DESCRIPTION

[0001] The present invention refers to the technical field of electric apparatuses, and more specifically to an electric circuit breaker as defined in the preamble of claim 1.

[0002] In modern electric energy distribution installations the need of installations with electric circuit breakers providing adequate selectivity characteristics of the installation is strongly felt. The selectivity of an electric energy distribution installation is necessary in order to ensure maximum service consistency- possible in such an installation in case of failure. In fact, after a failure in the electric distribution network, for example in case of a short circuit, the overcurrent which is formed in the electric network affects all the circuit breakers in the portion of installation included between the energy distribution point (generally the middle/low voltage transformer) and the failure .

[0003] Therefore, in order to ensure maximum service consistency of installation and to prolong to the maximum extent possible the technical life of circuit breakers, it is necessary that the failure is rapidly isolated from the circuit breaker, for example of the automatically-operated type, which is positioned immediately upstream of the failure, and it is required that the circuit breakers which are positioned at a higher level, i.e. further upstream with respect to such circuit breaker, hold the respective electric contacts in a closed position, even with the high overcurrents generated by the failure. In this way the service continuity is in fact ensured for the branches of the electric network which are not affected by the failure.

[0004] In this context, it is to be noted, that in the electric energy distribution installations of above said type, molded case electric circuit breakers are normally used, which comprise fixed and movable electric contacts, which are usually comprised of fixed and movable electrically conductive pads. ^' In these circuit breakers, the fixed pads are provided on respective supporting elements, which are integral with the external insulating case of the circuit breaker, whereas the movable pads are provided on respective supporting elements, which are fixed to a contact carrying shaft ^' . Such shaft may be operated by means of a suitable actuating mechanism in order to bring the movable pads in the respective operating positions corresponding to the opening and closing , states of the circuit breaker. Regarding the movable pads, in particular, these are not fixed to the contact carrying shaft but are supported in a way as to maintain a residual moving capability with respect to such shaft. The aim is here to compensate inevitable misalignments between the fixed pads of the circuit breaker and/or clearances caused by wear of fixed and movable pads. In this way a proper contact between the fixed and movable pads of circuit breaker is thus achieved.

[0005] However, molded case circuit breakers having above said architecture have a rather low upper limit of electric current value for which a proper electric contact between fixed and movable pads of circuit breaker is ensured. In practice, such circuit breakers are not able to resist to high overcurrents induced by a failure in another portion of the electric network.

[0006] In fact, when the circuit breaker is crossed by an electric current, repulsive electrodynamic forces are generated, whose intensity increases with an increase of electric current, which tend to separate the movable pads from the fixed pads. Such repulsive electrodynamic forces between the circuit breaker pads are contrasted, up to a predetermined limit of the value of electric current, by suitable compression springs provided between the contact carrying shaft and the supporting elements of movable pads in order to ensure a correct positioning of movable pads and a suitable contact force between such pads and fixed pads. In case of repulsive electrodynamic forces greater than said limit value, an undesirable separation between fixed and movable pads takes place. Such separation is allowed by the fact that the movable pads, as stated above, may move with respect to the contact carrying shaft even when the shaft is held in a fixed position by the corresponding actuation mechanism.

[0007] The solutions of the known art used for improving the selectivity characteristics of electric circuit breakers, i.e. for increasing the threshold value of electric current at which the separation phenomena between fixed and movable pads due to mutual repulsion takes place, are essentially based on the following two techniques: increasing the mechanical pressure between the movable and fixed pads by strengthening the compression springs; increasing the number of electric contact surfaces for each circuit breaker pole by using a plurality of supporting elements for the movable pads, which are connected in parallel for each pole .

[0008] However, both above said techniques have disadvantages which render the performance of molded case circuit breakers of the known art inadequate with respect to presently required performances in the field.

[0009] In fact, in the first case, the increase of the contact force between the movable and fixed pads inevitably requires an increase of the force which is required by the actuation mechanism in order to compress the compression springs, and therefore, of the force which acts on the command lever of the circuit breaker in order to drive above said actuation mechanism. Since the actuation of the circuit breaker is normally a manual operation, it follows that upper limits for the force which may be exerted on the fixed and movable pads exist, which are imposed by the actual possibility of commanding the circuit breaker by the user.

[0010] In the second case, the fractioning of the supporting elements for the movable pads allows the distribution of current over a plurality of contact zones, therefore reducing the repulsion threshold for each individual movable pad. The global effect on the single pole of the circuit breaker is therefore to rise the repulsion threshold of the whole group of movable pads. However, also in this case, there are constrains due to size of circuit breakers and force required for commanding the same. In fact, the increase of number of supporting elements for movable pads entails on one side and an increase of size of circuit breaker and on the other side an increase of total force for each pole required for maintaining a proper pressure of movable pads on fixed pads .

[0011] Above said drawbacks cause the molded case circuit breakers of the known art to not being able to maintain a proper contact between movable and fixed pads for current values higher than approximately 20 [kA] . Such limit, in particular, is absolutely inadequate for requirements of modern electric installations, in terms of selectivity. Therefore, in modern electric installations, in order to achieve higher selectivity values, it is currently necessary to use circuit breakers which are commonly called "air circuit breakers". Such circuit breakers, which are characterized by the fact of including a mechanism for accumulating elastic energy, in fact maintain forces which are so high as to compress the compression springs with a high load, and therefore maintain a proper contact between the respective pads up to currents in the order of 100 (kA) . However, the air circuit breakers are characterized by high sizes and costs and have a higher installation complexity with respect to molded case circuit breakers of above said type.

[0012] An object of the present invention is to provide an electric circuit breaker which is able to solve above said drawbacks with reference to installations and circuit breakers of the known art .

[0013] In particular, an object of the present invention is to provide an electric circuit breaker which is characterized by such performance as to allow the fabrication of electric installations having high performance in terms of selectivity characteristics.

[0014] More in particular, an object of the present invention is to provide an electric circuit breaker which allows an increase of the maximum current value, for which a proper contact between the respective electric contacts is ensured, without the need for an increase of force applied by the actuation mechanism of the circuit breaker.

[0015] This and other objects are achieved by the electric circuit breaker as defined and characterized in appended claim 1 in its more general form and in the dependent claims in some of its specific embodiments.

[0016] The invention will be more clearly understood from following detailed description of its embodiments, which is illustrative and therefore in no way limiting with reference to appended drawings, wherein:

- fig. 1 shows a perspective view of a molded case electric circuit breaker; fig. 2 shows a perspective view wherein a first supporting element comprising a plurality of electric contacts of the circuit breaker of fig. 1 and a circuit breaker first component which is associated to ' such supporting element are shown in a mutually separated configuration; fig. 3 shows a perspective view of an assembly including the first supporting element and the first component of fig. 2 in an assembled configuration;

- fig. 4 shows a sectional transversal view of the assembly of fig. 3;

- fig. 5 shows a perspective view of a second supporting element comprising a plurality of electric contacts of the circuit breaker of fig. 1;

- fig. 6 shows a perspective view, wherein a contact carrying shaft of circuit breaker of fig. 1 is shown; fig. 7 shows a perspective view of the assembly including the second supporting element of fig. 5 and the contact carrying shaft of fig. 6, which are positioned in an assembled configuration, and also include an actuation mechanism for the contact carrying shaft; fig. 8 shows a perspective view of the assembly of fig. 7, wherein such assembly is shown from ^' a different view angle;

- fig. 9 shows a sectional transversal view, wherein the assembly of fig. 3 and the assembly of fig. 8 are partially shown in a first operating configuration;

- fig. 10 shows a sectional transversal view, wherein the assembly of fig. 3 and the assembly of fig. 8 are partially shown in a second operating configuration;

- fig. 11 shows a sectional transversal view similar to fig. 10, wherein through arrows are schematically indicated the paths of flow of electric current flowing through the first supporting element of fig. 2 and through the second supporting element of fig. 5, as well as an electromagnetic force between such contacts;

- fig. 12a shows a perspective view, wherein the first supporting element and the first component of fig. 2 are shown, wherein, in particular, the first supporting element is shown according to a second embodiment and with some parts detached; fig. 12b shows a view from above of an assembly comprising components of fig. 12a in an assembled configuration;

- fig. 12c shows a sectional transversal view of the assembly of fig. 12b along line A-A of this figure; fig. 13a shows a perspective view, wherein the first supporting element and the first component of fig. 2 are shown, wherein in particular, the first supporting element is shown according to a third embodiment and with some parts detached; fig. 13b shows a view from above of an assembly comprising the components of fig. 13a in an assembled configuration;

- fig. 13c shows a transversal sectional view of the assembly of fig. 13b along line B-B of such figure;

- fig. 13d shows a perspective view, wherein the components of fig. 13a are shown in an assembled configuration;

- fig. 14a shows a perspective view, wherein the first supporting element and the first component of fig. 2 are ^' shown, wherein, in particular, the first supporting element is shown according to a fourth embodiment and with some of its parts detached; fig. 14b shows a view from above of an assembly comprising the components of fig. 14a in an assembled configuration;

- fig. 14c shows a sectional transversal view of the assembly of parts of fig. 14b along line C- C of same figure;

- fig. 14d shows a perspective view, wherein the components of fig. 14a are shown in an assembled configuration;

- fig. 14e shows a sectional transversal view of assembly of parts of fig. 14b, along line C"-C" of same figure;

- fig. 15 shows a lateral view of the first supporting element of fig. 2, according to a fifth embodiment;

- fig. 16 shows a lateral view of the first supporting element of fig. 2 according to a sixth embodiment, wherein arrows schematically indicate flows of electric current and an electromagnetic force; fig. 17 shows a lateral view of first supporting element of fig. 13a, wherein through arrows are schematically indicated flows of electric current and an electromagnetic force; fig. 18 shows a perspective view of first supporting element of fig. 2, according to a seventh embodiment;

- fig. 19 shows a perspective view of the first supporting element of fig. 18, wherein this element is shown from a different viewing angle.

[0017] In appended figures, same or like elements are indicated by the same reference numerals .

[0018] Firstly, with reference to fig. 1, an illustrative and non limiting embodiment of an electric circuit breaker, generally indicated by 1 is shown. In the particular embodiment of fig. 1, the circuit breaker 1 is for example a so called molded case circuit breaker, which is adapted to be used in electric low voltage distribution installations. In the example shown, the electric circuit breaker 1, is comprised, in a non limiting way, of an automatic three pole molded case circuit breaker. The circuit breaker 1 has a circuit breaker body 3 comprising a box-shaped case 5, made of insulating material, which has a supporting function for internal mechanisms of circuit breaker.

[0019] The case 5 has a front side 7, from which an operating lever 9 protrudes, which is provided for operating the circuit breaker, and a rear side 11 provided with suitable fixing means, which are not shown, as they are known per se, for fixing the circuit breaker 1 to an electrical switchboard.

[0020] On the upper side 13, the case 5 is provided with input clamps, not shown, for connecting the circuit breaker 1 to cables of an electric installation. Output clamps, which are analogous to the input clamps, not shown, are provided on the lower side 15 of case 5.

[0021] With reference to fig. 2, the circuit breaker 1 comprises at least a first electric contact 20, which is fixed to a first supporting element 22 or first contact carrying support. Preferably, as for example shown in fig. 9, the first supporting element is fixed to the case 5 of the circuit breaker, by means of screws 22A. Preferably, although in a non limiting way, the first supporting element 22 is made of copper or copper alloy, for example a copper-brass alloy.

[0022] In the embodiment shown in fig. 2, the first electric contact 20 comprises a first plurality of electric contacts, in this example, four electric contacts. Preferably, such electric contacts are made in the shape of first electrically conductive pads 23. Preferably, such pads are sintered pads made of silver alloys. Advantageously, the first contact carrying support 22 comprises a fixed portion 24 adapted to be fixed to the circuit breaker body 3 and which, in the present example, is an electric terminal. From now on, without introducing any limitation, the fixed portion will be also referred to as electric terminal 24. The first contact carrying support 22 also comprises a movable portion 26 which is movably connected to the fixed portion 24. According to an embodiment, the movable portion 26 is rotatably constrained to the terminal 24. In particular, in the examples shown, the movable portion 26 is hinged to terminal 24. It is to be stressed out that the movable portion 26 is electrically connected to terminal 24. As is shown in fig. 2, the first pads 23 are fixed, preferably welded, to the movable portion 26.

[0023] With reference to the embodiment of fig. 2, the movable portion 26 comprises a plurality of arms 28, four arms in this example, which are movably connected to the fixed portion 24. According to this embodiment, each arm 28 is provided with a respective first pad 23. According to an embodiment, each arm 28 comprises a connecting portion 28A (fig. 4), which is adapted to be received in a respective connection recess 29 (for example,' as shown in the embodiment of fig. 12a) which is defined between a pair of walls 29A, 29B of terminal 24. According to an embodiment, the terminal 24 has a comb-like end portion, including a plurality of connection recesses 29 defined between teeth of said comb. According to an embodiment, particularly suited for high power circuit breakers, the connection recesses 29 are produced by cutting, for example by milling and similar .

[0024] Now with reference to fig. 5, a second electric contact 30 of circuit breaker 1 is shown. The second electric contact 30 is fixed to a second supporting element 32 or second contact carrying support. According to an embodiment, the second electric contact 30 comprises a second plurality of electric contacts, four contacts in the example. Preferably such electric contacts are made in the shape of second electrically conductive pads 33. Preferably, the second pads 33 are welded to the second contact carrying support 32.

[0025] According to an embodiment, the second contact carrying support 32, which is made of electrically conductive material, comprises a first electrically conductive body or first plate 35, to which the second pads 33 are fixed, and a second electrically conductive body or second plate 37, which is connected to the first plate by means of flexible electric conductors 39.

[0026] The second, pads 33 are able to assume a first operating position or closing operating position (fig. 10 and 11) and a second operating position or opening operating position (fig. 9) . In particular, in the closing operating position, the second pads 32 are abutting against the first pads 23 in order to set the circuit breaker 1 in a closing state. In the opening position, on the contrary, the second pads 33 are set at a given distance from the first pads 23 in order to set the circuit breaker 1 in an opening state.

[0027] In this context, with reference to figs. 6-8, it is to be noted that the circuit breaker 1 comprises moving means 40, 42, for allowing the second pads 33 to assume the closing and opening operating positions, respectively. According to an embodiment, the moving means comprise a contact carrying shaft 40 (fig. 6) and an actuation or operating mechanism 42 (partially visible for example in fig. 7 and 8) for actuating such shaft. In particular, the contact carrying shaft 40, including the second contact carrying support 32, is adapted to be actuated by the actuation mechanism 42, in order to allow the second pads 33 to assume the closing (fig. 10) and opening operating positions (fig. 9) . It is to be noted that, although fig. 1 shows a three pole circuit breaker, fig. 7 and 8 illustratively show, as a non limiting example, a contact carrying shaft for a four pole circuit breaker, including in particular four second contact carrying supports 32. However, it is clear that the skilled in the art may easily modify the structure of contact carrying shaft 40 of fig. 7 and 8, in order to adapt it to electric circuit breakers having any number of poles, i.e. any number of second contact carrying supports 32.

[0028] With reference to figs. 9 and 10, it may be noted that arms 28 of the first contact carrying support 22 are operatively interposed between the terminal 24 and second contact carrying support 32.

[0029] Also with reference to figs. 9 and 10, it may be noted that the circuit breaker 1 comprises electromagnetic shielding means. According to an embodiment, the electromagnetic shielding means comprise at least a first electromagnetic shielding device 50 or first ferromagnetic shield, which is interposed between arms 28 and the second contact carrying support 32. According to a further embodiment, the circuit breaker 1 comprises a plurality of first ferromagnetic shields 50 (not shown) , whose number is equal to the number of first contact carrying supports 22, i.e. to the number of poles of circuit breaker 1.

[0030] - A first embodiment of the first ferromagnetic shield 50 is more clearly shown in figs. 2 and 3. In these figures, the first shield 50 is generally shaped like a case suitable for embracing an end portion 52 of first contact carrying support 22. In other words, as can be seen in figures, the first ferromagnetic shield is advantageously shaped substantially like a case for enveloping the terminal 24 and movable portion 26. According to an embodiment, the first shield 50 comprises at least a shielding wall 54 operatively directed towards the second contact carrying support 32. According to an embodiment, this shielding wall 54 generally extends from first pads 23 approximately up to the connection portion 28A of arms 28 ^' (fig. 4) . According to a first embodiment, for example shown in fig. 3, the first shield 50 comprises the shielding wall 54, a pair of mutually opposed lateral walls which are joined to the shielding wall and anchoring portions or anchoring tabs 58 which are joined to the pair of lateral walls and which are transversely positioned with respect to this pair of walls. In particular, the anchoring portions, in the example two anchoring tabs 58, are such as to cooperate with the terminal 24 in order to allow fixing of first shield 50 to first contact carrying support 22. As can be seen in the appended figures, the anchoring tabs 58 are in particular such as to be coupled with a rear wall of terminal 24, i.e. the terminal wall which is opposed to the one directed towards the rear side of arms 28. According to the embodiment of fig. 3, the first shield 50 particularly comprises anchoring means for fixing the first shield to the first contact carrying support 22. Such anchoring means may for example comprise holes (not shown) provided on anchoring tabs 58, through which suitable anchoring screws 59 may be inserted. In other words, the first shield 50 is advantageously adapted to be removably coupled with the first contact carrying support 22.

[0031] According to a further embodiment, the electromagnetic shielding means may comprise at least an additional electromagnetic shielding device or additional ferromagnetic shield 60 (figs. 3 and 4), which is constrained to the movable portion 26. According to an embodiment, the electromagnetic shielding means comprise a plurality of additional ferromagnetic shields 60. For example, with reference to fig. 2, four additional shields 60 are shown, each fixed to a respective arm 28 of first contact carrying support 22.- In particular, considering that each arm 28 has a front side, onto which the pads 23 are fixed and a rear side which is directed towards the terminal 24, the additional shields 60 laterally extend along the sides of each arm 28. Still with reference to fig. 2, it may be seen that each of additional shields 60 comprise a respective apex portion 62, in the example having a hooked or curved shape, which is arranged near the second pad 23 of the respective arm.

[0032] According to an embodiment, the electromagnetic shielding means comprise at least a second electromagnetic shielding device 70 or 000004

22

second ferromagnetic shield (fig. 9), which is interposed between the first shield 50 and second contact carrying support 32. With reference to fig. 6, a plurality of second shields 70 is shown, in particular four shields, which are integral with the contact carrying shaft 40. As may be seen in this figure, the second shields 70 each have a receiving seat 72 for a respective second contact carrying support 32. With reference to figs. 7 and 8, it may be noted that second shields 70 are such as to embrace each an intermediate portion, which does not include the second pads 33, of a respective second contact carrying support 32. In the embodiment shown in figs. 7 and 8, in particular, each of second shields 70 comprises at least a respective shielding wall 74, which approximately extends from second pads 33 up to flexible electric conductors 39.

[0033] Still with reference to fig. 2, it may be seen that the first contact carrying support 22 comprises first elastic means 80 which are interposed between the arms 28 and terminal 24. These first elastic means, in the example of fig. 2 comprising helical compression springs 82, are such as to act upon arms 28 in order to increase the contact pressure between the first 23 and second 33 pads when the second pads reach their closing operating position (fig. 10) .

[0034] The operation of a circuit breaker according to the present invention is now described.

[0035] With reference to fig. 9, wherein the second pads 33 are shown in the opening operating position, it may be noted that arms 28, under the thrust of helical springs 82, tend to be separated from terminal 24. However, the distancing of the arms 28 is limited by the first shield 50, against which these arms are able to abut. This advantageously allows to maintain a sufficient distance between the first 23 and second 33 pads of circuit breaker.

[0036] With reference to fig. 10, wherein the second pads 33 are shown in the closing operating position, it may be noted how the second pads 33 exert a pressure on the first pads, so that arms 28 are drawn towards the terminal 24, against the action of helical compression springs 82. In particular, the excursion of arms 28 is sufficient, for example, to compensate the misalignment and/or wear of first 23 and second 33 pads, ensuring a proper contact between the same pads. More in particular, the compression of helical compression springs 82 allows to provide a required contact force •

[0037] With reference to fig. 11, wherein the circuit breaker is shown in the same operating ^condition of fig. 10, a flow of electric current, generally indicated by I is schematically shown, which is able to cross the first 22 and second 32 contact carrying support, in the operating conditions of circuit breaker 1. In particular, in this figure it may be noted that the terminal 24 is such as to be crossed by a flow of electric current Ii in a set orientation, whereas the arms 28 are such as to be operatively crossed by a flow of electric current I ₂ , having a substantially opposed orientation and in this example an essentially parallel direction, with respect to those of the flow of current I ₁ crossing the terminal 24. The interaction between the current flows I ₁ , I ₂ gives rise to a repulsive electromagnetic force F (schematically shown by an arrow in fig. 11) which is able to distance the arms 28 from the terminal 24, therefore facilitating a contact pressure increase between the first 23 and second 33 pads. Still with reference to fig. 11, it may be however seen that the second contact carrying support 32 is such as to be operatively crossed by a flow of electric current I ₃ having a substantially opposed orientation and in the example an essentially parallel direction with respect to those of the flow of current I ₂ crossing arms 28. It follows that the conditions are given for the generation of a further electromagnetic force, of the repulsive type, which would tend to separate the arms 28 from the second contact carrying support 32, therefore amplifying the repulsive phenomenon which normally takes place in the contact zone between the first 23 and second 33 pads. This negative phenomenon is avoided by the first 50 and second 70 ferromagnetic shield. In fact, such shields 50, 70 essentially inhibit the magnetic fields generated by current flows I ₂ , I ₃ , flowing through the arms 28 and the second contact carrying support 32 respectively, from interacting with such current flows. In this way, the possible generation of further electromagnetic force is essentially eliminated, which otherwise would further increase the repulsion between the first 23 and second pads 33. [0038] It is worth noting that also the additional shields 60, if present, may help generate a positive effect with reference to maintaining the contact between first 23 and second 33 pads. In fact, the additional shields 60 are such as to electromagnetically cooperate with the first shield 50 by being attracted or drawn towards this shield. More in particular, the additional shields may interact with the first shield 50 in a way as to substantially- create an electromagnet/armature couple, wherein the first shield 50 is the electromagnet and the additional shields 60 are the armature. Therefore the generation of an electromagnetic force is enabled, which attracts the arms 28 towards the first shield 50 and which therefore helps maintaining the contact between first 23 and second 33 pads.

[0039] Summing up, the action exerted by the helical compression springs 82 is supplemented by the repulsive electromagnetic forces between the arms 28 and terminal 24, which are able to contrast the repulsive electromagnetic force normally generated in the contact zone between the first 23 and second 33 pads of circuit breaker 1.

[0040] Based on what has been described, it is therefore possible to understand how an electric circuit breaker according to the present invention may solve above said drawbacks with reference to the known art.

[0041] Particularly, it is to be noted that in a circuit breaker according to the present invention, due to the push exerted by the movable portion 26, no additional force is required from the actuation mechanism for maintaining the proper contact between first and second pads of the circuit breaker.

[0042] Advantageously, in a circuit breaker according to the invention, it is possible, for the same push exerted by the actuation mechanism, to sensibly raise, with respect to circuit breakers of the known art, the threshold value of electric current at which the separation of first 23 and second 33 pads of circuit breaker occurs. Specifically, a circuit breaker according to the present invention has characteristics in terms of selectivity which are very improved with respect to the present market offerings, even ensuring a proper contact between pads of the circuit breaker up to 40 [kA] and beyond.

[0043] With a circuit breaker according to the invention it is therefore possible to fully comply with the selectivity requirements of a modern electric distribution installation, by employing a circuit breaker of decidedly lower size and cost, with respect, for example, to present air circuit breakers .

[0044] It is also to be noted that in an electric circuit breaker of above said type, since there are no additional electromagnetic forces which determine a direct attraction between the fixed and movable pads, there are no forces opposed to a voluntary opening of circuit breaker by means of the actuation mechanism. Therefore, there is no degradation of the circuit breaker's performance pertaining the short-circuit breaking capacity. In this context, it is to be noted that also the electromagnetic force generated between the additional shields 60 and the first ferromagnetic shield 50, being adapted to attract the movable portion 26 towards the first ferromagnetic shield, i.e. towards the second contact carrying support 32, does not oppose a voluntary opening of circuit breaker by means of actuation mechanism. Therefore, also this characteristic advantageously allows to improve the selectivity characteristics of the circuit breaker, without degrading or negatively impacting the "control of the circuit breaker.

[0045] It is to be noted that the particular structure of the first ferromagnetic shield, which is essentially shaped like a case suitable for embracing the fixed portion and the movable portion 26 of the first contact carrying support, beside allowing an optimal electromagnetic shielding of the first contact carrying support, advantageously simplifies the assembling of the assembly comprising the first contact carrying support and the first electromagnetic shield, as well as the installation of this assembly into the respective mounting housing, which is provided inside the circuit breaker.

[0046] Moreover it is to be noted that such a configuration of the first ferromagnetic shield gives rise to a multifunctional ferromagnetic shield, which, besides being particularly efficient in providing the respective electromagnetic shielding, allows to maintain a predefined distance _^ between the first and second pads of the circuit breaker, when the second pads are set in the opening position. In particular, this allows to obtain a particularly efficient structure of the assembly comprising the first shield and the first contact carrying support, and therefore of the circuit breaker.

[0047] In the following, some of the modifications of a circuit breaker according to the present invention are described only as non limiting examples.

[0048] According to an embodiment of the circuit breaker 1, it may comprise means for improving the electric conductibility between the terminal 24 and arms 28. Such means are in particular interposed between the terminal and the same arms.

[0049] With reference to fig. 2, the means for improving the electric conductibility may comprise an electric conductive. hinge pin 100 for hinging the terminal 24 and arms 28. Advantageously, the pin 100 may be made of high electric conductive materials, such as, preferably but not in a limiting way, copper with a silver lining.

[0050] With reference to the particularly advantageous embodiment shown in figs. 12a to 12c, the hinge pin 100 comprises a plurality of hinge pins 102, which are aligned along the same hinge axis X. As can be seen in figs. 12a-12c, the hinge pin 100 may be subdivided into a plurality of shorter hinge ^' pins 102, for hinging, as an example, a respective arm 28. In this way, it is advantageously possible to increase the total number of contact zones between the hinge pin 100 and terminal 24 with respect to the case where only one hinge pin 100 is used.

[0051] According to an embodiment, the means for improving the electric conductibility may comprise, additionally or alternatively to what 'previously and subsequently described and shown, second elastic means suitable for engaging arms 28, for increasing the contact pressure between said arms and terminal 24. With reference to the embodiment shown in figs. 14a to 14e, the second elastic means comprise at least one belleville spring 104, which is interposed between each arm 28 and the walls 29A, 29B which define the respective connection recess 29. More particularly, in this embodiment, for example, a belleville spring 104 is provided, which is positioned between the connection portion 28A of each arm 28 and one of walls 29A, 29B of the respective connection recess 29. According to the embodiment shown in figs. 13a to 13d, the terminal 24 may comprise widened connection recesses 29, each being such as to receive the connection portions 28A of a pair of arms 29. In the example shown, in particular, one pair of belleville springs 104 is provided between two arms 28 received in the respective widened connection recess 29.

[0052] According to an embodiment, which is to be considered as additional or as an alternative to what has been and will be described, the means for improving the electric conductibility may comprise at least one flexible conductive element (not shown) , which is connected to terminal 24 and arms 28, respectively.

[0053] According to an embodiment, which is to be considered as additional or as an alternative to what has been and will be described and shown, the first elastic means 80 may comprise springs of different type with respect to helical compression springs 82 (fig. 2) . For example, with reference to the embodiment of fig. 15, the use of leaf springs 110, preferably one for each arm 28, is shown.

[0054] According to a further embodiment the first elastic means 80 may comprise traction springs instead of compression springs. For example, in the embodiment of figs. 18 and 19, the use of an helical tension spring 112 is shown. In particular, such a spring 112 has an end connected to a hooking pin 114 of terminal 24 and an opposed end which is connected to arms 28.

[0055] According to an embodiment, which is to be considered as additional or as an alternative to what has been and will be described and shown, the first contact carrying support 22 advantageously comprises electric insulating means interposed between the arms 28 and terminal 24. For example, with reference to the embodiments shown in figs. 13d and 14d, electric insulating means 120, 122 are shown, which are interposed between the arms 28 and first elastic means 80, in order to avoid that these elastic ^' means are electrified and may therefore be damaged due to overheating.

[0056] According to a particularly advantageous embodiment, which is to be considered as additional or as an alternative to what has. been and will be described and .shown, the first contact carrying support 22 comprises means for mutually- approaching the electric current flows I ₁ , I ₂ which flow through the terminal ^' 24 and arms 28, respectively. According to an embodiment, the means for mutually approaching the electric current flows comprise a reduced /thickness portion 130 (fig. 17) of terminal 24. The reduced thickness portion 130 may for example be provided by means of a groove 132 which is provided on the terminal 24 on the side opposite to arms 28. With reference to figs. 16 and 17, two embodiments of the first contact carrying support 22 are shown, with and without the reduced thickness portion 130, respectively. In these figures, arrows schematically indicate the current flows I ₁ , I ₂ , flowing through the terminal 24 and arms 29 as well as the repulsive electromagnetic force F generated between such elements. In particular, in these figures, the intensity of the repulsive electromagnetic force F is directly proportional to the number of respective arrows. Comparing fig. 16 and 17, it may be seen that the electric current Ii flowing through the terminal 24, due to the reduced thickness portion 130, is forced towards the electric current I ₂ flowing through the arms 28, so that an increase of the electromagnetic repulsive force F between the terminal 24 and arms 28 is achieved.

[0057] According to a particularly economic embodiment, which is to be considered as an addition or as an alternative to what has been and will be described and shown, the first contact carrying support 22 comprises fast coupling means, for removably coupling, even without the use of tools, the first ferromagnetic shield 50 to the first contact carrying support 22.

[0058] For example, with reference to the embodiments of figs. 16, 17 and 14e, the fast coupling means comprise a fast engagement recess 140 provided on the terminal 24.

[0059] For example, with reference to fig. 14e, when the first shield 50 is coupled to the first contact carrying support 22, the anchoring tabs 58 of the first shield are received inside the fast engagement recess 140. More particularly, in this condition, the first shield 50 remains firmly connected to the first contact carrying support, due to the pressure exerted on this shield by arms 28 by means of the first elastic means 80.

[0060] Such an assembly, when not mounted into circuit breaker 1, may therefore be easily moved without the danger of accidental disengagement.

[0061] Once said assembly has been • mounted into the circuit breaker 1, in a suitable seat for installation (not shown) , the conformation of the installation seat inhibits the first shield 50 from disengaging from the first contact carrying support 22, when arms 28 are not contacting this shield.

[0062] With reference to figs. 18 and 19, an embodiment of the first contact carrying support 22 is shown, which is particularly suited for low voltage electric circuit breaker. In these circuit breakers, wherein the terminal 24 has a relatively small thickness, the walls 29A, 29B which define the connection recess 29 may in fact be provided by bending of two portions 150 of terminal 24, instead of machining, as such as cutting.

[0063] It is to be noted that the invention has been described only as an example, with reference to electric single-breaking molded case circuit breakers. However, the skilled in the art may easily use the teachings of the present invention in the case of circuit breakers of different kind, such as, in particular, double- breaking molded case circuit breakers.

[0064] Based on the principles of the invention, the embodiments and construction details may be widely varied with respect to what has been described and shown, as a non limiting example, without departing from the scope of the invention, as defined in the appended claims.