ELECTRO-MECHANICAL CIRCUIT BREAKER

Abstract: An electro-mechanical circuit breaker has first and second normally open electrical contacts (14, 16) and a manual reset member (30) which can be moved axially, by pushing on a button (34), to set the circuit breaker by latching the contacts closed. In addition to normal tripping upon the occurrence of a predetermined current condition, the circuit breaker can be manually tripped in the absence of the predetermined current condition by rotating the rest member (30) about its own axis.

Description: Electro-Mechanical Circuit Breaker Technical Field The present invention relates to an electro-mechanical circuit breaker which can be fitted into suitable housings for use in portable RCDs (PRCDs) or socket RCDs (SRCDs) or other applications where opening of the circuit breaker by electrical or manual means is required. Background Art Electro-mechanical circuit breakers fall into two categories as follows: i) mechanically latched (ML) types. ii) electrically latched (EL) types. The mechanically latched (ML) circuit breaker will permit to be closed one or more sets of current carrying contacts due to a mechanical latch and will maintain the contacts closed until the mechanical latch is sufficiently displaced by electrical energisation of a coil . The electrically latched (EL) circuit breaker will only permit to be closed and maintain closed one or more sets of current carrying contacts when an energising current is flowing through an energising coil. When energisation of the coil is sufficiently reduced the circuit breaker will open automatically. The present invention provides an improved electromechanical circuit breaker which can be configured to be of either of the above types. Disclosure of Invention According to the present invention there is provided an electro-mechanical circuit breaker comprising first and second normally open electrical contacts, a manual reset member movable in a first manner to set the circuit breaker, and means for tripping the circuit breaker upon the occurrence of a predetermined current condition, the reset member further being movable in a second manner to trip the circuit breaker in the absence of the predetermined current condition. Preferably the circuit breaker includes first biasing means for urging the first contact away from the second contact to maintain the contacts normally open, wherein the manual reset member is movable in the first manner against the action of a second biasing means to couple with the first contact to draw the first contact into engagement with the second contact upon release of the reset member, and wherein the tripping means comprises means for de-coupling the reset member from the first contact upon the occurrence of the predetermined current condition thereby allowing the first contact to disengage the second contact under the action of the first biasing means, the reset member being movable in the second manner to de-couple the reset member from the first contact in the absence of the predetermined current condition. Preferably the circuit breaker further includes means for automatically returning the reset member to an initial position upon release thereof after movement in the second manner. Preferably, also, the first manner of movement of the reset member is along a substantially linear axis and the second manner of movement of the reset member is rotational movement, most preferably about the said axis. There is also provided, as a further independent invention, an electro-mechanical circuit breaker comprising: first and second electrical contacts; first biasing means for urging the first contact away from the second contact so as to maintain the contacts normally open; contact closure means mounted for movement relative to the second contact and arranged when moved in one direction to bring the first contact into engagement with the second contact against the action of the first biasing means; a manual reset member mounted for movement relative to the second contact; second biasing means urging the reset member towards a first position, the reset member being manually movable against the action of the second biasing means from the first position to a second position; and latch means movable relative to the closure means between latched and unlatched positions, the latch means, when in its latched position, coupling the reset member, when in its second position, to the closure means such that upon release of the reset member and return thereof to its firs:; position by the second biasing means the closure means is moved in the one direction to close and hold closed the contacts, a subsequent movement of the latch means to the unlatched position de-coupling the closure means from the reset member such that the first biasing means causes the contacts to open. There is also provided, as a yet further independent invention, an electro-mechanical circuit breaker comprising first and second normally open electrical contacts, a manual reset member to set the circuit breaker, and means for tripping the circuit breaker upon the occurrence of a predetermined current condition, wherein the reset member includes a manual reset button and the circuit breaker further includes a flag indicator visible through the reset button, the position of the flag indicator relative to the reset button differing according to whether the first and second contacts are open or closed. There is also provided, as a still further independent invention, an electro-mechanical circuit breaker comprising first and second normally open electrical contacts, a manual reset member movable in a first manner to set the circuit breaker, and means for tripping the circuit breaker upon the occurrence of a predetermined current condition, wherein the reset member carries a third electrical contact and is movable in a second manner to complete a test circuit. In the embodiments described herein the first and second biasing means are implemented by individual biasing members. However, in other embodiments they may be implemented by a common biasing member such as a single compression spring whose opposite ends act as the first and second biasing means respectively. Brief Description of Drawings Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a first embodiment of circuit breaker according to the invention in the tripped (unlatched) state; Fig. 2 is a perspective view of the circuit breaker in the set (latched) state; Fig. 3 is a schematic front view of the circuit breaker; Fig. 4 is a side view of the latch mechanism of the circuit breaker; Fig. 5 is a perspective view of the latch plate of the circuit breaker; Fig. 6A is a plan view of the latch plate showing the rotational position of the reset member when the latch plate is latched to the reset member; Fig. 6B is a plan view of the latch plate showing the rotational position of the reset member when the latch plate is unlatched from the reset member; Fig. 7 shows details of the reset spring; Fig. 8 shows how the circuit breaker can perform a test function; Fig. 9 is a perspective view of a second embodiment of circuit breaker according to the invention in the tripped (unlatched) state; Fig. 10 is a perspective view of the circuit breaker of Fig. 9 in the set (latched) state; Fig. 11 is a schematic front view of the circuit breaker; Fig. 12 is a side view of the latch mechanism of the circuit breaker; Fig. 13 is a perspective view of the latch plate of the second embodiment of circuit breaker; Fig. 14A is a plan view of the latch plate of Fig. 13 showing the rotational position of the reset member when the latch plate is latched to the reset member; Fig. 14B is a plan view of the same latch plate showing the rotational position of the reset member when the latch plate is unlatched from the reset member; Fig. 15A is a side view of the latch mechanism of a third embodiment of circuit breaker according to the invention in the tripped (unlatched) state; Fig. 15B is a side view of the latch mechanism of the third embodiment in the set (latched) state; Fig. 16A is a plan view of the latch plate of the third embodiment when the latch plate is not latched to the reset member; Fig. 16B is a plan view of the same latch plate when the latch plate is latched to the reset member; and Fig. 17 is a side view of the latch mechanism of a fourth embodiment of circuit breaker according to the invention. Detailed Description of Preferred Embodiments Referring now to Figs. 1 to 8 of the drawings, a first embodiment of circuit breaker 10 is shown mounted on a printed circuit board 12, although it can alternatively be fitted on to any suitable base. For convenience of description the circuit breaker will be described in the orientation shown in Figs. 1 and 2, that is, with the board 12 horizontal, but the use of the circuit breaker is not limited to that orientation. The circuit breaker comprises two fixed contacts 14 mounted directly on the board 12 and two movable contacts 16 mounted on respective arms 18. The movable contacts 16 are resiliently urged away from the fixed contacts 14 to maintain the two pairs of contacts 14, 16 normally open. In the embodiment shown, the biasing of the contacts 16 to the open position is effected by the arms 18, which are of a spring material such as beryllium copper, but the biasing means could also be provided by one or more separate springs . A moving contact closure member 20 straddles the movable contacts 16. The closure member 20 comprises a central block 22 and a pair of arms 24 extending horizontally from opposite sides thereof each over a respective movable contact 16. The block 22 is slidably mounted for vertical movement in a frame 26 fixed to the board 12, the frame having a vertical slot 28 on each side through which a respective arm 24 projects. A manual reset member 30 comprises a vertical shaft 32 having an enlarged head 34 at its lower end, constituting a manual reset button, and a retaining shoulder 36 at its upper end. The shaft 32 is a circular cylinder and it passes upwardly through a hole in the board 12, through a vertical bore in the block 22, and finally out through a hole in the top of the frame 26. Thus the block 22 is guided in its vertical movement both by the frame 26, which prevents it rotating in a horizontal plane, and by the shaft 32. The shaft 32 is free to move up and down along its own vertical axis, but it is biased by a compression spring 38, which surrounds the shaft between the button 34 and the underside of the board 12, into the rest position shown in Fig. 1 where the shoulder 36 bears against the top of the frame 26. The block 22 has a horizontal slot 40 extending through it in a direction normal to the axis of the arms 24. An L-shaped latch plate 42 (Figs. 5 and 6) has two arms 44 and 46, the arm 44 passing horizontally through the slot 40 and the arm 46 depending vertically down behind the block 22. The arm 44 has a generally rectangular aperture 48 through which the shaft 32 passes . The arm 44 is free to slide horizontally in the slot 40, in the direction normal to the axis of the arms 24, to the extent permitted by the shaft 32 passing through it. The shoulder 36 can be keyed so as to facilitate manufacture of the reset member 30 as a single part, the bore in the block 22 and the holes in the board 12, latch plate 42 and frame 26 also being keyed as necessary to facilitate passing of the keyed shoulder through them and retention of the shoulder when it is not aligned with the keyways . Stops on the frame or elsewhere may be used to limit the rotation of the shaft after assembly of the mechanism. The arm 46 of the latch plate 42 has a vertical slot 50 which embraces one end of a ferromagnetic plunger 52 which passes horizontally through a solenoid 54 mounted on the board 12. The edges of the slot 50 are trapped between two shoulders 56, 58 (Fig. 4) fixed to the end of the plunger 52 so that the latch plate 42 is constrained to move horizontally with the plunger. However, the vertical slot 50 allows the latch plate to move vertically with the block 22. The other end of the plunger 52, where it emerges from the back end of the solenoid 54, has a shoulder 60. A compression spring 62 extending between the back end of the solenoid and the shoulder 60 biases the plunger 52 away from the block 22 so that when the solenoid is not energised the shoulder 56 pulls the latch plate 42 to the right, as seen in Figs. 4 and 6, so that the edge 48a of the aperture 48 bears against the left side of the circumference of the shaft 32. If preferred the spring 62 could be located elsewhere to achieve the same effect. The circumference of the shaft 32 has a recess 64 (Fig. 4) formed on the side facing away from the solenoid 54, the recess defining a shoulder 66 substantially at right angles to the axis of the shaft 32. However, in the rest position of the reset member 30 shown in Fig. 1 the recess 64 is located well below the arm 44 of the latch plate 42 so that the edge 48a of the aperture 48 bears against the circular circumference of the shaft 32 and does not enter the recess 64. The operation of the circuit breaker is as follows, starting from the tripped or unlatched state shown in Fig. 1 where the pairs of contacts 14, 16 are open and the arms 24 of the closure member 20 rest on the movable contacts 16 suspending the block 22 away from the board 12. Now, if the button 34 is pushed upwardly against the bias of the spring 38, the shaft 32 moves upwardly in the frame 26, sliding through the block 22. At a certain point the recess 64 will draw level with the arm 44 of the latch plate 42 whereupon the spring 62 will cause the edge 48a of the aperture 48 to enter the recess 64 (Figs. 4 and 6A) and will hold it there. Now, if the button 34 is released, the spring 38 will move the shaft 32 downwardly once more in the frame 26 and, due to the engagement of the edge 48a of the aperture 48 under the shoulder 66, this will bring the latch plate 42 and block 22 with it, the slot 50 sliding over the plunger 52 between the shoulders 56 and 58. As the block 22 descends so too do the arms 24, which bear against the tops of the movable contacts 16 to force them downwards until they come to engage the fixed contacts 14 (clearly the downward force exerted by the spring 38 must be sufficient to overcome the spring bias of the arms 18 tending to keep the contacts open) . At this point, Fig. 2, the downward movement of the reset member 30 ceases and the spring 38 maintains a downward pressure on the movable contacts 16 to keep them pressed against the fixed contacts 14. Since further downward travel of the reset member is prevented the reset button 34 comes to rest at this position. The displacement of the reset button from its initial rest position (Fig. 1) to this latched position of the device (Fig. 2) provides a means of indicating when the contacts are in the closed position. This is the set state of the circuit breaker. Now, if the solenoid 54 is energised by an electric current having a magnitude greater than a certain threshold, it draws the plunger 52 inwards against the bias of the spring 62. The shoulder 58 of the plunger pushes the latch plate 42 horizontally towards the block 22 such that the edge 48a of the aperture 48 is no longer located within the recess 64. This frees the shaft 32 to move downwardly under the bias of the spring 38, while at the same time the movable contacts 16 move upwards under the spring bias of the arms 18, taking the block 22 with them, resulting in opening of the pairs of contacts 14, 16. The downward travel of the reset member is stopped when its shoulder 36 comes to rest on the top of the frame 26, with the reset button reverting to its rest position of Fig. 1 and thereby indicating that the contacts have opened. Circuit breakers are often used in residual current devices (RCDs) and similar products. A drawback of many such mechanisms is that once they are in the latched position, it is not readily possible to unlatch the mechanism and thereby facilitate manual opening of the contacts. This can be a desirable feature, for example in socket outlets fitted with an RCD when such sockets are not fitted with switches to isolate the load. In addition, if the socket outlet is a multiple outlet type, for example two-way or four-way, each socket outlet would need to be provided with a switch to provide for isolation of all loads connected to the outlets, adding considerably to cost. Another means of opening the contacts of RCDs is to operate a test device which creates a residual current to simulate a fault condition which causes activation of the solenoid or other opening means. However, during conditions of very low or lost supply, the test device would be unable to achieve opening of the RCD. Another problem that can arise is that the test device or circuit may fail, in which case it would not be possible to open the RCD. The present embodiment allows ready manual opening of the contacts 14, 16 from the latched state, Fig. 2. This is achieved simply by rotating the button 34, and hence the shaft 32, about its own axis so that the recess 64 is rotated away from the engaging edge 48a of the aperture 48. It will readily be seen that as the shaft 32 is rotated the edge 48a of the aperture 48 in the latch plate 42 is progressively cammed out of the recess 64, which extends only partially around the circumference of the shaft, until the edge 48a comes to bear on an unrecessed part of the cylindrical surface of the shaft, Fig. 6B. At this point the latch plate 42 will no longer hold the block 22 in train with the shaft 32 and the movable contacts 16 will be released to bring about opening of the contacts in just the same manner as if the plunger 52 had been drawn into the solenoid as previously described. To reclose the contacts, the reset member 30 has to be rotated back to its initial angular position to bring the recess 64 into vertical alignment with the left hand edge 48a of the aperture 48 in the latch plate. In this embodiment this is achieved automatically by providing each end of the spring 38 with an axial extension 70a or 70b, Fig. 7, the upper extension 70a being located within a hole in the board 12 and the lower extension 70b being located in a hole within the reset button 34. Engaging each end of the spring 38 in these respective positions causes the spring to act as a torsion spring as well as an axial compression spring. Now, if the button 34 is rotated from the initial or rest position where the recess 64 is aligned vertically below the left edge 48a of the aperture 48 in order to manually release the contacts 16, when the button 34 is released the energy stored in the spring 38 will rotate the button 34 back to the rest position. Another problem for RCDs is that the test circuit usually requires a second button to facilitate closing of the test circuit. This adds to problems of space and cost, etc. However, in the present embodiment the rotatable reset member 30 is adapted to provide the test function and obviate the need for a separate test button. In the manual opening operation described above with reference to Fig. 7 the reset button 34 is rotated clockwise to open the contacts 14, 16. However, the button 34 can also be rotated anti-clockwise and the torsion in the spring 38 will again return the button 34 to its initial position. This anticlockwise rotation of the button 34 is used to provide for the closing of a contact to activate a test circuit. To this end the button 34 is provided with a conductive arm 72, Fig. 8, which makes contact with a test conductor 74 mounted on the board 12 to complete a test circuit when the reset button is rotated sufficiently anticlockwise. The directions of rotation to achieve the manual opening and test functions as described above were clockwise and anticlockwise respectively. However, the directions to achieve these functions could be reversed if required without affecting the functionality of the circuit breaker . Fig. 8 also shows a further refinement of the test circuit arrangement, by using the spring 38 both as the means for closing the test circuit and for carrying the test current, thus obviating the need for a separate spring biased contact in the test circuit. Thus one end 70a of the spring 38 is electrically connected to a contact pad 76 on the board 12 and the other end 70b of the spring is electrically connected to the arm 72, which may in fact be a radial extension of the end of the spring. When the button 38 is rotated anticlockwise, the arm 72 is brought into contact with the conductor 74 and a test current flows from the conductor 74 via the spring 38 to the pad 76 thereby providing the test current for the test circuit operation. The contacts 14, 16 will open automatically when the solenoid 54 is activated in response to the flow of the test current. When the reset button 34 is released it will rotate back to its initial position. When a circuit breaker is used in an RCD, it is often desirable that the neutral contact always closes before the live contact, and always opens later than the Live contact. The present embodiment ensures that this happens . Referring to Fig. 3, it can be seen that one arm 24 of the closure member 20 (in Fig. 3 the right hand arm) has a larger diameter than the other. The result is that the movable contact 16 beneath that arm is at all times closer to its corresponding fixed contact 14 than the other movable contact. Thus, when the closure member 20 brings the movable contacts towards the fixed contacts, the pair of contacts 14, 16 under the larger diameter arm 24 will close before the other pair of contacts, at which point the block 22 will pivot slightly about a horizontal axis (it is designed with a small degree of freedom to do so) under the continuing downward pressure of the spring 38 to bring the other set of contacts together. Correspondingly, when the latch plate 42 is disengaged from the recess 64 and the closure member 20 starts to move upwards, the pivoting action is reversed with the result that the pair of contacts which closed last will now open first and the pair of contacts that closed first will now open last. If it is arranged that the early make/late break pair of contacts are connected to neutral, the desired result is achieved. A possible problem with the above embodiment is that if the contacts 14, 16 weld together under a high current condition, disengagement of the latch plate 42 from the recess 64 will lead to a return of the reset member 30 to its initial (Fig. 1) position but the contacts will still be closed. However, the user would expect the contacts to be open in such a situation. A flag indicator can therefore be fitted to the closure member 20 such that when the contacts are closed, and the block 22 is down close to the board 12, the indicator is visible through a transparent window. When the contacts open, the flag will be moved away from the window by the moving contacts 16, the absence of the flag thereby indicating that the contacts are open. To avoid fitting a transparent window to the housing within which the device is fitted, with its attendant additional parts and costs, the reset button 34 can be made transparent and the flag indicator arranged to be located within or behind the reset button when the contacts are closed, thereby enabling the flag indicator to be visible to the user. When the contacts open, the flag indicator will move away from the reset button to indicate that the contacts are open. Figs. 9 to 14 show a second embodiment of the invention. This second embodiment is in many respects the same as the first, and therefore only the differences from the first embodiment will be described. In Figs. 9 to 14, the same reference numerals plus 100 have been used for components which are the same or equivalent to components of the first embodiment. In the second embodiment, there is a pair of spaced apart fixed contacts 114 on each side of the frame 126, rather than the single contact 14 in the first embodiment. The movable contact 116 on each side of the frame now becomes a bridging contact which, when the circuit breaker is latched, Fig. 10, electrically shorts the respective pair of fixed contacts. Also, the bridging contacts 116 are now mounted directly on the arms 124. Biasing of the reset member 130 towards its rest position (Fig. 9) is achieved as before with a compression spring 138 bearing at its lower end on the reset button 134 and bearing at its upper end on the board 112. A separate compression spring 139, which also surrounds the shaft 132, is positioned between the board 112 and the block 122 to bias the block vertically upwards along the shaft 132. The upper end of the spring 139 extends into a recess 122a (Fig. 11) in the lower face of the block 122 to allow the block to approach the board 112 sufficiently closely to allow the contacts to close. A further difference is that in the second embodiment the recess 164 in the shaft 132 now faces towards the solenoid 154, and it is the opposite, right hand edge 148b of the aperture 148 which co-operates with the recess 164. In this case the compression spring 162 is on the left hand side of the solenoid, as seen in Fig. 12, biasing the right hand edge 148b of the aperture 148 into contact with the recess 164. Thus, when an energising current having a magnitude greater than a certain threshold is passed through the solenoid 154 the latter draws the plunger 152 to the right to de-latch the device and allow the spring 138 to move the reset button 134 to the rest position and the spring 139 to move block 122 to open the contacts 114, 116. The advantage of this arrangement is that the length occupied by the plunger/solenoid is shorter, leading to a more compact construction. The circuit breaker also has a flag indicator in the form of an elongated member 200 (Figs. 9 and 10) extending substantially parallel to the shaft 132. The upper end of the flag 200 is fixed to the block 122 and its lower end terminates behind the reset button 134 (in this context the rear of the reset button is the side facing the latch mechanism) . The reset button 134 is in the form of a hollow, shallow cylinder open at the rear, and has a diametric flange 202 on its front surface for grasping by a user. It will be understood that in use the circuit breaker is mounted in a housing (not shown) with the reset button 134 located in and projecting slightly proud of an aperture in the housing to facilitate axial and rotational movement of the rest button by the user and to provide visibility of the flag indicator . When the shaft 132 is coupled to the latch member 142 and the contacts 114, 116 are in engagement, Fig. 10, the lower end of the flag 200 extends into the reset button 134 and is clearly visible through the reset button (which may be transparent or have a viewing aperture for that purpose) from the front, top or side thereof. However, when the shaft 132 is decoupled from the latch member 142, Fig. 9, the flag 200 is retracted upwardly relative to the reset button 134 so as to be not visible, or be substantially less visible, through the reset button. Thus, the degree of visibility of the flag 200 through the reset button 134 gives a ready indication of the latched or unlatched state of the device . Finally, the lower end of the compression spring 138 has an extension arm 172 (Figs. 9 and 10) which first extends radially outwardly beyond the walls 204 of the reset button and then extends upwardly substantially parallel to the axis of the shaft 132 through an arcuate slot 206 in the printed circuit board 112, one end of the slot terminating at one of the fixed contacts 114. The radial part of the arm 172 passes through a notch 208 in the wall 204 so that as the reset button 134 is rotated the arm 172 is constrained to rotate with it. The arm 172 allows a test function to be performed, as follows. When the device is latched, Fig. 10, the arm 172 projects freely through the slot 206. If now the reset button 134 is rotated anti-clockwise, as seen from below in Figs. 9 and 10, the arm 172 moves along the slot 206 until it comes into electrical contact with the fixed contact 114. This completes a test circuit (not shown) through the spring 138, arm 172 and contact 114, which causes a current to flow through the solenoid 154 to trip the circuit breaker. Such test circuits are well known in the art and do not need to be described here . However, when it is desired to manually de-latch the device the button 134 is rotated in the opposite direction, i.e. clockwise as seen from below in Figs. 9 and 10, until the edge 148b is fully cammed out of the recess 164, Fig. 14B, the arm 172 in this case moving freely along the slot 206 away from the fixed contact 114. In both cases the reset button 134 is returned to its initial angular position, when the button 134 is released, by torsion in the spring 138, the latter being secured at its upper end to the block 122 and at its lower end to the rest button 134. The above embodiments of the invention are mechanically latched (ML) type circuit breakers. Figs. 15 and 16 show a third embodiment of the invention which is an electrically latched (EL) type circuit breaker. Except for the latch mechanism the third embodiment is in all respects the same as the second embodiment shown in Figs. 9 to 14. Therefore, only the latch mechanism of the third embodiment is shown in Figs. 15 and 16, in which the same reference numerals have been used for components which are the same or equivalent to components of the embodiment of Figs. 9 to 14. In the third embodiment the recess 164 is once again on the opposite side of the shaft 132 to the solenoid 154, facing away from the latter. Also, the right-angle shoulder 166 of the recess 164, against which, in the second embodiment, the edge 148b of the latch plate aperture 148 engages in the latched state of the circuit breaker, is replaced by an upwardly and outwardly sloping shoulder 166a. Finally, the compression spring 132 is omitted. The third embodiment operates as follows . In its tripped (unlatched) state, Fig. 15A, the recess 164 in the shaft 132 is below the arm 144 of the latch plate. If now an electric current is passed through the solenoid 154 the plunger 152 is urged to the right, as seen in Fig. 15A, in the direction tending to reduce the air gap between the plunger and a fixed pole piece 210. However, the plunger 152 cannot move beyond a point at which the left edge 148a of the aperture 148 meets the edge of the shaft 132, Fig. 16A. In order to reset the circuit breaker, the button 134 is pushed upwardly against the bias of the spring 138 so that the shaft 132 moves upwardly through the block 122. At a certain point the recess 164 will draw level with the arm 144 of the latch plate 142, whereupon the plunger 152 is free to move further to the right so that the left edge 148a of the aperture 148 enters the recess 164, Figs. 15B and 16B. If the reset button is now released there will be two opposing forces acting on the latch plate 142. The first is the force exerted by the plunger 152 tending to urge the latch plate 142 to the right and maintain the edge 148a in the recess 164. The second is the force exerted by the spring 138 tending to urge the shaft 132 downwards and hence, by a camming action of the sloping shoulder 166a on the edge 148a, to force the edge 148a out of the recess 164. The circuit breaker is designed such that, provided the current flowing in the solenoid 154 has a magnitude greater than a certain threshold, the first force will dominate to the extent that when the reset button 134 is released, the spring 138 will move the shaft 132 downwardly bringing the latch plate 142 and block 122 with it and closing the contacts 114, 116 as previously described. Thereafter, provided the magnitude of the current flowing in the solenoid 154 remains greater than the threshold, the force exerted on the latch plate 142 by the plunger 152 will be at all times greater than the force of the shoulder 166a tending to cam the edge 148a out of the recess. This is the reset or latched condition of the circuit breaker. However, if at any time the magnitude of the current flowing in the solenoid 154 should fall below the threshold, the force exerted by the plunger on the latch plate 142 will be insufficient to overcome the force of the compression spring 138 acting through the sloping shoulder 166a. At this point the edge 148a of the aperture 148 will be forced out of the recess 164, freeing the shaft 132 to move downwardly under the bias of the spring 138. At the same time the movable contacts 116 move upwards under the bias of the spring 139, resulting in opening of the contacts 114, 116. A fourth embodiment of the invention uses a modified form of the latch mechanism of Figs. 15 and 16, but is in all other respects the same as the second embodiment described with reference to Figs. 9 to 14. The modified latch mechanism is shown in Fig. 17. In the fourth embodiment the solenoid 154 includes a permanent magnet 212. The strength of the permanent magnet 212 is such that, in the absence of any current flow in the solenoid, it attracts the plunger 152 with sufficient force to enable the edge 148a to engage and remain engaged with the recess 164 despite the camming force applied by the sloping shoulder 166a on the edge 148a. Thus the mechanism can be reset in the manner previously described by pressing the button 134 upwardly against the bias of the spring 138 until the edge 148a engages the recess 164, and then releasing the button 134 so that the shaft 132 draws the latch plate 142 and block 122 downwardly until the contacts 116 engage the contacts 114. If, now, a current is passed through the solenoid 154 having a polarity which produces a magnetic field in opposition to that produced by the permanent magnet 212, the force on the plunger 152 will decrease until, when the magnitude of the current flowing in the solenoid 154 exceeds a certain threshold, the force exerted by the plunger on the latch plate 142 will be insufficient to overcome the force of the compression spring 138 acting through the sloping shoulder 166a on the edge 148a. At this point the edge 148a of the aperture 148 will be forced out of the recess 164, freeing the shaft 132 to move downwardly under the bias of the spring 138. At the same time the movable contacts 116 move upwards under the bias of the spring 139, resulting in opening of the contacts 114, 116. In a modification of the above embodiments the mechanism could additionally, or alternatively, be tripped or delatched by a force other than that from the solenoid or manual rotation of the shaft by the reset button. This alternative force could be applied directly to either side of the latch plate to cause a lateral movement of the plate and resultant tripping of the mechanism. For example, in the second embodiment, Figs. 9 to 14, if a force is applied directly to the free end of the latch plate in a direction towards the solenoid the mechanism will trip. Such a force could be applied by hand, or automatically in response to an electrical, thermal or mechanical condition. This would enable the circuit breaker to be used for applications such as overcurrent protection, over temperature protection, over voltage protection, etc., as well as providing the option of achieving manual tripping by acting directly on the latch plate instead of via the reset button. For example, one could pass the current through a bimetallic strip which, in the case of an overcurrent condition, heats up to such an extent as to bend towards and bear upon the latch plate sufficiently to delatch the mechanism. The invention is not limited to the embodiments described herein which may be modified or varied without departing from the scope of the invention.

Claims: Claims 1. An electro-mechanical circuit breaker comprising first and second normally open electrical contacts, a manual reset member movable in a first manner to set the circuit breaker, and means for tripping the circuit breaker upon the occurrence of a predetermined current condition, the reset member further being movable in a second manner to trip the circuit breaker in the absence of the predetermined current condition. 2. A circuit breaker as claimed in claim 1, including first biasing means for urging the first contact away from the second contact to maintain the contacts normally open, wherein the manual reset member is movable in the first manner against the action of a second biasing means to couple with the first contact to draw the first contact into engagement with the second contact upon release of the reset member, and wherein the tripping means comprises means for de-coupling the reset member from the first contact upon the occurrence of the predetermined current condition thereby allowing the first contact to disengage the second contact under the action of the first biasing means, the reset member being movable in the second manner to de-couple the reset member from the first contact in the absence of the predetermined current condition. 3. A circuit breaker as claimed in claim 2, wherein the reset member couples with the first contact via a latch member, the reset member coupling with the latch member when moved in the first manner and being decoupled from the latch member upon the occurrence of the predetermined current condition or when moved in the second manner . 4. A circuit breaker as claimed in claim 2 or 3, further including means for automatically returning the reset member to an initial position upon release thereof after movement in the second manner. 5. A circuit breaker as claimed in claim 2, 3 or 4 , wherein the first manner of movement of the reset member is along a substantially linear axis and the second manner of movement of the reset member is rotational movement . 6. A circuit breaker as claimed in claim 5, wherein the rotational movement is about the said axis. 7. A circuit breaker as claimed in claim 6, wherein the reset member includes an elongate member movable substantially linearly along its own axis for movement of the reset member in the first manner and rotatable about its own axis for movement of the reset member in the second manner . 8. A circuit breaker as claimed in claim 7 when indirectly dependent on claim 3, wherein the latch member is movable in a direction transverse to the said axis between a latched position wherein the latch member is coupled to the elongate member and an unlatched position wherein the latch member is de-coupled from the elongate member, the circuit breaker further including actuating means for urging the latch member into its latched position in the absence of the predetermined current condition and for urging the latch member to its unlatched position upon the occurrence of the predetermined current condition, the latch member also being moved to its unlatched position by a camming action of the elongate member as the latter is rotated about the said axis. 9. A circuit breaker as claimed in claim 8, wherein the elongate member has a recess formed partially around its circumference for engagement by the latch member, the latch member being cammed out of the recess upon rotation of the elongate member about its own axis. 10. A circuit breaker as claimed in claim 8 or 9 , wherein the actuating means comprises third biasing means for urging the latch member to its latched position and solenoid means for urging the latch member to its unlatched position, against the action of the third biasing means, upon the occurrence of the predetermined current condition. 11. A circuit breaker as claimed in claim 9, wherein the actuating means comprises solenoid means for urging the latch member to its latched position in the absence of the predetermined current condition, the solenoid means releasing the latch member upon the occurrence of the predetermined current condition, the actuating means further including an inclined surface of the recess for camming the latch member out of the recess, through the action of the second biasing means and without rotation of the elongated member, upon release of the latch member by the solenoid. 12. A circuit breaker as claimed in any one of claims 7 to 10 when indirectly dependent on claim 3, including a contact closure member mounted for movement towards and away from the second contact and slidably engaged by the latch member for movement of the latter between its latched and unlatched positions, the closure member being drawn by the latch member towards the second contact when the latch member is coupled to the reset member and the latter is released, such movement of the closure member bringing the first contact into engagement with the second contact against the action of the first biasing means. 13. A circuit breaker as claimed in claim 12, wherein the first contact is carried by the closure member. 14. A circuit breaker as claimed in claim 13, wherein there are a pair of second contacts and the first contact comprises a bridging contact for electrically shorting the pair of second contacts. 15. A circuit breaker as claimed in claim 14, wherein the bridging contact is carried by the closure member. 16. A circuit breaker as claimed in any one of claims 13 to 15, wherein the closure member is slidably mounted on the elongate member for movement along the axis thereof and the latch member passes through the closure member in a direction transverse the axis of the elongate member, the elongate member passing through an aperture in the latch member and the edge of the aperture engaging the recess in the elongate member when the latch member is in the latched position. 17. A circuit breaker as claimed in any one of claims 7 to 16, wherein the second biasing means comprises a compression spring surrounding the axis of the elongate member, the compression spring further acting as a torsion spring to return the reset member to the initial angular position after said rotational movement. 18. A circuit breaker as claimed in any one of claims 7 to 17, wherein the reset member further includes an enlarged head at one end of the elongate element and serving as a manual reset button, the reset button being pushable to effect said linear movement of the elongate member and rotatable to effect said rotational movement of the elongate member. 19. A circuit breaker as claimed in any preceding claim, wherein the reset member carries a third electrical contact and is movable in a third manner to complete a test circuit. 20. A circuit breaker as claimed in claim 19 when directly or indirectly dependent on claim 6, wherein the third manner of movement is rotation about the said axis in the opposite direction to said second manner of movement . 21. A circuit breaker as claimed in any preceding claim, wherein the reset member includes a manual reset button and the circuit breaker further includes a flag indicator visible through the reset button, the position of the flag indicator relative to the reset button differing according to whether the first and second contacts are open or closed. 22. A circuit breaker as claimed in any preceding claim, wherein the predetermined current condition is a current magnitude above a certain threshold. 23. A circuit breaker as claimed in any preceding claim, wherein the predetermined current condition is zero current or a current magnitude below a certain threshold.

Inventors: WARD PATRICK, WARD, PATRICK
Applicants: TRIPCO LTD, WARD PATRICK, TRIPCO LIMITED, WARD, PATRICK
Application year: 2000
Main classification: H01H73
IPC codes: H01H73