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

Junction Box for Interlocking Three Circuit Breakers
Field of the invention
The present invention generally to interlocking mechanism for circuit breakers, and more particularly, to a junction box for interlocking multiple circuit breakers using bowden cables.
Background of the invention
Restricting operation of circuit breakers is common to prevent unintended operation of individual interlocked circuit breakers which result in catastrophic effects. Limiting of the circuit breaker operation from OFF to ON, is desirable in situations where multiple power sources are used to supply power to a limited number of energy consuming devices.
For example, two power sources SI, S2 are used to power a load L at two different conditions, i.e., the power supply from distribution line, and the power from the diesel generator as shown in Figure 1. Generally, the load L should be powered by any one of the power sources S1 and S2 at any time. Therefore, any one of the circuit breakers A and B will be allowed to close at any instant. If both of them are closed at the same time, dead shot of S1 and S2 occurs. So if SI is active, say power is provided by EB, A is closed and B is in open. If S1 fails, EB turns off and diesel generator powers the unit. Now, A is opened and B is allowed to close. This explains the necessity of having mechanical interlock in places where two separate power sources are used to give input to same load.
Some critical loads need more than one backup power supply. Accordingly, an interlocking system is required, which allows only one circuit breaker to be in on switched "ON" out of the three connected circuit breakers.

For example, for a load normally supplied with supply EB and having two backup supplies as shown in figure 2: If supply EB fails, S2 should be switched ON; if supply S2 also fails, S3 should be switched ON. Accordingly, there is a need for an interlock system which allows only one circuit breaker in "ON" state at any time.
In the foregoing paragraph, necessity of interlocking system that allows only one breaker ON is explained with an example of a system involving two circuit breakers. Now, in the following paragraph, the special case of interlocking of three circuit breakers is explained.
To better understand the necessity of interlocking three circuit breakers, refer to figure 3, which is a typical case in many of the industries. Here, two sources S1. S2 are used to power two loads LI, L2.
The loads L1, L2 are powered separately with two sources S1, S2, via 'A', 'B; respectively. At this state 'C should not be able to move to "ON" position; otherwise dead shot of S1, S2 will happen. If source S1 is sufficient to power the loads Ll and L2, the circuit breakers A and C are switched ON. Now switching ON the third circuit breaker 'B' should be restricted to avoid dead shot if S2 is live. From this the necessity of interlocking three breakers is clearly understood.
There are various types of mechanical interlock available for circuit breakers. Specifically, walking beam type interlock is applicable for only two circuit breakers, out of which only one circuit breaker is ON at any time. The walking beam type interlock includes a pivoting rocker arm and a linkage assembly associated with each circuit breaker. The walking beam type interlocking enables only mounting of breakers in a fixed prescribed distance.

Another type of interlocking of switching devices is by using sliding bar arrangement fitted on the circuit breaker. The sliding bar arrangement prevents simultaneous closing of two circuit breakers by arresting motion of operating knobs of the interlocked breakers.
Further, the circuit breakers interlock using key locks is also available. In yet another type of interlock for circuit breakers, a cable type interlock system is used if there is a need for variable distance between the switching devices. For interlocking more than two circuit breakers, usually a sliding bar setup or key locking is used.
US Patent No. 5814777 discloses a cable interlock system for preventing at least two circuit breakers from being closed at the same time. The system comprises a first circuit breaker having a first operating handle, wherein the first operating handle is adapted to close or open the first circuit breaker, a second circuit breaker having a second operating handle, wherein the second operating handle is adapted to close or open the second circuit breaker, a first mounting bracket that is attached or secured to or otherwise associated with the first circuit breaker, a first lever arm movably attached or secured to or otherwise associated with the first mounting bracket, a second mounting bracket that is attached or secured to or otherwise associated with the second circuit breaker, a second lever arm movably attached or secured to or otherwise associated with the second mounting bracket, a cable assembly having one end adapted to be connected to the first lever arm of the first mounting bracket and having another end adapted to be connected to the second lever arm of the second mounting bracket, wherein said cable assembly and the first lever arm and the second lever arm operate together so as to prevent the first operating handle and the second operating handle from both being in the closed position.
Another US Patent No. 5726401 discloses a cable interlock system is provided for preventing at least two circuit breakers from both being closed. The system

comprises a first circuit breaker assembly comprising a first main contact, a first cross bar, a first cross bar plunger, a first transfer assembly and a first operating handle, wherein the first operating handle is adapted to close or open the first circuit breaker assembly, and wherein the first cross bar plunger is adapted to contact the first cross bar, and wherein the first transfer assembly is adapted to move the first cross bar plunger; a second circuit breaker assembly comprising a second main contact, a second cross bar, a second cross bar plunger, a second transfer assembly and a second operating handle, wherein the second operating handle is adapted to close or open the second, circuit breaker assembly, and wherein the second cross bar plunger is adapted to contact the second cross bar, and wherein the second transfer assembly is adapted to move the second cross bar plunger; a cable assembly having one end adapted for association with the first transfer assembly and having another end adapted for association with the second transfer assembly, wherein the one end of the cable assembly and the first transfer assembly cooperate with the first cross bar and the first cross bar plunger, and the another end of the cable assembly and the second transfer assembly cooperate with the second cross bar and the second cross bar plunger so as to prevent the first main contact and the second main contact from both being closed.
Yet another US Patent 4827089 discloses a moulded case circuit breakers connected to two different sources of power within an industrial application are interlocked to prevent one circuit breaker from being turned on while the other circuit breaker is already on. The circuit breakers include a moulded plastic crossbar arranged for rotation within the circuit breaker enclosure. The interlock arrangement consists of a pivoted bell crank assembly including a pair of pivotally mounted insulative posts on either end of the bell crank. A corresponding cam integrally formed on the circuit breaker crossbar is in interference with one of the upstanding posts when the circuit breaker is in the "OFF" position and is out of interference with the upstanding post when the circuit breaker is in its "ON" condition.

Still another US Patent 6060668 discloses set of switches mutual locking devices, comprising switches with actuator toggles and locking elements, each of the switches having a rocker supported by an elastic element and having Bowden type cables to be connected to the two arms of the rockers, the free end of a first cable of a switch being operationally connected to elements of actuation of a second switch and the free end of a second cable being operationally connected to the elements of actuation of a third switch, and the rockers being loaded at their ends to come into operational contact with the locking elements.
One more US patent 6225581 discloses an installation comprises at least one electrical switchgear apparatus a movable mechanism which is interlocked with a device such as an access door by a kinematic transmission cable comprising a flexible sheath and a core designed to slide in the sheath. The ends of the sheath and of the core are respectively fixed to a fixed part of the apparatus and to the movable mechanism by fixing apparatus comprising an end-piece operating in conjunction with the corresponding part of the cable, a housing designed to receive the end-piece, and a locking device with dead point passage designed to oppose insertion of the end-piece in the housing when the force exerted on the locking device in an insertion direction remains lower than an insertion threshold and to enable insertion of the end-piece in the housing when the force exerted on the device means in an insertion direction is greater than the insertion threshold.
Deficiencies of the prior art
1. With existing interlocking system, degree of flexibility is reduced. Specifically, existing walking beam and sliding bar concepts doesn't allow the flexible mounting of the circuit breakers.

2. Interlocking three inputs (circuit breakers) is not possible in walking beam
type of arrangement.
3. Interlocking three circuit breakers using sliding bar setup doesn't allow
variable combinations of interlocking.
4. Conventional interlocking system uses complex technologies for interlocking
three breakers.
5. Existing interlock kit for interlocking two breakers can't be adopted for
interlocking three circuit breakers.
6. Existing cable type interlocking for three breakers is usually mounted at sides
of the circuit breaker thereby taking up more space for mounting.
7. Mechanism located at the sides of circuit breaker makes flush mounting
impossible.
8. The number of cables used for interlocking three breakers is more and increases confusion.
9. Complex arrangement of components for achieving interlocking of three inputs (Circuit breakers).
10. Variable combinations of interlocking are not achievable.
Accordingly, there exists a need to provide a interlocking mechanism for multiple circuit breakers which overcomes the drawbacks of the prior art.
Objects of the invention
An object of the present invention is to provide interlocking three inputs (circuit breakers).
Another object of the present invention is simple technology for interlocking the circuit breakers.
Yet another object of the present invention is to provide variable combinations of circuit breaker interlocking.

Summary of the invention
Accordingly, the present invention provides a junction box for interlocking multiple circuit breakers. The junction box comprises a first plate member having at least three flanges attached to a base thereof. Each flange includes an opening configured thereon. Further, the junction box comprises a second plate member capable of being secured over the first plate member, and a plurality of links. Each link of the plurality of link includes an oblong slot configured at one end thereof. The plurality of links hinged at a centre of the first plate member. Specifically, the plurality of links forms at least three pairs of link and each link of each pair of links is configured with other link of the pair such that the slots of the two links of the pair of links correspond each other. Furthermore, the junction box comprises at least three bowden cables capable of passing through the opening of the three flanges. Each bowden cable of the three bowden cables includes one end coupled to each circuit breaker of the multiple circuit breakers and other end with a cable head is secured in the oblong slots of the pair of links. Wherein, when any one circuit breakers of the multiple circuit breakers is ON, the bowden cable attached thereto using the motion signal from the circuit breakers pulls the cable head thereby sliding within the oblong slots provided in the corresponding pair of link in which the cable head is secured, which then pulls the other pair of links towards the direction of pull thereby pulling the other bowden cables in other two pair of links inwards to the maximum thereby blocking the other circuit breakers of the three circuit breakers from switching to ON position/from getting closed.
Brief description of the drawings
Figure 1 shows schematic drawing of interlocking concept for two circuit breakers;

Figure 2 shows schematic drawing of interlocking concept for three circuit breakers;
Figure 3 shows schematic drawing of another interlocking concept for three circuit breakers;
Figure 4 shows an exploded view of a junction box for interlocking multiple circuit breakers, in accordance with the present invention;
Figure 5 shows an assembled view of a junction box for interlocking multiple circuit breakers, in accordance with the present invention;
Figure 6 shows arrangement of all components in the junction box of figure 5.
Figure 7 shows a front view of the junction box with all circuit breakers in OFF position;
Figure 8 shows the junction box when one circuit breaker is switched ON;
Figure 9 shows a front view of the junction box when one circuit breaker is in ON position;
Figure 10 shows the junction box when two circuit breakers are switched ON; and
Figure 11 shows a front view of the junction box when two circuit breakers.
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 embodiments.
The present invention provides a junction box for interlocking multiple circuit breakers. The junction box provides a simple technology for interlocking three circuit breakers. Further, the junction box provides variable combinations of circuit breaker interlocking.
Referring now to figures 4 to 11, various views of a junction box for interlocking multiple circuit breakers are shown. Specifically, figure 4 shows an exploded view of a junction box (100) for interlocking multiple circuit breakers, in accordance with the present invention. For the purpose of explanation interlocking of three circuit breakers is described. The junction box (100) includes a first plate member (10). a second plate member (20), a plurality of links (30) and at least three bowden cables (40).
The first plate member (10) includes at least three flanges (12a, 12b and 12c) attached to a base thereof. Further, each flange (12a, 12b and 12c) includes an opening (not numbered) configured thereon. The first plate (10) is capable of being covered by the second plate member (20). Specifically, the second plate member (20) is capable of being secured over the first plate member (10) such that the first plate member (10) and second plate member (20) forms a box like structure. More specifically, the first plate member (10) and second plate member (20) are blanked and then bent.
The first plate (10) includes protrusions (14) on the base thereof and the second plate member (20) includes matching profiles (22) thereon for screwing the box like structure formed by the first plate member (10) and the second plate member (20) onto the panel board. The box like structure formed by the first plate member (10) and the second plate member (20) also functions to house all

the interlocking components, protecting them from external disturbances. The first plate member (10) includes plurality of links (30) positioned thereon. For the purpose of explanation six links (32a. 32b, 32c, 32d. 34e and 34f) (alternatively referred to as 'the link assembly') are shown. The link assembly (32a, 32b, 32c, 32d, 34e and 34f) is the main component of the interlocking assembly which is made of sheet metal components made by simple blanking.
Each link of the link assembly (32a, 32b, 32c, 32d, 34e and 34f) includes a oblong slot (34a, 34b, 34c, 34d, 34e, 34f) configured at one end thereof and other end of each link (32a, 32b, 32c, 32d, 34e and 34f) includes an opening for hinging the links (32a, 32b, 32c, 32d, 34e and 34f) at a centre of the first plate member (10) such that the links (32a, 32b, 32c, 32d, 34e and 34f) forms three pairs of link. For example, the links (32a and 32d) form a first pair of link, the links (32b and 32e) forms a second pair of link and the link (32c and 32f) forms a third pair of link. The hinging of pair of links in the centre of the first plate (10) is achieved by using a centre pin (38) which is a machined component. Specifically, each link of the each pair of links configured with other link of the pair such that the oblong slots of the two links of the pair of links correspond each other. Each pair of links is capable of receiving head of the bowden cable (40) in the oblong slots thereof. For the purpose of explanation, three bowden cable (40a, 40b and 40c) are shown. For example, the first pair of link (32a and 32d) receives a cable head (42a) of the bowden cable (40a), the second pair of link (32b and 32e) receives a cable head (42b) of the bowden cable (40b), and the third pair of link (32c and 32f) receives a cable head (42c) of the bowden cable (40c).
Each opening on the flanges (12a, 12b and 12c) of the first plate member (10) carries one bowden cable of the three bowden cable (40a, 40b and 40c) therethrough respectively. The bowden cable (40a, 40b, 40c) is a type of flexible cable used to transmit mechanical force or energy by the movement of an inner cable made of steel or stainless steel relative to hollow outer cable housing. The

housing is generally of composite construction, consisting of a helical steel wire, often lined with plastic, and with a plastic outer sheath. The bowden cable (40a, 40b, 40c) includes threads and lock nuts (not shown) as fixing means for securing to the first plate member (10).
One end of the bowden cable (40a, 40b, 40c) is anchored at the respective circuit breaker out of three circuit breakers and the other end of the bowden cable (40a, 40b, 40c) having respective a cable head is secured in the oblong slots of the respective pair of links. The bowden cable (40a, 40b, 40c) is attached to the first plate member (10) using threads and lock nuts. Further, the bowden cable (40a, 40b, 40c) which bring the input for interlocking are hinged at the three flanges (12a, 12b and 12c) of the first plate member (10). Once the respective cable heads of the bowden cable (40a, 40b, 40c) are aligned in the oblongs slots in the three pairs of link, then the second plate member (20) is placed on the first plate member (10) and assembled to complete the installation procedures.
The entire assembly of the first plate member (10) with second plate member (20) is fixed on to the panel board as per positions specified by the customer. Specifically, the bowden cable (40a, 40b, 40c) used for interlocking ensures that the required degree of flexibility in mounting is provided.
CASE 1: ONLY ONE CIRCUIT BREAKER CAN BE ON, OUT OF 3 CIRCUIT BREAKERS
After the junction box (100) is assembled with the bowden cable (40a, 40b, 40c) properly adjusted for free play, an operation in any one of the circuit breakers of the three circuit breakers when ON (such as moving of the shaft or rotation of the knob), makes the corresponding cable head of the bowden cable, for example the bowden cable (40a) slide properly in the oblong slot provided in the pair of link, for example the first pair of link (32a, 32d), which then pull the

entire link assembly (other two pair of links) towards the direction of pull and towards the cable anchor point (not shown). Now the entire link assembly gets arranged so that bowden cables (40b, 40c) in other two pair of links are pulled inwards to the maximum. Accordingly, switching ON any of the other two circuit breaker is not possible due to blockage of either knob or shaft at the other circuit breakers to which the other two bowden cables (40b, 40c) are attached .
In case 1, the junction box (100) allows closing of only anyone circuit breaker out of the three circuit breakers possible at all the times. Switching ON two or more circuit breakers is not at all possible. But both may be permitted to remain in OFF condition simultaneously. Hence desirable interlocking between three breakers is achieved. The following table shows the possible combinations.

A B c
0 0 0
1 0 0
0 1 0
0 0 1
Here 'P represents ON state of breaker; '0' represents OFF state of breaker
Thus unintended operation of other tow circuit breaker is prevented while the first circuit breaker is made to ON.
FOR CASE 2: ANY TWO CIRCUIT BREAKERS CAN BE ON, OUT OF 3 CIRCUIT BREAKERS
Now the bowden cable (42a, 42b, 42c) are so adjusted that there is comparatively more free play as compared to case I by adjusting the locknut at

the cable fixing ends. When the first circuit breaker is in ON position, the corresponding bowden cable, for example the bovvden cable (40a) gets pulled at the circuit breaker end. Due to this motion, the cable head for that corresponding bowden cable slides inside the corresponding pair of link, for example. The pair of link (32a, 32d) and afterwards pulls the entire arrangement towards the bowden cable anchor point. Due to the free play of the bowden cables it is possible for another circuit breaker also to be switched ON which makes the link arrangement aligned so that the third cable is pulled maximum towards the junction box. This makes it impossible to switch the third circuit breaker to ON position under any circumstance.
In case 2, the junction box (100) allows closing of any two of the three interlocked circuit breakers possible at all times. Switching ON more than two circuit breakers is not possible. However, it may be allowed for all the three interlocked circuit breakers to be in OFF position at the same time. The following table shows the possible combinations.

A B c
0 0 0
1 0 0
0 1 0
0 0 1
1 1 0
0 1 1
1 0 1
Here '1' represents ON state of breaker; '0' represents OFF state of breaker

Thus unintended operation of third circuit breaker is prevented while two circuit breakers are made to ON.
For turning ON the third circuit breaker, under any circumstances, the operator has to first turn OFF either of the closed circuit breaker, and then move on to the third circuit breaker.
While turning ON the third circuit breaker, the same phenomena happens in the junction box as specified above.
Advantages of the invention
1. The junction box (100) makes it possible to interlock three circuit breakers and also in variable combinations using the same setup.
2. The junction box (100) uses flexible cable, hence placing circuit breakers anywhere within the reach of cable is possible.
3. The junction box (100) can be readily applied to an existing interlock setup which uses cable for interlocking.
4. The junction box (100) does not constraint the type of circuit whether it is fixed or plug-in type. It can be applicable to any type with the same components.
5. The junction box (100) is applicable to 3 pole or 4 poles or combination of 3 pole and 4 pole switching devices
6. In the junction box (100), the profile and arrangement of the links such that it acts as assembly guide and also transfers motion to subsequent components.

7. Using the junction box (100), the arrangement of circuit breakers in different orientations in the panel board and even in different modules is possible.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We claim:
1. A junction box for interlocking three circuit breakers, the junction box capable of being secured to a panel board, the junction box comprising:
a first plate member having at least three flanges attached to a base thereof, each flange having an opening configured thereon;
a second plate member capable of being secured over the first plate member;
a plurality of links, each link of the plurality of links having an oblong slot configured at one end thereof, the plurality of links hinged at a centre of the first plate member, wherein the plurality of links forms at least three pairs of links, each link of the each pair of links configured with other link of the pair such that the slots of the two links of the pair of links correspond to each other; and
at least three bowden cables capable of passing through the opening of the three flanges, each bowden cable of the three bowden cables having one end coupled to the respective circuit breaker of the three circuit breakers and other end with a cable head secured in the oblong slots of the pair of links;
wherein, when any one circuit breaker of the three circuit breakers is ON, the bowden cable attached thereto using the motion signal from the circuit breakers pulls the cable head thereby sliding within the oblong slots provided in the corresponding pair of link in which the cable head is secured, which then pulls the other pair of links towards the direction of pull thereby pulling the other bowden cables in other two pairs of links inward to the maximum extent, thereby blocking the other circuit breakers of the three circuit breakers from switching to" ON" position/from getting "closed".

2. The junction box as claimed in claim 1, wherein the first plate member comprises protrusions and the second member comprises matching profiles for screwing the junction box onto the panel board.