Wedge of a transition for cables etc

The disclosure concerns a compression unit, in the form of wedge, of a transition for cables, pipes or wires. The wedge is to be placed inside a frame together with a number of compressible modules, which modules are to receive cables etc. The wedge comprises a number of wedge elements. The wedge is moved between non activated and activated positions by means of a screw, received in a through opening of a first wedge element, and a sleeve, received in an opening of a second wedge element. The wedge further comprises at least one clip, of an electrically conductive material, placed inside the wedge. The at least one clip is placed to connect the screw with the frame to connect the screw to earth.

This application claims benefit of 1551281-7, filed 6 Oct. 2015 in Sweden, which application is incorporated herein by reference. To the extent appropriate, a claim of priority is made to the above disclosed application.

TECHNICAL FIELD

The present invention concerns protection against electrostatic discharge in a compression unit of a transition for cables, pipes or wires.

BACKGROUND

The present invention has been developed in view of transitions having a frame, in which frame a number of modules, for receiving separate cables, pipes or wires, and at least one compression unit are placed. Often the compression unit has the form of a so-called wedge, comprising a number of interacting wedge elements. Such wedges have normally one or more screws to activate the compression unit.

There is a risk that electrically conductive material builds up static charges. Such static charges might discharge at contact with a different potential. This could lead to ignition of possible hazardous gases present.

The one or more screws of the compression unit should be connected to earth in order to avoid the risk of an undesired electrostatic discharge. It is previously known to solve this problem by connecting the one or more screws to an external conductor.

SUMMARY

One object of the invention is to avoid that electrically conductive material builds up a static charge, which might cause a discharge at a contact with a part of a different potential.

One further object of the invention is to solve the problem in a way facilitating handling, and a fitter should not need to take any special measures to solve the problem. The solution is an integrated part of the compression unit, which functions directly at installation.

By means of the present invention the one or more screws of the compression unit is connected to the frame of the transition, by means of one or more clips. Thus, by means of said clips, being part of the compression unit, the one or more screws are connected to earth.

Further objects and advantages of the present invention will be obvious to a person skilled in the art when reading the detailed description below.

DETAILED DESCRIPTION

FIG. 1shows one example of a setting in which a compression unit is used. The shown example is a transition for sealed transfer of cable, pipes or wires through a wall or the like. It is commonly known to use this kind of transitions. It comprises a steel frame1, often placed in a wall. Inside the frame1a compression unit, often called a wedge2, is placed together with a number of modules3and stay plates4. Each module3is formed of two halves and has a number of peelable layers5, for adaptation to the outer diameter of the cable, pipe or wire to be received. Each module3has a central plug6, which is removed when a cable, pipe or wire is to be received. If no cable, pipe or wire is to be received in a specific module3, the central plug6is left inside the module when inserted inside the frame1. The stay plates4are used to keep the modules3safely inside the frame1. The wedge2is activated to compress the modules3. By expanding the wedge2the modules3will be compressed in one direction, leading to expansion in other directions, which will give a sealing effect around any cable, pipe or wire received inside a module3. There will also be a sealing effect in view of the frame1. This kind of sealing effect is well known to a person skilled in the art.

In a first embodiment of a compression unit or wedge7, which could be used in a transition as described above, the wedge7comprises four wedge elements8,9,10,11. The four wedge elements8,9,10,11could be made as one single unit, see e.g. WO 96/11353. Of said four wedge elements, a first wedge element8is placed opposite a second wedge element9in a common plane. The first and second wedge elements8,9have upper and lower inclined surfaces and said inclined surfaces incline downwards towards the other of said first and second wedge elements8,9. Of the four wedge elements a third wedge element10and a fourth wedge element11are placed on opposite sides of the first and second wedge elements8,9. Each of the third and fourth wedge elements10,11has two inclined surfaces which are placed adjacent one inclined surface of the first wedge element8and the second wedge element9, respectively. The first and second wedge elements8,9are arranged moveable towards and away from each other, by means of an arrangement of a screw13and a sleeve14. The screw13goes through a through opening12of the first wedge element8. The sleeve14, having an outer end15, is received and fastened in a through opening of the second wedge element9in the shown embodiment. The outer end15of the sleeve14has a larger outer diameter than the through opening of the second wedge element9. The second wedge element9and the sleeve14will move as one unit in relation to the screw13and the first wedge element8. In other embodiments the sleeve14is received and fastened in an opening not going all the way through the second wedge element9. The sleeve14has an inner thread for cooperation with an outer thread of the screw13. By turning the screw13in a first direction the screw13is screwed deeper into the sleeve14, shortening the distance between the first wedge element8and the second wedge element9. By screwing the screw13in a second direction the screw13is screwed in a direction out of the sleeve14, increasing the distance between the first wedge element8and the second wedge element9. When the distance between the first and second wedge elements8,9is decreased the third and fourth wedge elements11,12are moved away from each other, due to the inclined surfaces of the four wedge elements8,9,10,11. When the distance between the first and second wedge elements8,9is increased the third and fourth wedge elements10,11are moved towards each other, due to the inclined surfaces of the four wedge elements8,9,10,11.

In use the wedge7is inserted inside the frame in a non-activated position. In the non-activated position the first and second wedge element8,9are far from each other, while the third and fourth wedge elements10,11are close to each other. With all cables, pipes or wires placed inside one or more of the modules3inside the frame1, the wedge7is moved into an activated position by means of the screw13. In the activated position the first and second wedge elements8,9are moved towards each other and the third and fourth wedge elements10,11are moved away from each other. With the wedge7placed as indicated inFIG. 1, the third wedge element10will be pressed against the frame1in the activated position, at the same time as the fourth wedge element11will be pressed downwards. As the modules3are of a compressible material they will thereby be pressed against each other, against the cables etc. and the frame1.

On the inside of the wedge7, a clip16is placed. The clip16is made of an electrically conductive material. The clip16has a central through opening17placed on an elongated central part18. At opposite ends of the elongated central part18, there are two end parts19, bent in right angles to the central part18. The two end parts19are directed in the same direction in view of the central part18. The central part18and the bent end parts19are made in one piece. The clip16is placed at the first wedge element8of the wedge7, with the bent ends19of the clip16placed at opposite sides of the first wedge element8. In use the opening17of the clip16is to be placed at the end of and abutting the sleeve14of the wedge7. When the wedge7is activated in that the first and second wedge elements8,9are moved towards each other, the sleeve14will be pressed against the clip16, whereby the bent ends19of the clip16will be pressed against the inner sides of the frame1. The screw13will thereby be connected to earth, as the screw13is connected to the sleeve14.

In use the screw13is automatically connected to earth in the activated position of the wedge7, without a fitter having to do anything in addition to the normal handling of wedges of this kind.

A second embodiment of a wedge20has basically the same design as the wedge7of the first embodiment. Thus, the wedge20has a first wedge element21, a second wedge element22, a third wedge element23and a fourth wedge element24. The wedge20has further a screw26and a sleeve27, cooperating by means of threads with the screw26. The sleeve27has an outer free end28. The wedge elements21-24have inclined surfaces in mutual contact in the same way as previously described. The screw26is received in a through opening25of the first wedge element21and the sleeve27is received and fastened in a through opening of the second wedge element22. In a way corresponding to the previously described wedge7, the first and second wedge elements21,22are moved towards and away from each other depending on the direction of rotation for the screw26in the sleeve27. When the first and second wedge elements21,22are moved towards each other, the third and fourth wedge elements23,24are forced further apart. When the first and second wedge elements21,22are moved away from each other the third and fourth wedge elements23,24are moved towards each other.

In use the wedge20is placed inside the frame in a non-activated position, in which the first and second wedge elements21,22are far from each other. The wedge20is then moved to an activated position by means of the screw26, whereby the first and second wedge elements21,22are moved towards each other, forcing the third and fourth wedge elements23,24away from each other.

On the inside of the wedge20, two clips29are placed. Said clips29are identical in the shown embodiment, but turned 180°. Each clip29has an elongated central part30and two end parts31,32at opposite ends of the central part30. The two end parts31,32are bent in right angles to the central part30and are directed in the same direction in view of the central part30. One of the end parts31projects a shorter distance from the central part30than the other end part32. Thus, there is a shorter end part31and a longer end part32. The central part30and the end parts31,32are made in one piece. Each clip29is placed on the first wedge element21of the wedge20, with the shorter bent end31placed inside the through opening25of the first wedge element21, between the sleeve22of the wedge20and the inner surface of the through opening of the first wedge element, and with the longer bent end32placed at the side of the first wedge element21, between the first wedge element21and the frame1. Thus, in view of the first wedge element21, the shorter bent end31could be said to be placed at an inner position while the longer bent end32could be said to be placed at an outer position. When the wedge20is activated and the first and second wedge elements21,22are moved towards each other, the shorter bent end31of each clip29will be pressed against the sleeve27and the longer bent ends32of each clip29will be pressed against the inner sides of the frame1. Thus, the two clips29abut opposite sides of the frame1. The screw26will thereby be connected to earth as the screw26is connected to the sleeve27.

A person skilled in the art realizes that the wedges7,20and clips16,29are interchangeable. Thus, either of the clips16,29can be used with the wedge7of the first embodiment and the wedge20of the second embodiment, respectively.