GB2154798A

GB2154798A - Self releasable contact assembly

Info

Publication number: GB2154798A
Application number: GB08502478A
Authority: GB
Inventors: Jean Pierre Guery; Jacques Olifant
Original assignee: La Telemecanique Electrique SA
Current assignee: Telemecanique SA
Priority date: 1984-02-03
Filing date: 1985-01-31
Publication date: 1985-09-11
Also published as: SE8500375L; SE8500375D0; FR2559307B1; SE458408B; FR2559307A1; IT8519293A0; IT1184873B; GB8502478D0; GB2154798B

Abstract

The contact assembly comprises two fixed contacts and a mobile contact bridge (4) actuated by a switching assembly (not shown) and urged by a spring (3). The connection between the mobile contact bridge (4) and the switching assembly (1) is provided by a magnetic compensator (5, 6) connected to the switching assembly (1) by means of a load break coupling (43, 43', 44, 44', 9) adapted so that, when the compensating forces rise above a given threshold, the magnetic compensator (5, 6) is disengaged from the switching assembly (1) and becomes inoperative. <IMAGE>

Description

SPECIFICATION A contact equipped with self released magnetic compensator from a compensation force threshold and a contact makerbreaker using such a contact The present invention relates to a device for cleanly opening the mobile contacts of an onload current breaking apparatus such, for example, as a contact maker-breaker comprising at least two fixed contacts and a mobile contact bridge having at least two mobile contacts which are applied under the effect of a pole spring to the fixed contacts in the closed position of the contact maker.

Generally, as is known, when contact circuits have abnormally high currents passing therethrough, for example on the occurrence of a short circuit, the contacts are subjected to repelling forces by an electrodynamic effect.

This phenomen occurs in particular in contact circuits comprising fixed contact carrying conductors bent in the form of a J, following the passage of the two legs of the J and in the mobile contact bridge.

Thus, as soon as the current reaches an excess current threshold, these repelling forces overcome the action of the pole spring and cause the contact to open, which results in a cut-off of the current. This current cut-off causes the repellent forces to disappear,so that the mobile contacts urged by the spring fali back again onto the fixed contacts and thus close the circuit again.

In the case of high excess currents, such repulsion is very clear-cut and the mobile contacts are flung away from the fixed contacts and the risks of closing again with the current on are low.

On the other hand, for lower excess currents, the repelling forces make an appearance close to the current peak and, since they are much smaller, when they cease the contacts close again on a current which is still high so that an appreciable risk of welding results which is added to the other risks of destruction of the aparatus and to the inevitable wear of the contacts.

To overcome these disadvantages, it has been proposed to compensate for the effect of these repellent forces during the time intervals separating application of the excess current and opening of the circuit, so as to prevent the fixed and mobile contacts from separating at the wrong moment, with the consequences which would result therefrom for some values of the excess current.

This compensation may be achieved, in accordance with the solution proposed in French patent application n" 81 22957 filed in the name of the applicant, by using a first piece made from a magnetic material having the shape of a U whose base is coupled to the switching assembly of the contactor, and a second magnetic piece integral with the mobile contact carrying bridge, arranged so as to form an air gap with the upper ends of the legs of the U of the first piece, the mobile contact carrying bridge engaging in the opening of the U of the first piece so as to form a second air gap. With such a device, as long as the intensity of the overload current remains below an excess current threshold, the second magnetic piece exerts on the first a force of attraction sufficient to counter the effects of the repelling forces.Beyond this overcurrent threshold, the force exerted by the compensator reaches a limit value due to the saturation of the magnetic material pieces, whereas the repelling forces between the contacts continue to increase, so that opening of the contact occurs. However, in such a device, there exist operating zones in which the resultant force on the contact bridge varies slowly as a function of the excess values of the current flowing in the contact bridge. If this small variation occurs close to cancellation of the contacting force, the opening speed thereof will be slow which will cause cut off failure risks of the type described above.

There is further known, more especially from the French patent application n" 81 1 5606 filed in the name of the applicant, a device for releasing the mobile contacts of contact-makers, so as to limit the short circuit currents. This device uses more particularly a threshold coupling between the mobile contact bridge and the switching assembly which is associated therewith. In this device, the threshold coupling is formed by balls housed directly in a rod integral with the mobile contact bridge and cooperating with a resilient clamp connected to the switching assembly. It is therefore apparent that in this device the pole force causes a permanent stress on the threshold coupling in the operating state even when the current is less than the normal current of use.This stress, combined with the high number of switching operations which the apparatus must provide under normal conditions of use, causes fatigue of the coupling which may cause a considerable drift of the longitudinal holding force and thus considerable dispersion of the excess current values causing release of the coupling.

The aim of the invention is therefore to overcome all these disadvantages. It therefore provides a contact using a repulsion force compensation device of the type similar to the one described in the above mentioned French patent application n, 81 22957 but in which, when the electrodynamic repelling force due to an abnormal overcurrent exceeds a predetermined value opening of the contacts is obtained with a considerably increased speed and is maintained at least temporarily.

To arrive at this result, the contact circuit of the invention comprises first of all as men tioned above, at least two fixed contacts and a mobile contact bridge, actuated by a switching assembly and comprising at least two mobile contacts which are applied respectively under the effect of a pole spring, on the two fixed contacts, in the closed position of the contact-maker.The connection between the mobile contact bridge and the switching assembly is provided by a magnetic compensator comprising at least a first piece made from a soft magnetic material carried by the mobile contact bridge and a second magnetic piece integral with the switching assembly and forming, with said first piece made from soft magnetic material, at least one air gap so that the current passing through the mobile contact bridge generates, inside said pieces, a magnetic field tending to draw them closer together and thus to apply the mobile contacts on the fixed contacts against the action of the repelling forces which are then exerted between these contacts.

According to the invention, the connection between said second soft magnetic material piece and said switching assembly is provided by a load break coupling so that, when the compensation forces rise above a given threshold, the magnetic compensator is disengaged from the switching assembly and becomes inoperative and consequently a very sudden variation of the resulting repelling force is obtained and very rapid opening of the contact to the distinctly open stte.

Such an arrangement has the advantage of eliminating the permanent stresses on the coupling because the compensation force is only significant for abnormally high values of current.Thus, the over current value causing disengagement of the magnetic compensator will be constant whatever the number of switching operations effected before the appearance of the short circuit, and, since without stress, the fatigue of the load break connection wil be negligible. This latter will keep the initially defined disengagement force.

Said load break coupling may be advantageously formed by a resilient return hard point lock. It may further comprise means for holding it in the open position, so as to prevent an accidental reengagement.

Embodiments of the invention will be described hereafter, by way of non limitative examples, with reference to the accompanying drawings in which; Figure 1 is a schematical perspective view illustrating the principle of a contact equipped with a system for the magnetic compensation of the repelling forces exerted on the contacts.

Figure 2 is a schematical view showing the magnetic circuit of the compensator used in the contact shown in Figure 1.

Figure 3 is a diagram showing, as a function of the intensity of the current, the laws of variation of the forces acting on the mobile contact bridge.

Figure 4 shows in section one end of a switching assembly equipped with a coupling lock with release threshold for the magnetic compensator.

Fiugre 5 is a schematical sectional view illustrating another embodiment of the coupling lock.

Figure 6 is a diagram showing the laws of variation of the forces exerted on the mobile contact bridge when the part of the magnetic compensator coupled to the switching assembly may be suddenly released.

Figures 7A to E are sectional views for illustrating the operation of a contact circuit equipped with a coupling in accordance with the invention.

Figure 8 shows in section the contact carrying part of a contact maker-breaker in accordance with the invention.

As mentioned above, Figure 1 shows one example of a contact circuit equipped with a magnetic compensator of the type described in the above mentioned French patent application n" 81 22957. In this compensator, the switching assembly comprises an isolating piece or "rake" 1 which drives an amagnetic coupling stirrup 2 through a pole spring 3 which, in the operating condition, determines the contact force in the absence of any current. The mobile contact bridge 4, in the form of a beam, is coupled to the coupling stirrup 2 by a magnetic plate 5 which forms, with a magnetic U 6 enclosing the contact bridge 4, the magnetic circuit of an electromagnet whose operation is illustrated in Figure 2.The current I flowing through the mobile contact bridge 4 creates, in the magnetic circuit formed by plate 5 and the magnetic U 6, a magnetic flux 9 whose part passing through the air gape creates, between plate 5 and the magnetic U 6 and consequently between the mobile contact bridge 4 and the magnetic U 6, the compensating force. The fixed contact supports 7, 7' may advantageously have a J shape so as to promote the electrodynamic repulsion when a high current such as a short circuit overcurrent flows in the contact circuit.

In this known embodiment, the magnetic U of the compensator is rigidly fixed to the insulating rake 1. Thus, the compensating force although proportionally decreasing because the air gap e increases when the contact begins to open continues to exist during opening of the contact by short circuit repulsion thus tending to slow down the opening.

The variations in the compensating and repelling forces as well as the variation in the resulting force on the mobile contact bridge are shown in the diagram of Figure 3, in which curve C1 represents the force exerted by the compensation device, curve C2 represents the resulting force applied to the mobile contacts, the straight line C3 represents the pole force exerted by the pole spring and curve C4 represents the repelling force.

In this Figure 3, the different forces acting on the contact bridge 4 are shown as a function of the current flowing through the contact. The force of spring 3 (pole force, straight line C3) which is transmitted by the coupling stirrup is constant. The repelling and compensating forces are negligible for normal currents of use, i.e. which are always very much less than short circuit overcurrents. By way of example, these normal currents of use le may be less than 50 times smaller than the current I causing opening by repulsion. When the current rises at the beginning the compensating force increases more rapidly than the repelling force, then, when magnetic saturation of the compensator occurs, the compensating force increases more slowly. Thus, the resulting force applied to the contacts whichatthe beginning was increasing decreases then is reversed causing opening of the contact.

Although the compensating force tends to diminish, as soon as the contact is opened, because of the increase of the air gap e of the compensator, the rate of variation of the resultant force when passing to zero may be not sufficiently rapid to provide a perfect break if the shortcircuit current is just above the balance point where the resultant force is close to zero.

As mentioned above, Figure 4 is a sectional view of a magnetic compensator coupled to the switching assembly by a predetermined force threshold coupling (with load breaking) in accordance with the present invention. In this Figure, we find again a mobile contact bridge 4 integral with plate 5 of the compensator, as previously described. However, in this case, the U shaped part 6 of the compensator which is mounted in a pocket of the insulating rake 1 is fixed therein by means of a resilient return lock which will be described hereafter in greater detail. Such as shown, the contact is in the working condition under normal conditions of use. In this condition, the air gap e and accompanying over-travel a values are constants defined at the design stage.It will be noted in this connection that the value of air gap e could be possibly adjusted by using a mechanical connection adjustable for example by means of a screw between plate 5 of the compensator and the mobile contact bridge 4.

In this embodiment, the threshold coupling consists of a ball lock formed from a cage 41 fixed in the pocket of the insulating rake 1 by means of studs, respectively 42 and 42' for example. Cage 41 in which the magnetic U of the compensator is engaged comprises, on its inner face, two semi-spherical imprints 43 and 43' situated opposite each other and each cooperating with balls 44 and 44' housed in a hole 8 of the U of the compensator 6, a compression spring urging the balls 44 and 44' against cage 41.

In addition, in the vicinity of the opening of the pocket, two housings 45 and 45' are provided for retaining the balls when the lock has tripped. It is the values of the force of spring 9 and of the respective diameters of balls 44 and of the semi-spherical imprints 43 which determine the tear away force Fa of the U shaped part 6 of the compensator which is thus defined at the design stage.

Moreover, so as to accelerate its starting disconnection, inserting, between the magnetic U 6 and the bottom of the pocket of the insulating rake 1, a spring R preferably conical in shape, may be advantageous.

Of course, the invention is not limited to the method of coupling the U shaped part 6 of the compensator to rake 1 with predetermined tear away threshold using a resilient return lock.

Thus, for example, balls 44 may be replaced by semi-spherical cups. Similarly, the assembly formed by spring 9 and balls 44 or the cups may be replaced, as shown in Figure 5, by resilient leaf springs 51, 51' comprising projections 52, 52' cooperating with imprints formed in cage 41 as described above or, conversely, holes cooperating with rounded relief studs replacing the imprints in cage 41.

In the example shown in Figure 5, the resilient leaf springs 51, 51' are rivetted to part 6 of the compensator for example at points 53.

The diagram shown in Figure 6 better shows the advantages offered by a magnetic compensation contact equipped with a release threshold coupling lock of the magnetic compensator. In this diagram, the curves corresponding to those of the diagram of Figure 3 bear the same references to which a prime index has been added.

Thus, in Figure 6, we find again the increase of the positive resultant force (curve C2) on the mobile contact bridge 4 up to a value la of the intensity of the shortcircuit current which corresponds to a compensation force (curve C2) equal to the tear away force Fa of the lock. As soon as it is released under the effect of the compensating force, part 6 of the compensator is attracted towards part 5 and comes into abutment at the end of travel against the mobile bridge 4 thus cancelling out the compensating force (curve C,) and communicating a shock to the mobile bridge 5. Thus, the resultant force (curve C2) becomes suddenly negative and, after the shock phenomenon, becomes equal to the pole force less the repelling force which is much higher than its pole force. In the example shown in Figure 6, curves C'4 and C'2 are substantially superimposed from point 1 a.

Figures 7A to E illustrate the operation of the mobile contact circuit of a contact makerbreaker in accordance with the invention, it being understood of course that the fixed contacts of this contactor may consist of those shown in Figure 1.

It should be noted in this connection that in this contactor the switching assembly may be fixedly mounted on the armature of an electromagnet not shown whose winding is fed by a circuit comprising a quick break contact 83.

Thus, in Figure 7A, the contactor assembly is at rest, the lock formed by balls 44, spring 9 and the semispherical imprints is in the cocked or set position. The U shaped part 6 of the magnetic compensator abuts aainst the mobile contact bridge 4 and the quick break contact 83 of the winding supply circuit is open.

In Figure 7B, the switching assembly is in the work position, the quick break contact 83 is closed and the mobile contact bridge 4 is in abutment against the fixed contacts and is separated from the U shaped part 6 of the compensator by a distance a corresponding to the accompanying movement of the pole.

Figure 7C shows the assembly when a short circuit has just occurred. In this case, the over current has given rise to a compensating force greater than the tear away force of the lock, which is just beginning its release movement, the balls having escaped from the imprints.

The U shaped part 6 of the compensator has just come into abutment against the mobile contact bridge which has not yet moved.

In the moment which follows (Figure 7D), since the repelling force is no longer opposed by the compensating force, the pole spring 3 is over-crushed, the mobile contact bridge 4 and the quick break contact 83 of the winding supply circuit are in the open position and the lock which is completely disengaged is jammed in the tripped position in the imprints 45, 45'. As soon as the supply circuit is broken, the switching assembly returns to the rest position similar to the one shown in Figure 7A, but in which the opening between the contacts is greater because the lock is jammed in the tripped position and the assembly formed by the mobile contact bridge and the compensation device will be in a higher position with respect to the position which it occupies in Figure 7A.Thus it is easy, because of this feature, to distinguish the contacts opened by the normal return of the switching assembly (Figure 7A) from the contacts opened by disengagement of the mobile contact bridge following a short circuit (Figure 7E). Similarly, it is possible to distinguish the contacts opened in one of these opening modes from contacts closed during operation.

It is thus possible to provide a detection element, for example an end of travel micro switch disposed so as to transmit information when the contact is opened by disengagement of the magnetic compensator.

It should be noted that resetting of a contact opened by disengagement requires an external action, namely a pressure exerted for bringing the U shaped part 6 of the compensator back inside the cage until the balls 44, 44' again snap into the imprints 43, 43'.

This external action may consist of a simple manual action. It may also be performed by means of a remote controlled actuator, for example from a control panel.

In the case where it is performed by means of an actuator, this resetting may be provided automatically after a certain time delay (natural or planned) allowing the arc foot to move and the breaking zone to cool down before the contact is reclosed on a limited current so as to avoid any possibility of welding or damage.

As previously mentioned the magnetic compensation device with load break locking may be applied to the construction of a contact maker-breaker such for example as the one shown in Figure 8. This Figure shows in fact schematically a three pole contact makerbreaker in which the switching assembly 1 is connected to the mobile part 60 of the electromagnet by a coupling system 61. The three mobile contact bridges 4 are connected to the switching assembly 1 by means of a spring 3 and a coupling stirrup 2 and are each equipped with a magnetic compensator in the way shown in Figure 1, the U shaped part 6 of the compensator being connected to the switching assembly by a load break locking device having a predetermined tear away threshold, such as the one shown in Figure 4.

Each contact assembly which comprises a mobile contact bridge 4, a magnetic compensator and a locking device on the switching assembly 1 further comprises a quick break contact 81 82 83 for the winding of the electromagnet (not shown), these quick break contacts 81, 82, 83 being electrically connected in series in the winding supply circuit.

The mobile parts of these contacts are driven respectively by the coupling stirrups 2 through insulating bars 84 85, 86 integral with the coupling stirrups 2 and springs 87, 88 and 89. The mobile part of these quick break contacts 81, 82, 83 is mounted for sliding with limited play on the insulating bars 84,85,86 and is urged by the respective springs 87, 88, 89.

In this example, the upper part of the contact maker-breaker is enclosed in a case 800 in which is provided a window 801 through which the position of the switching assembly 1 may be seen, which may be either the position 0 which corresponds to the normal rest state of the switching assembly 1, or the position I which corresponds to the operating conditions such as shown in Figure 8.

To this end, the switching assembly 1 may comprise an element 802 serving as index used in combination with two marks 10 provided on case 800.

Resetting of the locking devices of the three contact assemblies may be achieved, as shown, by means of an excentric cam 804 mounted for rotation on case 800 which acts on a stud 805 provided on the switching assembly I so as to raise, after retraction of a normal rest, stop 803 provided on said cam 804. Rotation of this cam 804 may be provided by means of a spanner engaged on the stud shaft 806 (possibly hexagonal) of cam 804 or electrically by means of a motor driven reducer 807 coupled to said shaft 806. A second lockable case 808 may be further provided so that resetting can only be achieved by authorized personel.

Thus, during normal operation in position 0, the switching assembly 1 comes into abutment against stop 803 on cam 804. The upper part of the coupling stirrup 2 of the mobile contact bridges 4 is then on the line bb'. When a contact assembly is released for example because of a short circuit, this contact assembly is then in the position shown in Figure 7E. In this position, the upper part of the coupling stirrup 2 of this assembly is at the level of line c-c'.

Resetting is then obtained by rotating cam 804 which results in forcing the switching assembly 1 to rise until stud 805 comes into the position 805' shown with a broken line.

During this movement, plate 5 of the contact assembly which was released comes up against and is held against stops 809 provided on case 800. The magnetic U 6 of the compensator then slides in its cage 41 until, at the end of travel, balls 44 44' again snap into the imprints 43, 43' and thus cause relocking.

This arrangement has the advantage of allowing simultaneous resetting of the locks of the contact maker-breaker, in the open condition thereof, without the risk of causing any closure of the contacts.

The contact maker-breaker may further comprise an indicator lamp 811 controlled by links 820, 821, 822 hingedly connected at D and D' to the mobile assembly 1 and having pushers 81 2. The leverage ratios of these links are adapted so as to make the indicator light 811 visible through a window 810 formed in the front face of case 800 when any one of the locking devices is in the released position, the movements of the indicator lights 811 being identical which ever locking device is in the released position.

Claims

1. Contact equipped with a magnetic compensator self releasable from a compensating force threshold this contact comprising at least two fixed contact elements and a mobile contact bridge (4) actuated by a switching assembly (1) and carrying at least two mobile contacts which are applied respectively, under the effect of a spring, on the two fixed contacts in the closed position of the contactor, the connection between the mobile contact bridge (4) and the switching assembly (1) being provided by a magnetic compensator (5, 6) generating a compensating force tending to apply the mobile contacts on the fixed contacts under the effect of the current passing through the mobile contact bridge (4) and this against the action of the repelling forces which are then exerted between these contacts, characterized in that the connection between the magnetic compensator and the switching assembly (1) is provided by means of a load break coupling device (9, 43, 44) adapted so that when said compensating forces rise above a predetermined threshold, the magnetic compensator (5,6) is disengaged from the switching assembly (1) and becomes inoperative and so that consequently a very sudden variation of the resultant repelling force exerted at the level of the contacts is obtained with very rapid opening of the contact to the clearly opened position.

2. Contact according to claim 1, in which said magnetic compensator comprises at least a first magnetic piece (6) interlocked with the switching assembly (1) and a second soft magnetic piece (5) carried by the mobile contact bridge (4) and disposed so as to leave between it and said first piece (6) an air gap (e), at the level of which are exerted the compensating forces generated by the passage of the current through the mobile contact bridge (4), characterized in that the connection between the first piece made from a soft magnetic material and said switching assembly is provided by a load break coupling adapted so that when said compensating forces rise above a given threshold, said first piece is disengaged from the switching assembly.

3. Contact according to one of claims 1 and 2, in which said magnetic compensator comprises a first piece made from a soft magnetic material having the form of a U whose base is coupled to the switching assembly of the contact and a second magnetic piece interlocked with the contact-carrying mobile bridge, adapted so as to form a first air gap with the upper ends of the legs of the U of the first piece, the mobile contact-carrying bridge engaging in the opening of the U of the first piece so as to form a second air gap, characterized in that said first piece made from a soft magnetic material is connected to the switching-assembly and is formed by a load break coupling adapted so that, when said compensating forces rise above a given threshold, said first U shaped piece attracted towards the second piece is disenaged from the mobile assembly.

4. Contact according to one of claims 2 and 3, characterized in that said second piece made from a soft magnetic material (5) comprises a first abutment surface and the first piece made from a soft magnetic material (6) comprises a second abutment surface adapted so as to strike said first abutment surface when said first piece (6) is disengaged from the switching assembly (1) following an increase of the compensating forces beyond said predetermined threshold.

5. Contact according to one of the preceding claims, characterized in that said load break coupling consists of a lock formed from a cage (41) fixed in a pocket of an insulating piece integral with the switching assembly (1) and in which the first magnetic material piece (6) is partially engaged, said cage comprising on its inner face, at least a first imprint (43, 43') cooperating with a snap-fit element (44, 44') connected axially to said first magnetic material piece (6) and urged radially by a resilient means.

6. Contact according to one of the preceding claims, characterized in that it further comprises means for holding said first magnetic material piece (6) in a disengaged position, following disengagement caused when the compensating forces rise above said threshold.

7. Contact according to one of claims 5 and 6, characterized in that said means for holding said first magnetic material piece (6) in a disengaged position consist of a second imprint (45, 45') formed on the inner face of said cage (41) and spaced axially apart from the first imprint (43, 43').

8. Contact according to one of claims 5, 6 and 7, characterized in that said snap-fit element consists of a piece at least partially spherical (44, 44'), sliding in a hole (8) formed in the first magnetic material piece and urged by a compression spring (9) housed inside the hole (8).

9. Contact according to one of claims 5, 6 and 7, characterized in that said snap-fit element comprises at least one resilient leaf spring (51, 51') fixed by one end to the first magnetic material piece (6) and comprising, at its other end, a projection (52, 52') cooperating with said imprints (43, 43').

10. Contact according to one of the preceding claims, characterized in that it comprises a spring inserted between the first piece made from a soft magnetic material (6) and the switching assembly (1) so as to accelerate the beginning of disengagement.

11. Contact according to one of the preceding claims, characterized in that it comprises means for resetting the magnetic compensator disengaged following an overload, these means being adapted to reset the load break coupling device.

1 2. Contact according to one of claims 6 to 11, characterized in that said resetting means comprise an actuator for exerting a pressure on the mobile contact bridge (4) in the open position so as to bring the first magnetic material piece (6) back inside said cage (41) until said snap-fit element (44, 44), comes into engagement in the first imprint.

1 3. Contact according to one of the preceding claims, characterized in that it further comprises display Omeans (801, 802, 810, 811) for distinguishing opening of the contactor by normal return of the switching assembly from opening of the contactor with disengagement of the magnetic compensator.

14. A contact maker-breaker comprising at least one contact circuit of the type comprising, in accordance with one of the preceding claims, at least two fixed contacts and a mobile contact bridge (4) actuated by a switching assembly and having at least two mobile contacts which are applied respectively, under the effect of the spring (3), to the two fixed contacts, in the closed position of the contactor, the switching assembly (1) being fixedly mounted on the armature (60) of an electromagnet and connected to the mobile contact bridge (4) by means of a magnetic compensator, the connection between the magnetic compensator and the switching assembly (1) being provided by a load break device, characterized in that itfurther comprises a quick break contact (81, 82, 83) for the power supply circuit of the winding of the electromagnet, whose mobile part is connected to the contact carrying mobile bridge (4) through a mechanical connection.

1 5. Contact maker-breaker according to claim 14, in which the switching assembly (I) comprises an insulating piece which drives a coupling stirrup (2) made from an amagnetic material integral with the contact carrying mobile bridge (4), through a pole spring (3) characterized in that said mechanical connection comprises at least one insulating bar (84, 85, 86) integral with the coupling stirrup and supporting, with possibility of axial sliding, the mobile part of the quick break contact (81, 82, 83), as well as a spring (87, 88, 89) coming into abutment on said mobile part.