FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13).
1. TITLE OF THE INVENTION:
"Interlocking Mechanism for Switching Devices"
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. O. 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.

Interlocking Mechanism for Switching Devices Field of the invention
The present invention relates to electrical switches and more particularly, to an interlocking mechanism for switching devices such as contactors.
Background of the invention
In the prior art, it is generally known that the current technology uses a mechanical interlock module that is mounted between switching devices to provide mechanical interlocking between two switching devices that connects different sources or loads. The switching devices and the mechanical interlock module are placed adjacent to each other so that they are assembled in close proximity.
Accordingly, there is a need for an interlocking mechanism for switching devices that enables users the flexibility in mounting the contactors at any distance apart from each other.
Objects of the invention
An object of the present invention is to provide mechanical interlocking between two switching devices that connect different sources or loads.
Another object of the present invention is to provide compact module that enables flexibility in mounting switching devices at any distance apart from each other.
Summary

Accordingly, the present invention provides an interlocking mechanism for two switching devices. The two switching devices for example, contactors include a first switching device and a second switching device. The interlocking mechanism comprises a first lever, a second lever, a first stopper, a second stopper, a first spring, a second spring, a first pin, a second pin and an extendable cable.
The first lever is engaged with a first bridge of the first switching device of the two switching devices. The second lever is engaged with a second bridge of the second switching device of the two switching devices. The levers include a tail portion and a cam profile. The levers are capable of undergoing clockwise rotation.
The first stopper is adapted to support the first lever on the first bridge and the second stopper is adapted to support the second lever on the second bridge. The stoppers define a slope profile. The first spring is capable of biasing the first lever and the second spring is capable of biasing the second lever. The first pin is pivoted to the first lever and the second pin is pivoted to the second lever. The extendable cable at one end is connected to the tail portion of the first lever and at another end is connected to the tail portion of the second lever.
When the first switching device receives an electrical supply, the first bridge along with the first stopper moves downward to cause the first lever to undergo clockwise rotation. The first lever rotates and pulls the extendable cable that in turn pulls the tail portion of the second lever and causes the second lever to undergo clockwise rotation. The cam profile of the rotating second lever slides below the second bridge and the second stopper locks the second bridge thereby preventing downward movement of the second bridge and thus preventing switching ON of the second switching device.

When the electrical supply to the first switching device stops/fails, the springs bring the levers back to original positions thereby causing the first bridge and the first stopper to regain the original positions.
Brief description of drawings
Other features as well as the advantages of the invention will be clear from the following description.
In the appended drawings:
Figure 1 shows a front view of an interlocking mechanism in a default state when switching devices are in OFF conditions, in accordance with the present invention;
Figure 2 shows a front view of the interlocking mechanism of figure 1 in an interlocking state; and
Figure 3 shows an exploded view of the interlocking 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 an interlocking mechanism for switching devices such as contactors. The interlocking mechanism is very compact and built into the switching devices. The interlocking mechanism provides mechanical interlocking between the two switching devices having different bridge travel

and further allows the mounting distance between the switching devices to be varied according to the convenience of users by using different cable sizes.
The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures.
Referring to figures 1-3, an interlocking mechanism/ module (100) for switching devices in accordance with the present invention is shown. Specifically, the mechanism/ module (100) (herein after referred to as 'the mechanism (100)') is used for interlocking two switching devices (not shown). The two switching devices include a first switching device (not shown) and a second switching device (not shown) that connect different sources or loads. The first switching device includes a first bridge (110A) and the second switching device includes a second bridge (HOB). In an embodiment, the switching devices are contactors used when changeover switching between sources and loads are required. However, it is understood that the mechanism (100) can be used for other suitable switching devices known in the art.
The mechanism (100) is assembled with the two switching devices when the switching devices are in OFF conditions. The assembling is done by using any suitable coupling means (not shown) known in the art. When both the switching devices are in OFF conditions, the mechanism (100) is in a default state as shown in figure 1. When any one of the first switching device and the second switching device of the two switching devices receives an electrical supply, the mechanism (100) enters in an interlocking state as shown in figure 2.
The mechanism (100) comprises a first lever (10A), a second lever (10B), a first stopper (20A), a second stopper (20B), a first spring (30A), a second spring (30B), a first pin (40A), a second pin (40B) and an extendable cable (50). The first lever (10A) is engaged with the first bridge (110A) of the first switching

device of the two switching devices. The second lever (10B) is engaged with the second bridge (HOB) of the second switching device of the two switching devices. The levers (10A, 10B) include a tail portion (not numbered) and a cam profile (not numbered). The levers (10A, 10B) are capable of undergoing clockwise rotation in response to the electrical supply in the switching devices. Specifically, the levers (10A, 10B) are hinged levers. However, it is understood that levers (10A, 10B) of other types known in the art can be used as well.
The first stopper (20A) is adapted to support the first lever (10A) on the first bridge (110A). The second stopper (20B) is adapted to support the second lever (10B) on the second bridge (HOB). The stoppers (20A, 20B) are designed in a way to define a slope profile. The first spring (30A) is capable of biasing the first lever (10A). The second spring (30B) is capable of biasing the second lever (10B). The first spring (30A) and the second spring (30B) are coiled on the first pin (40A) and on the second pin (40B) respectively. The first pin (40A) is pivoted to the first lever (10A). The second pin (40B) is pivoted to the second lever (10B).
The extendable cable (50) alternately referred as extendable clutch cable is connected between the first lever (10A) and the second lever (10B). Specifically, the extendable cable (50) at one end (not numbered) is connected to the tail portion of the first lever (10A) and at another end (not numbered) is connected to the tail portion of the second lever (10B). The extendable cable (50) is capable of being pulled in response to the rotation of any one of the first lever (10A) and the second lever (10B) thereby providing flexibility in mounting the two switching devices at any distance apart from each other.
The mechanism enters in the interlocking state when a coil (not shown) of the first switching device of the two switching devices receives the electrical supply. The electrical supply to the first switching devices causes the first bridge (110A) to move downward. In response to the downward movement of the first bridge

(110), the first stopper (20A) also moves downward. As the first lever (10A) is held in position by the first stopper (20A), the first lever (10A) starts rotating in clockwise direction in response to the downward movement. The first lever (10A) rotates and pulls the extendable cable (50). The extendable cable (50) in turn pulls the tail portion of the second lever (10B) causing the second lever (10B) to undergo clockwise rotation.
The second lever (10B) rotates and slides below the second bridge (\10B). Specifically, as the second lever (10B) rotates, the cam profile of the second lever (10B) slides below the second bridge (110B) and the second stopper (20B) locks the second bridge (HOB) to prevent downward movement of the second bridge (HOB) thereby preventing switching ON of the second switching device of the two switching devices.
The hinged levers (10A, 10B) with cam profiles are designed in such a manner that the second bridge (110B) never moves down even when a coil (not shown) of the second switching device is given the electrical supply, while the first switching device is still in ON condition. The slope profile of the stoppers (20A, 20B)) facilitates instantaneous locking of the bridges (110A, HOB) of the two switching devices.
When the electrical supply to the first switching device of the two switching devices stops/fails, the levers (10A, 10B) return back to original positions. The first lever (10A) is biased to the original position by the first spring (30A). The second lever (10B) is biased to the original position by the second spring (30B). As a result, the first bridge (110A) and the first stopper (20A) also move to the original positions.
Advantages of the invention

1. The mechanism (100) achieves mechanical interlocking between two switching devices having different bridge travel.
2. The mechanism (100) is very compact and allows the mounting distance between the switching devices to be varied according to the convenience of users by using different cable sizes.
3. Even if the switching devices are already mounted, the mechanism (100) is capable of being procured at a later date when the need arises and fitted on site with minimal labor or training.
4. The mechanism (100) is disengaged to disable the interlocking between the switching devices.
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.

We claim:
1. An interlocking mechanism (100) for two switching devices, the interlocking mechanism (100) comprising:
• a first lever (10A) and a second lever (10B), the first lever (10A) engaged with a first bridge (110A) of a first switching device of the two switching devices, the second lever (10B) engaged with a second bridge (HOB) of a second switching device of the two switching devices, the levers (10A, 10B) having a tail portion and a cam profile, the levers (10A, 10B) being capable of undergoing clockwise rotation;
• a first stopper (20A) and a second stopper (20B), the first stopper (20A) adapted to support the first lever (10A) on the first bridge (110A), the second stopper (20B) adapted to support the second lever (10B) on the second bridge (11 OB), the stoppers (20A, 20B) defining a slope profile;
• a first spring (30A) and a second spring (30B), the first spring (30A) being capable of biasing the first lever (10A), the second spring (30B) being capable of biasing the second lever (10B);
• a first pin (40A) and a second pin (40B), the first pin (40A) being pivoted to the first lever (10A), the second pin (40B) being pivoted to the second lever (10B); and
• an extendable cable (50) having one end connected to the tail portion of the first lever (10A) and another end connected to the tail portion of the second lever (10B);
wherein, when the first switching device receives an electrical supply, the first bridge (110A) along with the first stopper (20A) moves downward causing the first lever (10A) to undergo clockwise rotation and to pull the extendable cable (50) that in turn pulls the tail portion of the second lever (10A) and causes the second lever (10B) to undergo clockwise rotation, the cam profile of the rotating second lever (10B) slides below the second bridge (110B) and the second stopper (20B) locks the second bridge (HOB) thereby preventing

downward movement of the second bridge (HOB) and thus preventing switching ON of the second switching device, and when the electrical supply to the first switching device stops/fails, the springs (30A, 30B) bring the levers (10A, 10B) back to original positions thereby causing the first bridge (110A) and the first stopper (20A) to regain the original positions.
2. The interlocking mechanism (100) for switching devices as claimed in claim 1, wherein the first lever (10A) and the second lever (10B) are hinged levers.
3. The interlocking mechanism (100) for switching devices as claimed in claim 1, wherein the switching devices are contactors.