulty in successfully designing modified service entrance cables, in view of the need for such cables to successfully pass stringent tests, exemplified by the 300 amp. test described above.

For instance, the inventor herein is personally familiar with an attempt to provide an acceptable modification, wherein the asphalt lacquer finish of glass-cotton or all-glass fiber braid of the conventional service entrance cable as described above was replaced with a layer of extruded PVC resin. The cable so modified fails to pass the 300 amp. test although the knowledgeable people who constructed it thought it would pass the test. Although the reasons for failure are not known, it is now speculated that the glass fiber braid and PVC covering fused and sparked during the test, thus igniting the gaseous products evolving from thermally degraded cable insulation.

SUMMARY OF THE INVENTION

A service entrance cable is provided which can be made more rapidly, since in situ sheath braiding is obviated; all-glass fiber may be incorporated therein, as may other flame retarding materials; and the cable successfully passes the Underwriters Laboratories, Inc. 300 amp. test.

About the normal grouping of insulated (and in some constructions neutral uninsulated) conductors, and filler, there is spirally wound at least one layer of tape made of open-weave glass fiber having a skim coating of flame retarding unvulcanized polychloroprene (Neoprene) in turn covered by an extruded in place adherent tubular layer of polyvinylchloride (polychloroprene can be used for this layer, but is more expensive).

The principles of the invention will be further hereinafter discussed with reference to the drawing wherein preferred embodiments are shown. The specifics illustrated in the drawing are intended to exemplify, rather than limit, aspects of the invention as defined in the claims.

BRIEF DESCRIPTION OF THE DRAWING

In the Drawing:

FIG. 1 is a transverse cross-sectional view of a preferred embodiment of the service entrance cable of the invention;

FIG. 2 is a top-plan view of a short piece of open weave glass fiber cloth skim coated with flame retarding polychloroprene and used as the helical tape wrap of the FIG. 1 cable;

FIG. 3 is a fragmentary longitudinal sectional view of the lapping of the helical wrap of tape on the cable of FIG. 1; and

FIG. 4 is a view similar to FIG. 3, showing an alternative form of lapping using two such tapes to produce a complete double thickness layer of tape.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Service entrance cables generally have two or three insulated conductors and often an uninsulated neutral conductor which is nonconcentric, stranded, solid, or where concentric the wires are radially distributed so as to be coaxial with the group of insulated conductors.

In other instances, even the neutral conductor is insulated.

Fillers or nonconducting material, such as paper rope, are usually used to fill spaces between conductors exteriorly or interiorly of the grouped conductors. SOmetimes the configuration of conductors is such that they produce acceptably round cable with little or no addition of filler. In the embodiment depicted, the service entrance cable 10 comprises three insulated conductors 12, an uninsulated neutral conductor 14 and filler of nonconducting material 16, usually paper, the number and placement of these conductors and filler shown and so far described is exemplary and these elements will be collectively referred to hereinafter, generically, as "grouped conductors" 18. The insulated conductors may be insulated with any of the accepted insulating coatings or coverings 13 such as chemically cross-linked polyethylene; SB-R, EPDM, EPM or IIR rubbers.

The grouped conductors 18 are provided with at least one complete layer of helically wrapped tape 20 which is an open weave glass fiber cloth 22 provided with a skim coating 24 of unvulcanized, flame retardant polychloroprene (Neoprene). In the presently preferred, illustrated embodiment the glass fiber cloth consists of about 20 bundles of approximately 204 filaments of 150-1/0 glass fibers per inch along the length (warp) of the tape and about 10 bundles of approximately 204 of 75-1 /0 glass filaments per inch along the width (woof) of the tape. The presently preferred glass fiber cloth 22 has a weight of 1.6 to 1.9 ounces per square yard and preferably about 1.6 ounces per square yard including up to 10 weight percent of binder and a for strength of at least about 70 pounds per lineal inch, both widthwise and lengthwise of the tape. For the all-glass fiber preferred composition there may be substituted a blended fiber cloth made of an open weave of blended glass and asbestos fibers with an epoxy or silicone binder. One such binder is aminopropyltriethoxysilane. A typical such cloth has the following composition: ---------------------------------------------------------------------------

Constituent Weight Percent __________________________________________________________________________ Glass fiber 50-70 Asbestos fiber 25-40 Binder 5-10 __________________________________________________________________________

The presently preferred skim coating 24 consist of fame retarding unvulcanized Neoprene (polychloroprene-compound), a presently preferred commercially available formulation being: ---------------------------------------------------------------------------

Ingredient Percent by Weight __________________________________________________________________________ Neoprene 50.00 Antioxidant 1.00 Carbon Black filler 30.75 Acid acceptor (Magnesium oxide) 2.00 Paraffin 2.37 Lubricant (stearic acid) 1.87 Mineral Oil (softener) 6.26 Flame-retardant (Antimony OXIde) 2.00 Zinc Oxide 3.75 __________________________________________________________________________

The coating 24 is applied to produce a layer of about 6-7 mils in which the glass fiber cloth 22 is partly embedded to firmly mechanically connect the cloth 22 and the coating 24.

The composite tape 20 preferably has a finished weight of about 35-40 pounds per 100 square yards. The tape 20 is preferably made in wide widths of for instance 60 inches wide and slit to desired width and stored in convolute wound condition on rolls. A typical finished width is 1.75 inches.

In certain instances the skim coating may be discontinuous in the sense of leaving the composite tape reticulated, or the coating may be constituted by the glass-cloth binder or sizing itself.

In contrast to the need to braid in situ the conductor grouping covering for conventional service entrance cables, the tape 20 is preferably completely manufactured prior in time to the point of its use and may in fact be manufactured by another entity or at another location than the cable manufacturing plant.

It should be noticed that the glass fiber cloth 22 is woven in the sense that longitudinally directed strands pass over and under alternating ones of encountered transversely directed strands and vice versa. Weaving is believed necessary for dimensional stability of the cloth during calendering thereto of the coating 24, and during subsequent slitting and application to the cable core of grouped conductors. In addition, since the Neoprene coating 24 is thin and unvulcanized, it adds no appreciable strength to the product. The weave imparts tensile strength longitudinally and transversely, permitting the composite tape 20 to be helically applied without edge fraying or tearing. This is especially important when the tape is applied with overlaps (FIG. 3) under tension.

When wrapping the grouped conductors of the cable core with a single tape 20 (FIG. 3), the tape is overlapped by at least one-fourth inch. When wrapping the cable core with two tapes 20.sup.a, 20.sup.b (FIG. 4) the adjacent edges of each tape are preferably butted and the outer tape 20.sup.b placed with its center over the edge butt line 30 of the inner tape 20.sup.a. A double thickness of tapes can also be obtained by intercalating two tapes.

The decision whether to place the glass fiber cloth side of the tape 20 faceup or facedown with respect to the cable core is not based on consideration for successful operability of the cable, since both orientations result in highly acceptable cables. Rather the decision is based on a consideration of trouble-free manufacture. It has been found that the glass fiber cloth in a face-upward position helps in production, as adjacent layers on reels of partly completed cable would tend to stick together were the vulcanized Neoprene coating 24 facing outwardly. Accordingly, in the FIG. 3 construction the tape 20 is preferably applied so that its cloth side faces outwardly and in the FIG. 4 construction, the two tapes 20.sup.a, 20.sup.b are preferably applied with coatings 24 thereof face to face.

The cable 10 is completed by extrusion thereonto by now-conventional techniques, of a jacket 32 of flame retarding thermoplastic material, preferably polyvinylchloride for instance 0.031 to 0.080 inch thick. As aforementioned, other electrically insulating, extrudible, flexible thermoplastics such as flame retarding Neoprene chloroprene could be used, but PVC is preferred because of its low cost.

The heat in the polyvinylchloride as it is extruded onto the tape-wrapped cable core causes the layer 24 to become firmly bonded to the jacket 32.

The mechanical strength of the new service entrance cable 10 is not significantly different from that of the conventional service entrance cables as described above.

The new service entrance cable 10 is susceptible of some modification from the preferred designs just described. For instance, should it be desired, a layer of helically wrapped Mylar polyethylene terephthalate tape with or without adhesive, waterproofing coating may be installed about the cable core prior to wrapping the tape 20 thereupon, should such a layer be desired. Preferably, in order to obtain all of the manufacturing and economic advantages of the invention, the extra layer just described is not provided.

As outlined hereinabove, the core of the service entrance cable need not be as depicted, in order to take advantage of the wrap of the present invention. For instance, the core may consist of two insulated conductive stands surrounded by multiple bare neutral wires, this core having been wrapped by the composite tape 20 (or 20.sup.a, 20.sup.b) and provided with an extruded in place jacket 32.

In the preferred service entrance cable according to the invention, the Mylar and lacquered, asphalt-coated in situ glass cotton fiber braid layers of conventional service entrance cable are replaced with a helically wound wrapping of composite barrier tape made of an open weave of glass fiber cloth partly embedded in a skim coating of uncured fire resistant plastic material such as Neoprene or Hypalon synthetic rubber. An outer sheath of PVC or the like is extruded onto the tape wrap and the heat of the extruded material fuses the plastic material of the sheath to the plastic material of the tape wrap (where exposed between glass-fiber bundles) thereby forming an impervious covering around the grouped conductors of the cable. The service entrance cable 10 has a good appearance. Its jacket can be cut away conveniently to expose the inner wrap 20, which, in turn, can be pulled away conveniently to expose the conductor strands for cable termination in the field.

It should now be apparent that the wrapped service entrance cable as described hereinabove possesses each of the attributes set forth in the specification under the heading "Summary of the Invention" hereinbefore. Because the wrapped service entrance cable of the invention can be modified to some extent without departing form the principles of the invention as they have been outlined and explained in this specification, the present invention should be understood as encompassing all such modifications as are within the spirit and scope of the following claims.

* * * * *

Current U.S. Class:	174/115 ; 174/110AR; 174/116; 174/121SR; 174/124GC
Current International Class:	H01B 7/17 (20060101); H01B 7/285 (20060101); H01B 7/295 (20060101); H01b 003/00 ()
Field of Search:	174/115,124.1,124.2,121,121.1,121.3,113