Electro-Magnetic Screening Device for Electrical Cabling Constituting Bundles of Cables Comprising Tappings

1. Field of the Invention

This invention relates to an assembly of electro-magnetic screening devices.

2. Summary of the Prior Art

Numerous electrical or electronic installations comprise bundles of cables which must be protected from disturbing electro-magnetic radiation. To this end, these bundles of cables comprise an external sheath, generally constituted by metallic braiding forming a Faraday cage, serving as high frequency screening. When such bundles comprise tappings it is important that there should be no crack of the screening in the zone of the junction of the tapping with the main bundle. This problem is particularly acute whenever it is important that the various low level signals must not be subjected to any disturbance due to electro-magnetic radiations having a very wide range of frequencies and from various sources. In the same manner, these cable bundles may carry voltages which may be a source of disturbances from which it is important to preserve their environment. As a consequence, the requirements for the material are more and more severe and in numerous instances it is necessary to minimize the presence of defects in the screening of the cable bundles, particularly at the junctions with branches or tappings. Such a requirement was rarely satisfied in the prior art although it was generally customary to interconnect electrically the metallic sheaths of the main cable and of the tapping, by forming a type of enrobing at the junction itself. It has also been contemplated to make braided metallic sheaths in a complex way in order to match the tapping perfectly, but this solution is very costly and inflexible in use. Furthermore, such arrangements give rise to the disadvantage of mechanical fragility, as a result of which it is readily possible to create openings in the screening. Even small openings may quickly be the cause of substantial disturbances under the action of high frequency electro-magnetic waves.

According to the present invention there is provided an assembly of electro-magnetic screening devices comprising a first cable, a second cable, a third cable, said cables being interconnected at a junction, a first metallic braided screening sheath enclosing the first cable, a second metallic braided screening sheath enclosing the second cable, a third metallic braided screening sheath enclosing the third cable, and metal rings associated with each cable and the corresponding sheath at said junction, the metal ring of the first cable enclosing the remaining rings and end portions of the sheaths and serving to clamp the assembly together.

In accordance with one preferred embodiment, each metallic ring which surrounds a tapping is placed around the metallic screening sheath of the tapping and is externally covered by a return-fold of said sheath.

Advantageously, the metallic rings which surround the tappings have complementary profiles which reproduce, after juxtaposition, an external profile similar to that of the main cable and that of the inter-connection of the assembly is ensured by tapping of the external metallic ring or by any other clamping means.

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 illustrates, in longitudinal section, one assembly of electro-magnetic screening devices in accordance with a first embodiment of the invention;

FIG. 2 illustrates, in longitudinal section, a preferred embodiment of an assembly of electro-magnetic screening devices in accordance with a second embodiment of the invention;

FIG. 3 illustrates, in cross section, metallic rings used in carrying out a third embodiment of the invention;

FIG. 4 illustrates, in cross-section, a second combination of metallic rings; and

FIG. 5 illustrates, in cross-section, a third combination of metallic rings .

As has been illustrated in FIG. 1, a main bundle 1 of electric cables divided into two secondary bundles 2 and 3. Each bundle of cables is built up, from the inside to the outside, of the cables themselves, and a metallic braided screening sheath, respectively 11,21 and 31 is applied externally. The assembly of devices specifically aims to achieve perfect continuity of the electro-magnetic screening provided by the sheaths 11,21 and 31. To this end, an end portion of the bundle 2 of cables is surrounded by a metallic ring 23 of which the internal section corresponds to the external section of the bundle 2 and which is externally covered by the sheath 21. An end portion of the bundle 3 carries a metallic ring 33 and the bundle is externally covered by the metallic sheath 31.

The rings 23 and 33 are juxtaposed and the assembly thus formed is externally covered successively by an end portion of the metallic screening sheath 11 of the bundle 1 and by a metallic ring 13 serving to ensure locking of the assembly, preferably by clamping.

In the preferred embodiment illustrated in FIG. 2, the metallic ring 23 is externally covered by a return fold of the metallic sheath 21. Similarly, the metallic ring 33 is externally covered by a return fold of the metallic sheath 31. This arrangement, which leads to a cross-sectional bulk slightly greater than that of the preceding embodiment, has, however, mechanical qualities, particularly under tension, which are improved.

As the three examples illustrated in FIGS. 3, 4 and 5, the metallic rings 23,33 and 43 preferably have complementary profiles which reproduce, after juxtaposition, an external profile similar to that of the main bundle for enclosing the second, third and a fourth bundle of cables. The shapes to be adopted for the rings depend upon the sections and the orientations of the bundles. FIGS. 3-5 are only possible examples of shapes of rings that can be mounted according to the structure shown in FIG. 1 or 2. FIG. 5 shows a secondary bundle 4 identical with bundle 2 represented in FIGS. 1 and 2.

Besides providing excellent electro-magnetic screening properties, the devices in accordance with the invention have a good mechanical strength in traction, with reduced bulk in comparison with known devices. Furthermore, the devices enable relative displacement of the cables within the bundles, and facilitate repair.