More particularly the invention relates to an electrical cable gland for use on cables of the type having what is generally termed armouring located between an inner electrically insulating sheath and an outer electrically insulating sheath. Still more particularly the invention relates to a cable gland which is capable of being employed on a wide variety of different types of cable having armouring of various different thicknesses.

It is to be understood that the term armouring is used in this specification in a broad sense in that the armouring could be a mechanically protective layer in the form of longitudinally extending relatively stiff wires of significant thickness arranged to form an electrically conductive (generally used for earthing purposes) armour layer between the inner and outer insulating sheaths and having substantial tensile strength; or the armouring could be in the form of fine, substantially more flexible, optionally braided, wires or even metal tape not having such substantial tensile strength and often serving one or more functions including reinforcing the cable ; providing an electromagnetic shield ; or simply an electrically conductive earth. These different forms of armouring have substantially different thickness and the invention relates to a cable gland capable of accommodating such different thickness.

BACKGROUND TO THE INVENTION It is common practice to design cable glands with an armour clamp in the form of a cone having an outer conical surface for engaging the inside of the armouring and adapted to cooperate with a clamping ring having an inner surface of complementary conical shape so that the armouring can be clamped firmly between the two conical surfaces. The appropriate locking cone angle and other constraints on the length of cable gland and material content do not naturally lend themselves to accommodating distinctly different thickness of armouring and in times gone by it was common practice to provide different dedicated cable glands for use on cables having the various different types of armouring.

It has, however, long been recognized that it is generally impractical and highly costly to provide different cable glands for each of the different types of cables, and more significantly, the different thickness of armouring provided on electrical cables which are otherwise of a similar size and nature.

One proposal that has been put forward to accommodate different thickness of armouring is set out in British Patent No 2,269,710 which describes a substantially conventional cone and clamping ring in which the cone must be made substantially longer, or the clamping ring shorter, or both, simply to accommodate different armour thickness with a substantially conventional arrangement. This proposal is not particularly appealing where substantial differences in thickness of armouring is to be accommodated as the entire gland must be made substantially longer thereby requiring more material with accompanying increased cost.

British Patent No 2,269,711 describes another proposal in which the ring has two conical surfaces facing in opposite axial directions and adapted to be

selectively engaged with different thickness cable armouring by selectively axially reversing the ring in its position in the gland. The instructions for installing such a gland are extremely difficult to perceive from the outer surface of the clamping ring and this arrangement is viewed by applicant as impractical and possibly even dangerous if the clamping ring is not installed in the correct orientation.

British Patent No 2,296,998 provides another proposal in which the outer conical surface of the cone is stepped to provide two different diameter cone surfaces of the same cone angle for selective engagement, according to the thickness of the armouring, with the same clamping ring. Of necessity the operative length of the clamping surface is limited and proper installation of such a cable gland requires that the free ends of the armouring be trimmed rather accurately which is extremely difficult to achieve and control in the field with normal hand tools available.

Irrespective of the above, many cable glands have a loose cone or ring, or both, and designs such as that of British Patent No 2,269,711 make it impossible to correct this situation. The problem with loose parts is that a technician installing a gland may have difficulty in holding all the necessary components; may drop and possibly lose a cone or ring; and may close the gland with the dropped or lost part missing with possible serious consequences.

OBJECT OF THE INVENTION It is an object of this invention to provide a cable gland which can more easily an reliably accommodate the different thickness of different types of armouring provided on different cables.

It is another object of the invention to provide a cable gland of this type which may, if required, be configured so that it does not require loose components and the gland can be made in the form of two sub-assemblies for ease of installation.

SUMMARY OF THE INVENTION In accordance with this invention there is provided a cable gland comprising an armour clamp assembly having an armour clamping cone and a cooperating clamping ring and wherein the armour clamping cone and clamping ring each have a first cooperating conical clamping surface of substantially conventional and relatively small cone angle, the cable gland being characterized in that at the larger diameter end of the first conical clamping surface of each of the cone and ring, a second cooperating clamping surface diverges outwardly from the first conical surface, the second cooperating clamping surfaces being adapted to clamp between them armouring of relatively small thickness whilst the first cooperating clamping surfaces are adapted to clamp between them armouring of relatively larger thickness.

Further features of the invention provide for the first cooperating conical clamping surfaces to have a cone angle of from 15 to 25 degrees and preferably about 20 degrees so that the first clamping surfaces make an angle of from 7.5 to 12.5 and preferably about 10 degrees with the axis of the cable gland ; for the second cooperating clamping surface in each case to be conical but of substantially larger cone angle than the first conical surface, the conical surfaces preferably having a cone angle of between about 60 and 90 degrees so that the second clamping surfaces make an angle of from about 30 to about 45 degrees with the axis of the cable gland, the preferred cone angle being about 70 degrees in which case the second clamping surfaces makean angle of 35 degrees with the axis of the cable gland ; for the

cable gland to have a two-part construction with the cone being held captive in a first body part and the clamping ring being held at least temporarily captive in a second body part with the two body parts being movable axially by virtue of cooperating screw threads thereon; and for the cable gland to embody both inner and outer compression seals for sealing onto the inner and outer sheaths of the cable.

The invention makes use of the fact that relatively thick armouring such as the relatively stiff longitudinally extending wires mentioned above must be clamped to withstand substantial tensile force in substantially conventional manner whilst the thinner armouring such as relatively fine braided wires and metal tape which can be effectively clamped between the second clamping surfaces primarily require the formatrion of good electrical contact between the clamping surfaces and the armouring. It is not generally required of a cable gland to withstand substantial tensile force in the case of the less robust and relatively thin armouring.

In order that the invention may be more fully understood one embodiment thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:- Figure 1 is an elevation of a cable gland according to the invention with the upper half thereof shown in section; Figure 2 is a schematic sectional view showing the relationship between the cone and clamping ring in the case where thicker armour wires are clamped between them; and,

Figure 3 is a view similar to Figure 2 but showing the relationship between the cone and clamping ring where thinner armouring is clamped between them.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS In the embodiment of the invention illustrated in the drawings a cable gland, generally indicated by numeral (1), is composed of two body parts (2) and (3), the first (2) of which has an armour clamping cone (4) held captive relative to it and the second (3) of which has a clamping ring (5) held captive relative to it, preferably releasably captive. The two body parts have cooperating screw threads (6) whereby they may be urged axially towards each other to move the cone (4) into the ring (5). The cone has a rearwardly directed extension (7) which simultaneously compresses an inner elastomeric seal (8) in well established manner. The entry end of the gland has an outer elastomeric compression seal (9) which is independently brought into service by means of a union nut (10) screwed onto the entry end of the body.

The cone (4) and ring (5) have cooperating first conical clamping surfaces indicated by numerals (11) and (12) respectively. The cone angle of these surfaces is substantially conventional, for example 20 degrees (ie an angle of 10 degrees to the axis of the gland) so that these first conical clamping surfaces are of self locking type. These surfaces are adapted to clamp between them the usual rather thick, stiff armour wires (13) of a widely used type as illustrated in Figure 2. These surfaces provide a substantially conventional armour clamp arrangement.

In addition, and as provided by this invention, each of the cone and ring have, at their larger diameter end, a second conical clamping surface indicated by numerals (14) and (15) respectively. The cone angle of these

second conical clamping surfaces is substantially greater than that of the first clamping surfaces and in a preferred arrangement the cone angle is about 70 degrees in which case the second conical surfaces extend at an angle of 35 degrees to the axis of the cable gland. These surfaces are arranged such that, as the cone moves further into the ring, and beyond the point where the thicker wires (13) would become clamped and thus prevent further movement of the cone into the ring, these second surfaces approach each other and become capable of clamping between them armouring indicated by numeral (16) of substantially lesser thickness as illustrated in Figure 3.

Because the clamping of this type of armouring is generally not expected to accept appreciable tensile forces on the cable, the axial length of the second clamping surfaces can be relatively short as the primary objective is to create effective electrical continuity by way of these surfaces and this is most easily and effectively achieved using relatively short surfaces. Clearly, these second conical clamping surfaces are not of a self locking type.

It will be seen that the cone and clamping ring are automatically functional without either of them needing to be removed from its associated body part in order to render it functional. This being so, the gland can be made in the form of two easily manageable sub-assemblies for easy and swift installation without the danger of any loose part being dropped or lost and thus possibly omitted from the cable gland.

It will be understood that numerous variations may be made to the embodiment of the invention described the without departing from the scope hereof. In particular, the second clamping surfaces need not be conical but could be of another shape, such as curved in longitudinal section.

The invention therefore provides an effective and simple solution to the problem set out in the background hereto.