FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION [See section 10 and rule 13)
1. TITLE OF THE INVENTION:
Switching Mechanism for Residual Current Circuit Breakers
2. APPLICANT:
(a) NAME: Larsen & Toubro Limited
(b) NATIONALITY: Indian Company registered under the
provisions of the Companies Act-1956.
(c) ADDRESS: LARSEN & TOUBRO LIMITED,
L&T House, Ballard Estate, P. 0. Box: 278, Mumbai 400 001, India
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

Switching Mechanism for Residual Current Circuit Breakers
Field of the invention
The present invention relates to residual current circuit breakers, and more particularly, to a switching mechanism for latching in residual current circuit breakers.
Background of the invention
Generally, residual current circuit breakers [RCCB) are intended to protect persons against indirect contact, exposed conductive parts of the installation being connected to an appropriate earth electrode. Specifically, the RCCBs are used to provide protection against fire hazards due to a persistent earth fault current.
The RCCBs are available in two pole and four pole versions. They have a linkage mechanism to switch the RCCB ON/OFF. The same linkage mechanism has to ensure that breaking of contacts as the leakage current is sensed by the RCCB. As the tripping mechanism of the RCCB is very sensitive, it becomes necessary to ensure proper tripping operation accompanied by proper manual switching on/off the RCCB.
Generally, moving contacts of the RCCB have to simultaneously make contact with fixed contacts for all poles. This displacement is to be provided by the switching mechanism. However, irregularity or delay in making contact in individual poles may cause nuisance tripping after installation of the RCCB which causes de-latching phenomena of the RCCB which is not desirable.

Further, improper resetting of the tripping mechanism and a trigger (PMR) ( Permanent Magnet Relay) leads to non operation of the RCCB. Also, failure to operate the RCCB in turn makes the RCCB unusable.
Accordingly, there exists a need to provide a switching mechanism for RCCB which overcomes abovementioned drawbacks.
Object of the invention
An object of the present invention is to avoid irregularity in making contact in individual poles of the RCCB.
Another object of the present invention is to avoid improper resetting of the tripping mechanism.
Summary of the invention
Accordingly, the present invention provides a switching mechanism for a residual current circuit breaker. The switching mechanism comprises a lock lever, and a lever connected to the lock lever by a lever link. The lever includes a cam surface with sharp corners which overlaps and latches the lock lever. The lever link is connected to a knob of the residual current circuit breaker through a knob link.
Further, the switching mechanism comprises a spring member having one end engaged with arm of the lock lever for imparting a reverse effect and other end secured to the top plate of a housing of the residual current circuit breaker.

Furthermore, the switching mechanism comprises a reset lever for resetting a trigger (PMR) after every trip operation. The tripping force provided by the trigger (PMR) causes disengagement of the lock lever and the lever resulting in to tripping, wherein the reset lever is actuated by backward movement of a rotor link.
Also, the switching mechanism comprises a release lever for releasing the lock lever from latching position to free position after every trip operation. The reset lever and the release lever ensures proper resetting of the trigger (PMR) after every trip operation thereby having a consistent ON, OFF and TRIP operation of the residual current circuit breaker.
Brief description of the drawings
Figure 1 is shows an perspective view of a switching mechanism for residual current circuit breaker, in accordance with the present invention;
Figure 2 is shows a perspective view of latching components of the switching mechanism of figure 1 in ON position;
Figure 3a, 3b and 3c shows engagement of a lever with a surface of a lock lever of the switching mechanism of figure 1;
Figure 4 shows a spring member of the switching mechanism of figure 1; and
Figure 5 shows an assembly of the spring member in the switching mechanism of figure 1.

Detailed 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 switching mechanism for a residual current circuit breaker. The switching mechanism avoids irregularity in making contact in individual poles of the residual current circuit breaker (RCCB). Further, the switching mechanism avoids improper resetting of the tripping mechanism.
Residual current circuit breakers are installed in a circuit as per IS 12640-1/IEC 61008-1. The residual current circuit breakers perform ON/OFF AND TRIP operation with the help of a switching mechanism.
Generally, the switching mechanism is made up of combination of two "four bar linkage mechanism". The ON/OFF operation is achieved by fixing one link by means of a "latch" mechanism so as to constraint the motion in only one "4 bar mechanism" out of the two. Similarly, trip operation is performed by releasing the created latch in one of the "four bar linkage mechanism".
Referring to figure 1-6, there is shown a switching mechanism for residual current circuit breaker and various components thereof. Specifically, the figure 1 and 2 shows a switching mechanism (100). The switching mechanism (100)

includes a lock lever [10), a lever (20), a spring member (30), a reset lever (40), and a release lever (50).
The lock lever (10) is connected to the lever (20) by a lever link (22). The lever (20) includes cam surface which overlaps and latches the lock lever (10). In an embodiment, the lever (20) is a pressed part made out of stainless steel sheet. The lever link (22) is connected to a knob (60) of the residual current circuit breaker (RCCB) (not shown) through a knob link (62). The knob (60) and the knob link (62) forms links of the four bar chain mechanism of the RCCB.
The cam surface of the lever (20) has sharp corners at the latching area. Specifically, smooth and flat surface of the cam at latching area with the locking lever (10) ensures improved consistency in latching and tripping. Further, the sharp corner on the cam surface of lever (20) allows positive overlap and latching with the lock lever (10) which results in avoiding slipping tendencies which are profound if corner radius is present on the cam edge of the lever (20). Specifically, figure 3a, 3b, and 3c shows engagement of a lever with a surface of a lock lever of the switching mechanism of figure 1;
The spring member (30) includes one end engaged with arm of the lock lever (10) for imparting a reverse effect and other end secured to the top plate (70) of a housing of the RCCB. The spring member (30) ensures proper loading on all latching components by uniform loading of such components. Specifically, a left hand turn of the spring member (30) which is engaged with the arm of the lock lever (10) results into proper application of load on the lock lever (10). The spring member (30) is a wire form part made out of stainless steel material. Specifically, figure 5 shows a spring member (30) and figure 6 shows an assembly of the spring member (30) in the switching mechanism (100).

Further, the reset lever (40) resets a trigger (PMR) after every trip operation, wherein tripping force provided by the trigger (PMR] causes disengagement of the lock lever (10] and the lever (20) resulting in to tripping. Specifically, the reset lever is actuated by backward movement of a rotor link (80).
Specifically, the tripping force provided by the trigger (PMR) creates an imbalance in the latch and causes the disengagement of the lock lever (10) and the lever (20) resulting in to tripping of the mechanism.
The release lever (50) releases the lock lever (10) from the lever (20) from latching position to free position after every trip operation. The reset lever (40) and the release lever (50) ensures proper resetting of the trigger (PMR) after every trip operation thereby having a consistent ON, OFF and TRIP operation of the RCCB.
Advantages of the invention
1. The mechanism (100) ensures proper ON/OFF and TRIP operation of the RCCB.
2. The mechanism (10) provides right protection against leakage currents.
3. The mechanism (100) provides consistency in case of tripping at leakage current
4. The^echanism (100) ensures proper resetting of the PMR with the help of the reset lever and the release lever.
5. The mechanism (10) do not cause de-latching in RCCBs.

The foregoing object the invention is 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.

We Claim
1. A switching mechanism for a residual current circuit breaker, the switching mechanism comprising:
a lock lever;
a lever connected to the lock lever by a lever link, the lever having cam surface with sharp corners for overlapping and latching the lock lever,
a spring member having one end engaged with arm of the lock lever for imparting a reverse effect and other end secured to the top plate of a housing of the residual current circuit breaker,
a reset lever for resetting a trigger (PMR) after every trip operation, wherein tripping force provided by the trigger (PMR) causes disengagement of the lock lever and the lever resulting in to tripping, wherein the reset lever is actuated by backward movement of a rotor link; and
a release lever for releasing the lock lever from the lever after every trip operation,
wherein the reset lever and the release lever ensures proper resetting of the trigger (PMR) after every trip operation thereby having a consistent ON, OFF and TRIP operation of the residual current circuit breaker.
2. The switching mechanism of claim 1 wherein the lever link is connected to a knob of the residual current circuit breaker through a knob link.