AU2005234093A1

AU2005234093A1 - Switchgear

Info

Publication number: AU2005234093A1
Application number: AU2005234093A
Authority: AU
Inventors: Paul Kadan; Franz Reil; Adolf Tetik
Original assignee: Moeller Gebaudeautomation GmbH
Current assignee: Moeller Gebaudeautomation GmbH
Priority date: 2004-04-19
Filing date: 2005-04-15
Publication date: 2005-10-27
Anticipated expiration: 2025-04-15
Also published as: SI1741117T1; ES2371257T3; EP1741117B1; WO2005101443A3; BRPI0510011A; WO2005101443A2; AU2005234093B2; JP2007533083A; PL1741117T3; RS51972B; EP1741117A2; CN1957432A; AT504607A1; ATE521077T1; CN1957432B

Description

Verification of Translation I, Jeffrey J. Waldock, akad.U. (university trained translator), c/o Quick Translation Vienna, Helmholtzgasse 10/4, A-1210 Vienna, Austria declare as follows: 1. That I am well acquainted with both the English and German languages, and 2. That the attached document is a true and correct translation made by me to the best of my knowledge and belief of the text of the PCT Application PCT/AT2005/000132 as filed on 15 April 2005. 11 October 2006 . . . . .. . . . . . . . . . . . . ° . . . . . . . . . . . . . . . . . . . . . ..

° ° (Date) (Signature of Translator) (No witness required) 1 A switchgear The invention relates to a switchgear comprising a housing, especially a circuit-breaker, in which at least one terminal is arranged in a receiver arranged in the switchgear housing, with the front side being sealed off at least in sections by a cover. Such switchgears are used as circuit-breakers, especially miniature circuit-breakers, in a large variety of application types. Electrical switchgears must meet predetermined security regulations. The close-packed use of such electrical switchgears in switch-boxes requires special security features for such switchgears. Regulations such as the US-American UL 489 define minimum spaces between the externally accessible live conductors of adjacent electrical switchgears. For switchgears up to an operating voltage of UN of less than and equal to 300V a clearance in air of not less than 19.1 mm is required between two adjacent live conductors. At an operating voltage of UN > 300V the required minimum clearance in air between two adjacent live conductors is already 25.4 mm. Such clearances in air between close-packed switchgears are realized by means of wider housings. This leads to switchgears which have volumes or widths of housings which would not be necessary for their functioning. In addition to resulting higher costs for production, storage and transport of such switchgears, they especially require a lot of space. In addition to the flashover between the electrically conductive parts of two adjacent switchgears, the leakage currents which occur especially in the housing parts of electrical components represent a safety risk. An electric flashover can occur not only through air. The housing walls of an electrical device represent a far lower resistance for electric current than clearance in air. The required minimum distances along a housing wall are required to be respectively larger in order to prevent a conductive connection between two adjacent terminals by leakage currents. When arranging several switchgears adjacent to one another, the leakage current distance typically corresponds to the clearance in air. That is why for fulfilling the required minimum leakage current distance the switchgears are usually larger than would be required by the 2 clearance in air. The use of narrow configurations usually employed in the low-voltage range is therefore no longer possible in switchgears from a certain operating voltage. It is therefore the object of the present invention to provide a switchgear of the kind mentioned above which offers a high amount of security against flashovers between the electroconductive parts of two adjacent switchgears of especially the same configuration, without relevantly changing the width of the switchgear. It is a further object of the invention to provide a switchgear which with possibly unchanged external dimensions provides an increased level of security against leakage currents between the electrically conductive parts of two adjacent switchgears of especially the same configuration. It is a further object to provide a switchgear with several breaker gaps in which an increased security against flashover or leakage currents is offered between two adjacent terminals. This is achieved in accordance with the invention in such a way that a plate-like or rib-like shielding element which projects beyond the front cover is integrally formed on the housing. The clearance in air and the leakage current distance to an adjacent switchgear and its terminals can be increased in this way by maintaining the same width of the switchgear. Switchgears with virtually the same external dimensions as in low-voltage devices can be used at higher application voltages. The terminals can thus be screened effectively against flashovers. It can be provided in a further development of the invention that the plate-like or rib-like shielding element extends substantially over the entire height of the housing. As a result, the area between a terminal opening and an adjacent terminal screw opening or any other exposed conductor can be protected effectively against a flashover. In this connection it can be provided in a further development of the invention in a switchgear in which terminal openings and/or terminal screw openings are provided for the connection terminals in the front cover that two substantially mutually parallel shielding elements are arranged on either side of the terminal openings and/or the terminal screw openings, so that at least two separate shielding elements each are provided between two adjacent terminal openings which form a free gap between the two shielding elements. In the case of adjacently arranged terminal openings, the path of the occurring leakage currents is thus extended very effectively because the creepage path is extended substantially by the gap. As a result of the arrangement of two shielding elements, the switchgear comprises on two sides the required clearance in air to the 3 adjacent terminals. By arranging two shielding elements, the switchgear has the required clearance in air to the adjacent terminals. According to a further embodiment of the invention it can be provided that the shielding elements are arranged in an inwardly offset manner parallel to the exterior of a housing and at a distance from the exterior of the housing, so that when two switchgears are arranged next to one another two adjacently situated shielding elements form a free gap. The path of the occurring leakage currents is thus extended in a very effective manner in the case of adjacently arranged, similar switchgears, because the shielding elements of two adjacent similar switchgears will not lie on each other and a substantially extended creepage path is obtained by the distance between the shielding elements and the gap thus formed. In a further embodiment of the invention it can be provided that in the region of the free gap depressions are provided on the housing, preferably on the exterior of the housing, especially in the region of the terminal screw opening, in order to enlarge the depth of the free gap. As a result of the housing geometry, the terminal screw openings represent a special danger by occurring leakage currents in the case of adjacently arranged similar switchgears. They are effectively prevented in this manner. It can be provided in a further embodiment of the invention that the at least one shielding element comprises a recess on at least one side which preferably extends over the entire surface of the shielding element, with the recess forming a boundary edge which is elevated relative to the same. The creepage path is thus further extended. In this connection it can be provided in a further development of the invention that the at least one shielding element comprises at least one stiffening rib. The shielding element can thus withstand higher mechanical loads as occur during the mounting for example without being damaged. Defective shielding elements represent a higher security risk. The invention further relates to a switchgear, especially a circuit-breaker, for electrical systems with a housing having terminals, with at least one arrangement for extending the creepage path being provided on at least one housing part. It is the object of the invention to provide a switchgear in which a higher security is given against leakage currents between the electrically conductive regions of the terminals, specially the 4 terminal screw openings, of two adjacent switchgears of similar configuration with possibly unchanged external dimensions. This is achieved in accordance with the invention a recess, depression or the like is each arranged on the side of a terminal screw opening associated with the terminal on the exterior of the housing, with a free gap being formed between two adjacently arranged housings in the region of the terminal screw openings. The creepage path can be extended substantially while retaining an unchanged width of the housing. This keeps the dimensions of switchgears at the level of low-voltage switchgears even in the case of higher operating voltages. The invention relates to a switchgear, especially a circuit-breaker, for electrical systems with a housing, at least one cable clamp, comprising a movable box, a fixed box wrapped around the same and a clamping screw which can be screwed through a lead-through opening of the fixed box into a thread of the movable box with a head against a clamping support, with the movable box forming together with the fixed box a terminal opening for cable ends which is adjustable by means of the clamping screw, and further comprising a clamping opening for cable lugs formed between the head of the clamping screw and the fixed box. Switchgears with such cable clamps are known and much in use. However, merely cable ends and so-called tubular fork-type cable lugs can be clamped with such cable clamps. So-called ring cable lugs cannot be clamped with such a clamp or can only be clamped with much effort. For clamping the ring cable lug, the clamping screw must completely release the clamping opening in order to enable the introduction of the ring cable lug into the clamping opening. Means are provided in a number of embodiments of switches which prevent the clamping screw from dropping out of the cable clamp. Such switches cannot be used at all for operation with ring cable lugs. A special tool or gravity is necessary in the case of embodiments which allow the removal of the clamping screw from the cable clamp. Apart from the fact that installed electrical appliances in many cases cannot be brought to a position which promote dropping the clamping screws, dropped conductive parts represent a high safety risk in electrically sensitive environments. The 5 use of special tools for getting out the clamping screw from the clamping area also represents an unsatisfactory solution. The handling of a screw with pliers is laborious, and the screw may be lost in this way. It is therefore the object of the invention to provide a switchgear according to the preamble of claim 9 with which the known disadvantages can be avoided and which allows secure operation of ring cable lugs on such a switch. This is achieved in accordance with the invention in such a way that means for completely twisting out the clamping screw from the clamping opening are provided. This helps ensure that the clamping screw releases the clamping region for the introduction of a ring cable lug without any additional auxiliary means and without any help by gravity and without removing the clamping screws from the switchgear. It can be provided in a further development of the invention that the means for completely twisting out the clamping screw from the clamping opening comprises a thread-free region of the clamping screw which is arranged adjacent to the clamping screw head. This allows to provide means close to the screw which are not influenced by the thread of the screw. In this connection it can be provided in a further development of the invention that the thread free region of the clamping screw has a portion tapering over the cross section. A region of the clamping screw can thus be formed which is suitable to receive a portion with an inside thread without moving the same. It can be provided in a further development of the invention that the means for completely twisting out the clamping screw from the clamping opening comprise small plates which are arranged in a twist-proof manner on the side of the clamping support of the terminal which is averted from the box and parallel to the same and whose thickness corresponds to not more than the height of the thread-free region of the clamping screw. According to a further development of the invention it can be provided that the small plate comprises a lead-through opening for the clamping screw which comprises at least parts of a thread. As a result of the characterizing features of claims 12 and 13, such a small plate with an inside thread can be arranged on the thread-free cross-sectional constriction of the clamping 6 screw without impairing the same in the normal operation of the clamping opening for cable ends. When the clamping screw is twisted out of the thread of the movable box, the threaded part of the small plate receives the screw and ensures complete twisting out of the clamping region which is now formed between the small plate and the clamping support. The invention is now explained in closer detail by reference to the enclosed drawings showing embodiments, wherein: Fig. 1 shows two switchgears according to claims 1 and 6 in an axonometric view; Fig. 2 shows two switchgears according to Fig. 1 in a top view; Fig. 3 shows a cable clamp of a switchgear according to claim 9 in an axonometric view; Fig. 4 shows a cable clamp according to Fig. 3; Fig. 5 shows a cable clamp according to Fig. 3 with a ring cable clamp; Fig. 6 shows a sectional view of a switchgear according to Fig. 1 with a cable clamp according to Fig. 5 in an axonometric view; Figs. 1 and 2 show two switchgears S in accordance with the invention, comprising a housing 2, especially a circuit-breaker, in which at least one terminal 1 is arranged in a receiver 36 formed in the housing 2, with the receiver 36 being sealed off on the front side at least in sections by a cover 30, with at least one plate-like or rib-like shielding element 3 which protrudes beyond the front cover 30 is formed integrally on the housing 2. The invention is not limited to the application in switchgears S with merely one breaker gap. It can be used in switchgears S with a plurality of breaker gaps (especially two or four). Switchgears in accordance with the invention comprise a housing 2 which is composed of insulating material. The housing comprises a basic body with exterior sides 32 of the housing which is provided in the preferred arrangement of switchgears in accordance with the invention on a mounting rail as a contact surface to an adjacent switchgear of the same or similar configuration. The basic body of the housing 2 of switchgears S in accordance with the invention 7 further comprises a cover surface 37 which may comprise breakthroughs for control elements such as a handle 38 or a test button. The basic body further comprises front sides 35 of the housing which are substantially adjacent to the exterior sides 32 of the housing or are delimited by the same. The housing 2 comprises at least one receiver 36 for at least one terminal 1. The receiver 36 is arranged in the housing 2 in the region of the front side 36 of the housing and is sealed at least in sections by a front-side cover 30. It can be provided that the cover is formed integrally with the housing 2, such as when a bipartite housing is provided as in the illustrated preferred embodiments. It can also be provided that the receivers 36 are sealed or covered by means of removable covers 30. Clamping openings 6 and/or clamping screw openings 7 for the terminals I are preferably formed in the cover 30 or in the housing 2. A large variety of switchgears S, especially circuit-breakers, are arranged in close proximity in switchboxes and fuse boxes. In order to house the largest possible number of such switchgears S on a limited basic surface, they are usually arranged in a relatively narrow manner and in such a way that they can be arranged next to one another in an advantageously compact manner. When arranged close to one another, the likelihood of a spark-over rises due to low safety distances between the exposed live conductors. These conductors usually concern parts of the terminals I which cannot be insulated completely. It is therefore necessary to maintain safety distances between the live conductors. Relevant regulations such as the US-American UL 489 define minimum distances between the externally accessible live conductors which need to be fulfilled by a switchgear S in order to be marketed on a certain market. A clearance in air of not less than 19.1 mm between two adjacent live conductors is required for a switchgear S up to an operating voltage of UN of less than and equal to 300V. At an operating voltage of UN > 300V, the required minimum clearance in air between two adjacent live conductors is already 25.4 mm. Switchgears S usually used up to voltages of 300V fulfil the minimum clearance in air merely by the overall size of housing 2 which is necessary to receive the electromagnetic and/or electromechanical modules of the switchgear S. Switchgears S with such external dimensions could also be used at substantially higher operating voltages. This is counteracted by the required minimum clearance in air between adjacent live conductors.

8 The minimum clearance in air required for the use at operating voltages of over 300V between adjacent live conductors leads to housing dimensions which are not justified by the function of the switchgear S. Especially the width of the switchgear S rises, which thus dramatically reduces the number of switchgears S which are housed on a given surface area. In order to overcome or avoid this disadvantage and to use the switchgear S with smaller external dimensions, especially with a smaller width and lower distances to adjacent terminals, at higher operating voltages, the switchgears S in accordance with the invention and in accordance with claim 1 comprise at least one plate-like or rib-like shielding element 3 which protrudes beyond the front cover 30 and which is integrally formed on the housing 2. The width of the housing can thus be kept to the level of low-voltage switchgears (e.g. approx. 17.5 mm). This allows arranging substantially more switchgears S on a given surface than was previously possible. It has proven to be especially advantageous that the at least one shielding element 3 is arranged as a substantially planar plate 4 or rib 4. Such a plate 4 or rib 4 enables enlarging the clearance in air between the terminals 1 of adjacent switchgears S in an especially simple way. The concrete shaping of such a plate 4 or rib 4 and generally the shaping of a shielding element 3 in accordance with the invention is derived from the housing dimensions and the required clearances in air between two adjacent switchgears S. It can be provided for in an especially preferred embodiment of the invention that the plate-like or rib-like shielding element 3 extends substantially over the entire height h of the housing, as a result of which the region between a clamping opening and an adjacent clamping screw opening can be protected effectively against a flashover. The height h of the housing designates the height of the housing 2 in the region of the front side 35 of the housing or in the region of the side of the housing on which the terminals are arranged. Shielding elements 3, and especially the plates 4 and ribs 4, which are often made of a thin walled plastic material, have a considerable likelihood for destruction. Improper handling especially during the mounting of the connections or the switchgear itself can lead to damage or breaking of the shielding element 3. Damaged or missing electrical shielding elements 3 represent a safety risk and can lead to the failure of apparatuses or systems or to the injury of humans. That is why it has been proved to be advantageous that the at least one shielding element 3 comprises at least one stiffening rib 5. Such a stiffening rib 5 substantially increases the mechanical stability under load of the shielding element 3 with a minimum of effort. It is 9 provided to adjust the type and concrete configuration of the stiffening rib 5 to the concrete situation. The invention is especially aimed at the use of switchgears S which are provided for arrangement next to one another and are characterized by uniform dimensions of the housing. In the case of such switchgears S in which the arrangement of the exterior side of the next switching device S is not clear prior to mounting, it is advantageous when the switchgear S has two mutually spaced shielding elements 3. The air gap between the live parts of two adjacent switchgears S can be extended in the most effective way when the shielding elements 3 are arranged substantially parallel about the clamping openings 6 and/or the clamping screw openings 7 of the terminals 1. With a minimum use of shielding elements 3 it is thus possible to extend the clearance in air most effectively, which occurs irrespective of the point where the switchgear S is arranged in a possible assembly of switchgears. A possible conductive connection between adjacent live parts by air is not the only safety risk in the operation of electric switchgears S in narrow proximity. Virtually any solid material, even insulators, have a substantially lower resistance than air. Parasitic electric currents which are so called leakage currents can propagate along the surfaces of housing and thus lead to a conductive connection with an adjacent switchgear S. In order to prevent this, there are regionally binding regulations for the creepage paths to be maintained as a minimum by switchgears S between the exposed live conductors of two adjacent switchgears S. As a result of the lower resistance than that of air which the housing 2 sets against the electric current, the required minimum creepage paths are longer than the clearances in air. The US-American UL 489 requires for switchgears S a creepage path of at least 31.8 mm between two adjacent live conductors up to an operating voltage of UN less than and equal to 300V. At an operating voltage UN > 300V the required creepage path between two adjacent live conductors is already 50 mm. If conventional switchgears S are arranged next to one another without any additional constructional measures, then the creepage path is equal to the clearance in air. This entails that electric switchgears S which meet the required creepage paths are several times larger than would be necessary for securely fulfilling the switching tasks. This leads to a substantial increase in the required space and the resulting costs.

10 The switchgears S in accordance with the invention preferably comprise two shielding elements 3 which are substantially parallel with respect to each other on either side of the clamping openings 6 and/or the clamping screw openings 7, so that at least two separate shielding elements 3 are each provided between two adjacent clamping openings 6 which form a free gap 31 between the two shielding elements 3. In the case of switchgears S which have more than one breaker gap it can therefore be provided that two shielding elements are arranged between adjacent terminals. In the case of breaker gaps which are arranged close to the exterior 32 of a housing, it is preferably provided that the shielding elements 3 are arranged parallel to an exterior 32 of the housing and at a distance from the exterior 32 of the housing offset to the inside, so that in the case of adjacently arranged switchgears S two shielding elements 3 lying close to one another form a free gap 31. This is clearly shown in Figs. 1 and 2. The shielding elements 3, which are arranged in Fig. 2 as plate 4 or rib 4, are positioned inwardly to such an extent away from the exterior 32 of the housing that it is ensured that the shielding elements 3 do not have any contact to a possibly present adjacent switchgear S or to a shielding element 3 that may be present on the same. As a result, the shielding elements 3 of adjacent switchgears S do not lie on top of one another and thus contribute to the extension of the creepage path. In the preferred embodiments of switchgears S in accordance with the invention, the shielding elements 3 do not extend up to the region around the clamping screw openings 7. It can also be provided however to arrange shielding elements 3 in this region or to provide shielding elements 3 which also extend into this region. It is preferably provided in embodiments in which the shielding elements 3 do not extend up to the region of the clamping screw openings 7 that in the region of the free gap 31 depressions 8 are provided on the housing 2, preferably on the exterior 32 of the housing, and especially in the region of the clamping screw opening 7, in order to increase the depth t of the free gap 31 which is determined substantially by the shielding elements 3 to the depth ti in the region of the clamping screw opening 7 without enlarging the shielding elements 3. The depressions 8 clearly recognizable in Fig. 1 lead to a considerable extension of the existing creepage path at a width of the housing which is unchanged as compared with conventional components. The configuration, number and shaping of the depression 8 in accordance with the invention depends on the local conditions and is adjusted to the geometry of the respective switchgear S.

11 In order to further extend the creepage path without increasing the depth t of gap 31 or the shielding elements 3 it can be provided that the at least one shielding element 3 comprises a recess 33, with the recess 33 forming a boundary region 34 which is elevated relative to the same. The creepage path is further extended by such a recess 33 or by the boundary region 34 thus formed. A rough surface or a surface relief can also be provided on at least one shielding element 3, as a result of which the creepage path is extended even further. Figs. 1 and 2 show two adjacently arranged, especially preferred embodiments of a switchgear S in accordance with the invention, specially circuit-breakers, for electrical systems comprising a housing 2 with terminals 1, with at least one arrangement for extending the creepage path being provided on at least one housing part, with one recess 8 being arranged on the side of one clamping screw opening 1 associated with the terminal 1 on an exterior 32 of the housing, with a free gap 31 being formed between two adjacently arranged housings 2 in the region of the clamping screw openings 7. It is advantageous to arrange the at least one depression 8 in the region of the terminal I because a higher occurrence of leakage currents can be expected especially in this region. It is especially advantageous to arrange a depression 8 each on the side of the clamping screw opening 7. As a result, the creepage path can be extended in the most effective way with a minimum of material removed from the housing surface because a free gap 31 is thus formed. The depression can also be formed by a recess. Figs. 3 to 6 show the terminal 1 of a switchgear S, especially a circuit-breaker, for electrical systems, comprising a housing 2, at least one terminal 1, a movable box 10, a fixed box 11 enclosing the same, and a clamping screw 15 which can be screwed through a pass-through opening 9 of the fixed box into a thread 12 of the movable box with a head 13 against the clamping support 14, with the movable box 10 forming in combination with the fixed box 11 a clamping opening for cable ends 16 which is adjustable by means of the clamping screw 15, and further comprising a clamping opening for cable lugs 17 formed between the head 13 of the clamping screw 15 and the fixed box 11, with means being provided for completely turning out the clamping screw 15 from the clamping opening 17. Switchgears S comprise in many cases terminals 1 which are suitable for receiving cable ends and/or fork-type cable lugs.

12 So-called ring cable lugs R cannot be clamped with such a terminal 1 or only with much difficulty. It needs to be ensured for the introduction of a ring cable lug R into a terminal 1 that the clamping screw 15 releases the clamping region 17 before the clamping rest 14. It is certainly not unusual to provide means which prevent the clamping screw 15 from falling out of the clamping screw opening 7. Switchgears S with such terminals 1 are unsuitable for the operation with ring cable lugs R. If it is possible to remove the clamping screw 15, then this needs to occur with the help of a special tool or gravity. The means provided in a switchgear S in accordance with the invention guarantee that the clamping screw 15 can be fully twisted out of the clamping opening 17 and allow the operation of a switchgear S with ring cable lugs R. The means for the complete screwing out of the clamping screw 15 from the clamping opening 17 comprise a clamping screw 15 which comprises a thread-free region 18 arranged adjacent to the screw head 13, which region further comprises tapering cross-sectional portion 19 as compared with the cross section of the thread. The means for completely twisting out the clamping screw 15 from the clamping opening 17 further comprise a small plate 20 arranged in a twist-proof manner on the side of the clamping support 14 of terminal 1 which is averted from the box 11 and parallel to the same, and whose thickness corresponds at most to the height of the thread-free region 18 of the clamping screw 15. It is provided that the plate 20 comprises a pass-through opening 21 for the clamping screw 15 which comprises at least parts of a thread 22. Said pass-through opening 21 can be provided with a configuration which is open around the edges. An especially simple partial thread 22 can thus be realized. The small plate 20 which does not necessarily meet the shapes of the plate 20 as shown in Figs. 3 to 6 is arranged between the clamping support 14 of the fixed box 11 and the clamping screw 15 and offers the possibility to rest on the housing parts. Notice must be taken that the plate 20 can be removed so far from the clamping support 14 before it rests on the housing parts that the cavity arising between the clamping rest 14 and the plate 20 is capable of receiving a ring cable lug R. Embodiments for receiving more than one cable ring lug R can be provided.

13 In the case of the closed or partly closed terminal 1 such as during the clamping of a cable end, the late 20 is arranged on the thread-free, tapering region 18, 19 of the clamping screw 15. For this purpose it is necessary to screw the clamping screw 15 through the plate 20. If the terminal 1 is to be opened to such an extent that the clamping opening is released for cable lugs 17 by the clamping screw 15, the screw 15 is actuated in such a way that this will lead to an opening of the terminal 1. Once the terminal 1 is completely opened and the clamping screw 15 is moved further in the same way, the clamping screw 15 will be screwed out of the last convolutions of the thread 12 in the movable box 10. The clamping screw 15 will be lifted over the clamping support 14 and entrains the plate 20 until the movement of the plate 20 is stopped by the housing parts. A further twisting of the clamping screw 15 will lead to the consequence that the thread of the clamping screw 15 will screw into the partly present thread 22 of the plate 20. Since the plate 20 is prevented from performing a radial movement by the housing parts, a further twisting of the clamping screw 15 will lead to the clamping screw 15 being moved out of the fixed box 11 and from the clamping opening for cable lugs 17, as shown in Fig. 5. After the release of the clamping opening 17, a ring cable lug R can be introduced into the clamping opening 17. It can be provided that the clamping screw 15, when the clamping opening 17 has been fully opened, will protrude to such an extent from the clamping screw opening 7 that the same can be removed manually. This is not required for the operation of a switchgear S with ring cable lugs R. Means are provided in the preferred embodiment of a switchgear S in accordance with the invention, which means prevent the clamping screw 15 from falling out of the clamping screw opening 7. This can be achieved by a small reduction in the diameter in the clamping screw opening 7. As a result, the clamping screw 15 can no longer leave or be removed from the clamping screw opening 7. The length of the clamping screw 15 must be chosen in such a way that it will press the plate 20 against the housing 2 when nearly completely twisted out from the thread 12 of the movable box 10, such that the partial thread 22 of plate 20 comes into engagement with the thread of the clamping screw 15. It is understood that it is also possible to choose the length of the thread 12 of the movable box 10 in such a way that this condition is fulfilled. For closing the terminal 1 it is merely necessary to move the clamping screw 15 in the rotational direction provided for this purpose. Shortly before the clamping screw 15 comes out of 14 engagement with the partial thread 22 of the plate 20, the clamping screw 15 comes into engagement with the thread 12 of the movable box 10 and can now be closed in the known manner. Fig. 6 shows a switchgear S with a shielding element 3 and a terminal 1 with the ring cable lug R arranged in the same.

Claims

1. A switchgear (S) comprising a housing (2), especially a circuit-breaker, in which at least one terminal (1) is arranged in a receiver (36) arranged in the switchgear housing (2), with the receiver (36) being sealed off on the front side at least in sections by a cover (30), characterized in that a plate-like or rib-like shielding element (3) which projects beyond the front cover (30) is integrally formed on the housing (2).

2. A switchgear (S) according to claim 1, characterized in that the plate-like or rib-like shielding element (3) extends substantially over the entire height (h) of the housing.

3. A switchgear (S) according to claim 1 or 2, in which clamping openings (6) and/or clamping screw openings (7) for the terminals (1) are formed in the front cover (30), characterized in that two substantially mutually parallel shielding elements (3) are arranged on either side of the terminal openings (6) and/or the terminal screw openings (7), so that at least two separate shielding elements (3) each are provided between two adjacent terminal openings (6), which shielding elements form a free gap (31) between the two shielding elements (3).

4. A switchgear (S) according to claim 3, characterized in that the shielding elements (3) are arranged parallel to an exterior (32) of the housing and at a distance from the exterior (32) of the housing offset to the inside, so that in the case of adjacently arranged switchgears (S) two shielding elements (3) lying close to one another form a free gap (31).

5. A switchgear (S) according to claim 3 or 4, characterized in that in the region of the free gap (31) depressions (8) are provided on the housing (2), preferably on the exterior (32) of the housing, especially in the region of the terminal screw opening (7), in order to enlarge the depth (t) of the free gap (31).

6. A switchgear (S) according to one of the claims 1 to 5, characterized in that the at least one shielding element (3) comprises a recess (33) on at least one side which preferably extends over the entire surface of the shielding element (2), with the recess (33) forming a boundary edge (34) which is elevated relative to the same. 16

7. A switchgear (S) according to one of the claims 1 to 6, characterized in that the at least one shielding element (3) comprises at least one stiffening rib (5).

8. A switchgear (S), specially a circuit-breaker, for electrical systems with a housing (2) having terminals (1), with at least one arrangement for extending the creepage path being provided on at least one housing part, characterized in that one recess (8) each is arranged on the side of one clamping screw opening (7) associated with the terminal (1) on an exterior (32) of the housing, with a free gap (31) being formed between two adjacently arranged housings (2) in the region of the clamping screw openings (7).

9. A switchgear (S), especially a circuit-breaker, for electrical systems with a housing (2), at least one terminal (1), comprising a movable box (10), a fixed box (11) wrapped around the same and a clamping screw (15) which can be screwed through a lead-through opening (9) of the fixed box (11) into a thread (12) of the movable box (10) with a head (13) against a clamping support (14), with the movable box (10) forming together with the fixed box (11) a terminal opening for cable ends (16) which is adjustable by means of the clamping screw (15), and further comprising a clamping opening for cable lugs (17) formed between the head (13) of the clamping screw (15) and the fixed box (11), characterized in that means are provided for completely twisting out the clamping screw (15) from the clamping opening (17).

10. A switchgear (S) according to claim 9, characterized in that the means for completely twisting out the clamping screw (15) from the clamping opening (17) comprise a thread free region (18) of the clamping screw (15) arranged adjacent to the clamping screw head (13).

11. A switchgear (S) according to claim 10, characterized in that the thread-free region (18) of the clamping screw (15) comprises a tapering cross-sectional portion (19).

12. A switchgear (S) according to one of the claims 9 to 11, characterized in that the means for completely twisting out the clamping screw (15) from the clamping opening (17) comprise small plates (20) which are arranged in a twist-proof manner on the side of the clamping support (14) of the terminal (1) which is averted from the box (11) and parallel to the same and whose thickness corresponds to not more than the height of the thread- 17 free region (18) of the clamping screw (15).

13. A switchgear (S) according to claim 12, characterized in that the small plate (20) comprises a lead-through opening (21) for the clamping screw (15) which comprises at least parts of a thread (22).