Shielded electrical cable

This invention relates to shielded electrical cable.

Coaxial electrical cables are well known, such cables generally being terminated by the use of electrical connectors having coaxial conductive members separated by dielectric material.

Also known are shielded electrical cables comprising one or more insulated signal conductors surrounded by a shielding layer formed, for example, by a metal foil. To facilitate termination of such a cable a further uninsulated conductor is sometimes provided between the shielding layer and the insulation of the signal conductor or conductors, termination of this further conductor constituting termination of the shielding layer. Such a cable is disclosed in US-A-3775552.

Both these known forms of cable normally require the use of specifically designed connectors for termination, these connectors not being suitable for the use of mass termination techniques, that is the simultaneous connection of a plurality of conductors to individual contacts in a connector, but requiring individual attention. This is a particular problem with cables comprising a plurality of conductors arranged in a planar array in a common insulating body, when it is desired to use a connector having so-called slotted plate contacts each having a plate portion having a slot open to one edge of the plate into which slot a conductor can be urged such that the slot walls grip the conductor and establish an electrical connection between the conductor and the contact.

In EP-A-0068665, published on 5.1.1983 and hence lying in the Article 54(3) field, there is disclosed an electrical cable comprising an outer layer of insulating material surrounding a signal conductor and an associated ground conductor and a common shielding layer in electrical contact with the ground conductor but separated from the signal conductor by an inner layer of insulating material surrounding the signal conductor, with the signal and ground conductors extending in spaced parallel relationship in a common plane, each surrounded by an individual outer layer of insulating material, the two outer layers of insulating material being integrally formed with a web extending between the two outer layers of insulating material, the shielding layer extending about the inner layer of insulating material on the signal conductor, through the web, and about the ground conductor.

Such a cable has the advantage that the spacing between the signal and ground conductors can be set to accord with the spacing between the relevant contacts in a connector to be used to terminate the cable whereby a mass termination technique can be used without the operator having to rearrange the cable conductors.

Preferably the signal and ground conductors are substantially the same size, and the diameter of the^*outer layer of insulating material surrounding the ground conductor is substantially equal to the diameter of the inner layer of insulating material surrounding the signal conductor.

. Such a choice of dimensions enables the use of slotted plate contacts having the same size slots for termination of the signal and ground conductors, thus facilitating assembly of a connector to be used to terminate the cable since identical contacts can be used for all conductors. For termination the outer layer of insulating material and the shielding layer are stripped from a length of the signal conductor, this leaving an insulated signal conductor and a ground conductor surrounded by the shielding layer and the outer layer of insulating material, of substantially equal diameter.

A composite cable can be formed from a plurality of such cables arranged in side-by-side relationship, the cables being connected by an integrally formed web extending between the outer layers of insulating material of the cables.

Such a composite cable can be readily mass terminated with a minimum of pre-preparation using conventional techniques and a connector having a plurality of contacts with identical slotted plate contact portions, the conductors in the cable being spaced in accordance with the spacing of the associated contacts of the connector.

In the cable specifically disclosed in the above noted application each signal conductor has an individually associated ground conductor, each pair of conductors having an individually associated shielding layer.

However, such an arrangement is not always essential, it being possible for a single ground conductor to be associated with a plurality of signal conductors.

In GB-A-2047947 there is disclosed such a cable, in which the shielding layer surrounding the inner layer of insulating material surrounding each signal conductor, extending through the webs, and about the ground conductor is formed from a single layer of conductive polymer. However, this prior specification does not disclose the conductor and insulation size relationships discussed above.

A further cable sharing some of the features of the present invention is described in EP-A-73 622, published on 9.3.1983 and hence lying in the Article 54(3) field.

According to this invention there is provided an electrical cable comprising a plurality of conductors extending in spaced parallel relationship in a common plane each surrounded by an outer layer of insulating material, the outer layers of insulating material around each conductor being integrally formed with web portions extending between adjacent conductors, each of certain conductors which in use constitute signal conductors, being surrounded by a shielding layer separated from the conductor by an inner layer of insulating material surrounding the conductor, the shielding layer being extended through the web portions between adjacent conductors, and being in direct contact with at least one other conductor which in use constitutes a ground conductor, characterised in that each signal conductor is surrounded by an individual shielding layer surrounding the inner layer of insulating material surrounding the conductor, a shielding connection member extending through the web portions and contacting the individual shielding layer of each signal conductor and contacting said one other conductor thereby to establish connections between the individual shielding layers and said one other conductor and the diameter of the outer layer of insulating material surrounding the or each other conductor forming an outer diameter which is substantially equal to the outer diameter of the inner layer of insulating material surrounding each signal conductor.

An electrical cable according to the invention will now be described by way of example with reference to the drawing, in which:- <ul id="ul0001" list-style="none"><li>Figure 1 is a perspective view of the cable; and</li><li>Figure 2 is a transverse sectional view through the cable.</li></ul>

The cable comprises four seven-strand signal conductors 1 and a single seven-strand ground ^. conductor 2, the conductors 1 and 2 being substantially the same size.

Each signal conductor 1 is surrounded by an inner layer 3 of insulating plastics material, which is in turn surrounded by an individual shielding layer 4 formed, for example, of an aluminium foil. The shielding layer 4 is in turn surrounded by an outer layer 5 of insulating plastics material.

. The signal and ground conductors 1 and 2 are arranged in spaced parallel relationship in a planar array, the spacing between adjacent conductors being equal to the spacing between adjacent contacts in a connector to be used to terminate the cable.

The ground conductor 2 is contacted by a shielding connection member 6 in the form of a metal foil, and is surrounded by an outer layer 7 of insulating plastics material.

The outer layers 5 and 7 of insulating material surrounding adjacent conductors 1, or 1, and 2, are joined by integrally formed web portions 8 through which the shielding connection member 6 extends, the shielding connection member 6 being in electrical contact with the individual shielding layer 4 of each signal conductor 1.

Thus, the individual shielding layer 4 of each signal conductor 1 serves to shield the signal conductor 1 throughout its length, and can easily be terminated at a connector in a similar manner to the signal conductor 1 by means of the ground conductor 2 which is electrically connected thereto by the shielding connection member 6.

For termination of the cable, the outer layer 5 of insulating material and the individual shielding layer 4 and shielding connection member 6 are removed from a length of each signal conductor 1 to leave the signal conductor 1 with the inner layer 3 of insulating material thereon substantially equal in diameter to the diameter of the ground conductor 2 with the shielding connection member 6 and outer layer 7 of insulating material thereon. The web portions 8 with the shielding connection member 6 are also removed from between adjacent conductors 1, or 1 and 2.

The cable can then be terminated using conventional mass termination apparatus (not shown) and using a connector having contacts with identical insulation displacement contact portions, in known manner.

The cable of this invention can be manufactured using known extrusion techniques which do not require detailed description herein.