SWITCH

Abstract: A switch comprises a fixed contact (8A) on a fixed contactor (8), a movable contact (6A) on a movable contactor (6), a number of metallic arc extinguishing plates (13), an arc horn (6B), and a commutating plate (15). The lowest metallic plate (13g) is extended to surround the contact point of the two contacts (6A,8A) without disturbing the movement. When the two contacts (6A,8A) are detached, an arc (12) is generated between them and gradually changes its path (12A,12B,12C,12D) to be absorbed in the metallic plates (13). The process is quickened by the extended lowest plate (13g).

Description: The present invention relates to a switch according to the preamble of claim 1; i.e. a switch for opening and closing an electric current which has an arc extinguishing mechanism. BACKGROUND ART Switches for electric circuits are used for various fields. As conventional switches, there are known ones as proposed in, for instance, the specification of US-A-4477704, US-A-4521655 and so on. Figure 1 shows an example of a conventional switch. In Figure 1, a reference numeral 1 designates a fitting block formed by a synthetic resin, a numeral 2 designates a fixed iron core formed by silicon steel plates on the fitting block, a numeral 3 designates a movable iron core formed by the same silicon steel plates which is placed opposing the fixed iron core 2, a numeral 4 designates an operating coil to impart a driving force to attract the movable iron core 3 to the fixed iron core 2 against a trip spring (not shown), and a numeral 5 designates a cross bar having a rectangular window 2, which is formed by a synthetic resin and supports at its lower end the movable iron core 3. A numeral 6 designates a movable contactor which is inserted in the rectangular window of the cross bar 5 and is held by a compression spring 7, a numeral 6A designates a movable contact provided on the movable contactor 6, a numeral 6B designates an arc horn provided at the end of the movable contactor 6, a numeral 8 designates a fixed contactor provided facing the movable contactor 6 to feed an electric current, a numeral 8A designates a fixed contact provided on the fixed contactor 8, and a numeral 8B designates a terminal portion of the fixed contactor 8. The arc horn 6B may be formed integrally with the movable contactor 6. A numeral 9 designates a screw for the terminal part to connect the main body of an electromagnetic contactor to an outer electric circuit, a numeral 10 designates a base to which the fixed contactor 8 is fitted, and a numeral 11 designates a cover for covering the upper surface of the electromagnetic contactor, in which arc extinguishing metallic plates 13 made of a magnetic substance are provided to extinguish an arc 12 produced between the fixed contact 8A and the movable contact 6A. The arc extinguishing metallic plates 13 are arranged vertically in multe-stage, with predetermined distances, in parallel to each other and above the fixed contactor 8 so as to face the movable contactor 6. A numeral 15 designates a commutation plate provided above the movable contactor 6. In Figure 1, only the right portion from the center line of the switch is shown in cross-section because the right and left portions are symmetric. The switch has the construction mentioned above. Accordingly, when the operating coil 4 of the electromagnetic contactor is rendered to be inactive, the movable iron core 3 is separated from the fixed iron core by means of the trip spring although it is not shown in the Figures. Accordingly, the cross bar 5 is rendered to be a state as shown in Figure 1, and the fixed contact 8A is separated from the movable contact 6A to thereby produce the arc 12 therebetween. The arc 12 takes progress as shown in Figure 2. Namely, it is attracted to the arc extinguishing metallic plates 13; it is stretched to be an arc 12A; then takes the form of an arc 12B and an arc 12C successively; the leg of the arc 12C on the arc horn 6B is transferred to the commutation plate 15; the arc 12 finally takes the form of an arc 12D; and it is cooled and extinguished by the arc extinguishing metallic plates 13. In the conventional switch having the above-mentioned construction and operations, the arc extinguishing metallic plates 13 of the magnetic substance are positioned apart from a position where the arc is produced at the initial stage. Accordingly, there was tendency that the rising speed of an arc voltage at the initial stage 5 is low. Accordingly, the current limiting ability is poor with the result that arc energy becomes large and the breaking ability is also poor. An arc extinguisher according to the preamble of claim 1 is known from DE-A-1 926 355. The arc extinguishing chamber described in this document comprises a plurality of arc extinguishing metallic plates arranged with predetermined distances therebetween and in parallel to a fixed contactor. Each of said arc extinguishing metallic plates has one end which extends in a direction towards the movable contactor, said one end having a spaced formed therein so that the movable contact is movable therethrough. Further, the US-A-1,963,643 describes an arc extinguishing circuit breaker comprising a plurality of arc extinguishing metallic plates. Each of these arc extinguishing metallic plates have leg end portions which extend in the direction of the movable contactor, some of them extending beyond a perpendicular line of the mutual contact between the fixed contact and the movable contact. However, in a case that an arc is produced at a position deviating from the center line of the leg portions of the plates the arc receives a force to be driven toward these leg portions. In this case, the arc is cooled at the leg portions of the arc extinguishing plates where they have only a small heat capacity. Accordingly, the arc cannot be sufficiently cooled. As a result, the current interruption performance of the switch is not satisfying. The object of the present invention to eliminate the above-mentioned problems and to provide a switch having excellent current limiting ability and current breaking ability. The present invention, therefore, provides a switch comprising the features of claim 1. In accordance with the present invention, an arc is rapidly attracted to the arc extinguishing metallic plates close to the fixed contactor or the commutation plate to thereby increase the rising speed of an initial arc voltage or an arc voltage. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a vertical cross-sectional view of a part of a switch as a prior art technique; Figure 2 is a cross-sectional view of an important part of the switch to illustrate arc extinguishing operation; Figure 3 is a vertical cross-sectional view showing a first embodiment of the switch according to the present invention; Figure 4 is a plan view showing a relation of an arc extinguishing metallic plate to a fixed contactor; Figure 5 is a cross-sectional view showing a second embodiment of the present invention; Figure 6 is a cross-sectional view showing an important part of another embodiment of the present invention; Figure 7 is a perspective view of the fixed contactor having a part modified according to the present invention; Figures 8 and 9 are respectively cross-sectional views of other embodiments of the present invention; Figures 10 to 12 are respectively cross-sectional views of other embodiments of the present invention; Figure 13 is a cross-sectional view of a part of a movable contactor as an example in which an improvement is added according to the present invention; Figure 14 is a cross-sectional view showing another embodiment of the present invention; Figure 15 is a side view for illustrating an embodiment of the present invention in which the shape of an arc horn is changed; Figure 16 is a cross-sectional view of on important part of another embodiment for illustrating arc extinguishing operation; Figure 17 is a diagram showing in detail the operation of the embodiment shown in Figure 16; Figure 18a is a view showing the shape of an arc extinguishing metallic plate; Figure 18b is a view showing the shape of another embodiment of the arc extinguishing metallic plate; Figure 19 is a cross-sectional view of an important part of another embodiment for illustrating arc extinguishing operation; Figure 20 is a cross-sectional view of an important part of another embodiment for illustrating arc extinguishing operation; Figure 21 is a cross-sectional view of an important part of another embodiment to illustrate arc extinguishing operation; Figure 22 is a diagram showing another embodiment of the present invention; Figure 23 is a cross-sectional view of another embodiment of the present invention; Figure 24 is a cross-sectional view of an important part to illustrate arc extinguishing operation; Figure 25 is a plan view showing a relation of an arc extinguishing metallic plate to a fixed contactor; Figure 26 is a cross-sectional view showing another embodiment; Figure 27 is a cross-sectional view of an embodiment in which a fixed contactor partly improved is used; Figure 28 is a cross-sectional view of an embodiment; Figure 29 is a side view showing an important part of another embodiment of the present invention; Figure 30 is a plan view of the important part; Figure 31 is a cross-sectional view of an important part of another embodiment to illustrate arc extinguishing operation; Figure 32 is a perspective view of the arc extinguishing metallic plate shown in Figure 31; Figure 33 is a cross-sectional view showing another embodiment; Figure 34 is a plan view showing a relation of an arc extinguishing metallic plate to a fixed contactor; Figure 35 is a cross-sectional view of an important part of another embodiment to illustrate arc extinguishing operation; Figure 36 is a perspective view showing an insulating plate used for the embodiment; Figure 37 is a cross-sectional view of an important part of another embodiment of the present invention; Figure 38 is a cross-sectional view of an important part of another embodiment to illustrate arc extinguishing operation; Figure 39 is a perspective view showing on insulating plate used for the embodiment; Figure 40 is a cross-sectional view showing another embodiment of the present invention; Figure 41 is a cross-sectional view showing another embodiment of the present invention; Figure 42 is a cross-sectional view of an important part of another embodiment of the present invention to illustrate arc extinguishing operation; Figure 43 is a cross-sectional view of another embodiment of the present invention; Figure 44 is a cross-sectional view of an important part of another embodiment to illustrate arc extinguishing operation; Figure 45 is an enlarged front view of a part of the commutation plate to illustrate the progress of an arc; Figures 46 and 47 are respectively cross-sectional views showing other embodiments of the present invention; Figure 48 is a cross-sectional view of an important part of another embodiment of the present invention to illustrate arc extinguishing operation; Figure 49 is a diagram showing the operation of the embodiment shown in Figure 48; Figure 50a is a diagram showing the shape of an embodiment of the arc extinguishing metallic plate; Figure 50b is a diagram, showing the shaped of another embodiment of the arc extinguishing metallic plate; Figure 51 is a cross-sectional view of an important part of another embodiment of the present invention to illustrate arc extinguishing operation; Figure 52 shows a bottom view and a side view of another embodiment of the commutation plate of the present invention respectively; Figure 53 is a cross-sectional view of an important part of an embodiment to illustrate arc extinguishing operation in the case that the commutation plate in Figure 52 is used; Figures 54a and 54b are respectively bottom views showing other embodiments of the commutation plate respectively; Figure 55 is a cross-sectional view of an important part of another embodiment to illustrate arc extinguishing operation; Figure 56 is a perspective view showing the arc extinguishing metallic plate; Figure 57 is a perspective view showing the arc extinguishing metallic plate before improvement; Figure 58 is a cross-sectional view of an important part of another embodiment to illustrate arc extinguishing operation; Figure 59 is a perspective view showing an arc extinguishing metallic plate having the both surfaces to which insulating plates are attached; Figure 60 is a cross-sectional view of an important part of another embodiment of the present invention; Figure 61 is a cross-sectional view of an important part of another embodiment to illustrate arc extinguishing operation; Figure 62 is a perspective view of the insulating plate used for the above-mentioned embodiment; Figure 63 is a cross-sectional view of another embodiment of the present invention; Figure 64 is a plan view of another embodiment to show an arc extinguishing metallic plate and the wall surface of a casing to protect the plate; Figure 65 is a cross-sectional view of an important part of the above-mentioned embodiment to illustrate arc extinguishing operation; Figure 66 is a cross-sectional view of an important part of another embodiment to illustrate arc extinguishing operation; Figure 67 is a perspective view of the arc extinguishing metallic plate used for the above-mentioned embodiment; Figures 68 and 69 are respectively cross-sectional views of an important part of other embodiments; Figures 70 and 71 are respectively perspective views of a fixed contactor according to other embodiments of the present invention; Figure 72 is a perspective view showing a fixed contactor according to another embodiment of the present invention; Figure 73 is a cross-sectional view of an important part of an embodiment in which the fixed contactor shown in Figure 72 is used; Figures 74 and 76 are respectively perspective views of other embodiments of the fixed contactor according to the present invention; and Figure 75 is a cross-sectional view of an important part of another embodiment in which the fixed contactor shown in Figure 74 is used. BEST MODE OF THE PRESENT INVENTION In the following, embodiments of the present invention will be described with referenced the drawings. Since the embodiments are similar to the conventional switch shown in Figure 1, only different points will be described. The construction in the outline is similar to that shown in Figure 1, and therefore description of it will be omitted. The embodiments of the arc extinguishing plates shown in figures 16, 19, 20, 21, 24, 26, 27, and 28 and in figures 31, 33, 35, 38, 44, 53, 55, 58, 61, 65, 66, 68, 69, and 73 serve for illustration purposes only and do not form part of the invention. An embodiment of the present invention is shown in Figure 3. The embodiment as shown in Figure 3 is different from the conventional switch shown is Figure 1 in that an arc extinguishing metallic plate 13g closest to the fixed contactor among an arc extinguishing metallic plates 13 is provided with two legs 13ga as shown in Figure 4. In Figure 3, an arc 12 is produced as shown in the figure when a movable contact 6A is separated from a fixed contact 8A. Since a magnetic flux  is formed around the arc 12 as shown in Figure 4, the arc 12 is received a force in the direction indicated by an arrow mark F. However, since the legs 13ga are provided in the arc extinguishing metallic plate 13g, the force F becomes strong and the arc 12 is easily elongated, whereby the rising speed of an arc voltage at the initial stage is increased. Namely, in the present invention, the rising speed of an arc resistance is increased to thereby increase the current limiting ability. Thus, the arc 12 produced between the both contacts progresses in such a manner that as shown in Figure 3, it takes the form of an arc 12A in a short time; the arc 12A is attracted to the arc extinguishing plates other than the plate 13g to take the form of an arc 12B and an arc 12C successively; and finally, it takes the form of an arc 12D, during of which the arc is cooled and extinguished by the arc distinguishing metallic plates 13. Thus, since the driving of the arc just after the generation of the arc and the shift of the arc from the state of the arc 12C to the state of the arc 12D are satisfactorily carried out, time for current interruption is shortened. Also, the current limiting ability is increased as described before, whereby arc energy is reduced at the time of the current interruption, and therefore, it is possible to interrupt a large electric current. In the above-mentioned embodiment, the arc horn 6B is joined to the end of the movable contactor 6A, however, the arc horn 6B may be formed integrally with the movable contactor 6A. Further, the arc horn 6B may be omitted as shown in Figure 5. In the case of the apparatus described with reference to Figure 3, only the arc extinguishing metallic plate 13g closest to the fixed contactor 8 is extended to the upper part of the fixed contact. However, it is possible to construct in such a manner that an arc extinguishing metallic plate 13a closest to the commutation plate 15 have the same length as an arc extinguishing metallic plate 13f as shown in Figure 6. The arc extinguishing operation of an arc extinguishing structure in the apparatus will be described with reference to Figure 6. The arc 12 is produced between the movable contact 6A and the fixed contact 8A in the same manner as the switch of the above-mentioned embodiment. The arc 12 is elongated by and attracted to the arc extinguishing metallic plate 13a made of a magnetic substance in addition to the arc extinguishing metallic plate 13f of the magnetic substance to become an arc 12A. The behavior of the arc is the same as described before. In this case, the arc horn 6B may be omitted, and the fixed contactor 8 may be provided with an arc runner 14 as shown in Figure 7. In the embodiment shown in Figure 7, the arc runner 14 which is bent in an inverse L-shape is electrically connected to the end part of the fixed contactor 8 on the side of the fixed contact 8A, and further, a notched portion 14A is formed in the bent portion of the arc runner 14 so that the movable contactor 6 is passed through it to come in contact with the fixed contact 8A. The arc extinguishing structure of the device will be described with reference to Figure 8. When the arc 12 is produced between the movable contact 6A and the fixed contact 8A, the lower leg of the arc 12 on the fixed contact 8A is easily transferred to the arc runner 14 to take the form of an arc 12A because the arc runner 14 is provided at a higher position than the surface of the fixed contactor 8. When the lower leg of the arc 12 is transferred to the arc runner 14, an electric current flows in the arc runner 14 in the direction of an arrow mark X in Figure 8, whereby the arc 12A is further urged toward a terminal portion 8B in the fixed contactor. The upper leg of the arc 12A is transferred from the movable contact 6A to the end of the movable contactor 6 to be attracted to the arc extinguishing metallic plates 13, and the lower leg is moved on the arc runner 14 by an arc extinguishing plates 13c - 13e among the arc extinguishing metallic plates 13. Then, the upper leg of the arc 12B transferred to the movable contactor 6 is driven by the arc extinguishing metallic plates 13, and it is upwardly driven by a magnetic field which produces an electric current flowing in the arc runner 14 so that the arc is transferred from the fixed contactor 6 to the arc horn 6B to move toward the upper part of the arc horn 6B to thereby reach the upper end portion of the arc horn 6B. The arc 12C extended from the upper end portion of the arc horn 6B through the arc extinguishing metallic plates 13 reaches the arc runner 14 through the whole of the arc extinguishing plates 13a - 13e of the arc extinguishing metallic plates. The upper leg of the arc 12C is transferred to the commutation plate 15; it is moved on the commutation plate 15 in the outer direction (on the right hand in the figure) and it traverses the whole of the arc extinguishing plates 13a - 13e of the arc extinguishing metallic plates 13 to become the arc 12D which communicates the arc runner 14, and it is extinguished. Thus, by providing the arc runner 14, the driving of the arc 12 is further accelerated, and accordingly, both of the current limiting ability and the current breaking ability are further increased. In the device described with reference to Figure 8, only the arc extinguishing metallic plate 13e closest to the fixed contactor 8 is extended to the upper portion of the fixed contact. However, it is possible to so constructed that the arc extinguishing metallic plate 13a has the same length as the arc extinguishing metallic plate 13e as shown in Figure 9. The arc extinguishing operation is generally similar to that in Figure 8. Namely, the arc 12 is attracted to the arc extinguishing metallic plate 13a in addition to the arc extinguishing metallic plate 13e of the magnetic substance. Accodingly, the arc takes a further elongated form to thereby accelerate the movement of the arc. The subsequent behavior of the arc is the same as described before. Another embodiment will be described with reference to Figure 10. The embodiment shows an example in which the arc horn 6B and the arc extinguishing metallic plates 13 are used for a switch having a fixed contactor 8 in the form of ⊐. An arc 12 produced is not only attracted to the arc extinguishing metallic plate 13f of the magnetic substance but also is driven by a magnetic field formed by an electric current flowing in the fixed contact 8 (an arrow mark X in Figure 10). Accordingly, the lower leg of the arc 12 is easily transferred from the fixed contact 8A to the fixed contactor 8 to reduce the wearing of the fixed contact 8A, and at the same time, an arcing time is shortened because the arc 12 is strongly urged. Thus, currnet breaking ability is further improved. Figure 11 shows a modification of a part of Figure 10, in which the length of the arc extinguishing metallic plate 13a near the commutation plate 15 as well as the arc extinguishing metallic plate 13f placed near the fixed contactor is elongated. In this case, the same function as the previously mentioned embodiments can be expected. Figures 12 and 13 show the case in which the present invention is applied to a circuit breaker for wiring, in which a reference numeral 17 designates a pivotal shaft, and a numeral 18 designates a twisted wire through which the movable contactor 6 is electrically connected to the commutation plate 15. In this case, the same function can be obtained in the same manner as the previously mentioned embodiments. In Figures 12 ans 13, it is apparent that the function of the present invention can be obtained without the arc runner 14. An embodiment as shown in Figure 14 is provided with the arc extinguishing metallic plates 13a and 13b placed between the movable contact 6A and the commutation plate 15, which have the same shape as the arc extinguishing metallic plate 13g, namely, they are provided with legs 13fa as indicated by a numeral 13ga in Figure 4. In the case of Figure 14, the leg of the arc 12c extended from the arc horn 6B is strongly attracted to the arc extinguishing metallic plates 13a, 13b of the magnetic substance; accordingly, the rising speed of an arc voltage is accelerated and current limiting ability and current breaking ability are improved. The arc extinguishing metallic plate with the legs 13fa placed between the movable contact 6A and the commutation plate 15 may be a single or plural. In the embodiments described above, the arc horn 6B is exteded at a right angle from the end of the movable contactor 6. However, it is not limited that it is extended at the right angle as shown in Figure 15. Each of the embodiments have been described on the assumption that the present invention is applied to an electromagnetic contactor or a circuit breaker for wiring. However, the present invention can also be applied to an air circuit breaker. In accordance with the construction of each of the embodiments, both the current breaking ability and the current limiting ability can be improved. Figures 16 to 18 show another embodiment in which a plurality of arc extinguishing metallic plates placed between the commutation plate and the movable contactor are extended to the side of a space in which the movable contactor is movable. Namely, Figure 16 is a cross-sectional view of an important part of the embodiment of the present invention to illustrate its arc distinguishing function; Figure 17 is a diagram showing the operation of the embodiment as shown in Figure 16 in detail; Figure 18a is a diagram showing an arc extinguishing metallic plate; and Figure 18b is a diagram showing the shape other than the above-mentioned arc distinguishing metallic plate. In Figure 16, a reference numeral 6 designates a movable contactor, 6A designates a movable contact, 8 designates a fixed contactor, 8A designates a fixed contact and 15 designates a commutation plate placed above the movable contactor 6. A numeral 13 designates arc distinguishing metallic plates consisting of a plurality of arc distinguishing metallic plates 13a to 13g which are arranged with predetermined distances and in parallel to the fixed contactor 8 and at the side of the movable contactor 6. Among the arc extinguishing metallic plates 13, the arc extinguishing metallic plates 13a to 13d placed between the commutation plate 15 and the movable contactor 6 are respectively provided with a pair of legs 13fa - 13fd whose ends are extended to the side part of the space in which the movable contactor 6 is movable. Among the arc extinguishing metallic plates 13, the other arc extinguishing metallic plates 13g and 13f placed between the movable contactor 6 and the fixed contact 8 are respectively provided with a pair of short legs 13fe - 13fg whose end portions reach near the end portion of the movable contactor 6 as shown in Figure 18a. Figure 18b shows a modification of the arc extinguishing metallic plates 13g and 13f shown in Figure 18a, in which a mountain-like projection 13h is formed at the center of the edge portion of each of the arc distinguishing metallic plates 13e and 13f. The reason why the arc distinguishing metallic plates 13e - 13g have the short legs 13fe - 13fg is that if the longer legs 13fa as in the arc extinguishing metallic plate 13a is formed, the arc produced between the movable and fixed contacts 6a, 8a is transferred to the side part of the arc extinguishing metallic plates 13 to cause thermal deterioration of an insulating material between the arc extinguishing plates to thereby cause inability of breaking or losing function. Namely, an insulation resistance between the arc distinguishing plates becomes zero, and there is a drawback that the arc 12 is not transferred to the commutation plate 15. In the switch constructed as above-mentioned, when the movable contact 6A is separated from the fixed contact 8A, a arc is produced between the movable contact 6A and the fixed contact 8A as shown in Figure 16. A magnetic flux is generated around the arc 12, and a force urges the arc 12 toward the arc extinguishing metallic plates 13e and 13f made of the magnetic substance so that it takes the form of an arc 12A. The upper leg of the arc 12A is transferred from the movable contact 6A to the end portion of the movable contactor 6 and the arc 12 is drawn to the arc extinguishing metallic plates 13d - 13g, whereas the lower leg is moved on the fixed contactor 8 to become an arc 12B. The upper leg of the arc 12A transferred to the movable contactor 6 causes a magnetic flux  around the leg portion which receives a force as indicated by an arrow mark F. Since the arc extinguishing metallic plates 13a - 13d are respectively provided with the legs 13fa - 13fd extending to the side of the movable contactor 6, the force F is so strong that the arc 12B is urged in the direction of F and easily extendable vertically. Accordingly, the rising speed of an arc voltage at the initial stage is fast. Namely, since the rising speed of an arc resistance becomes fast, current limiting ability is improved. Thus, when the arc 12B is urged in the F-direction and the upper leg of the arc 12B is extended upwardly, the arc is transferred from the movable contactor 6 to the arc extinguishing metallic plates 13b, 13c to become an arc 12C. The arc 13C reaches the fixed contactor 8 via the arc extinguishing metallic plates 13d - 13g. Then, the upper leg of the arc 12C is moved on the commutation plate 15 in the outer direction (on the right hand in the figure) via extinguishing metallic plate 13a; thereafter, the arc traverses all of the arc extinguishing metallic plates 13a - 13g constituting the arc extinguishing metallic plates 13; and finally becomes an arc 12D which communicates with the fixed contactor 8 to be extinguished. As described above, since the plurality of arc extinguishing metallic plates 13a - 13d placed between the commutation plate 15 and the movable contactor 6 are respectively provided with legs 13fa - 13fd extending to the side of the space in which the movable contactor 6 is movable, the urging of the arc to the commutation plate 15 is satisfactorily obtained even when the arc is produced. Accordingly, a time required for current interruption is shortened and current limiting ability is also improved, whereby arc energy at the time of interruption is decreased. It is possible to interrupt a large electric current. Further, since the legs 13fa - 13fd provided in the arc extinguishing metallic plates 13a - 13d are extended only to the side of the movable contactor 6, the structure is minimized in the same manner as the above-mentioned embodiments. Figure 19 is a cross-sectional view of on important part of another embodiment of the present invention to illustrate arc extinguishing function. In the embodiment, an arc horn 6B is formed at the end of the movable contactor 6. The other structure is the same as that of the embodiment shown in Figure 16. By providing the arc horn 6D, the commutation of the arc to the commutation plate 15 is further accelerated. Figure 20 is a cross-sectional view of an important part of still another embodiment of the present invention to illustrate arc extinguishing function. In the embodiment, an arc runner 14 is provided with a pair of legs 14a formed by bending it in a shape of ⊐, which are positioned at an end of the fixed contact 8A of the fixed contactor 8, and the base portion of the arc runner 14 is determined to be in parallel to the arc extinguishing metallic plates 13. In the embodiment, when an arc 12 is produced between the movable contact 6A and the fixed contact 8A, the arc is attracted to the arc extinguishing metallic plates 13e - 13g to become an arc 13A by the function of elongation. In this case, since the arc runner 14 is placed at a position higher than the surface of the fixed contactor 8, the lower leg of the arc 12 in contact with the fixed contact 8A is easily transferred onto the arc runner 14 to thereby take the form of an arc 12A. When the lower leg of the arc 12 is transferred onto the arc runner 14, the arc runner 14 is excited by a magnetic flux produced around the arc 12A, as the result that the arc 12A is further urged toward the terminal portion of the fixed contactor 6. The upper leg of the arc 12A is transferred from the movable contact 6A to the end portion of the movable contactor 6 and it is attracted to the arc extinguishing metallic plates 13. Then, the lower leg is moved on the arc runner 14 via the arc extinguishing metallic plates 13e - 13g among the arc extinguishing metallic plates to take the form of an arc 12B. Then, the upper leg of the arc 12B transferred on the movable contactor 6 is further transferred from the movable contactor 6 to the arc extinguishing metallic plates 13b, 13c to become an arc 13C in the same manner as the above-mentioned embodiments. The arc 12C reaches the arc runner 14 via the arc extinguishing metallic plates 13b - 13g. The upper leg of the arc 12C is transferred onto the commutation plate 15 via the arc extinguishing metallic plate 13a, then it is moved on the commutation plate 13 outwardly (on the right hand on the drawing) to take the form of an arc 12D communicating with the arc runner 14 after it traverses all of the arc extinguishing metallic plates 13a - 13g; thus, the arc is extinguished. Thus, by providing the arc runner 14, the urging of the arc 12 can be accelerated, and accordingly, both the current limiting ability and current breaking ability can be further increased. Figure 21 is a cross-sectional view of an important part of another embodiment of the present invention to illustrate arc extinguishing function. Of the arc extinguishing metallic plates 13 in the embodiment, two arc extinguishing metallic plates 13c, 13d placed near the movable contactor 6 are respectively provided with a pair of legs 13fc, 13fd which are extended to the side of a space in which the movable contactor 6 is movable. The remaining arc extinguishing metallic plates 13a, 13b, 13e, 13f, 13g are respectively provided with a pair of short legs 13fa, 13fb, 13fe, 13ff, 13fg at the end part of the movable contactor 6. A commutation plate 15 is provided with an end portion 15a in the shape of ⊐ which comes near the movable contactor 6. Further, there is provided an arc runner 14 having a leg portion 16a formed by bending it in the shape of ⊐. In the embodiment, when an arc is produced between the movable contact 6A and the fixed contact 8A, the arc 12 is attracted to the arc extinguishing metallic plates 13e - 13g of a magnetic substance and is elongated. The lower leg of the arc 12 is transferred onto the arc runner 14 to take the form of an arc 12A and urged toward the terminal portion of the fixed contactor 8. The upper leg of the arc 12A is transferred from the movable contact 6A to the end portion of the movable contactor 6, and it is attracted to the arc extinguishing metallic plates 13e - 13g. On the other hand, the lower leg is moved on the arc runner 14 via the arc extinguishing metallic plates 13d - 13g among the arc extinguishing metallic plates 13 to take the form of an arc 12B. Then, the upper leg of the arc 12B transferred on the movable contactor 6 is easily extendable upwardly since the leg portions 13fc are formed in the arc extinguishing metallic plate 13c and an end portion 15a is formed in the commutation plate 15 so as to close to the movable contactor 6. Accordingly, an arc 12C is formed by the transfer of the upper leg of the arc 12B from the movable contactor 6 to the end portion 15a of the commutation plate 15. The arc 12C reaches the arc runner 14 via the arc distinguishing metallic plates 13d - 13g. Then, the upper leg of the arc 12C is moved on the commutation plate 15 outwardly (on the right hand in the figure) to become an arc 12D communicating with the arc runner 14 via all of the arc extinguishing metallic plates 13a - 13g and it is extinguished. Thus, by providing the bent portion 15a in the commutation plate 15 which comes close to the movable contact 6 in addition to provision of the arc runner 14, the arc is further accelerated by the upper and lower legs. Accordingly, both the current limiting ability and current breaking ability can be further increased. As described above, since the embodiments shown in Figures 16 - 21 are provided with the plurality of arc extinguishing metallic plates extending to the side of the space in which the movable contactor is movable, the plurality of plates being placed in the commutation plate and the movable contactor, these arc extinguishing metallic plates are positioned near a position where the arc is produced at the initial stage. Accordingly, there are advantages that a speed of the shifting of the arc to the commutation plate by the attraction of it, i.e. the rising speed of initial arcing is increased; the current limiting ability and the current breaking ability are improved; time for interrupting can be shortened and the wearing of the contacts is minimized. Therefore, the life time is prolonged, and a small-sized device is obtainable. Figure 22 shows still another embodiment of the present invention in which an arc horn 6B is joined to the end of the movable contactor 6A. In this case, a separate element may be used for the movable contactor 6A and the arc horn 6B, or they may be formed in one piece. The arc extinguishing structure of the device will be described. In the same manner as the embodiments as described before, when an arc 12 is produced between the movable contact 6A and the fixed contact 8A, the arc is attracted to the arc runner 14 by the aid of the arc extinguishing metallic plates 13 of a magnetic substance and is elongated to be an arc 12A. In this case, since the arc runner 14 is provided at a position higher than the front surface of the fixed contactor 8, the lower leg of the arc 12 on the fixed contact 8A is easily transferred onto the arc runner 14 to take the form of an 12A. When the lower leg of the arc 12 is transferred onto the arc runner 14, an electric current passes in the arc runner 14 in the direction of an arrow mark X in Figure 22 so that the arc 12A is furter urged toward the terminal portion 8B of the fixed contactor. The upper leg of the arc 12A is transferred from the movable contact 6A to the end portion of the movable contactor 6, and the arc 12 is drawn in the arc extinguishing metallic plates 13. On the other hand, the lower leg is moved on the arc runner 14 via the arc extinguishing metallic plates 13c - 13d among the metallic plates 13. Then, the upper leg of the arc 12B transferred on the movable contactor 6 is urged by the arc extinguishing metallic plates 13 and at the same time, it is urged upwardly by a magnetic field formed by an electric current flowing in the arc runner 14; the arc is transferred from the movable contactor 6 on the arc horn 6B to be moved on the arc horn 6B whereby it reaches the end portion of the arc horn 6B. Then, the arc 12C elongated from the upper end portion of the arc horn 6B via the arc extinguishing metallic plates 13 reaches the arc runner 14 via all of 13a - 13e of the arc extinguishing metallic plates 13. Then, the upper leg of the arc 12C is transferred onto the commutation plate 15 and is moved on the commutation plate 15 outwardly (on the right hand in the figure) and thereafter, it traverses all of the arc extinguishing plates 13a - 13e constituting the arc extinguishing metallic plates 13, whereby an arc 12D communicating the arc runner 14 is formed and it is extinguished. Thus, by providing the arc runner 14, the arc 12 can be urged at a further high speed, whereby both the current limiting ability and current breaking ability can be further increased. Another embodiment will be described with reference to Figure 23. The embodiment is provided with a fixed contactor 8 having the shape of ⊐. An arc 12 produced is not only attracted to the arc extinguishing metallic plates 13 of a magnetic substance, but also is urged by a magnetic field formed by an electric current flowing in the fixed contactor 8 (an arrow mark X in Figure 23). Accordingly, the lower leg of the arc 12 can be easily transferred from the fixed contact 8A to the fixed contactor 8, whereby the wearing of the fixed contact 8A can be reduced. Further, since the arc 12 is strongly urged, an arcing time is shortened to thereby further improve current breaking ability. An embodiment shown in Figures 24 to 28 is featurized by extending the leg portion of all of the arc extinguishing metallic plates 13 to the side of a space in which the movable contactor 6 is movable. Namely, all of the arc extinguishing metallic plates 13 are respectively provided with two legs 13ga at the end portion facing the movable contactor 6. The embodiment shown in Figure 26 is the same as that in Figure 24 provided that the arc horn 6B is omitted; the embodiment in Figure 27 is characterized by providing an arc runner 14. The embodiment in Figure 28 is provided with an arc horn 6B and arc extinguishing metallic plates 12 in a switch having a fixed contactor 8 having the shape of ⊐. An arc 12 produced is not only attracted to the arc extinguishing metallic plate 13f of a magnetic substance, but also is urged by a magnetic field formed by an electric current flowing in the fixed contactor 8 (an arrow mark X in Figure 28). Accordingly, the lower leg of the arc 12 can be easily transferred from the fixed contact 8A to the fixed contactor 8, whereby the wearing of the fixed contact 8A is reduced and an arcing time is shortened because of a strong urging force imparted to the arc 12, whereby current breaking ability is further improved. In an embodiment as shown in Figure 29, long arc extinguishing metallic plates 13a, 13b, 13c, 13d in which leg portions are formed by cutting the central portion of each of the edges and shorter arc extinguishing metallic plates 13e, 13f, 13g are arranged alternately one by one so that the end portion of the longer arc extingushing metallic plates are placed above or below the movable contactor 6. With such construction, the arc is attracted first to the longer one which is near the fixed contact and the movable contactor, and then, is attracted to the shorter one successively to thereby increase attractive effect to the arc. Thus, current breaking ability is improved. Namely, in the figure, reference numerals 13a - 13d designate the longer arc extinguishing metallic plates. As shown in Figure 30, the end portion is cut at its central portion to form a pair of leg portions 13db at the both edges. Reference numerals 13e - 13g designate the shorter arc extinguishing metallic plates. The longer arc extinguishing metallic plates 13a - 13d extend to the position overlapping the movable contactor 6, and the movable contact 6a and the fixed contact 8a are positioned in the cut portion 13da. Between the longer arc extinguishing metallic plates 13a - 13d, the shorter arc extinguishing metallic plates 13e - 13g are arranged with predetermined distances with respect to the contacts 6A, 8A. The other ends of the two kinds of the arc extinguishing metallic plates 13a - 13d and 13e - 13g are respectively positioned in the same plane. In the present invention constructed as described above, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced between the both contacts 6A, 8A as shown in Figure 29. A magnetic flux  is produced around the arc 12 as shown in Figure 30, and the arc 12 is received a force in the direction of an arrow mark F. Since the leg portions 13db are formed in the longer arc extinguishing metallic plates 13a - 13d, the force F is strong, and attracting effect of the arc extinguishing metallic plates 13c, 13d is increased to form an arc 12A in a short time. Then, the arc is attracted to the other arc extinguishing metallic plates to take the forms of an arc 12B, 12C and 12D successively, and the arc is cooled and extinguished by the arc extinguishing metallic plates 13. Thus, in accordance with the embodiment, since the urging of the arc just after the production of the arc and the shift of the arc from the state of the arc 12C to the state of the arc 12D rapidly take place, and current limiting ability and current breaking ability are improved to allow the interruption of a large electric current. An embodiment as shown in Figures 31 - 34 concerns a switch comprising a plurality of arc extinguishing metallic plates arranged at the end portion of the movable contactor and a commutation plate above the movable contactor in which a projection is formed in each of the arc extinguishing metallic plates at a position slightly inside from the edge portion of it. Namely, the shape of the arc extinguishing metallic plates 13 used in the embodiment as shown in Figure 31 is characterized by providing a projection 13h extending in the substantially entire width in each of the arc extinguishing metallic plates 13. In Figure 31, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced as shown in Figure 31. Deformation is caused in the arc 12 by an attracting force resulted by the arc extinguishing metallic plates 13 of a magnetic substance, whereby the arc takes the form of an arc 12A. The upper leg of the arc 12A shifts to the edge portion of the movable contactor 6, and the lower leg is separated from the fixed contact 8A, passing around a part of the arc extinguishing metallic plates 13 to form an arc 12B communicating with the fixed contactor. Further, the upper leg of the arc 12 moves from the lower part to the upper part at the end portion of the movable contactor 6 and then it becomes an arc 12D. In this case, since the projection 13h is formed on the surface of each of the arc extinguishing metallic plates 13, there produces no unstable arc 12D and it is cooled at a predetermined position and is extinguished. The present invention is not limited to the above-mentioned embodiment but is applicable to a device having the construction as shown in Figure 33 as a modified form. Namely, in the embodiment as shown in Figure 33, it is most important point to modify the shape of the lower most arc extinguishing metallic plate 13g among the arc extinguishing metallic plates 13 as shown in Figure 34. By constructing it to have such shape, the arc 12 is received a force in the direction as indicated by an arrow mark F because a magnetic flux  is produced (Figure 34) around the arc 12. Since the leg portions 13ga are formed in the arc extinguishing metallic plate 13f as shown in Figure 34, the force F is so strong that the arc is easily elongated, whereby the rising speed of an initial arc voltage is increased. Namely, in the device in the above-mentioned case, the rising speed of an arc resistance is increased to thereby increase current limiting ability. Accordingly, the arc 12 between the contacts takes the form of an arc 12A in a short time as described with reference to Figure 31 and it is attracted to the arc extinguishing metallic plates other than 13f, and the arc takes the progress of an arc 12B, an arc 12C and finally an arc 12D successively and then, it is cooled by the arc extinguishing metallic plates 13 to be extinguished. Thus, the urging of the arc just after the production of the arc and the shift of the arc from the state of the arc 12C to the state of the arc 12D are satisfactorily take place. Accordingly, time required for interruption is shortened and the current limiting ability is increased as described above, whereby arcing energy at an interrupting time is reduced to allow interruption of a large electric current. In the case of the device described with reference to Figure 33, only the arc extinguishing metallic plate 13g closest to the fixed contactor 8 is extended over the fixed contact 8A. However, the arc extinguishing metallic plate 13f may have the same construction. As another embodiment, for instance, the fixed contactor 8 provided with the arc runner 14 used for the previously mentioned embodiments may be used. Further, the arc horn 6B as in each of the previously mentioned embodiments may be provided at the end portion of the movable contactor 6. In the embodiment as shown in Figures 31 - 34, the projection is provided at a specified position of the arc extingusihing metallic plates. Accordingly, there causes no unstable arc and the arc is extinguished in a predetermined position, with the result that there is no damage to an insulating material constituting the outer wall, and both the current breaking ability and current limiting ability can be improved. An embodiment of the switch as illustrated in Figures 35 and 37 is so constructed that an insulating material having the same shape as the arc extinguishing metallic plates 13 (Figure 36) is inserted between the arc extinguishing metallic plates 13, whereby the arc is prevented from staying between them to thereby improve current breaking ability. Namely, in the embodiment shown in Figure 35, insulating plates as shown in Figure 36 are interposed between the arc extinguishing metallic plates 13. In Figure 35, when the movable contact 6A is separated from the fixed contact 8A, an arc is produced as shown in the figure. The arc 12 takes such progress that it takes the form of an arc 12A in a short time; then is attracted to the arc extinguishing metallic plates 13 to be an arc 12B, then is transformed into an arc 12C and finally becomes an arc 12D, which is cooled by the arc extinguishing metallic plates 13 to be extinguished. In this case, since the urging of the arc after the production of the arc and the shift of the arc from the arc 12C to 12D are satisfactorily take place, time required for interruption is shortened and current limiting ability is increased as described before. Accordingly, arc energy at the time of interruption is decreased to allow the interruption of a large electric current. By arranging insulating plates 30 between the arc extinguishing metallic plates 13, there causes no direct contact of the arc extinguishing metallic plates 13 since the insulating plates 14 are between the arc extinguishing metallic plates 13 even though the arc extinguishing metallic plates 13 become swollen by an inner gas which is caused the arc. Accordingly, there is no short-circuiting phenomenon in the arc distinguishing metallic plates 13. In the embodiment shown in Figure 35, the arc horn 6B is joined to the end portion of the movable contactor 6A. However, the arc horn 6B may not be provided at the end portion of the movable contactor 6. Further, the arc horn 6B may be formed integrally with the movable contactor 6A. In the case of the device described with reference to Figure 35, the arc extinguishing metallic plates 13 have the same length. However, as shown in Figure 37, for instance, the shape of the end portion of the arc extinguishing metallic plates 13 may be in a forked form as illustrated in Figure 34. The fixed contactor 8 with the arc runner 14 as used in the previously mentioned embodiments may be used instead of the fixed contactor 8. Thus, by providing the arc runner 14, the urging of the arc 12 can be obtained at a further high speed. Accordingly, both current limiting ability and current breaking ability can be further increased. In the case of the device described with reference to Figure 37, only the arc extinguishing metallic plate 13e closest to the fixed contactor 8 is extended to the upper part of the fixed contact. However, it goes without saying that the arc extinguishing metallic plate near the commutation plate 15 may have the same length and shape. As described above, in accordance with the embodiment as in Figures 35 - 37, the insulating plates 30 are arranged between each of the arc extinguishing metallic plates. Accordingly, there is no direct contact between the arc extinguishing metallic plates even though staying of the arc causes the arc extinguishing metallic plates 13 to be swollen. Accordingly, both of the current breaking ability and current limiting ability can be improved. A switch as shown in Figures 38 - 41 is so constructed that an insulating material is disposed at the opposite side of the arc extinguishing metallic plates 15 with respect to a portion to which an arc enters. With the construction, arc gas is controlled to be discharged outside; current breaking ability is improved by avoiding the staying of the arc; an arc space is reduced, and arc touch is prevented. Namely, in Figure 38, an insulating plate 19 as illustrated in Figure 39 is provided so as to be along the arc extinguishing metallic plates 13 at a position opposite the arc entrance part with respect to the arc extinguishing metallic plates 13. In Figure 38, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced as illustrated in the figure and the arc takes such progress that it takes the forms of 12A, 12B and 12C successively; finally, the arc takes the form of an arc 12D, and is cooled by the arc extinguishing metallic plates 13 to be extinguished. In this case, since the urging of the arc after the generation of the arc and the shift of the arc from the state of the arc 12C to the state of the arc 12D are satisfactorily take place, time required for interruption is shortened and the current limiting ability is also increased as described before. Accordingly, arc energy is decreased at the interruption time and interruption of a large electric current is possible. Thus, by disposing the insulating plate 19 so as to be along the end portion of the arc extinguishing metallic plates 13, the arc gas is prevented from being directly discharged. Accordingly, a broad arc space as required in the conventional device is not necessary, and the staying of the arc at the end portions of the arc extinguishing metallic plates 13 can be avoided. In the above-mentioned embodiment, the arc horn 6B is not joined to the end poriton of the movable contactor 6A. However, the arc horn 6B may be provided at the end portion of the movable contactor 6, or the arc horn 6B is formed integrally with the movable contactor 6A. In the case of the device described with reference to Figure 38, the arc extinguishing metallic plates 13 have the same length. However, the arc extinguishing metallic plate 13g closest to the fixed contactor 8 among the arc extinguishing metallic plates may have a length extending to a position corresponding to the fixed contactor 8A, for instance. In this case, the end portion of the arc extinguishing metallic plate 13g may have two-forked legs at the end portion as described in the previous embodiments. Further, a fixed contactor 8 with an arc runner 14 in which a window 14A to have the movable contact 6A passed may be used to give the construction as illustrated in Figure 41, instead of the fixed contactor 8 as in Figure 38. As described above, in accordance with the embodiment shown in Figures 38 - 41, the discharging of the arc gas to each part is controlled by the insulating plate 19 as an insulating material; miniaturization of the arc space can be expected as well as the control of stagnant the arc at the end part of the arc extinguishing metallic plates 13, and current breaking ability can be improved. In an embodiment of the switch shown in Figures 42 - 43, the portion corresponding to the movable contact 6A of a commutation plate 15 is bent on the side of the movable contact 6A to form a U-shaped leg portion 15A. With such construction, the rising speed of an initial arcing voltage is increased to improve current limiting ability and current breaking ability. As described above, in accordance with the embodiment as in Figures 42, 43, the leg portion 15A is formed at the commutation plate 15, whereby both the current breaking ability and current limiting ability can be improved. In an embodiment of the switch as shown in Figures 44 - 47, the portion corresponding to the movable contact 6A of a commutation plate 15 is bent on the side of the movable contact 6A to form a leg portion in which the free end of the commutation plate is bent so as to be inclined on the side of the arc extinguishing metallic plates to thereby form the leg portion. With such construction, the rising speed of an initial arcing voltage is increased to improve current limiting ability and current breaking ability. Namely, the switch as shown in Figure 44 is featurized by the fact that a part of the commutation plate is bent on the side of the movable contact 6A and the bent portion is inclined on the side of the free end. In Figure 44, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced as shown in the figure. The arc 12 take a progress that it is changed to an arc 12A in a short time; the arc is attracted to the arc extinguishing metallic plates to take the form of an arc 12B and an arc 12C successively; and finally takes the form of an arc 12D, and then it is cooled by the arc extinguishing metallic plates 13 to be extinguished. As described above, since the leg portion is formed in a part of the commutation plate 15, the arc 12 produced at the substantially central portion of the movable contact 6A is moved to the movable contactor 6 via the circumference portion of the movable contact 6A. In this case, the leg portion of the commutation plate is inclined as described above, and the shift of the leg of the arc can be obtained without difficulty, with the result that time required for interruption can be shortened. The function of the commutation plate 15 will be described with reference to Figure 45. Figure 45 shows a part of the commutation plate. The horizontal part constitures the leg portion of the commutation plate 15. This embodiment is featurized by using the commutation plate 15 with the leg portion inclined at an angle of 90 ° C >  > 0 ° C with respect to the horizontal plane. In Figure 45, when the arc 12 is moved on the lower end of the leg portion of the commutation plate 15, an electric current I₁ flowing in the commutation plate 15 intersects an electric current I₂ forming the arc so that an electromagnetic force caused by I₁ acts on the arc 12 to drive it upwardly. Then, the arc 12 is rapidly urged upwardly with the consequence of increasing the rising speed of an arc voltage to thereby improve the current-limiting ability and current breaking ability remarkably. Such effect can be obtained by determining the value of  to be, for instance, about 30 ° C. However, such value should not be considered to be fixed, normally, it is selected from a range of about 5 ° - 60 ° C depending on requirements. In the switch having such effect, an arc extinguishing metallic plate with two legs 13ga as shown in Figure 25 may be used as the arc extinguishing metallic plate 13g closest to the fixed contact among the arc extinguishing metallic plates 13. Figure 46 shows a switch in which the above-mentioned arc extinguishing metallic plates 13 are assembled. Figure 47 is a sectional view of another embodiment in which an arc runner 14 is provided on the fixed contactor 8. Figures 48 - 51 show still another embodiment of the present invention which is constructed in such a manner that a bent portion having a substantially U-shape of a cummutation plate is disposed between the movable contactor and arc extinguishing metallic plates so that the top portion of the bent portion is determined to be on the substantially same level as a position where open-circuit of the movable contactor is completed; some of the arc extinguishing metallic plates located between the fixed contactor and the movable contactor at the position of the completion of open-circuit are extended to the side of a space in which the movable contactor is movable, and the arc extinguishing metallic plates are all positioned near the area where an arc is produced at the initial stage, whereby the arc produced by the separation of the movable contact from the fixed contact is urged and accelerated by the arc extinguishing metallic plates; moving speed of the arc to the commutation plate, i.e. the rising speed of an arcing voltage is increased; the arc transferred onto the commutation plate is smoothly moved to the end of the commutation plate without staying at the central poriton of the surface of the end portion, and the moving speed of the arc on the commutation plate is increased. Figure 48 is a cross-sectional view of an important part of the embodiment to illustrate arc extinguishing function; Figure 49 is a diagram of an element shown in Figure 48; Figure 50a is a diagram showing the shape of an arc extinguishing metallic plate; and Figure 50b is a diagram showing the shape of another arc extinguihsing metallic plate. In Figure 48, a numeral 15 designates a commutation plate whose base portion is disposed above the movable contactor 6. An end portion 15a in a U-shaped portion extending toward the fixed contactor 8 is formed at the side of the end of the commutation plate 15. The bent portion 15a of the commutation plate 15 is disposed between the movable contactor 6 and the arc extinguishing metallic plates 13, and further, it is so determined that the top end of the bent portion 15a is substantially flush with a position where the open-circuit of the movable contactor 6 is completed. Of the arc extinguishing metallic plates 13, two arc extinguishing metallic plates 13e, 13f placed between the fixed contactor 8 and the movable contactor 6 at the position of the open-circuit are respectively provided with a pair of legs 13fe, 13fe, 13ff, 13ff which are extended from the both end sides to the side of the space where thee movable contactor 6 is movable. Further, of the arc extinguishing metallic plates 13, four arc extinguishing metallic plates 13a - 13d placed between the commutation plate 15 and the movable contactor 6 at the position of completion of the open-circuit are respectively provided with a pair of short legs 13fa, 13fa - 13fd, 13fd which are respectively close to the side of the bent portion 15a of the commutation plate 15 by extending from the short side of the edge, as shown in Figure 50a. Figure 50b shows a modified embodiment of the arc extinguishing metallic plates 13a - 13d as shown in Figure 50a which are respectively provided with a small-sized projection 13h at the center of its end. In the switch constructed as above-mentioned, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced between the both contacts 6A, 8A as shown in Figure 48. A magnetic flux  is formed around the arc 12, and the arc 12 is elongated by receiving a force as indicated by the arrow mark F directing to the arc extinguishing metallic plates 13e, 13f of magnetic substance, whereby it is moved toward the arc extinguishing metallic plates 13. In this case, since leg portions 13fe, 13ff extending to the side of the movable contactor 6 are formed in the arc extinguishing metallic plates 13e, 13f, the arc extinguishing metallic plates 13e, 13f are close to the position where the arc is produced at the initial stage, namely, the magnetic resistance becomes small while the magnetic flux  becomes strong so that the force of F is strengthened. Then, the arc 10 is accelerated in the direction of F, and the moving speed of the arc 12 to the commutation plate 15, i.e. the rising speed of the initial arcing volatage is increased. Then, the upper leg of the arc 12 is transferred from the movable contact 6A to the center of the end portion of the movable contactor 6, and the lower leg is transferred to the center of the end portion of the fixed contactor 8 to thereby become an arc 12A. The upper leg of the arc 12A transferred to the center of the end portion of the movable contactor 6 is smoothly transferred to the center of the top portion of the bent portion 15a of the commutation plate 15 which is the closest to the center of the end portion of the movable contactor 6 since the end of the bent portion 15a of the commutation plate 15 is provided at the position near the end portion of the movable contactor 6 and substantially flush with it. The lower leg is moved on the surface of the fixed contactor 8 to become an arc 12B. The upper leg of the arc 12B transferred to the commutation plate 15 is moved upwardly on the surface of the bent portion 15a by receiving a force directing toward the arc extinguishing metallic plates 13 by the aid of a magnetic flux generated around the arc to thereby become an arc 12C. The arc 12C reaches the fixed contactor 8 via parts 13c - 13f of the arc extinguishing metallic plates. The leg of the arc 12C is moved outwardly from the bent portion 15a of the commutation plate 15 to the flat plate portion 15 (on the right hand in the figure) and the arc traverses the whole of the arc extinguishing metallic plates 13a - 13f to thereby become an arc 12D communicating with the fixed contactor 8 to be extinguished. Figure 51 is a cross-sectional view of an important part of another embodiment of the present invention to illustrate arc extinguishing function. In the embodiment, a pair of leg portions 14a formed by bending an arc runner 14 into a shape of ⊐ are positioned at the side of the fixed contact 8A in an end of the fixed contactor 8. The arc runner 14 is so provided that the upper end portion 14a of the arc runner 14 is in parallel to the arc extinguishing metallic plates 13, and the lower end portion 14c of the arc runner 16 is in parallel to the base portion of the fixed contactor 8 to provide the same arc extinguishing function as the embodiment described with reference to Figure 48. In the embodiments as in Figures 48 - 51, the moving speed of the arc on the commutation plate is increased, current limiting ability and current breaking ability are improved to shorten an interruption time. Further, the wearing of the contacts, damage in the contactors, the commutation plate and matallic plates can be small with the result of elongation of the life time. In addition, an arcing chamber can be minimized by the structure in which the arc runs at the center of the commutation plate. An embodiment as shown in Figures 52 - 54 is constructed under the consideration that during the commutation of the arc on the commutation plate 15 which is horizontally formed, the arc runs along the edges of the commutation plate without running in its central area, with the result that the arc causes the thermal deterioration of the inner wall of the arcing chamber to thereby reduce the inching life. In view of the above-mentioned, a projection is formed in the longitudinal direction of the central part of the commutation plate 15. This structure not only restricts the area for moving the arc, but also increase the moving speed of the arc, and at the same time current breaking ability and the inching life are improved. Figures 52a and 52b respectively show the bottom view and the side view of the above-mentioned embodiment of the present invention. As understandable from the figures, the width of the commutation plate 15 is partly narrowed in the longitudinal direction of the plate 15, and projections 15A are formed continuously or intermittently in the longitudinal direction on the center line. A structure for arc extinction in which the commutation plate 15 as shown in Figure 52 is used will be described. Namely, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced as shown in Figure 53. The arc 12 takes the progress that the arc is attracted to the arc extinguishing metallic plates 13 of magnetic substance to assume an arc 12A in a short time while the upper and lower legs separate from the contacts at the first stage; then, the arc changes its state to be an arc 12B and an arc 12C successively; it takes finally the form of an arc 12D, and is cooled by the arc extinguishing metallic plates 13 to be extinguished. The upper leg of the arc 12 produced around the substantially central part of the movable contact 6A moves along the outer edge of the movable contactor 6 to reach the commutation plate 15 through the arc horn 6B. In this case, the arc 12 having reached the commutation plate 15 from the peripheral part of the movable contact 6A via the movable contactor 6 immediately starts its movement along the projections 15A since the projections 15A are formed in the longitudinal direction at a part in the commutation plate 15. Accordingly, time required for interruption can be remarkably shortened. Figures 54a and 54b show the lower surface of or around the end portion of the commutation plate 15 in which the projections 15A are continuously or intermitently formed in the longitudinal direction of the commutation plate 15. Figures 55 - 57 show another embodiment of the present invention. This embodiment is proposed from the viewpoint that in the case that the arc extinguishing metallic plates 13 of magnetic substance are made flat, it is difficult to determine which course the arc passes among positions x, y, z in each of the arc extinguishing metallic plates 13 as illustrated in Figure 57, and if the arc often passes the position y or z without passing through the position x, for instance, an insulating material constituting side walls of the arc extinguishing metallic plates 13 often suffers a high temperature radiation to thereby damage the insulating material. This embodiment is characterized by providing a projection at the central portion of each of the arc extinguishing metallic plates. In Figure 55 showing an embodiment of the present invention, the arc extinguishing metallic plates 13 used for the embodiment respectively have a projection 13h as illustrated in Figure 56. In Figure 55, when the movable contact 6A is separated from the fixed contacto 8A, an arc 12 is produced as shown in the figure. The arc 12 is attracted to the arc extinguishing metallic plates 13 of a magnetic substance to change its form to an arc 12A. The upper leg of the arc 12A passes around the end portion of the movable contactor 6, and the lower leg is separated from the fixed contact 8A, passing a part of the art extinguishing metallic plates 13 to reach the fixed contactor to thereby become an arc 12B. The arc 12B is finally changed to an arc 12D via the state of an arc 12C which is formed by the movement of the upper leg from the lower part of the arc horn 6B to the upper part of it, the arc 12C jumping from the top of the arc horn 6B. In this case, the arc 12D does not become unstable because the projection 13h is formed on the surface of the arc extinguishing metallic plates 13 and the arc 12D is cooled at the predetermined position to be extinguished. As described above, in accordance with this embodiment, the arc does not become unstable and is extinguished in a predetermined cource because the projection is formed at a predetermined position of the arc extinguishing metallic plates. Accordingly, there is no damage to an insulating material which forms the outer wall, and both current breaking ability and current limiting ability can be improved. An embodiment as shown in Figures 58 - 60 will be described. When the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced. When the arc 12 is attracted to the arc extinguishing metallic plates 13 for extinction, stagnancy in the arc 12 is sometimes caused at certain portions in the arc extinguishing metallic plates 13 during the period of extinction. Then gas around the arc extinguishing metallic plates 13 is expanded by heat, with the result that the arc extinguishing metallic plates 13 become swollen. In the worst case, there causes mutual contact of the arc extinguishing metallic plates 13 to cut the arc 12 and to reduce cooling effect. This may cause incapability of interruption. This embodiment is to eliminate such problem and to obtain a switch capable of maintaining for a long time performance inherently expected to a switch. This embodiment is characterized by coating an insulating material on at least one surface of each of the arc extinguishing metallic plates. The embodiment will be concretely described. The device as shown in Figure 58 has a feature that one surface of each arc extinguishing metallic plate 13 is covered by an insulating plate 31 as shown in Figure 59. As material for the insulating plate 31, it is sufficient to cause evaporation when it is subjected to a high temperature. Generally an organic meterial is used. In Figure 58, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced as shown in the figure. The arc 12 is attracted to the arc extinguishing metallic plates 13 of a magnetic substance to change its form into an arc 12A. The upper leg of the arc 12A passes around the end portion of the movable contactor 6 and the lower leg is separated from the fixed contact 8A while it passes through a part of the arc extinguishing metallic plates 13, whereby an arc 12B extending to the fixed contactor is formed. The arc 12B is finally becomes an arc 12D by the movement of the upper leg on the commutation plate 15. In this case, the presence of the insulating plate 19 on one surface of each of the arc extinguishing metallic plates 13 prevents the mutual contact of the arc extinguishing metallic plates 13 even when there causes the staying of the arc 12 around the arc extinguishing metallic plates 13 due to any cause in the period from generation of the arc to its extinction. The arc can be cut in a stable manner; a stable cooling effect can be obtained, and current breaking ability can be improved. The present invention is not only effective to the above-mentioned embodiment, but also effective to modified embodiments. For instance, the lowermost arc extinguishing metallic plate 13g among the arc extinguishing metallic plates 13 may have a forked shape at its end as illustrated in the arc extinguishing metallic plate 13e as in Figure 49. Figure 60 shows an example using the arc extinguishing metallic plates 13 having the shape. The progress of the arc 12 in this case is substantially the same as that as described with reference to Figure 58. As described above, in accordance with the embodiment shown in Figures 58 - 60, there is no risk of direct contact of the arc extinguishing metallic plates even though the stagnant arc causes the arc extinguishing metallic plates swollen because the insulating material is covered on at least one surface of each of the arc extinguishing metallic plates. Accordingly, both current breaking ability and current limiting ability can be improved. An embodiment as shown in Figures 61 - 63 will be described. In the previously mentioned embodiments, the switch has such construction that arced gas produced at an interruption time is directly discharged outside. Accordingly, there is a point to be improved. That is, an arc space formed between a switch and a casing, a switch board containing the switch, or the door of the switch board has to be large. Further, from the viewpoint of its function, there is disadvantages that an arc 12 generated at an interruption time is strongly attracted to the arc extinguishing metallic paltes of the magnetic substance having flat surfaces, whereby the arc often reaches the end portion of the arc extinguihing metallic plates 13 to cause the staying of an arc 12D at its end portion to thereby invite inability of interruption. In view of such disadvantage, the present embodiment is featurized by covering the end portion of each of the arc extinguishing metallic plates with an insulating material to control discharging of the arced gas to the outside. In accordance with the embodiment shown in Figures 61 - 63, the discharging of the arced gas is controlled and the position of the arc generated is given at a predetermined area to minimize the staying of the arc by slightly modifying the outer portion of the arc extinguishing metallic plates, whereby a switch capable of improving current breaking ability can be provided. An embodiment of the present invention will be described with reference to the drawing. The switch shown in Figure 61 has a characteristic feature that an insulating plate 32 as shown in Figure 62 is used which is in contact with the end portion of the arc extinguishing metallic plates 13. In Figure 61, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced as shown in the figure. The arc 12 is attracted to the arc extinguishing metallic plates 13 of a magnetic substance to change its form into an arc 12A. The upper leg of the arc 12A passes around the end portion of the movable contactor 6, and the lower leg is separated from the fixed contact 8A while it passes through a part of the arc extinguishing metallic plates 13 to thereby become an arc 12B reaching the fixed contactor. The arc 12B finally chances to an arc 12D by the movement of the upper leg to a downwardly bent portion of the commutation plate 15. In this case, the arced gas produced in the period from generation of the arc to its extinction can not be directly discharged outside owing to the insulating plate 32 provided at the end portion of the arc extinguishing metallic plates 13, but is discharged from another discharging route gradually. Thus, by controlling the movement of the arced gas, the arc 12D is prevented from shifting to the end portion of the arc extinguishing metallic plates 13, and accordingly, the staying of the arc 12 at the end portion of the arc extinguishing metallic plates 13 is not caused and the arc is cooled at a perdetermined position to be extinguished. The present invention is not only applicable to the above-mentioned embodiment, but also it is applicable to a device, as a modified embodiment, having the construction as shown in Figure 63. Namely, the feature of the device as in Figure 63 is that the lowermost arc extinguishing metallic plate 13g among the arc extinguishing metallic plates 13 has a forked end portion. The embodiment of Figure 63 provides the same function and effect as that of Figure 61. An embodiment as shown in Figures 64 - 65 will be described. The embodiment as shown in Figures 64 - 65 is so constructed that the width of the end portion of each of the arc extinguishing metallic plates 13 is made thin at the side of the contacts, and a casing wall around the arc extinguishing metallic plates 13 is also narrowed, whereby an arc is strongly urged for extinction by utilizing pressure difference (air gap function) caused by the generation of the arc near the contacts in association with the above-mentioned two arc driving sources. The embodiment of the present invention will be described with reference to Figures 64 and 65. Figure 64 shows a part of the arc extinguishing metallic plates 13 used in the example in a plane view. As seen from the view, the end portion of the arc extinguishing metallic plate 13 has a thin, narrowed shape. With such construction, the pressure of gas caused by the arc generated is increased, and the pressure is utilized as a driving source for the arc. Figure 65 shows an example of the present invention in which the arc extinguishing metallic plates 13 which are processed to have the shape as shown in Figure 64 are used. In Figure 65, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced in the same manner as the previously mentioned embodiments. The arc 12 takes the progress that it changes into an arc 12A in a short time by the influence of the magnetic substance; the arc is attracted to the arc extinguishing metallic plates 13 to take the form of an arc 12B and an arc 12C successively; the arc finally changes into an arc 12D; and it is cooled by the arc extinguishing metallic plates 13 to be extinguished. In the movement of the arc, the gap effect it obtained by making the end portion of the arc extinguishing metallic plates thin and by making the wall of the casing 40 surrounding the plates 13 to be narrowed. The generation of the arc, the urging of the arc and the shift of the arc from the state of an arc 12C to the state of an arc 12D are satisfactorily carried out, and time required for breaking is shortened and current limiting ability is also increased as described before, whereby arc energy at an interruption time is decreased to allow interruption of a large electric current. In the above-mentioned embodiment, description has been made as to the case that the arc horn 6B is joined to the end portion of the movable contactor 6. However, the arc horn 6B may be omitted. In the case of the device described with reference to Figure 65, the length of the arc extinguishing metallic plates 13 is the same. However, it is possible that for instance, at least one of the arc extinguishing metallic plates 13 has the shape extending to a position near the fixed contactor 8A, and the arc extinguishing metallic plate has its end portion which is forked to provide leg portions. As described above, in accordance with the embodiment shown in Figures 64 and 65, the urging force of the arc can be further improved in comparison with the conventional device by simply changing the shape of the arc extinguishing metallic plates and by narrowing the surface of the casing for protecting the circumference so as to correspond to the shape of the arc extinguishing metallic plates. This means improvement of the current breaking ability and the current limiting ability of the switch, and the effect of it is remarkably large. An embodiment as shown in Figures 66 - 69 will be described. In the above-mentioned embodiments, a plurality of the arc extinguishing metallic plates 13 of the magnetic substance are merely arranged in parallel to each other. Accordingly, the arc may be discharged outside during the length of the arc being short, whereby there may cause a trouble of grounding or external short-circuiting. In the embodiment shown in Figures 66 - 69, the ends of or the areas near the ends of the commutation plate and the arc extinguishing metallic plates are radially broadened. Since the switch of the present invention is provided with the arc extinguishing metallic plates whose end portion is made in a radial form, it is effective to prolong the length of the arc by inclining the arc extinguishing metallic plates and the commutation plate. Accordingly, chance of contacting of the arc with air is increased and a cooling effect is large, whereby an arc voltage is rapidly raised and the arc can be diffused, with the result of increasing current breaking ability. The above-mentioned embodiment of the present invention will be described with reference to the drawing. The embodiment of the present invention shown in Figure 66 has a featurized construction that the arc extinguishing metallic plates 13, the commutation plate 15 and the fixed contactor 8 are broadened toward their end portions. In Figure 66, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced. The arc 12 is attracted to the arc extinguishing metallic plates 13 of a magnetic substance to become an arc 12A. Then, the arc changes into an arc 12B and an arc 12C successively. When the arc 12 progresses beyond the broadened portions of the arc extinguishing metallic plates 13, the commutation plate 15 and the fixed contactor 8, and becomes, for instance, an arc 12A, chance of contacting of the arc with air suddenly increased which functions to cool the arc 12. The arc extinguishing metallic plates 13 used for this purpose are formed by bending their part (it is unnecessary to bend the arc extingusihing plate placed at the center) as shown in Figure 67. Thus, the arc 12 is completely extinguished without causing grounding or external short-circuiting. In this case, the arc extinguishing metallic plate 13g closest to the fixed contact 8A may have a forked portion which provides two legs at the part corresponding to the fixed contact 8A. Figure 68 shows an example of an arc extinguishing metallic plate 13g provided with leg portions. The arc 12 produced between the contacts takes a progress that it becomes an arc 12A in a short time as shown in Figure 68; the arc is attracted to the arc extinguishing metallic plates other than 13g to thereby take the form of an arc 12B and an arc 12C successively; it finally becomes an arc 12D, and is cooled by the arc extinguishing metallic plates 13 to be extinguished. Thus, since the urging of the arc just after the generation of the arc and the shift of the arc from the state of the arc 12C to the state of the arc 12D are satisfactorily obtained. Time required for interruption is shortened and the current limiting ability can be increased in the same manner as described before. Accordingly, arc energy at a breaking time is decreased to allow interruption of a large electric current. In the embodiment as shown in Figure 69, an arc runner 14 having an inversed L-shape is electrically joined to the end portion of the fixed contactor 8 at the side of the fixed contact 8A, and the arc runner 14 is so constructed that the movable contactor 6 is passed through a notched portion 14e of the arc runner 14 to come into contact with the fixed contact 8A. Thus, by providing the arc runner 14, the urging of the arc 12 can be further accelerated, and both current limiting ability and current breaking ability can be further increased. As described above, in accordance with the embodiment as shown in Figures 66 - 69, each end portion of the arc extinguishing metallic plates, the fixed contactor and the commutation plate is widened to diffuse the arc. Accordingly, rising of an arc voltage is increased and arc can be elongated to thereby improve the current breaking ability. An embodiment as shown in Figures 70 and 71 will be described. In the above-mentioned embodiments, the width of the fixed contact 8 is uniformly. Accordingly, it is difficult to carry out a rapid urging of the arc on the fixed contactor. Further, thermal deterioration of the side wall at the side of the fixed contactor is great, and the inching life is short. Thus, there are many poblems to be improved. In this embodiment, the fixed contact is provided on the upper surface of the fixed contactor and an arc runner having a narrow path is formed in the fixed contactor. The embodiment of Figures 70 and 71 is attained as a result of study on the shape of the fixed contactor, and the rapid urging of an arc on the fixed contactor can be obtained by positioning the arc runner having the narrow path at the outer side of the fixed contact of the fixed contactor. The concrete example will be described. The fixed contactor used in the embodiment is one as shown in a perspective view in Figure 70. As is recognized from the view, an arc runner 14 is provided with a forked portion 14d which are outside of the fixed contact 8A and gradually converges to the free end. And it is also provided with a piece having the same width as the fixed contactor. Namely, the arc runner 14 is connected to the fixed contactor 8 by narrow pathes. Thus, by using the fixed contactor having the above-mentioned shape, an urging force to the arc produced can be increased. Figure 71 shows another embodiment of the arc runner 14. By providing the arc runner 14 as illustrated, the urging of the arc 12 can be further accelerated, and both current limiting ability and current breaking ability can be increased. An embodiment as shown in Figures 72 - 76 has a fixed contactor 8 improved in the same manner as the embodiment shown in Figures 70 and 71. Namely, the embodiment of Figures 72 - 76 has been attained as a result of study on the shape of the fixed contactor 8. By forming a ridge-like projection at the central portion of the fixed contactor 8 at the outer side of the fixed contact 8A and along its longitudinal direction an arc is rapidly urged. This embodiment minimizes the influence of heat against the side wall surrounding the fixed contactor and the inching life can be prolonged. The embodiment of the present invention will be described with reference to the drawing. The embodiment of Figure 72 is characterized by forming a ridge-like portion 8C at the central portion of an arc runner 14 in its longitudinal direction and at the outer side so as to extend toward the free end with respect to the fixed contact 8A, and the width of the central portion of the arc runner is narrowed, while the width at the free end side is made broad. Figure 73 shows an embodiment of the present invention in which the fixed contact 8 made as shown in Figure 72 is used. In Figure 73, when the movable contact 6A is separated from the fixed contact 8A, an arc 12 is produced. The arc 12 takes a progress that it becomes an arc 12A in a short time by the influence of magnetic substance; it is attracted to the arc extinguishing metallic plates 13 and moves on the arc runner 14 to take the form of on arc 12B and then an arc 12C successively; it finally becomes an arc 12D, and it is cooled by the arc extinguishing metallic plates 13 to be extinguished. In the movement of the arc, since the projection is formed on the arc runner in the fixed contactor 8, arc attracting effect is increased so as to urge the arc. When the urging of the arc after the generation of the arc and the shift of the arc from the state of the arc 12C to the state of the arc 12D are satisfactorily obtained. Time required for interruption is shortened, and the current limiting ability is increased as described before. Accordingly, arc energy at an interruption time is decreased to allow interruption of a large electric current. In the above-mentioned embodiment, an arc horn 6B is joined to the end portion of the movable contactor 6A. However, the arc horn 6B may be omitted. In the case of the device described with reference to Figure 73, the length of the arc extinguishing metallic plates 13 is made the same. However, the length can be determined in such a manner that at least one of the arc extinguishing metallic plates 13 is extended to a position corresponding to, for instance, the fixed contactor 8A as described in the previously mentioned embodiment (with reference to, for instance, Figure 49), and the end portion of the elongated arc extinguishing metallic plate is forked to have two legs. Further, a fixed contactor 8 provided with an arc runner 14 as illustrated in Figure 74 may be used instead of the fixed contactor 8 as in Figure 72. In this case, the end portion at the side of the fixed contact 8A of the fixed contact 8 is bent in an inversed L-shape. An arc extinguishing structure in which the above-mentioned fixed contactor is used will be described with reference to Figure 75. In the same manner as the embodiments described before, when an arc 12 is produced between the movable contact 6A and the fixed contact 8A, the lower leg of the arc 12 on the fixed contact 8A is easily transferred onto the arc runner 14 whereby the state of the arc 12A is changed to the state of the arc 12B because the projection 8C is formed on the arc runner 14. When the lower leg of the arc 12 is transferred onto the arc runner 14, an electric current flows in the arc runner 14 in the direction of an arrow mark X as shown in Figure 75, and the arc 12A is further urged toward the terminal portion of the arc runner 14. The upper leg of the arc 12A is transferred from the movable contact 6A to the end portion of the movable contactor 6 and the arc is attracted to the arc extinguishing metallic plates 13. The lower leg runs on the arc runner 14 from the fixed contact 8A. The upper leg of the arc 12B transferred on the movable contactor 6 is successively urged by arc extinguihsing metallic plates 13, and the arc 12C elongated by the arc extinguishing metallic plates 13 is transferred to the arc runner 14 by moving on all of the arc extinguishing plates 13a - 13e of the arc extinguishing metallic plates 13, and is finally extinguished. Thus, by providing the projection on the arc runner 14, the urging of the arc 12 is further accelerated, whereby both current limiting ability and current breaking ability can be further increased. As modified examples on the fixed contactor 8 as shown in Figure 72, ones as shown in Figures 76a, 76b and 76c may be used. It goes without saying that the same effect as in the previously mentioned embodiments can be obtained even in these cases. In the previously mentioned embodiments, the arc extinguishing metallic plates 13 with the legs 13ga placed between the fixed contact 8A and the movable contact 6A may be a single or a plural number. INDUSTRIAL APPLICABILITY The present invention is widely applicable to a switch such as an electromagnetic contactor, a breaker for wiring, an air circuit breaker and so on used for factories, homes and so on.

Claims: A switch comprising a fixed contact (8A) joined to a fixed contactor (8), a movable contact (6A) joined to a movable contactor (6) to face said fixed contact, a plurality of arc extinguishing metallic plates (13) arranged with predetermined distances therebetween and in parallel to said fixed contactor (8) at an end portion of said movable contactor (6), and a commutation plate (15) placed at a side of said arc extinguishing metallic plates (13) opposite said fixed contactor (8) so that said movable contactor (6) is positioned between said commutation plate (15) and said fixed contactor, at least one plate (13g) of said arc extinguishing metallic plates (13) located adjacent said fixed contactor (8) has one end which extends in a direction toward said movable contactor (6) and is spaced from said fixed contactor (8), and said one end has a space formed therein so that said movable contact (6A) is movable therethrough for being brought into contact with said fixed contact (8A), characterized in that said one end includes first and second leg portions (13ga) which extend beyond a perpendicular line of the mutual contact between said fixed contact (8A) and movable contact (6A) and that the remaining arc extinguishing metallic plates are formed as having no such leg portions. The switch according to Claim 1, wherein the arc extinguishing metallic plate (13g) closest to said fixed contact (8A) and the extinguishing metallic plate (13a) closest to said commutation plate (15) are extended beyond a perpendicular line of the mutual contact between said fixed contact (8A) and movable contact (6A). The switch according to Claim 1, wherein some of said arc extinguishing metallic plates (13a, 13b) closest to said commutation plate (15) are extended to the side of a space in which said movable contact or (6) is movable. The switch according to Claim 1, wherein the arc extinguishing metallic plate (13a) closest to said commutation plate (15) is extended to the side of a space in which said movable contactor (6) is movable. The switch according to Claim 1, wherein an end portion of all of said are extinguishing metallic plates (13) is extended to the side of a space where said movable contactor (6) is movable. The switch according to Claim 1, wherein longer arc extinguishing metallic plates (13a, 13b, 13c, 13d) having leg portions at both sides of their one end formed by cutting the central portion of the end and shorter arc extinguishing metallic plates (13e, 13f, 13g) are arranged alternately so that the end portion of said longer arc extinguishing metallic plates are placed above or below said movable contactor (6). The switch according to one of the preceding Claims, wherein a projection (13a) is formed at an end portion of each of said arc extinguishing metallic plates (13). The switch according to Claim 7, wherein said projection (13h) is formed on the front surface facing said commutation plate (15) or said fixed contactor (8). The switch according to Claim 1, wherein an insulating material is interposed between adjacent ones of said arc extinguishing metallic plates (13). The switch according to one of the preceding Claims, wherein said commutation plate (15) is bent into a U-shape so that the end of the leg portion (15a) faces in the vicinity of the back face of said movable contact (6). The switch according to Claim 10, wherein said leg portion (15a) of the commutation plate (15) has a side inclined to its free end side. The switch according to one of the preceding Claims, a bent portion (15a) having a substantially U-shape is formed in said commutation plate (15) so that said bent portion is arranged between said movable contactor (6) and said arc extinguishing metallic plate (13), and the top portion of said bent portion is substantially flush with a position where open-circuiting of said movable contactor is completed. The switch according to one of the preceding Claims, wherein the width of said commutation plate (15) is broaden at its both ends, and a projection (15A) is formed at its central portion so as to contact to an arc. The switch according to one of the preceding Claims, wherein a projection (15A) is formed on said commutation plate (15) at its central portion at the free end side so as to contact to an arc. The switch according to one of the preceding Claims, wherein a projection (13a) is formed on said arc extinguishing metallic plates (13) at their central portion in the width direction. The switch according to one of the preceding Claims, wherein at least one surface on said arc extinguishing metallic plates (13) is covered by an insulating material (31). The switch according to one of the preceding Claims, wherein an insulating material covers a part on the same side of each of said arc extinguishing metallic plates (13) to control the discharging of arc gas. The switch according to one of the preceding Claims, wherein the width of said arc extinguishing metallic plates (13) at the side of said movable contact (6) is narrow, and the width of the end portion at the opposite side is broad. The switch according to one of the preceding Claims, wherein said commutation plate (15) and said arc extinguishing metallic plates (13) are so formed that they are radially broaden as they are apart from said movable contact (6). The switch according to one of the preceding Claims, wherein an arc runner (14) is continuous to said fixed contactor (8A). The switch according to Claim 20, wherein the arc runner (14) is connected to said fixed contactor (8) through a narrow path. The switch according to Claim 20 or 21, wherein a projecting part is formed at the central portion in the longitudinal direction of said arc runner (14). The switch according to one of the preceding Claims, wherein an arc horn (6B) is formed at the end portion of said movable contactor (6) which faces the end portion of said arc extinguishing metallic plates (13) with a distance. A switch according to one of the preceding claims, characterized in that the ends or the portions near the ends of the arc extinguishing plates (13) which extend in a direction away from the movable contactor (6) are radially broadened so that the length of arc between the arc extinguishing plates (13) is prolonged. A switch according to one of the preceding claims, characterized in that an insulating material (19, 32) is disposed at that end of the arc extinguishing plates (13) which is directed away from the movable contactor to control arc gas. A switch according to one of the preceding claims, characterized in that a projection (15A; 8c) is formed on the commutation plate (15) or the fixed contactor (8) on a surface thereof facing the fixed contactor (8) or the commutation plate (15), respectively. A switch according to one of the preceding claims, characterized in that insulating plates (30; 31) are inserted between the arc extinguishing plates (13).

Inventors: HIRAKI HARUMI MITSUBISHI DENKI, MASUDA SHIGERU MITSUBISHI DENK, MORI TEIJIRO MITSUBISHI DENKI, NISHIZAKO SHIZUTAKA MITSUBISHI, SUTOH SYUNICHI MITSUBISHI DENK, TATEISHI TOKIO MITSUBISHI DENK, HIRAKI, HARUMI MITSUBISHI DENKI K. K., MASUDA, SHIGERU MITSUBISHI DENKI K. K., MORI, TEIJIRO MITSUBISHI DENKI K. K., NISHIZAKO, SHIZUTAKA MITSUBISHI DENKI K. K., SUTOH, SYUNICHI MITSUBISHI DENKI K. K., TATEISHI, TOKIO MITSUBISHI DENKI K. K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1987
Main classification: H01H9
IPC codes: H01H9