Electric cable for communication purposes

An electric cable for communication purposes, for instance a one-pair party station cable which is designed as twin cable and includes a cross-section-wise relatively flat envelope or cover of thermoplastics or elastomers and includes conductors arranged in spaced relationship to each other and also includes traction relief members in about the middle between the conductors. The traction relief members are embedded in the envelope or cover and are adapted to exert the traction forces exerted on the cable in the longitudinal direction thereof. The traction relief members include high-strength fibers arranged symmetrically with regard to the longitudinal central plane of the cable and with regard to the conductors. The enveloping substance includes thermoplastics or elastomers.

The present invention concerns an electric cable for communication purposes 
for instance a one-pair party station cable which is designed as twin 
cable and comprises a cross-section-wise relatively flat envelope or cover 
of thermoplastics or elastomers and includes conductors arranged in spaced 
relationship to each other, and also includes traction relief means 
arranged in about the middle between said conductors, said traction relief 
means being embedded in said cover or envelope and being adapted to absorb 
the traction forces exerted upon the cable in the longitudinal direction 
thereof. 
With a heretofore known electric cable having the above mentioned features, 
the traction relief means are formed by a supporting cable and consist of 
steel wire. Such traction relief means have the drawback that they have a 
relatively considerable weight and have a relatively poor bending 
capability which affects the bending capability of the cable. Furthermore, 
the said known cable has inherent thereto the danger that the supporting 
cable of steel wire, in case of damage to the cover or envelope, will be 
exposed to the influence of inclement weather as a result of which the 
steel wire rusts and may eventually break. This possibility also exists 
when it is intended to cut the cable, inasmuch as in such an instance 
moisture can enter the cable from the end face thereof. 
The insertion of a conductive metallic traction relief means requires that 
the latter has to be grounded, whereby the transmitting properties of the 
cables are affected. 
Self-supporting air cables have become known which are built up centrally 
symmetrical and the outer mantle of which contains longitudinal strands of 
glass fibers which serve as traction relief means. In this connection, the 
strands consist of bundles of glass fiber yarns, and the bundles are 
arranged in a relatively great number along a circular line which 
symmetrically surrounds the cable core. 
It is an object of the present invention to outfit also electric party 
station cables of the twin or comparable flat construction in such a way 
that they will have the same advantages as heretofore known air cables 
without having to incorporate the arrangement of glass fiber strands 
surrounding the conductors. 
It is a further object of this invention to provide an electric party 
station cable as set forth in the preceding paragraph, which, in 
comparison to the heretofore known cables with steel wire, will be lighter 
and more flexible than air cables while also being simpler to handle when 
installing such cable.

The electric cable according to the present invention is characterized 
primarily in that the traction relief means comprise at least two 
supporting members which are symmetrically arranged with regard to the 
conductors and which consist of high-strength fibers. A cable designed in 
this manner has a relatively light weight, is very flexible, and can 
easily be handled when installing the cable. Moreover, in contrast to 
heretofore known cables of the above general type, the cable according to 
the present invention greatly increases the safety against damage when the 
cable is being handled because the working with heavy cutting tools is no 
longer necessary. In particular, the cable according to the invention has 
the advantage that the line will be practically rot-proof. In this 
connection, the traction relief means in the form of high-strength fibers 
for instance glass fibers, graphite fibers, or fibers of aromatic 
polyamides, offer the greatest resistance against rotting. 
According to a further development of the invention, the supporting members 
of high-strength fibers may on the connecting line between the conductors 
be arranged parallel adjacent to each other. In this way, a particularly 
flat cross section of the cable can be realized. If, however, another 
design is selected so that the supporting members when viewed in cross 
section are located in an arrangement other than in line, for instance, 
along the outline of a quadrangle, there exists the possibility of 
providing a relatively greater number of supporting members in the cable 
which arrangement is desired in special instances. 
Referring now to the drawing in detail, the cable construction comprises 
primarily two copper conductors 10 which are arranged in spaced 
relationship to each other and are surrounded by an envelope or cover 11 
of high density polyethylene which faces said copper conductors 10 in 
their position. The cover or envelope 11 has a flat oblong cross section 
and has rounded edges while one of the narrow sides is provided with an 
orienting projection 12. The top and bottom sides of the cable envelope 11 
are provided with customary longitudinally extending grooves 13. 
According to FIG. 1, along a connecting line drawn between the copper 
conductors 10, there are provided three individual glass fiber strands 14 
which respectively are formed of bundles of six glass yarns intertwined 
with each other. For instance, a bundle may have 60,000 individual glass 
fiber filaments. The glass fiber strands 14 are not pre-impregnated and 
join directly with the material of the envelope 11 surrounding said glass 
fiber strands. During the manufacture of the cables, a positive connection 
between the supporting members 14 and the envelope 11 is established. In 
this connection, the supporting members 14 are undulated in the 
longitudinal direction of the cable whereby the mechanical anchoring or 
intertwining of the supporting members with the surrounding sleeve or 
cover 11 is intensified and the bendability of the cable is improved. 
According to FIG. 2, the supporting members 14 are arranged in the central 
portion of the envelope 11 between the grooves 13 along the two imaginary 
lines evenly spaced from each other and parallel to an imaginary line 
interconnecting the copper conductors 10. In this way the supporting 
members 14 define the corners of a quadrangle. 
The arrangement of the supporting members 14 according to FIG. 3 
corresponds to the arrangement of the supporting members in FIG. 2 with 
the difference that there is a fifth supporting member arranged which is 
located symmetrically in the center between the four other supporting 
members. 
It is, of course, to be understood that the present invention is, by no 
means, limited to the specific showing in the drawing, but also comprises 
any modifications within the scope of the appended claims.