US2663752A - Shielded electrical conductor with grounding strand - Google Patents

Description

A. J. WIER 2, 3,

SHIELDED ELECTRICAL CONDUCTOR WITH GROUNDING STRAND Dec. 22, 1953 Filed March 10, 1950 INVENTOR A.J.W/ER B) a 4 ATTORNEY Patented Dec. 22, 1953 SHIELDED ELECTRICAL CONDUCTOR WITH GROUNDING STRAND Anthony J. Wier, Cranford, N. J assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application March 10, 1950, Serial No. 148,832

2 Claims. (Cl. 174-36) 1 2 This invention relates to electrical conductors pair of conductors having an insulating coverand, more particularly, to shielded cables. ing l2, which may be of polyethylene, is shielded l-Ieretofore, it has been common practice to by braid M constructed in accordance with this provide conductors which may be subjected to invention. An outer braided fiber sheath I5 of the adverse ehect of electrostatic or inductive some material such as cotton is provided for interference, with conductive shields which, the cable to insulate and protect the shield I 4 when fiexibility is desired, are made up in a Intermediate the sheath l5 and the shield I4 is braided form. To attain maximum flexibility, a layer of crepe paper 5 which is applied by the strands making up the braided shield comwrapping a crepe paper tape running longituprise a plurality of fine wires, which, in connectdinally of the cable around the shield prior to the ing the shield to ground, must all be gathered braiding of the sheath thereon. This tape pertogether and connected, as by soldering, to some mits the sheath to be readily slipped back at the convenient grounding means, such as a lug. To end of the cable without catching on the metal avoid this time-consuming operation, it has been braid of the shield, thereby facilitating the stripcommon practice to incorporate under the ping and joining of the cable. strands of the shielded cable a bare, large diam- The shield M, which may be constructed of an eter wire which is in contact with the strands of equal number of strands, half of which are the shield throughout the major portion of its wound in a clockwise direction and the other length and may be employed as a grounding lug half in a counter-clockwise direction, is braided at the end of the shield. The use of a large di- 29 so that each strand passes under two and then ameter bare wire laid longitudinally under the over two of the strands running in the opposite braided shield has been found troublesome in direction. Each strand I! of the braid is made the manufacture of cables containing wire insuup of a plurality of fine wires to provide flexibillated by soft insulation, such as polyethylene, y ity in the completed cable. These fine wires, for Since y pressure o the b a tends to push example, may be No. 36 A. W. G. tinned copper. the ground Wire through the insulation of the the tin coating providing high conductivity conwire, thereby shorting the conductors to the tact surfaces so that substantially all of the shield and to ground. elements of the braid are interconnected elec- One Object of this invention is to facilitate trically at the points of contact to form a subthe grounding of braided shields. A more par- 30 stantially continuous shield. ti ject is to enable a ground wire to be The braided shield according to this invenemployed with a braided shield while eliminattion difiers in one way from those constructed ing the danger of such a wire when the shield is according to prior practice in that a grounding subjected to external pressure to rupture the inmeans in the form of a large diameter wire 18 sulation of the underlying conductors. 3.3 is woven into it in place of one of the multiple One feature of this invention resides in prostranded braid strands. The grounding strand, viding a large d ameter ground wire in place o which should have a high conductivity surface one of the stranded braid strands of the shield, so that it is electrically connected to the other thereby ntaining the ground Wire in eXcclstrands of the braid at each point of physical lent electrical contact with the strands of the 4: contact, may be, for example, a No. 24 A. W. G. shield and reducing the pressure which it exerts tinned copper wire. on the conductor insulation for a given applied One advantage of incorporating the ground force to the shield by increasing its eirective wire as a strand of the braid is to insure intimate supporting area to that of the entire shield. contact with the other strands, thereby elimi- Other objects and features of this invention nating the need to gather all or a substantial will be more clearly understood from the followportion of the fine wires making up the strands ing detailed description when read in conjuncof the braid in order to connect them to ground. t ith th accompanying drawing wherein Further, the ground wire is of such size as may the single figure shows in elevation a length of be conveniently grounded without the need of cable employing the shield constructed in ao- 50 terminating it W a Connector l ecordance with the invention with portions of chanically, this structure is also advantageous, the various layers of the cable broken away to particularly where soft insulation, such as polymore clearly illustrate details of its construe ethylene, is employed on the shielded conduction. tors. The alternative methods are to include In the form of cable shown in the drawing, a a ground Wire amo e d t s to Spiral it around with the conductor bundle. This would put a relatively large diameter wire against the soft insulation on the shielded conductors, which relationship with the application of a compressive force to the shield would eventually force the ground wire through the insulation of the conductors, thus shorting them to ground. Since in accordance with this invention, the ground wire is incorporated in the shield, its tendency to localize the effect of such compressive forces is removed, since the associated strands of the braid support it so that the efiect of any external forces are distributed over the area of the shield.

In producing the shielded cable in accordance with this invention, it has been found that no material change is necessary in the manufacturing machinery. The major alteration in the equipment is the substitution of a single strand carrier in the shield braiding machinery to carry the ground wire braid strand for the ordinary multiple strand carrier.

What is claimed is:

1. A cable comprising a conductor, a layer of insulating material on said conductor, and a braided shield surrounding said insulating layer,

4 said shield consisting of a plurality of metallic strands, one of said braid strands consisting of a single strand, and the remaining braid strands each comprising a plurality of strands each of smaller cross section than said single strand.

2. A cable comprising a conductor, a layer of insulating material on said conductonand a braided shield surrounding said insulated wire, said shield consisting of a plurality of metallic strands, one of said braid strands consisting of a relatively heavy wire and the remaining braid strands each comprising a plurality of metallic fibers, each of smaller cross section than said wire.

ANTHONY J. WIER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 568,756 Guilleaume Oct. 6, 1896 1,697,142 Roller Jan. 1, 1929 1,939,451 Hull Dec. 12, 1933 2,028,793 Mascuch Jan. 28, 1936 2,166,420 Robertson July 18, 1939 2,415,652 Norton Feb. 11, 1947

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