FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION:
CIRCUIT BREAKER MECHANISM TO RESTRICT CHANGE IN
KNOB POSITION
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai, 400 001, Maharashtra . INDIA.
PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

A) TECHNICAL FIELD
[0001 ] The present invention generally relates to electrical power supply
and switching devices. Particularly the present invention relates to miniature circuit breakers, residual current circuit breaker and isolators. More particularly the present invention provides a mechanism to restrict the movement of knob from ON to OFF position, when current carrying contacts of the circuit breaker are welded.
B) BACKGROUND OF THE INVENTION
[0002] Generally the circuit breakers designed for residential and light
commercial applications are referred to as miniature circuit breakers. The miniature circuit breakers have pole mechanisms which include separable contacts, a spring powered operating mechanism with a handle for manually opening and closing of the separable contacts and a trip assembly for automatically opening the separable contacts. The trip assembly includes a bimetal providing a thermal or delayed trip in response to a persistent over current condition, and a magnetic armature providing a magnetic or instantaneous trip in response to a higher level of over current condition.
[0003] When the contacts of the circuit breaker are welded in a scheme, the
circuit breaker limits damage to the hand lever and to the circuit breaker during the movement of the hand lever to OFF position and prevents electrical arcing during the rotation of the hand lever. However, the scheme limits the maximum force that the circuit breaker withstands when the operator tries with a lot of force to separate the contacts by applying a large rotational torque on the hand lever. Moreover the circuit breaker fails to indicate the position of the hand lever irrespective of whether the circuit breaker is ON or OFF.
[0004] Yet another scheme calibrates the circuit breaker in assembled state.
However when a person accidentally or forcefully tries to switch the circuit
2

breaker to OFF position in this mechanism, the knob of the circuit breaker will not come back to original ON position even during the application of thrice the amount of torque to the knob. Moreover the mechanism doesn't provide true indication of the operating condition of current carrying contacts of the circuit breaker such as ON or OFF condition of the circuit breaker. Further the circuit breaker requires an additional indication window for displaying the true operating condition / status of the circuit breaker. Moreover the circuit breaker is operated by a motor operator or an external mechanical means in some installations to move the operating handle of the circuit breaker to OFF position forcefully even though the contacts are welded.
[0005] In light of the foregoing discussion, there exists a need to provide a
circuit breaker with a mechanism to restrict a user to change knob position from ON position to OFF position despite the enforcement of thrice the amount of torque on the knob, when current carrying contacts of the circuit breaker are welded. Also there exists a need to provide the circuit breaker with compact design which is used in full or half module width (17.5mm) space. Further, there exists a need to provide the circuit breaker without a separate indicator to indicate the true status of the circuit breaker, such as ON or OFF status. Moreover, there exists a need to provide the circuit breaker with few linkages resulting in less operating time of the circuit breaker.
[0006] The above mentioned shortcomings, disadvantages and problems are
addressed herein and which will be understood by reading and studying the following specification.
C) OBJECT OF THE INVENTION
[0007] These and other objects and advantages of the present invention will
become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
3

[0008] The primary object of the invention is to develop a miniature circuit
breaker with a mechanism to restrict a user to change knob position from ON position to OFF position despite the enforcement of three times the amount of torque on the knob, when current carrying contacts of the circuit breaker are welded.
[0009] Another object of the invention is to develop a miniature circuit
breaker with a mechanism to restrict change in knob position, to make the knob to go back to its original ON position, when the applied force with thrice the amount of torque on the knob, is released by a user.
[0010] Yet another object of the invention is to develop a miniature circuit
breaker with a mechanism to restrict change in knob position, and to provide a true indication of the operating status of the circuit breaker thereby eliminating the need for a separate indicator to exhibit the true operating condition of the circuit breaker.
[0011] Yet another object of the invention is to develop a miniature circuit
breaker with a mechanism to restrict the change in knob position, with compact design which is used in one full or half module width (17.5mm) space.
[0012] Yet another object of the invention is to develop a miniature circuit
breaker with a mechanism to restrict the change in knob position, with few linkages resulting in quick operation of the circuit breaker.
D) SUMMARY OF THE INVENTION
[0013] The various embodiments of the present invention provide a
miniature circuit breaker mechanism to restrict a user to change knob position from ON position to OFF position despite the enforcement of thrice the amount of torque on the knob, when current carrying contacts of the circuit breaker are welded.
4

[0014] According to one embodiment of the present invention, a circuit
breaker device is provided with a moving contact, a fixed contact and an operating knob. A piston and carrier assembly is connected to the operating knob. A compression spring is provided in the piston and carrier assembly. The piston and carrier assembly restricts the movement of the operating knob from ON position to OFF position, when the moving contact and the fixed contact are welded and a preset operating torque is applied.
[0015] The piston and carrier assembly is connected to the operating knob
through a U-shaped pin. The piston and carrier assembly has a piston connected to the operating knob through the pin. The carrier is connected to the piston through the compression spring. The piston and carrier assembly restricts the movement of the operating knob to OFF position from ON position as the operating knob is pulled by the compression spring in a direction which is opposite to the direction of application of the operating force, when the moving contact and the fixed contact are welded and a preset operating torque is applied. The preset operating torque is equals to three times the normal operating torque level.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The other objects, features and advantages will occur to those skilled
in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0017] FIG. 1 is a front sectional view of a circuit breaker in ON condition
according to one embodiment of the present invention.
[0018] FIG. 2 is a front sectional view of a circuit breaker in OFF condition
according to one embodiment of the present invention.
5

[0019] FIG. 3 is a side perspective view of the assembly of mechanism for
restricting the change in position of the operating knob in a circuit breaker according to one embodiment of the present invention.
[0020] FIG. 4 is an exploded perspective view of the assembly of
mechanism for restricting the change in position of the operating knob in a circuit breaker according to one embodiment of the present invention.
[0021] Although specific features of the present invention are shown in
some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[0022] In the following detailed description, reference is made to the
accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0023] The various embodiments of the present invention provide a
miniature circuit breaker with a mechanism to restrict a user to change knob position from ON position to OFF position despite the enforcement of thrice amount of torque on the knob, when current carrying contacts of the circuit breaker are welded.
6

[0024] According to one embodiment of the present invention, a circuit
breaker device is provided with a moving contact, a fixed contact and an operating knob. A piston and carrier assembly is connected to the operating knob. A compression spring is provided in the piston and carrier assembly. The piston and carrier assembly restricts the movement of the operating knob from ON position to OFF position, when the moving contact and the fixed contact are welded and a preset operating torque is applied.
[0025] The piston and carrier assembly is connected to the operating knob
through a U-shaped pin. The piston and carrier assembly has a piston connected to the operating knob through the pin. The carrier is connected to the piston through the compression spring. The piston and carrier assembly restricts the movement of the operating knob to OFF position from ON position as the operating knob is pulled by the compression spring in a direction which is opposite to the direction of application of the operating force, when the moving contact and the fixed contact are welded and a preset operating torque is applied. The preset operating torque is equals to three times the normal operating torque level.
[0026] FIG. 1 is a front sectional view of a circuit breaker in ON condition
according to one embodiment of the present invention. With respect to FIG. 1, a knob 1 is connected to a U-pin 2. The U-pin 2 is in turn connected to a piston 3. The piston 3 is further connected to a carrier 4 through a compression spring. When the knob 1 is rotated, the rotational motion from the knob 1 is transferred to the piston 3 through the U-pin2. The fixed and moving current carrying contacts associated with the circuit breaker are welded. During the normal operation of circuit breaker in ON condition, when the current carrying contacts of the circuit breaker are welded and further when a user accidentally or forcefully tries to switch the circuit breaker from ON to OFF condition, the knob 1 restricts the torque enforced by the user. Despite the enforcement of thrice the amount of torque on the knob 1 to switch the circuit breaker from ON to OFF condition, movement of the knob 1 is restricted. Further the enforcement of thrice the amount
7

of operating torque on the knob 1 will not let the circuit breaker go OFF and knob 1 to come to OFF position. Hence following the enforcement of thrice the amount of torque on the knob 1, the knob 1 remains in ON position and the circuit breaker remains in ON condition.
[0027] FIG. 2 is a front sectional view of a circuit breaker in OFF condition
according to one embodiment of the present invention. With respect to FIG. 2, a knob 1 is connected to a U-pin 2. The U-pin 2 is in turn connected to a piston 3. The piston 3 is further connected to a carrier 4 by a compression spring. When the knob 1 is rotated, the rotational motion from the knob 1 is transferred from the knob 1 to the piston 3 through the U-pin2. The fixed and moving contacts associated with the circuit breaker are welded. During the normal switching operation of the circuit breaker from ON to OFF condition or from OFF to ON condition when a fault current and voltage is detected in the circuit breaker the circuit breaker is tripped and goes to OFF condition and the knob 1 remains in OFF position.
[0028] FIG. 3 is a side perspective view of the assembly of the mechanism
for restricting the change in position of the operating knob in of a circuit breaker according to one embodiment of the present invention. With respect to FIG. 3, a knob 1 is connected to a U-pin 2. The U-pin 2 is in turn connected to a piston 3. The piston 3 is further connected to a carrier 4 by a compression spring. The assembly includes the piston 3 and the carrier 4 which has the compression spring inserted into the assembly. When the knob 1 is rotated, rotational motion from the knob 1 is transferred from the knob 1 to the piston 3 through the U-pin2. The Fixed and the moving current carrying contacts associated with the circuit breaker are welded. During the normal operation of the circuit breaker in ON condition, when the current carrying contacts of the circuit breaker are welded and further when a user accidentally or forcefully tries to switch the circuit breaker from ON to OFF condition, the knob 1 restricts the torque enforced by the user. Despite the enforcement of thrice the amount of torque on the knob 1 to switch the circuit
8

breaker from ON to OFF condition, movement of the knob 1 is restricted. Further, enforcement of thrice the amount of operating torque on the knob 1 will not let the circuit breaker go to OFF and knob 1 to come to OFF position. Hence, following the enforcement of thrice the amount of torque on the knob 1, the knob 1 remains in ON position and the circuit breaker remains in ON condition.
[0029] When the Fixed and moving current carrying contacts associated
with the circuit breaker are welded, movement of the knob 1 is restricted while switching the circuit breaker knob 1 from ON to OFF position. The compression spring provided in the assembly of the piston 3 and the carrier 4 facilitates restriction in movement of the knob 1, despite the enforcement of thrice the amount of torque on the knob 1. When the user tries to pull the knob 1 towards OFF position, the knob 1 is pulled by the compression spring in opposite direction of enforced torque, and hence the circuit breaker remains in ON condition. Further, following the release of the enforced torque, the knob 1 is pulled back to its original ON position indicating true operating condition of the circuit breaker. Hence, despite the enforcement of thrice the amount of torque on the knob 1, to switch the circuit breaker OFF the circuit breaker remains in ON condition and the knob 1 remains in ON position.
[0030] FIG. 4 is an exploded perspective view of the assembly of
mechanism for restricting the change in position of the operating knob in a circuit breaker according to one embodiment of the present invention. The FIG. 4 shows a knob 1, a U-pin 2 which is used to connect to the knob 1. The exploded view is also provided with an assembly the assembly includes a piston 3 and a carrier 4. The piston 3 and the carrier assembly 4 has a compression spring inserted into the assembly which connects the piston 3 and the carrier 4. The compression spring provided in the assembly of the piston 3 and the carrier 4 facilitates restriction in movement of the knob 1, despite enforcement of thrice the amount of torque on the knob 1. The knob 1 is pulled by the compression spring in opposite direction of when torque is enforced on the knob 1.
9

G) ADVANTAGES OF THE INVENTION
[0031 ] Thus the various embodiments of the present invention provide a
miniature circuit breaker with a compact mechanism to restrict a user to change knob position when current carrying contacts of the circuit breaker are welded. The mechanism restricts movement of the knob to OFF position by a user despite enforcing thrice amount of torque on the knob. The circuit breaker mechanism provides a cost effective means to restrict a user to change the knob position when current carrying contacts of the circuit breaker are welded. The circuit breaker makes the knob go back to its original ON position when applied torque is released by the user. The circuit breaker also provides true indication of operating condition status of the circuit breaker, which is either ON or OFF status without need for a separate indicator to indicate the true status of the circuit breaker. The circuit breaker is compact in design which is used in one OR half module width (17.5mm) space. Operation of the circuit breaker takes less time due to fewer linkages provided in the circuit breaker.
[0032] Although the invention is described with various specific
embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0033] It is also to be understood that the following claims are intended to
cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.
Place: Bangalore RAKESH PRABHU
Date: 31 July 2009 Patent Asent
10

CLAIMS
What is claimed is:
1. A circuit breaker device with mechanism to restrict change in knob position
comprising:
A moving contact;
A fixed contact;
An operating knob;
A piston and carrier assembly connected to the operating knob; and
A compression spring provided in the piston and carrier assembly;
Wherein the piston and carrier assembly restricts the movement of the
operating knob from ON position to OFF position, when the moving contact
and the fixed contact are welded and a preset operating torque is applied.
2. The device according to claim 1, wherein the piston and carrier assembly is connected to the operating knob through a pin.
3. The device according to claim 1, wherein the pin is a U-shaped pin.
4. The device according to claim 1, wherein the piston carrier assembly has a piston connected to the operating knob through the pin.
5. The device according to claim 1, wherein the carrier is connected to the piston through the compression spring.
6. The device according to claim 1, wherein the piston and carrier assembly
restricts the movement of the operating knob to OFF position from ON
position as the operating knob is pulled by the compression spring in a
direction which is opposite to the direction of application of the operating
force, when the moving contact and the fixed contact are welded and a preset
operating torque is applied.
11

7. The device according to claim 1, wherein the preset operating torque is equals to three times the normal operating torque level.

RAKESH PRABHU Patent Agent,
ALMT Legal,
#2, Lavelle Road, Bangalore-560 001
To,
The Controller of Patents, The Patent Office, Mumbai
12