US3865972A - Nonmetallic sheathed cable - Google Patents

Abstract

A nonmetallic sheathed cable with a bare grounding conductor has a U-shaped paper separator surrounding the bare conductor on three sides only, the bare conductor is in direct contact with a shallow depression in the jacket on the fourth side.

Description

nite States Norris atent [191 [451 Feb. 11, 1975 NONMETALLIC SHEATHED CABLE [75] Inventor: Walter R. Norris, Winder, Ga.

[73] Assignee: The Anaconda Company, New

York, NY.

221 Filed: Feb. 22, 1974 211 App1.No.:444,929

[52] [1.5. Cl. 174/115, 174/121 B, 174/121 SR [51] Int, Cl. H0lb 7/02 [58] Field of Search ..174-/115,121B,121SR,

[56] References Cited UNlTED STATES PATENTS 1,837,795 l2/l93l Schneider 174/115 3,800,065 3/1974 Bunish 174/115 Primary Examiner-E. A. Goldberg Attorney, Agent, or Firm-Victor F. Volk [57] ABSTRACT A nonmetallic sheathed cable with a bare grounding conductor has a U-shaped paper separator surrounding the bare conductor on three sides only, the bare conductor is in direct contact with a shallow depression in the jacket on the fourth side.

7 Claims, 1 Drawing Figure 1 NONMETALLIC SHEATHED CABLE BACKGROUND OF THE INVENTION Nonmetallic sheathed cable is an art recognized designation for a power cable that is used for 600 volt service in buildings and, under the Underwriters codes of many localities, can be installed without conduit. Because conduit may not be required, the cable must meet certain established requirements, particularly with reference to its resistance to crushing loads and to critical construction features. One of the construction requirements relevant to the present invention resides in the fact that although it is permissible to include a bare grounding conductor in the cable, a separator, such as a strip of paper or plastic is required between this bare conductor and the outer surfaces of the insulated conductors by the Underwriters Laboratories. Indeed, it has been found that in the absence of such a separator the cable cannot usually pass the crush test. Conventionally, a paper tape has been folded and wrapped completely around the bare conductor to serve as a separator. When, however, due to unavailability of paper or efforts to reduce cost reduction has been made in the number-of layers of paper used as separators, performance in the crush test has been sacrificed. The present invention has resulted from efforts to discover a new modification in cable structure which would improve crush resistance without increasing the expenditure for separator paper.

SUMMARY I have invented a nonmetallic sheathed cable comprising two parallel insulated aluminum or copper conductors, a bare conductor such, preferably, as a copper conductor laid parallel between the two insulated conductors and a paper separator, partially enclosing the bare conductor. The separator surrounds the bare conductor on three sides, two of which face the insulated conductors, and it opens away from the bare conductor on the fourth side so as to fold slightly around the insulated conductors. An extruded polymeric jacket which may advantageously comprise polyvinyl chloride surrounds the three conductors. The jacket has a shallow lengthwise groove and the bare conductor fits directly into the groove. In preferred embodiments the paper separator will comprise at least three layer thicknesses and the conductor insulation will comprise polyvinyl chloride.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION OF PREFERRED EMBODIMENT A cable of my invention includes two insulated conductors 1 l, 12 having walls of insulation l3, l4 surrounding size Awg 14, 12 or 10 copper or aluminum wires 16, 17. The conductors 11 and 12 are laid parallel and have between them an uninsulated, bare copper grounding conductor 18. An extruded jacket or sheath l9 protects the conductors, both insulated and bare. The grounding conductor is spaced from the conductors ll, 12 by a paper separator 21 having a general U shape so that the conductor 18 is enclosed on the bottom and two sides by the separator, but on the top is free to makecontact with the jacket 19. During the extrusion operation, while the jacket stock is soft and deformable a shallow groove or depression 22 is formed in the jacket by the contacting surface of the conductor 18. This groove contributes to the retention of the conductor 18 in the center of the cable. The paper separator 21, originally a strip of 5-mil creped kraft 2 /2 inches wide has been folded to form 3 layer thicknesses 23, 24, 26 doubled again at the sides, as shown in the drawing. The folds of paper open away from the conductor 18 in the areas 27, 28 to curve around the insulated conductors 16, 17. As depicted in the TABLES this novel configuration has had the surprising effect of improving crush resistance, compared to known cable structures where the paper separator surrounded the bare grounding conductor on all four sides.

In the edgewise crush test, which has been established by Underwriters Laboratories, a length of cable including a twist is compressed between 2-inchlong steel plates until the insulated conductors short to each other or to one of the plates. Because of the 180 twist the effective crushing force is endwise. In reporting this test the average load at failure is given for 10 trials.

TABLE I Edgewise Crushing Test Standard Cable with Separator on Four Sides New Separator U-Shape Average of IO Trials 1,287 pounds 1,466 pounds TABLE II Flatwise Crushing Test Standard Cable with New Separator Separator on Four Sides U-Shape Average of IO Trials 624 pounds 782 pounds I believe that the superior performance of my cable reported in TABLE Il may be accounted for by the superior distribution of the paper. By partially curving outwardly at the areas 27 and 28 the separator becomes wedged under the compression rod and contributes to the crush resistance of the cable.

In the cables tested in TABLES l and II the insulation and jacket material was polyvinylchloride. The advantages of my improvement wouldnot be limited however to this material of construction. My superior paper distribution would improve the crushing test performance where other insulating compositions such as polyethylene, polyethylene-polypropylene copolymer, chlorosulfonated polyethylene, neoprene, or rubber are employed for extruding the insulation on jacket.

I have invented an improvement in nonmetallic sheathed cable structures of which the foregoing description has been exemplary rather than definitive and for which I desire an award of Letters Patent as defined in the following claims:

l claim:

1. A nonmetallic sheathed cable comprising:

A. two parallel insulated conductors,

B. a bare conductor laid parallel between said two conductors,

C. a paper separator partially enclosing said bare conductor, said separator,

a. surrounding said bare conductor on three sides,

two of said sides facing said insulated conductors, and

b. opening away from said bare conductors on a fourth side thereof so as to fold slightly around said insulated conductors,

D. an extruded polymeric jacket surrounding said conductors, said jacket comprising a lengthwise groove and said bare conductor fitting directly into said groove on said fourth side.

2. The cable of claim 1 wherein said separator comprises at least three layer thicknesses.

3. The cable of claim 1 wherein said jacket comprises polyvinyl chloride.

4. The cable of claim 1 wherein said insulated conductors comprise insulating walls of polyvinyl chloride.

5. The cable of claim 1 wherein said bare conductor comprises copper.

6. The cable of claim 5 wherein said insulated conductors comprise copper.

7. The cable of claim 1 wherein said insulated conductors comprise aluminum.

Claims (7)

1. A NONMETALLIC SHEATHED CABLE COMPRISING: A. TWO PARALLEL INSULATED CONDUCTORS, B. A BARE CONDUCTOR LAID PARALLEL BETWEEN SAID TWO CONDUCTORS, C. A PAPER SEPARATOR PARTIALLY ENCLOSING SAID BARE CONDUCTOR, SAID SEPARATOR, A. SURROUNDING SAID BARE CONDUCTOR ON THREE SIDES, TWO OF SAID SIDES FACING SAID INSULATED CONDUCTORS, AND B. OPENING AWAY FROM SAID BARE CONDUCTORS ON FOURTH SIDE THEREOF SO AS TO FOLD SLIGHTLY AROUND SAID INSULATED CONDUCTORS, D. AN EXTRUDED POLYMERIC JACKET SURROUNDING SAID CONDUCTORS, SAID JACKET COMPRISING A LENGTHWISE GROOVE AND SAID BARE CONDUCTOR FITTING DIRECTLY INTO SAID GROOVE ON SAID FOURTH SIDE.

2. The cable of claim 1 wherein said separator comprises at least three layer thicknesses.

3. The cable of claim 1 wherein said jacket comprises polyvinyl chloride.

4. The cable of claim 1 wherein said insulated conductors comprise insulating walls of polyvinyl chloride.

5. The cable of claim 1 wherein said bare conductor comprises copper.

6. The cable of claim 5 wherein said insulated conductors comprise copper.

7. The cable of claim 1 wherein said insulated conductors comprise aluminum.

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