DESC:Locking Mechanism for Racking Assembly of Draw-out Circuit breaker

Field of the invention

The present invention relates to protection devices such as circuit breakers and more particularly, to a locking mechanism for a racking assembly of a draw-out circuit breaker.

Background of the invention

The circuit breakers are generally placed inside an electrical switchboard panel (herein after ‘the panel’) having a door. While the breaker is in use that is while conducting current through main contacts or power contacts, the panel door should remain closed. To achieve this, a locking device that provides inter-latching between the panel door and the circuit breaker is used.

For a draw-out type of circuit breaker, additionally a chamber like unit known as a cradle arrangement is generally required. The draw out circuit breaker is supported on a rail assembly which is an integral part of the cradle arrangement. Through the cradle arrangement, current carrying parts of the circuit breaker get connected to the current carrying parts of the panel. The positions of the draw-out circuit breaker with respect to the cradle arrangement are normally defined as 'Disconnected/Isolated', 'Test' and 'Connected/ Service'.

The draw-out circuit breaker is racked-in and racked-out to and from the cradle arrangement. When the draw-out circuit breaker is completely racked-in to the 'Connected' position, breaker terminals come in contact with cradle terminals through cradle jaws. In this condition, both power (main) circuit and control circuit are connected and the draw-out circuit breaker can be switched ON. In the ‘Test’ position, control circuit contacts of the draw-out circuit breaker and the cradle arrangement get connected. In the 'Test’ position, the main circuit is not connected but the control circuit is connected. When the draw-out circuit breaker is completely racked out to the 'Disconnected' position, both the main circuit and the control circuit are disconnected. The draw-out circuit breaker can also be drawn out to a ‘Maintenance’ position where it can be lifted off the cradle arrangement for servicing and maintenance activities.

The prior art position indicating and locking devices take position input from either a power screw or a sliding rack threaded to the power screw of a racking assembly. The input component has slots corresponding to a switchgear locking location and at these particular points, an interacting component interlocks with the racking screw thus stopping racking movement thereof. However, the current methods based on the power screws and the rack positions have an inherent error built into their mechanisms as these take reference from components that are not true indicators of absolute position of the draw-out circuit breaker within the cradle arrangement.

Further, there exists a possibility that the reference component’s positions may differ in rack-in and rack-out operations and will result in backlash errors. Moreover, these locking mechanisms are complex and involve a vast number of cost intensive components. Reliability of these locking systems depends on a large number of variations and play-in intermediate components and dimensional inaccuracy since position input is not taken directly from the circuit breaker.

Accordingly, there is a need of a locking mechanism for a racking assembly of a draw-out circuit breaker that overcomes the above mentioned drawbacks of the prior art.
Objects of the invention

An object of the present invention is to provide multi position locking of a racking assembly of a cradle arrangement for a draw-out type circuit breaker (herein after ‘the circuit breaker’).

Another object of the present invention is to provide a direct indication of a breaker position depending on a breaker travel thereby eliminating any disparity between position indication locking and actual position of the circuit breaker within the cradle arrangement.

Yet another object of the present invention is to identify attainment of each distinct position without subjective difference in opinion of different operators while observing position indication.

Still another object of the present invention is to provide locking and acknowledgement to help user to control racking of the circuit breaker thereby leading to greater operation reliability thus avoiding under and over racking of the circuit breaker.

Still further object of the present invention is to provide position locking irrespective of a sequence of racking-in and racking-out operations thereby eradicating backlash error.

Summary of the invention

Accordingly, the present invention provides a locking mechanism for a racking assembly of a draw-out circuit breaker. The draw-out circuit breaker is mounted on a cradle arrangement through a bottom strip thereof for moving to any one of 'Disconnected’, 'Test' and 'Connected’ positions during a racking operation carried by the racking assembly. The racking assembly includes a racking support plate mounted on a base plate of the cradle arrangement, a racking screw assembled on the racking support plate and a sliding rack.

The locking mechanism comprises an input link, a position cam, a first spring, a transfer link, a second spring, an interlatch, a third spring, a lock link, a fourth spring, a transfer stud and a push button shaft.

The input link is rigidly fixed to the bottom strip for moving therewith during the racking operation to provide a position input of the draw-out circuit breaker. The position cam is slidably mounted on the racking support plate to remain in continuous positive contact with the input link to receive the position input of the draw-out circuit breaker therefrom.

The position cam includes at least three cam crests, at least two cam troughs and a cam rivet configured thereon. The at least three cam crests correspond to the 'Disconnected’, 'Test' and 'Connected’ positions of the draw-out circuit breaker. The position cam is mounted on the racking support plate by at least two position cam mounting screws threaded into the racking support plate and the cam rivet riveted onto the position cam. The first spring is fixed between the cam rivet and the base plate. The first spring is adapted to keep the position cam in continuous positive contact with the input link.

The transfer link is mounted on the racking support plate. The transfer link is capable of rotating to contact the position cam. The transfer link includes a top cam surface, a locking cam surface and a bottom cam surface configured thereon. The top cam surface is capable of being pressed by any one of the at least three cam crests and the at least two cam troughs. The second spring is fixed between the transfer link and the base plate. The second spring is adapted to bring the transfer link in contact with the position cam.

The interlatch is pivoted on a pivot screw on the racking support plate. The third spring is fixed between the interlatch and the base plate. The third spring is adapted to bias the interlatch upwards from the base plate. The transfer link and the interlatch are mounted rotatably on the racking support plate by the single pivot screw pivoted on the base plate.

The lock link is mounted on the racking support plate by at least two lock link mounting screws to traverse linearly thereon. The at least two lock link mounting screws include a lock nut fitted thereon. The lock link is capable of sliding over the lock nut for locking the racking screw of the racking assembly. The fourth spring is fixed between a lock link spring support and the lock link. The fourth spring is adapted to bias the lock link to slide over the lock nut.

The transfer stud is supported on the lock link. The transfer stud is capable of being locked / unlocked by any one of the interlatch and the locking cam surface depending on position of the bottom cam surface of the transfer link. The push button shaft is supported on the lock link. The push button shaft includes a push button snap fitted thereon for being pressed by a user for circumventing the locking of the racking screw.

Brief description of the drawings

The objectives and advantages of the present invention will become apparent from the following description read in accordance with the accompanying drawings wherein,

Figure 1 shows a cradle arrangement with a circuit breaker housing in a rail assembly, in accordance with the present invention;

Figure 2 shows an overview of a racking assembly of the cradle arrangement of figure 1;

Figure 3 shows the racking assembly with a locking mechanism in an acknowledged condition, in accordance with the present invention;

Figure 4 shows the racking assembly in a locked condition with the locking mechanism, in accordance with the present invention;

Figure 5 shows a detailed view of the locking mechanism, in accordance with the present invention;

Figure 6 shows an overview of the locking mechanism, in accordance with the present invention;

Figure 7 is a top view of the locking mechanism showing various springs thereof, in accordance with the present invention;

Figure 8 shows a side view of the locking mechanism in an intermediate position, in accordance with the present invention; and

Figure 9 shows the side view of the locking mechanism in a distinct position, in accordance with the present invention.

Detail description of the invention

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiment.

The present invention provides a locking mechanism for a racking assembly of a draw-out circuit breaker. The locking mechanism achieves multi position locking of the racking assembly of a cradle arrangement for the draw-out type circuit breakers by taking a position input from a breaker housing and locking a racking screw when distinct locking positions are attained. The locking mechanism is provided with a provision for a user circumvention thereby allowing the user to circumvent the locking by acknowledging this and pressing a push button thereby proceeding further with a racking operation.

The present invention is illustrated with reference to the accompanying drawings, wherein numbers indicated in the bracket represent the components of the invention throughout the description.

Referring now to figures 1 to 9, a locking mechanism (100) for a racking assembly (140) of a draw-out type of circuit breaker (200) in accordance with the present invention is shown. Specifically, the draw-out type of circuit breaker (200) (hereinafter ‘the circuit breaker (200)’) is an air circuit breaker. The circuit breaker (200) through a bottom strip (190) thereof is mounted on a cradle arrangement (not numbered). The bottom strip (190) is a lower portion of a breaker housing (not numbered). The circuit breaker (200) is movable between 'Disconnected/Isolated', 'Test' and 'Connected/ Service' positions with respect to the cradle arrangement in a racking operation thereof carried by the racking assembly (140).

The cradle arrangement includes a pair of side plates (110), a pair of rail assembly (120) (herein after ‘the rail assembly (120)’), a base plate (130), the racking assembly (140), a drop plate assembly (150) and a cam (160) as shown in figure 1. The cam (160) is fitted on a cam shaft (155). The cam shaft (155) includes a camshaft pinion (145) fitted thereon. In an embodiment, the cam (160) is welded on the cam shaft (155) and the cam shaft (155) includes the camshaft pinion (145) welded thereon. The pair of side plates (110) has flanges (not numbered) which guide and constrain the circuit breaker (200) and the rail assembly (120) allowing only a single degree of freedom to move to and fro within the cradle arrangement. The circuit breaker (200) is supported on guide ways such as the rail assembly (120). The rail assembly (120) includes slots (not numbered) for receiving projections (not shown) of a breaker housing thus facilitating the draw-out feature of the circuit breaker (200). The base plate (130) is bolted rigidly to the pair of side plates (110). The base plate (130) provides a base for mounting of the racking assembly (140).

The racking assembly (140) mounted on the base plate (130) is responsible for the racking operation of the circuit breaker (200). The input of the racking operation from the racking assembly (140) is taken and sent as an output by the cam shaft (155) having the cam (160) welded thereto. The cam (160) is linked to the circuit breaker (200) by means of the drop plate assembly (150). The drop plate assembly (150) is rigidly coupled to the rail assembly (120) by means of rivets (not shown).

The racking assembly (140) includes a detachable crank or a handle (not shown), a racking support plate (132), a racking screw (134) and a sliding rack (136) as shown in figure 2. The detachable crank rotates to cause the circuit breaker (200) to move in or out of the cradle arrangement. The rotation of the detachable crank in a clockwise direction causes a racking-in operation (‘Disconnected’ – ‘Test’ – ‘Connected’) and a counter-clockwise rotation thereof causes a racking-out operation (‘Connected’ – ‘Test’ – ‘Disconnected’) of the circuit breaker (200).

The racking support plate (132) is mounted on the base plate (130). The racking screw (134) is assembled on the racking support plate (132) and threaded into the sliding rack (136). The racking screw (134) is capable of rotating freely about an axis thereof upon application of an input torque thereto by a user to enable the racking operation of the breaker. The rotation of the racking screw (134) in the clockwise or anticlockwise directions causes the sliding rack (136) to rotate which otherwise is constrained by the base plate (130). The sliding rack (136) in turn imparts rotational motion to the cam shaft (155) by means of a rack and pinion arrangement (not numbered) with the camshaft pinion (145). Rotation of the cam shaft (155) causes the rotation of the cam (160) welded thereon. The drop plate assembly (150) being linked to the cam (160) is pushed/pulled depending on any one of the racking-in and racking-out operations. Eventually, the rail assembly (120) linked to the drop plate assembly (150) is also pulled/pushed. The circuit breaker (200) being mounted on the rail assembly (120) undergoes a change in the position thereof. When the circuit breaker (200) attains any one of the ‘Disconnected’, ‘Test’ and ‘Connected’ positions, the racking assembly (140) is locked by the locking mechanism (100).

The locking mechanism (100) comprises an input link (10), a position cam (20), a first spring (25), a transfer link (30), a second spring (35), an interlatch (40), a third spring (45), a lock link (60), a fourth spring (65), a transfer stud (70) and a push button shaft (80).

The input link (10) is mounted directly on the circuit breaker (200) to provide an accurate, absolute and true position input reference of the breaker position to the locking mechanism (100). Specifically, the input link (10) is a flat input link rigidly fixed to the bottom strip (190) of the circuit breaker (200) by means of screws (not shown). When the circuit breaker (200) and hence the bottom strip (190) moves to any one of the three distinct positions to and fro in the cradle arrangement upon the racking operation, the input link (10) also moves therewith to provide a position input of the circuit breaker (200) to the position cam (20) in response to the change in the position of the circuit breaker (200).

The position cam (20) is slidably mounted on the racking support plate (132) to remain in continuous positive contact with the input link (10). The position cam (20) is adapted to receive the position input of the circuit breaker (200) from the input link (10) when the circuit breaker (200) is racked in or racked out. The position cam (20) includes at least three cam crests (12), at least two cam troughs (14) and a cam rivet (16) configured on a surface (not numbered) thereof. The at least three cam crests (12) correspond to the three distinct positions: 'Disconnected’, 'Test' and 'Connected’ positions of the circuit breaker (200). In an embodiment, the position cam (20) is mounted on the racking support plate (132) by at least two position cam mounting screws (18) and the cam rivet (16). The at least two position cam mounting screws (18) are threaded into the racking support plate (132). The position cam (20) is free to slide upon and guided by the at least two position cam mounting screws (18). The cam rivet (16) is riveted on the position cam (20).

The first spring (25) is fixed between the cam rivet (16) of the position cam (20) and the base plate (130). The first spring (25) is adapted to keep the position cam (20) in continuous positive contact with the input link (10) such that the input link (10) provides the position input to the position cam (20) when the circuit breaker (200) is racked in or racked out.

The transfer link (30) mounted on the racking support plate (132). The transfer link (30) is capable of rotating to contact the position cam (20). The transfer link (30) includes a top cam surface (22), a locking cam surface (24) and a bottom cam surface (26) configured thereon. The top cam surface (22) is capable of being pressed by any one of the at least three cam crests (12) and the at least two cam troughs (14).

The second spring (35) is fixed between the transfer link (30) and the base plate (130). The second spring (35) is adapted to bring/bias the transfer link (30) to remain in contact with the position cam (20).

The interlatch (40) is pivoted on a pivot screw (36) on the racking support plate (132). Specifically, the transfer link (30) and the interlatch (40) are mounted rotably on the racking support plate (132) by the single pivot screw (36) pivoted on the base plate (130). Thus, the pivot screw (36) also acts as a pivot center for the interlatch (40). The interlatch (40) includes an interlatch rivet (38) fitted thereon. The interlatch rivet (38) and hence the interlatch (40) are capable of being operated by the bottom cam surface (26).

The third spring (45) is fixed between the interlatch (40) and the base plate (130). The third spring (45) is adapted to bias the interlatch (40) upwards from the base plate (130).

The lock link (60) is mounted on the racking support plate (132) of the racking assembly (140) and is free to traverse linearly thereon. Specifically, the lock link (60) is mounted on the racking support plate (132) with the help of at least two lock link mounting screws (55). The at least two lock link mounting screws (55) includes a lock nut (50) fitted thereon. The lock link (60) includes a slot (not shown) configured thereon which corresponds to the lock nut (50). In an embodiment, the lock nut (50) is a square lock nut which gets locked in a square slot on the lock link (60). The lock link (60) is biased toward and capable of being sliding over the lock nut (50) for locking the racking screw (134) of the racking assembly (140).

The fourth spring (65) is fixed between a lock link spring support (56) and the lock link (60). The fourth spring (65) is adapted to bias the lock link (60) to slide over the lock nut (50).

The lock link (60) also supports the transfer stud (70) and the push button shaft (80) thereon. The transfer stud (70) is capable of being locked / unlocked by any one of the interlatch (40) and the locking cam surface (24) depending on a position of the bottom cam surface (26) of the transfer link (30).

The push button shaft (80) includes a push button (75) fitted thereon. In an embodiment, the push button (75) is snap fitted on the push button shaft (80). The push button (75) is capable of being pressed by a user for circumventing the locking of the racking screw (134).

Referring again to figures 1-9, working of the locking mechanism (100) for a locking operation, a locking circumvent operation and an unlocking operation of the racking assembly (140) is described in accordance with the present invention.

Locking operation of the racking assembly (140):
When the circuit breaker (200) attains any one of the three distinct positions such as 'Disconnected’, 'Test' and 'Connected’ positions during the racking operation, the input link (10) being mounted on the bottom strip (190) provides the position input of the circuit breaker (200) to the position cam (20). The movement of the circuit breaker (200) due to the racking operation causes the input link (10) on the bottom strip (190) to move therewith. The movement of the input link (10) results in the movement of the position cam (20) on the racking support plate (132) such that one of the at least three cam crests (12) depending on the 'Disconnected’/ 'Test'/ 'Connected’ position presses the top cam surface (22) resulting in an anticlockwise rotation of the transfer link (30). This anticlockwise rotation of the transfer link (30) causes the locking cam surface (24) to leave/unlock the transfer stud (70) unrestricted for movement. As a result, the transfer stud (70) and thus the lock link (60) are biased/moved towards the lock nut (50) to slide thereon due to the fourth spring (65) thereby locking the racking screw (134) of the racking assembly (140) as shown in figure 9. Due to locking of the racking screw (134) of the racking assembly (140), any torque applied on the racking screw (134) is transferred from the lock nut (50) to the lock link (60) and then to the base plate (130) but not beyond the base plate (130) thereby preventing further racking operation of the circuit breaker (200).

Operation to circumvent the locking of the racking assembly (140):
The circuit breaker (200) locked in any one of the three distinct positions is acknowledged by the user visually by viewing popping out of the push button (75) from the base plate (130) and physically by sensing the locking of the racking screw (134). In order to continue the racking operation, the user has to circumvent the locking of the racking screw (134). For circumventing the locking of the racking assembly (140), the user presses the push button (75) to move the lock link (60) and hence the transfer stud (70) away from the lock nut (50) against the bias of the fourth spring (65) thereby circumventing the locking of the racking assembly (140). The third spring (45) causes the interlatch (40) to bias upwards from the base plate (130) for latching the transfer stud (70) when pushed back by the user. Therefore, the lock link (60) fails to move towards and relock the lock nut (50) in the same position thus allowing further racking operation. Thus, the interlatch (40) acts as an interlock for the lock link (60) thereby circumventing the locking of the racking assembly (140) and thus allowing further racking operation as shown in figure 3.

Unlocking operation of the racking assembly:
When the breaker is in any of the non distinct positions (when breaker position is neither ‘Connected’, ‘Test’ or ‘Disconnected’), the input link (10) moves the position cam (20) on the racking support plate (132) such that one of the at least two cam troughs (302) presses the top cam surface (22) resulting in a clockwise rotation of the transfer link (30). The clockwise rotation of the transfer link (30) causes the locking cam surface (24) to lock the transfer stud (70) restricting movement thereof and the bottom cam surface (26) to depress the interlatch rivet (35) for releasing the interlatch (40) from the transfer stud (70). The interlatch (24) is released in the non distinct position to allow locking of the racking assembly (140) when the distinct position is achieved. The lock link (60) due to the restricted transfer stud (70) remains away from the lock nut (50) thus keeping the racking assembly (140) unlocked for allowing/resuming the racking operation.

Advantages of the invention

• The locking mechanism (100) resolves the problem of difference between the actual breaker position within the cradle arrangement and the indicated locked breaker position by taking position input directly from the breaker housing and thus gives accurate visual indication and physical locking of the racking assembly (140) when each of the three distinct positions namely Connected, Test and Disconnected is reached.
• Since the position indication is directly dependent on the breaker travel, any disparity between position indication locking and actual position of the circuit breaker (200) is eliminated and attainment of each distinct position without subjective difference in opinion of different operators while observing position indication is easily identified. Thus, subjectivity in position indication is eradicated completely since distinct visual indication and physical locking provision is achieved at all distinct positions. Also, a need of constant observation of the existing visual continuous indication is avoided.
• The position cam (20) is mounted on the racking support plate (132) and the transfer of breaker movement takes place via the input link (10) mounted directly on the breaker housing. The breaker position is precisely and positively represented by the input link (10) which is responsible for the input given to position locking of the racking assembly (140). This gives absolute and true position input reference to the locking mechanism (100) and eliminates the possibility of error variance in locking positions arising due to play in intermediary components.
• Locking and acknowledgement helps the user to control racking of the circuit breaker (200) and leads to greater operation reliability. Under and over racking of the circuit breaker (200) is avoided which would otherwise result in overheating and damage to the breaker terminals and a cradle jaw assembly.
• The locking mechanism (100) is simple, reliable and accomplishes function using few parts that are cost effective and easy to manufacture, consisting mainly of flat sheet metal components.
• The locking mechanism (100) gives positive locking and negligible backlash error at multi distinct positions identified irrespective of the sequence of the racking in and racking-out operations.
• The locking mechanism (100) avoids the over stressing of the components of the racking assembly (140). The locking of the racking screw (134) of the racking assembly (140) takes place by the lock link (60) sliding over the lock nut (50) on the racking screw (134). Thus, any torque applied on the racking screw (134) is transferred to the lock link (60) and then to the base plate (130) thereby restricting further force transmission to linkages and thus safeguarding the racking assembly (140) from abuse.
• Ergonomic design constraints have been considered for user comfort.
• Users are able to circumvent the entire locking mechanism (100) by keeping the acknowledgement/push button (75) pressed during entire operation.
• The functional linkages, latches and locking arrangement combine to form an independent mechanism for position based locking, without actually affecting the normal functioning of the racking assembly (140) except in conditions of locking which is its primary objective.

The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiment. Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, or matter. The embodiments of the invention as described above and the methods disclosed herein will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the spirit and scope of the invention.
,CLAIMS:We claim:

1. A locking mechanism (100) for a racking assembly (140) of a draw-out
circuit breaker (200), the draw-out circuit breaker (200) mounted on a cradle arrangement through a bottom strip (190) thereof for moving to any one of 'Disconnected’, 'Test' and 'Connected’ positions during a racking operation carried by the racking assembly (140), the racking assembly (140) having a racking support plate (132) mounted on a base plate (130) of the cradle arrangement, a racking screw (134) assembled on the racking support plate (132) and a sliding rack (136), the locking mechanism (100) comprising:
• an input link (10) rigidly fixed to the bottom strip (190) for moving
therewith during the racking operation to provide a position input of the draw-out circuit breaker (200);
• a position cam (20) slidably mounted on the racking support plate (132) to
remain in continuous positive contact with the input link (10), the position cam (20) adapted to receive the position input of the draw-out circuit breaker (200) from the input link (10), the position cam (20) having,
at least three cam crests (12) configured thereon corresponding to the
'Disconnected’, 'Test' and 'Connected’ positions of the draw-out circuit breaker (200),
at least two cam troughs (14) configured thereon, and
a cam rivet (16) riveted thereon;
• a first spring (25) fixed between the cam rivet (16) and the base plate
(130), the first spring (25) adapted to keep the position cam (20) in continuous positive contact with the input link (10);
• a transfer link (30) mounted on the racking support plate (132), the transfer
link (33) being capable of rotating to contact the position cam (20), the transfer link (30) having,
a top cam surface (22) configured thereon for being pressed by any one
of the at least three cam crests (12) and the at least two cam troughs (14),
a locking cam surface (24) configured thereon, and
a bottom cam surface (26) configured thereon;
• a second spring (35) fixed between the transfer link (30) and the base plate
(130), the second spring (35) adapted to bring the transfer link (30) in contact with the position cam (20);
• an interlatch (40) pivoted on a pivot screw (36) on the racking support
plate (132),
• a third spring (45) fixed between the interlatch (40) and the base plate
(130), the third spring (45) adapted to bias the interlatch (40) upwards from the base plate (130);
• a lock link (60) mounted on the racking support plate (132) to traverse
linearly thereon, the lock link (60) being capable of sliding over a lock nut (50) for locking the racking screw (134) of the racking assembly (140);
• a fourth spring (65) fixed between a lock link spring support (56) and the
lock link (60), the fourth spring (65) adapted to bias the lock link (60) to slide over the lock nut (50);
• a transfer stud (70) supported on the lock link (60), the transfer stud (70)
capable of being locked/unlocked by any one of the interlatch (40) and the locking cam surface (24) depending on position of the bottom cam surface (26) of the transfer link (30); and
• a push button shaft (80) supported on the lock link (60), the push button
shaft (80) having a push button (75) snap fitted thereon for being pressed by a user for circumventing the locking of the racking screw (134).

2. The locking mechanism (100) as claimed in claim 1, wherein the position cam
(30) is mounted on the racking support plate (132) by at least two position cam mounting screws (18) threaded into the racking support plate (132) and the cam rivet (16) riveted onto the position cam (20).

3. The locking mechanism (100) as claimed in claim 1, wherein the transfer link
(30) and the interlatch (40) are mounted rotatably on the racking support plate (132) by the single pivot screw (36) pivoted on the base plate (130).

4. The locking mechanism (100) as claimed in claim 1, wherein the lock link
(60) is mounted on the racking support plate (132) by at least two lock link mounting screws (55).

5. The locking mechanism (100) as claimed in claim 1, wherein the lock nut
(50) is fitted on the at least two lock link mounting screws (55).