Abstract:
A switching device is disclosed which includes a neutral conductor and arranged for opening and closing an electric circuit. The switching device includes a frame, through which the electric circuit&#39;s neutral conductor having a first end and a second end passes. The neutral conductor includes a movable middle portion that is arranged for breaking the neutral conductor inside the frame, the movable middle portion being movable with respect to the first and the second end of the neutral conductor and located between them.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a switching device provided with a neutral conductor. 
   Switching devices are apparatuses that are used for opening and closing an electric circuit. A switching device comprises at least one pole connected to a phase conductor and a control device for opening and closing this pole. Examples of switching devices are switches and switch fuses. 
   It is known to arrange a neutral conductor to pass through a switching device. 
   In some situations, for example when a switching device is installed or serviced, it is necessary to perform measurements or tests where the influence of the neutral conductor has been eliminated. Breaking the neutral conductor may be required in connection with an insulation level measurement, for instance. In prior art switching devices, however, the breaking of a neutral conductor is often difficult, or the structure of the breaking mechanism is complex. 
   BRIEF DESCRIPTION OF THE INVENTION 
   The object of the invention is to provide a switching device provided with a neutral conductor to solve the above-mentioned problems. The object of the invention is achieved by a switching device which is characterized by features of the disclosure. Additional embodiments of the invention are also disclosed. 
   The invention is based on the neutral conductor comprising a movable middle portion for breaking the neutral conductor. 
   An advantage of the switching device according to the invention is that the neutral conductor can be broken quickly and easily for measurements or testing, for example. A further advantage is that the structure of the breaking mechanism is simple. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     The invention will now be described in greater detail by means of preferred embodiments, with reference to the accompanying drawings, in which 
       FIG. 1  is a top view of a partly dismantled control device module of a switching device according to an embodiment of the invention; and 
       FIG. 2  is a cross-sectional side view of the control device module of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the control device module of  FIG. 1 , a neutral conductor  4 , which is arranged to be broken, passes through a frame  2 . The neutral conductor  4  comprises a first end  6 , a second end  8  and a movable middle portion  10 . 
   The first end  6  of the neutral conductor  4  is close to the first side of the frame  2  and the second end  8  of the neutral conductor  4  is close to the second side of the frame  2 . The first and the second side of the frame are opposite to each other. The movable middle portion  10  of the neutral conductor can be moved with respect to the first  6  and the second  8  end of the neutral conductor  4 , and it is located between them so that the first end  12  of the movable middle portion  10  is close to the first end  6  of the neutral conductor  4  and the second end  14  of the movable middle portion  10  is close to the second end  8  of the neutral conductor  4 . 
   Both the first  6  and the second  8  end of the neutral conductor are formed of a substantially rectangular planar preform by bending it so as to provide it with a cross-sectional shape that resembles the letter U, where one of the branches of the letter U is longer than the other. The longer branch extends outside the frame  2  and is arranged to be connected to the neutral wire of the electric circuit or to another similar structure. The first  6  and the second  8  end are arranged so that the longer branch of the letter U is located lower than the shorter branch. 
   The movable middle portion  10  of the neutral conductor is formed of a planar preform by bending the middle portion of the preform so that it is at a right-angle towards the rest of the preform. Thus the middle portion of the preform forms portion  24  which is at an angle of 90° with respect to the plane in which the first  12  and the second  14  end of the movable middle portion  10  are located. 
   The portion  24  of the movable middle portion  10  is in a different plane than the ends of the middle portion  10  since a control shaft  26  of the switching device passes in the middle of the frame  2 , the control shaft being arranged to control the switching device. The bent structure of the movable middle portion  10  thus improves space utilization inside the frame  2 . In addition to the movable middle portion  10 , attention is preferably paid to space utilization in the design of the first  6  and the second  8  end of the neutral conductor  4 , too, i.e. to the arrangement of other components inside the frame  2  as well as to their easy installation. The components to be mounted inside the frame  2 , which are preferably taken into account in the shaping of the neutral conductor  4 , include auxiliary contacts and microswitches and the main shaft of the switching device. These components are not shown in the figures. 
   The parts of the neutral conductor  4  are shaped to enable the portion  24  to slide to the side of the second end  8  of the neutral conductor, whereby the portion  24  is partly between the second end  8  of the neutral conductor and the frame  2  wall. 
   When the first end  6  of the neutral conductor  4  is desired to be in contact with the second end  8  of the neutral conductor  4 , the movable middle portion  10  is pressed against the first  6  and the second end  8  by pressing means  16 . The pressing means  16  comprise one screw member  18  per each end of the movable middle portion  10 . Each screw member  18  comprises a threaded portion and a head portion, the diameter of the head portion being larger than that of the threaded portion. The lower surfaces of the head portions of the screw members  18  are arranged to press the movable middle portion  10  against the first  6  and the second  8  end of the neutral conductor when the screw members are tightened. 
   The materials of the neutral conductor  4  and pressing means  16  have been selected and dimensioned to correspond to the currents passing in the neutral conductor. 
   In the structure illustrated in  FIG. 2 , the counterparts for the screw members  18  are integrated into the first  6  and the second  8  end of the neutral conductor  4 , i.e. the ends are provided with threads that are arranged to cooperate with the respective threaded portion of the screw member  18 . Alternatively, separate nuts can be employed. 
   The movability of the middle portion  10  is achieved by two slots. At the first end  12  of the movable middle portion  10 , there is an open slot  20 , and at the second end  14  a closed slot  22 . The open slot  20  has one open end and one closed end. The both ends of the closed slot  22  are closed. The slots  20  and  22  are arranged to receive the threaded portion of the respective screw member  18 . Each slot forms an opening extending through the middle portion  10  so that the threaded portion of the respective screw member  18  may pass through the movable middle portion  10  via the slot. The threaded portion of the screw member  18  can be slid through the open end of the open slot  20 , whereas each closed end of the slots prevents sliding the threaded portion therethrough. 
   The width of both the open slot  20  and the closed slot  22  is slightly larger than the diameter of the respective screw member and smaller than the diameter of the head portion. In the direction perpendicular to the longitudinal axis of the screw member  18 , the length of the slots  20  and  22  is greater than the diameter of the screw member  18 . The closed slot  22  is substantially longer than the open slot  20 . 
   The first end  12  of the movable middle portion  10  is detachable from the first end  6  of the neutral conductor without removing the respective screw member  18 . When the respective screw member  18  has been loosened by turning it a bit in the opening direction, the first end  12  of the movable middle portion  10  can be slid away from below the head of the screw member  18 . The second end  14  of the movable middle portion  10  cannot be fully detached from the second end  8  of the neutral conductor without removing the respective screw member  18 . 
   In a preferred embodiment of the invention, the closed slot  22  is made so long that the movable middle portion  10  can be slid, without removing the respective screw member  18  of the closed slot  22 , into a position where the middle portion  10  is not in a conductive contact with the first end  6  of the neutral conductor  4  even though the respective screw member  18  of the closed slot  22  were retightened. The neutral conductor  4  is thus broken by loosening the screw members  18  and by sliding the movable middle portion  10  along the upper surface of the first  6  and the second  8  end of the neutral conductor towards the second end  8  of the neutral conductor. By tightening the screw member  18  at the second end  8 , the movable middle portion  10  can be locked in a desired position, in which case it cannot accidentally move into a conductive contact with the first end  6  of the neutral conductor. An advantage of this embodiment is that the conductive contact between the ends  6  and  8  of the neutral conductor  4  can be reliably maintained broken during measurements or testing without having to detach any part of the neutral conductor  4  or the pressing means  16  from the switching device. As a result, none of the parts of the neutral conductor  4  or pressing means is at the risk of disappearing during the measurement or testing. 
   In an alternative embodiment, both ends of the movable middle portion  10  comprise a slot having an open end. In that case, the slots can be adapted such that the movable middle portion  10  can be detached from the switching device after the screw members  18  have been loosened, i.e. neither of the screw member  18  needs to be completely removed for detaching the movable middle portion  10 . 
   In  FIG. 2 , the dashed line illustrates a lid  28  that covers the neutral conductor  4  during the normal use of the switching device. The lid  28  is quickly detachable and attachable for easy access to the neutral conductor  4 . In an embodiment, the lid  28  is arranged to be openable without tools. 
   The switching device structure according to the invention, which comprises a neutral conductor that can be broken, was described above in connection with a modular switching device. It is clear that the structure according to the invention is also applicable to switching devices where the control apparatus is mounted in the same frame part with the switch poles. 
   It is obvious to a person skilled in the art that the inventive concept can be implemented in various ways. The invention and its embodiments are thus not limited to the above examples but they may vary within the scope of the claims.