F O R M 2

THE PATENTS ACT, 1970
(39 of 1970)

&

The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)

1. Title of the invention. - IMPROVED MECHANISM FOR MOULDED CASE
CIRCUIT BREAKER WITH PLUG-IN CONTACT
UNIT

2. Applicant(s)

(a) NAME : LARSEN & TOUBRO LIMITED

(b) NATIONALITY : An Indian Company.

(c) ADDRESS : L & T House, Ballard Estate, Mumbai 400 001, State of Maharashtra, India

3. PREAMBLE TO THE DESCRIPTION

The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION

The present invention relates to low voltage Circuit Breakers (MCCB) for electrically connecting it to panel boards having plug-in contact unit. More particularly, the invention relates to improved mechanism for MCCB adapted to reduce temperature rise in plug-in contact unit, simpler plug-in and plug-out operations and ensure tripping of the breaker while plug-in and plug-out operations.

BACKGROUND OF THE INVENTION

The plug-in device is used in panel boards to mount the circuit breaker. The main purpose of the plug-in base is to reduce the downtime in replacing the breaker. All the busbars or the cables to the breaker are connected in the plug-in base and the rear connector in the circuit breaker makes a direct contact to the plug-in base contacts. At any point of time, the breaker can be easily replaced by the new one.

The plug-in contacts designed in the prior art employ the parallel path of the current in the fixed contact more than two. So number of electrical joints per path is two. Joint resistance is one of the major causes of the temperature rise in contact systems.

As the number of joints increases the I2R losses increases, this increases the temperature of the product when in use. Spring force is inversely proportional to temperature rise. For a temperature rise to be desirably minimum higher spring force is required. The upper limitation of the spring force is only by the dimensional space constraint to accommodate huge springs. As the spring force is reduced the force required to plug-in and plug-out is less.

The current product has its limitation in the usage of spring force which eventually results in high temperature. The extension garter spring is used to provide the necessary contact pressure for cylindrical type moving contacts. The garter springs apply necessary contact pressure through radially. Whenever heavy springs are used it will aid in increase in the diameter of the fixed contact which in turn increases the overall space requirement to accommodate the contact system.

In order to get uniform radial pressure distribution and for the ease of manufacturing, the design employs a minimum of four current paths, for which each current path results in two electrical contact points, Where the necessary contact pressure for each contacts are provided by the above said garter springs. Each electrical contact contributes to increase in contact resistance and hence the temperature rise.

The Plug-in and plug out operation have to overcome this contact spring force. So higher the spring force will result in the application of more force by the user for plug-in and plug out operation.

In the existing product for draw out operation the user have to hold the breaker and to apply the out ward force directly in the breaker.

US 4,728,914 discloses a molded plastic rating plug enclosure houses the molded case circuit breaker rating plug printed circuit board. The rating plug enclosure is inserted within the circuit breaker cover and is adapted for removal from the circuit breaker cover by means of a special extractor tool. Access means for connecting a test jack with the circuit breaker trip unit printed circuit board and visual access means for an indicating diode are formed within the cover of the rating plug enclosure.

US 5,381,120 discloses a molded case circuit breaker having a thermal-magnetic trip unit is provided with a mechanical rating plug to allow a number of circuit breakers of different ampere ratings to be used within a common-sized enclosure. The rating plug interacts with a thermal-magnetic trip unit to set the circuit breaker ampere rating.

US 5,446,386 discloses a molded case circuit breaker containing a digital trip unit is field-tested for both electronically-induced as well as mechanically-induced test conditions by means of a portable test kit unit. The test kit circuit components are contained within a miniature test plug that temporarily connects with the circuit breaker trip unit by insertion within the rating plug receptacle formed within the circuit breaker cover. A compact power supply plug is received within the test plug to provide operating power to the circuit breaker trip unit components and associated accessories.

US 5,392,016 discloses a molded case circuit breaker having a thermal-magnetic trip unit is provided with a mechanical rating plug to allow a number of circuit breakers of different ampere ratings to be used within a common-sized enclosure. Multiple mechanical rating plugs are stored at the place of distribution to adapt the common enclosure to a specific ampere rating at a substantial savings in time, labor and materials
US 5,877,925 discloses a ground fault/rating plug for molded case circuit breakers is inserted within the circuit breaker cover for electrical connection with the circuit breaker electronic trip unit. A rating resistor within the ground fault/rating plug enclosure sets the circuit breaker ampere rating. Rotary switches on the outer surface of the ground fault/rating plug enclosure configure the trip unit for ground fault protection.

US 6,274,833 discloses a plug-in trip unit joint 900 for a molded case circuit breaker 10, with the circuit breaker 10 having an operating mechanism 40 with a movable contact arm 45 mounted on a cross-bar 55, a trip bar 618 and a line terminal mounted in a first housing and a trip unit 600 and a load terminal 16 mounted in a second housing. The plug-in trip unit joint 900 comprises a trip unit stab 910 coupled to the trip unit 600 and load terminal 16 and extends from the second housing and a movable contact arm clamp assembly 909 mounted in the first housing and aligned to selectively engage the trip unit stab 910 wherein the line terminal 18 and the load terminal 16 are electrically coupled together and with the trip unit in selective contact with the operating mechanism 40 of the circuit breaker 10. The movable contact arm clamp assembly 909 comprises a pair of connectors 916, 918 with one connector 916 positioned along one side of the movable contact arm 45 and one connector 918 positioned on a corresponding opposite side of the movable contact arm 45. Each connector 916, 918 has a first end 930 and a second end 932 with the first end 930 configured to engage one side of the movable contact arm 45 and the second end 932 configured to engage one side of the trip unit stab 910. A biasing member 920 positioned to engage both connectors between the first and second ends 930, 932 of each connector 916 is installed to urge both connectors 916, 918 against the movable contact arm 45 and the trip unit stab 910 and establishes an electrical and mechanical coupling. The contactors sandwich the contact arm 45 and the trip unit stab 910 between them and is held together with a U-shaped spring. In one embodiment, each end of the connector 916 includes a spherical surface for engagement with the movable contact arm 45 and the trip unit stab 910.

US 2008/0157906 discloses a terminal of a standard, plug-in or box type molded case circuit breaker, a terminal module assembly for a molded case circuit breaker capable of being removable by easily selecting the terminal type, and a molded case circuit breaker having the terminal module assembly, the terminal module assembly comprising a plurality of terminals provided to selectively have a standard, plug-in or box type and electrically connected to fixed contactors, a plurality of terminal bases provided as many as the number of the terminals and selectively having the standard, plug-in or box type, thus to fixedly support each of the terminals, wherein each terminal is assembled to each terminal base to obtain a terminal module intermediate assembly, and a common supporting base for supporting all of the plurality of intermediate assemblies regardless of the terminal type or terminal base type, wherein the terminal module assemblies having the construction can be attached/detached to/from the molded case circuit breaker.

US 7,786,831 discloses a modular terminal for a molded case circuit breaker by which various types of terminals can be joined together and configuration and assembly are simplified, the modular terminal comprising a plurality of terminal bases each of which is provided for each phase, a terminal which is detachably supported at each terminal base, and a joint piece which connects a pair of the terminal bases adjacent to each other to form a terminal module.

One of the disadvantages of the above mentioned prior art is that the contacts have to engage and disengage frequently. And in engaged condition it has to carry continuous rated current and get heated up quickly and hence reduces the life and performance.

The new concept occupies less vertical space as compared to others for the same ampere rating.

In the present invention the design consists of two parallel paths in fixed contact, so it only aids to two spring loaded electrical joints per parallel path. In contrast the older/prior art designs comprise four parallel paths, which in turn increases the overall electrical contact resistance.

The present inventors have found to efficiently reduce the temperature rise of the Plug-in contacts with lesser spring force and the space required to accommodate the contact system in plug in base. The effort required by the user to plug-in and plug-out the breaker from plug-in base is less due to lesser spring force employed in the contact system.

Thus there is a need to provide with an improved mechanism where the circuit breaker is electrically connected with the plug-in base. The plug-in base is connected to the panel board, where the terminals of the plug-in base are bolted to the bus bars of the panel board. The present concept looks into the possibilities of reducing the temperature effectively, the overall dimension to accommodate and the ease of operation with much lesser effort.
OBJECTS OF THE INVENTION

An object of the present invention is to overcome the problems/disadvantages of the prior art.

Another object of the present invention is to provide an improved mechanism in MCCB for electrically connecting it to panel boards having plug-in contact unit adapted to reduce temperature rise in plug-in contact unit.

Yet another object of the present invention is to provide an improved mechanism in MCCB for electrically connecting it to panel boards having plug-in contact unit adapted for simpler plug-in and plug-out operations.

Yet another object of the present invention is to provide an improved mechanism in MCCB for electrically connecting it to panel boards having plug-in contact unit adapted to ensure tripping of the breaker while plug-in and plug-out operations.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided an improved mechanism for Modeled Case Circuit Breakers (MCCB) with plug-in base for electrically connecting it to panel boards, said mechanism comprising
(i) a molded case circuit breaker (MCCB) comprising plurality of moving contacts protruding on the rear side of said breaker; a hanging means placed substantially below said moving contacts with a hanging profile; a trip mechanism means placed in proximity to said hanging means adapted to ensure tripping of the breaker while plug-in and plug-out operations and
(ii) a plug in means operatively associated with said molded case circuit breaker, said plug in means comprising plurality of fixed contacts unit having hollow cylindrical profile means to accommodate said moving contacts inside and said fixed contacts operatively connected with said moving contacts adapted to reduce temperature rise in said fixed contact unit; a box means substantially placed at the center of said plug in means adapted for plug-in and plug-out operations ; a pull lever means operatively connected with box means adapted to initiate plug-in and plug-out operations.
DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to improved mechanism of MCCB for electrically connecting it to panel boards having plug-in contact unit.

The mechanism comprises a molded case circuit breaker (MCCB) having plurality of moving contacts protruding on the rear side of the breaker; a hanging means/hook means placed substantially below the moving contacts with a hanging profile; a trip mechanism means placed in proximity to the hanging means adapted to ensure tripping of the breaker while plug-in and plug-out operations.

The mechanism further comprises a plug in means operatively associated with the molded case circuit breaker. The plug in means has plurality of fixed contacts unit having hollow cylindrical profile means to accommodate the moving contacts inside, a box means substantially placed at the center of said plug in means and a pull lever means operatively connected with box means.

According to one of the embodiment of the present invention there is provided a mechanism of the said MCCB is to reduce the temperature rise of the Plug-in contact system with reduced electrical contact joints and the spring force thereof.

The present invention employs only two parallel paths. The fixed contact system/unit consists of two clamped shaped halves where the total number of the spring connected electrical contact made to be four. The halves are made of copper sheet metal components which are easy to manufacture and vertical space required is less to accommodate in plug-in base. However, use of copper sheets should not be considered as restricting the scope of the invention and any other metal sheets can be used which provides ease for manufacturing the halves and can accommodate itself in a less vertical space.

The fixed contact unit/system as mentioned above comprises of a first and a second plate of metal means with substantially U shaped profile with a bent substantially at its center to form a substantially clamped shaped means. The clamped shaped means having a slit like provision on one of its end and said clamp means having plurality of holes at its corners ; a connector means with substantially T-shaped profile locked with the slit provided within said clamped shaped means; a terminal means with substantially L-shaped profile connected with said connector ; plurality of extension spring means operatively connected with said clamp means , said clamp means is having plurality holes on its corners to accommodate said spring means ; plurality of mild steel means with plurality of holes at its corners, said holes matches with said holes of the clamp to accommodate said spring means within it and a rod means operatively connected with said connector means at its center by click fitting adapted to accommodate said moving contact .

The bent of the first plate and the second plate face each other to form a substantially round shaped profile enclosing the connector means to accommodate said moving contact. The plurality of spring means having four springs providing predetermined contact pressure. The spring means is adapted to reduce temperature rise in said fixed contact unit.

The important feature of this invention is a fixed contact system/unit in which the spring loaded electric contacts are reduced, which in turn reduces the temperature rise and the use of higher spring force. The higher the spring force higher is the spring size which in turn increases the overall size of the contact system, which is reduced in the present invention. The mechanism of the present invention comprises of moving contact and fixed contact which is connected with the plug-in base, and springs for contact pressure.

According to another embodiment of the present invention there is provided a mechanism to reduce effort to plug-in and plug out operation by the introduction of handle and cam arrangement plug-out and plug-in operation is made simpler.

A cam and rail arrangement present inside the box means is provided for easy engagement and disengagement of the breaker at plug-in and plug-out operation. The cam and rail arrangement for the easy plug out and plug-in is implemented in the present invention so that the breaker can be ejected or inserted from the plug-in base easily.

The draw out operation is made simpler in this invention by the introduction of a rail and a cam arrangement arranged inside the plug-in base which is actuated by a lever. However, use of rail and cam should not be considered as restricting the scope of the present invention as any other components which is technically equivalent to the rail and cam can provide with required draw out operation. By pulling this lever the breaker can be easily withdrawn from the plug-in base. Likewise for plug-in the breaker have to hang in to the moving rail by the hook like structure provided in the back-plate, which have to be connected in the rear side of the breaker. After that the breaker can be easily plugged in with the help of this handle, by pushing it.

The box means having a rail means having a slot; a metal means with a substantially U-shaped profile, accommodated inside the slot provided in said rail means .The metal means operatively connected with said MCCB; cam means operatively connected with said metal means adapted to perform plug-in and plug-out operations. The rail means comprising a trigger pin and cam means is operatively connected with a shaft means associated with said pull lever means adapted to perform plug-in and plug-out operations.

The box means further comprising plurality of guiding pin means and a center pin. The rail means comprises of plurality of slots to accommodate said guiding means adapted to guide said metal means.

To perform the plug-in and plug-out operations the following mechanism is followed:

The cam means is rotated in anticlockwise direction when said lever means is pulled down (anticlockwise) and said metal means that is operatively connected with said cam means is pushed out through the slot provided in said rail, said rail means pushes said MCCB to get plug-out operation.

The cam means is rotated in clockwise direction when said lever means is pulled up ( clockwise) and said center pin is pulled backwards to get plug-in operation.

According to yet another embodiment of the present invention there is provided trip unit mechanism of MCCB which ensures tripping of the breaker while plug-in and plug-out operation.

A safety trip mechanism/ trip unit mechanism that ensures tripping of the breaker both at plug-in and plug-out operation.

A safety trip device is also employed so that even if it tried to plug-out or plug-in with the breaker in on condition before making the breaker contacts with the plug-in base contact, it will trip the breaker. The safety trip mechanism that is mounted on the back plate of the circuit breaker trips the breaker both in the plug-in and plug-out operation, with minimum number of components.
The trip mechanism is incorporated in plug-in, so that just before the circuit breaker contact makes contact with the plug-in contact, it will trip the breaker. After the full insertion, the mechanism removes the trip command and breaker is free to work. Likewise while plug-out before the circuit breaker contact leaves the plug-in contact, it trips the breaker. Because of the introduction of this mechanism, the hazard involving the accidental plug-out or plug-in in the on condition of the circuit breaker is eliminated.

The trip mechanism means comprises a casing having a hollow cylindrical profile inside at its center with a rectangular slit at the center of said cylindrical profile; a trip plate means located outside said casing adapted to perform the tripping mechanism; a trip pin means having a rectangular cross sectional area with a first end accommodated inside the slit of said casing and second end accommodated inside the rear side of breaker; a compression spring located inside said hollow cylindrical profile of casing and operatively connected with said trip pin means ; double torsion spring operatively connected with said trip plate means adapted to push said trip plate means in anticlockwise direction; a stopper pin located at a predetermined location placed inside said casing adapted to set/fix the motion of said trip plate means till said predetermined location.

The trip pin means is operatively connected with said trip plate means such that the movement of said trip pin actuates the trip plate means adapted to trip said breaker while in plug-in and plug-out operation. The trigger pin is operatively connected with said trip plate means adapted to actuate said tripping of said MCCB.

Benefits:
• Lesser number of electrical contact joints
• Less space required.
• Ease of operation because of lesser spring force employed for contacts
• Easy engagement and disengagement with the help of cam and rail arrangement.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

Figure 1 illustrates the view of the circuit breaker plugged in Plug-in base
Figure 2 illustrates the view of the circuit breaker plugged out from Plug-in base
Figure 3 illustrates the rear side of the circuit breaker connected with the moving contacts, back plate and trip mechanism unit
Figure 4 illustrates the plug-in base
Figure 5 illustrates the fixed contact assembly inside plug-in base.
Figure 6 illustrates the exploded view of the contact system
Figure 7 illustrates the rail and cam arrangement in the plug-in position
Figure 8 illustrates the rail and cam arrangement in the plug-out position
Figure 9 illustrates the handle, shaft and cam arrangement
Figure 10 illustrates the trip mechanism unit
Figure 11 illustrates the trip mechanism unit connected to the rear side of the breaker and the trigger pin connected to the rail on the plug-in base.
Figure 12 illustrates the trip actuator just touches the trigger pin while plugging in.
Figure 13 illustrates the position of trip actuator after touching the trigger pin on further plugging in causing the trip plate actuating pin to move inside.
Figure 14 illustrates the position of trip actuator after the complete plugging in operation.
Figure 15 illustrates the position of trip actuator during plugging out operation.
Figure 16 illustrates the rear side of the plug-in base showing arrangement of terminal suitable for rear connection.
Figure 17 illustrates the moving contact connected to the circuit breaker just before entering the plug-in base. (Circuit breaker and Plug-in base are not shown)
Figure 18 illustrates the moving contact connected to the circuit breaker just before making the contact with the fixed contact of plug-in base. (Circuit breaker and Plug-in base are not shown)
Figure 19 illustrates the moving contact connected to the circuit breaker after making the contact with the fixed contact of plug-in base. (Circuit breaker and Plug-in base are not shown)

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWING

Figure 3 illustrates the hollow cylindrical copper contacts (4) connected with the terminals (3) of the circuit breaker by bolting. It will protrude in the rear side of the breaker as shown in Fig 3.

Figure 4, 5 and 6 illustrates the fixed contact (7) is situated in the plug-in base consist of two plates of copper sheet with a bend at the center, forming a clamp shaped piece (17). One ‘T’ shaped copper connector (15). ‘L’ shaped terminal (3).

Figure 5 and 6 illustrates the two copper clamp holds in such a way that the bend of each piece will face each other and is hold in that position by four extension springs (19) situated in the holes provided in the corners of the copper clamp (17). To get the necessary extension for the extension spring(19), four mild steel pieces are also employed having two holes each, which matches with the holes provided in the copper clamp(17). One end of each copper clamp (17) is locked with the ‘T’ shaped copper connector (15) with help of the slit provided in the copper clamp (17). The plastic rod (16) is connected to the fixed contact (7), at the centre of the ‘T’ connector (15), by click-fitting. It provides the finger proofing along with the shield given in plug-in base (2). The whole assembly is placed in the rectangular hole provided in the plug-in base (2). The ‘L’ shaped terminal (3) can be connected in two positions, so that front and rear connection at the termination is possible by the single component shown in figure 16. Whenever the breaker plugged in, the moving contact’s (4) of the breaker enters in between the two cylindrical face of the copper clamp (17). The plastic rod (16) moves through the center hole provided in the moving contact (4).

The current from the bus-bar enters into the incoming ‘L’ terminal (3), which is bolted to the ‘T’ connector (15). From there the current divides into two and enters into the clamp shaped fixed contact half’s (17). The contact pressure at this point is provided by the two springs (19) at the terminal side. From there the current enters to the moving contact (4) and flows to the breaker (1). The contact pressure at the moving contact (4) side is provided by the pair of springs (19) situated at the moving contact side. The overall spring loaded contacts comes to be four numbers where as prior available plug-in of other manufactures consist of 8 (schneider) to 20 (Moeller) numbers. This reduction plays the major role in bringing down the resistance value as the contact joints’ resistance forms the major portion of the overall system’s resistance. In order to bring down the contact resistance greater spring force is required. For the same bigger springs have to be used, which will aid to the increase in overall size of the contact system, which is reduced in the present invention.

The increased spring force will also affect the performance of the plug-in, As the user have to exert more force to plug-in and plug-out the breaker from the plug-in base(2). With the reduction of the spring force plug-in and plug-out operations made simple.

For the prior plug-in, the user has to hold the breaker and pulled back manually for plugging-out operation. The difficulty is over come here by the handle (8) provided at the side of the plug-in base as illustrated in fig 7.

Figure 7 illustrates a rail (20) that is also provided in the plug-in (2) for the free in and out movement. The circuit breaker(1) is directly mounted in the rails (20) by hanging by the hook (28) like structure provided in the back plate, which is to be connected at the rear side of the breaker as shown (figure 3 and 4).

An ‘U’ shaped mild steel (11) is connected to the rail (20), in which the circuit breaker (1) mounted and contain three pins. In which two pins (21) are used for guiding purpose in the rail (20), third one (22) is provided for the cam action. The handle (8) is connected to the shaft (10); in which a cam (9) is fixed. This cam (9) is always engaged with the centre pin (22) situated at the centre of the ‘U’ shaped mild steel piece (11). When the handle (8) is pulled down, it will rotate the shaft (10) in anticlockwise direction, the cam (9) which connected in the shaft (10) also rotates in the same degrees. As the cam (9) is in contact with the ‘U’ shaped MS piece (11), it will push it out through the slot provided in the rail (20). The circuit breaker(1) is directly connected to this ‘U’ shaped MS piece(11) it will also pushes out the breaker (1) from the plug-in base (2) and thus the rear connections in the breaker (1) leaving the plug-in base contacts (7), which can be easily taken out at this position thus achieving the plug-out operation successfully.

Likewise in plug-in operation, after hanging the circuit breaker (1) in the ‘U’ shaped MS piece (11), rotate the handle (8) in clockwise direction which in turn rotates the cam (9) in clockwise direction. This results in pulling the centre pin (22) connected in the ‘U’ shaped MS piece (11) through the rail(20) towards the plug-in base(2), thus making the circuit breaker(1) rear connections with the plug-in base contacts(7), achieving the successful plug-in operation.

In plug-in base (2) the Plug-in contacts (7) are always at live condition, in which the circuit breaker (1) is to be connected. So it is essential that the circuit breaker (1) have to be in tripped condition or in off condition, both in plug-in operation and in Plug-out operation, after this operation the breaker (1) should work independently. This can be achieved by the introduction of a safety trip mechanism in the breaker, which will trips the breaker while plug-in operation and plug-out operation.

Figure 10 illustrates the safety trip mechanism consists of a plastic case (24) having a hollow cylindrical profile in the centre, with a rectangular slit at the centre of this cylindrical profile, a position retaining compression spring (28) , a position retaining double torsion spring (26), a trip plate actuating rectangular pin(29) , a special shaped trip plate actuator (25), a stopper pin (27) located in the plastic case (24), a trigger pin(23) ( not shown in fig 7), and an actuator holder pin( not shown in fig 7).

The trip plate actuating pin (29) is a long pin having a rectangular cross section, which is extended from the rear side of the breaker to the trip plate inside the circuit breaker(1). It is arranged in such a manner that a slight inside movement of this pin (29)will actuate the trip plate(25), which in turn trips the breaker (1). It has a cylindrical head, which will exactly fits the hollow cylindrical cut in the plastic casing. It also has a wedge shaped cut at the cylindrical head. The plastic case (24) is to be fitted in the provision given in the back plate, which is connected at the rear side of the breaker. The trip plate actuating pin(29) is placed in the rectangular slit in the plastic casing (24) and the rectangular slit at the rear side of the breaker(1). The position retaining compression spring (28) is located in the cylindrical hole of the plastic casing (24) pushing the trip plate actuating head outside. The trip plate actuator (25) is located inside the plastic casing (24) and on mounted on a pin (29). It has one wedge shaped cutting on one end, which is always in contact with the trip plate actuating pin head and the other end protruded outside the plastic casing(24). This trip plate actuator (25) is always pushed in anticlockwise direction by the double torsion spring (26) which is also located in the same pin, where this trip plate actuator seated. This motion is restricted not beyond an angle by the stopper pin (27), which is also located in the plastic case. The whole arrangement is located in the special provision given in the back plate, which is connected at the rear side of the circuit breaker, and moves along with the circuit breaker in the plug-in and plug-out operation. The trigger pin (23) is located in the plug-in base connected to the rail as shown in figure (figure 11).
While plug-in, the protruded end of the trip plate actuator (25) makes first contact with the triggering pin (23).
On the further inside movement causes the trip plate actuator (25) to rotate downwards, against the double torsion spring (26) action. This in turn results in pushing of trip plate actuating pin (29), which in turns actuate the trip plate (25) of the circuit breaker (1) causing the tripping of the breaker (1) before the plug-in contacts (7) makes contact with the circuit breaker rear contacts. At the full insertion time the trip plate actuator (25) profile again comes in the home position because of the special shape of the trip plate actuator (25) accompanied by the action of the double torsion spring (26). The trip plate actuating pin (29) also comes into home position because of the action of the compression spring (28) on its cylindrical head. Now the trip plate (25) of the circuit breaker is free and the breaker is free to operate, thus achieving a successful tripping operation at the plug-in operation.

While Plugging out, the trip plate actuator profile (25) again get contact with the triggering pin (23) , causing it to rotate downwards, against the double torsion spring (26) action, this in turn results in pushing of trip plate actuating pin (29), which in turns actuate the trip plate (25) of the circuit breaker (1) causing the tripping of the breaker before the plug-in contacts leaves the rear contacts of the circuit breaker thus achieving a successful tripping operation at the time of drawing out operation.

WE CLAIM

1. An improved mechanism for Molded Case Circuit Breakers (MCCB) with plug-in base for electrically connecting it to panel boards, said mechanism comprising
(i) a molded case circuit breaker (MCCB) comprising plurality of moving contacts protruding on the rear side of said breaker; a hanging means placed substantially below said moving contacts with a hanging profile; a trip mechanism means placed in proximity to said hanging means adapted to ensure tripping of the breaker while plug-in and plug-out operations and
(ii) a plug in means operatively associated with said molded case circuit breaker, said plug in means comprising plurality of fixed contacts unit having hollow cylindrical profile means to accommodate said moving contacts inside and said fixed contacts operatively connected with said moving contacts adapted to reduce temperature rise in said fixed contact unit; a box means substantially placed at the center of said plug in means adapted for plug-in and plug-out operations ; a pull lever means operatively connected with box means adapted to initiate plug-in and plug-out operations.

2. Mechanism as claimed in claim 1 wherein said fixed contact unit comprising
(a) a first and a second plate of metal means with substantially U shaped profile with a bent substantially at its center to form a substantially clamped shaped means, said clamped shaped means having a slit like provision on one of its end and said clamp means having plurality of holes at its corners ;
(b) a connector means with substantially T-shaped profile locked with the slit provided within said clamped shaped means;
(c) a terminal means with substantially L-shaped profile connected with said connector ;
(d) plurality of extension spring means operatively connected with said clamp means , said clamp means is having plurality holes on its corners to accommodate said spring means ;
(e) plurality of mild steel means with plurality of holes at its corners, said holes matches with said holes of the clamp to accommodate said spring means within it and
(f) a rod means operatively connected with said connector means at its center by click fitting adapted to accommodate said moving contact .

3. Mechanism as claimed in claim 2 wherein said bent of the first plate and the second plate face each other to form a substantially round shaped profile enclosing the said connector means adapted to accommodate said moving contact.

4. Mechanism as claimed in claim 2 wherein said plurality of spring means comprising four springs providing predetermined contact pressure.

5. Mechanism as claimed in claim 4 wherein said spring means is adapted to reduce temperature rise in said fixed contact unit.

6. Mechanism as claimed in claim 1 wherein said box means comprising

(a) a rail means having a slot ;
(b) a metal means with a substantially U-shaped profile , accommodated inside the slot provided in said rail means , said metal means operatively connected with said MCCB;
(c) cam means operatively connected with said metal means adapted to perform plug-in and plug-out operations.

7. Mechanism as claimed in claim 6 wherein said rail means comprising a trigger pin.

8. Mechanism as claimed in claim 6 wherein said cam means is operatively connected with a shaft means associated with said pull lever means adapted to perform plug-in and plug-out operations.

9. Mechanism as claimed in claim 6 wherein said box means further comprising plurality of guiding pin means.

10. Mechanism as claimed in claim 7 wherein said rail means comprises of plurality of slots to accommodate said guiding means adapted to guide said metal means.

11. Mechanism as claimed in claim 6 wherein said box means further comprising a center pin.

12. Mechanism as claimed in any of the preceding claims wherein said cam means is rotated in anticlockwise direction when said lever means is pulled down ( anticlockwise) and said metal means that is operatively connected with said cam means is pushed out through the slot provided in said rail , said rail means pushes said MCCB to get plug-out operation.

13. Mechanism as claimed in any of the preceding claims wherein said cam means is rotated in clockwise direction when said lever means is pulled up ( clockwise) and said center pin is pulled backwards to get plug-in operation.

14. Mechanism as claimed in claim 1 wherein said trip mechanism means comprising

(a) a casing having a hollow cylindrical profile inside at its center with a rectangular slit at the center of said cylindrical profile;
(b) a trip plate means located outside said casing adapted to perform the tripping mechanism;
(c) a trip pin means having a rectangular cross sectional area with a first end accommodated inside the slit of said casing and second end accommodated inside the rear side of breaker;
(d) a compression spring located inside said hollow cylindrical profile of casing and operatively connected with said trip pin means ;
(e) double torsion spring operatively connected with said trip plate means adapted to push said trip plate means in anticlockwise direction;
(f) a stopper pin located at a predetermined location placed inside said casing adapted to set/fix the motion of said trip plate means till said predetermined location.

15. Mechanism as claimed in claim 14 wherein said trip pin means is operatively connected with said trip plate means such that the movement of said trip pin actuates the trip plate means adapted to trip said breaker while in plug-in and plug-out operation.

16. Mechanism as claimed in claim 7 wherein said trigger pin is operatively connected with said trip plate means adapted to actuate said tripping of said MCCB.

17. The improved mechanism for Modeled Case Circuit Breakers (MCCB) with plug-in base for electrically connecting it to panel boards as substantially described hereinbefore with reference to accompanying drawings.