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 use in Moulded Case Circuit Breaker
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.

Interlocking Mechanism for use in Moulded Case Circuit Breaker
Field of the invention
The present invention relates to moulded case circuit breaker, and more specifically, to an interlocking mechanism for use in moulded case circuit breaker.
Background of the invention
Generally, moulded case circuit breakers (referred here after as MCCB) can be divided into four main structural assemblies, such as contact system assembly (1], operating mechanism assembly (2), release and sensor assembly [3], and parts forming outer body (4) as shown in figure 1.
The contact system (1) forms the current carrying path of the MCCB. The contact system (1) has two states, i.e. contacts open state (referred as OFF condition of MCCB) and contacts close state (referred as ON condition of the MCCB). The operating mechanism (2) is used for transition of the contact system (1) states. Further, sensing of fault conditions of the MCCB and indicating it to the operating mechanism (2) is done by the release and sensor assembly (3). Furthermore, the outer body parts (4) form outermost structure of the MCCB, which is used for covering all the breaker components for IP (Ingress Protection) and operator safety.
The operating mechanism (2) has spring loaded parts which move with high velocity and high force during transition of MCCB states. If the spring loaded parts are exposed to the operator, there are high chances of injury to the operator while operating the MCCB. Similarly, to protect the MCCB components from outside interference and for IP, it is necessary to cover the MCCB components. The operating mechanism (2) has three stable states ON, OFF and TRIP, where ON and OFF conditions are same as explained in the contact system (1). In the TRIP condition, the contacts are open and the operating mechanism (2) is de-latched.

The TRIP condition is completely discharged state of the operating mechanism (2). Hence, the TRIP condition of the MCCB posses least risk to the operator.
In addition to the mechanical safety of the operator, the opening of a front cover of the MCCB in ON condition could also result in operator touching live parts and therefore being subjected to electric shock.
To overcome the above problem, the MCCB generally is provided with a front cover [5) above the operating mechanism (2], as shown in figure 2. When, the front cover (5] is removed, the operating mechanism (2] components are accessible. A knob (6) from the operating mechanism (2) protrudes out from the front cover (5) which is used to change the state of the MCCB.. In normal MCCB operations, the front cover (5) need not be removed. However, in certain cases like insertion of accessories like UV release and the like, the front cover (5) has to be removed to access the accessory mounting space. Accordingly, there is provided a provision such as like screw fitting or snap fit arrangement to remove the front cover (5) at user end.
In conventional MCCBs, instructions are given, to remove the front cover (5} only in the TRIP condition of the MCCB. However, there is no interlock for removing the front cover (5) in ON and OFF conditions. The front cover (5) can be removed in all the three states of the MCCB. Any unskilled operator opening the front cover [5] in ON or OFF conditions is prone to get injured.
Accordingly, there exist a need to provide an interlocking mechanism in which the front cover (5) cannot be removed in ON and OFF conditions of the MCCB.
Objects of the invention
An object of the present invention is to provide safety to operator while handling the moulded case circuit breaker.

Summary of the invention
Accordingly, the present invention provides an interlocking mechanism for use in moulded case circuit breaker. The moulded case circuit breaker includes a contact system assembly, an operating mechanism assembly, a release and sensor assembly, housing and a knob protruding from the operating mechanism through a front cover of the housing for changing state of the moulded case circuit breaker to any one of ON, OFF and TRIP condition.
Characterised in that, the interlock mechanism comprises the knob which includes a first member secured to a fork of the operating mechanism and a second member capable of removably securing to the first member. Further, the interlock mechanism comprises the front cover having an elongated slot from which the first member of the knob protrudes outside the housing when the front cover is assembled to the housing. The elongated slot includes ribs configured along both side of a first end at which the knob defines ON position of the moulded case circuit breaker and either side of a second end at which the knob defines OFF position of the moulded case circuit breaker. The elongated slot has width less than the second member of the knob.
When the front cover is assembled to the housing, the first member of the knob protrudes though the slot of the front cover, and when the second member is secured to the first member, the second member arrest movement of the front cover by locking the front cover against the ribs thereby restricting the front cover to come out from the housing in ON and OFF conditions of the moulded case circuit breaker.
Brief description of the drawings
Figure 1 shows an exploded view of a moulded case circuit breaker, of prior art;

Figure 2 shows another exploded view of the moulded case circuit breaker, of the prior art;
Figure 3 shows an exploded view of the interlocking mechanism, in accordance with the present invention;
Figure 4 shows an exploded view of a knob assembly of an interlocking mechanism in moulded case circuit breaker, in accordance with the present invention;
Figure 5 shows an assembled view of the knob assembly of figure 4;
Figure 6 shows another exploded view of the knob assembly of figure 4;
Figure 7 shows a front view of a front cover of the interlocking mechanism, in accordance with the present invention;
Figure 8 shows interlocking feature of the front cover and a knob of the interlocking mechanism, in accordance with the present invention;
Figure 9, 10 and 11 shows the interlocking mechanism along with a knob and a front cover, in accordance with the present invention;
Figure 12 shows the moulded case circuit breaker in ON condition;
Figure 13 shows the moulded case circuit breaker in OFF condition; and
Figure 14 shows the moulded case circuit breaker in TRIP condition;
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.
Referring now to figure 3 to 14, there is shown an interlocking mechanism (100) for use in moulded case circuit breaker and various components thereof. The moulded case circuit breaker includes a contact system assembly, an operating mechanism assembly, a release and sensor assembly, housing and a knob protruding from the operating mechanism through a front cover of the housing for changing state of the moulded case circuit breaker to any one of ON, OFF and TRIP condition. The contact system assembly, the operating mechanism assembly, the release and sensor assembly are similar to the components used in moulded case circuit breaker of the prior art, hence not described in detail for the sake of brevity of the description. Figure 3 shows an exploded view of the interlocking mechanism (100], in accordance with the present invention.
Characterised in that, the interlocking mechanism (100) comprises the knob (10) and the front cover (20).
As shown in figures 4, 5 and 6, the knob (10) includes a first member (12) secured to a fork (32) of the operating mechanism (30). In an embodiment, the first member (12) is rigidly secured to the fork (32). For example, the first member (12) is secured to the fork (32) by means of nut and bolt. The knob (10) further includes a second member (14) capable of removably securing to the first member (12). In an embodiment, the second member (14) is a sleeve like member secured to the first member (12) of the knob (10) by means of a screw. The knob (10) protrudes out from the front cover (20).
Specifically, the front cover (20) as shown in figure 7, includes an elongated slot (22) from which the first member (12) of the knob (10) protrudes outside the housing (40) when the front cover (20) is assembled to the housing (40). The

elongated slot (22) includes ribs (24a) configured along both side of a first end (22a) thereof at which the knob (20) defines ON position of the moulded case circuit breaker. Specifically, the ON position of the moulded case circuit breaker is shown in figure 12. The elongated slot (22) further includes ribs (24b) configured on both side of a second end (22b) at which the knob (10) defines OFF position of the moulded case circuit breaker. Specifically, the OFF position of the moulded case circuit breaker is shown in figure 13. The elongated slot (22) has width less than the second member (14) of the knob (10).
Further, a cut (24c) is provided on either side of the elongated slot (22) of the front cover (20) in between the ribs (24a, 24b) configured on the first end (22a) and the second end (22b) respectively. The cut (24c) allows the second member (24) of the knob (10) to pass through elongated slot (22) when the knob (20) is in TRIP condition. Accordingly, the front cover (20) may be removed from the housing (40) in TRIP condition of the moulded case circuit breaker but not in ON/OFF condition thereof. Figure 14 shows a trip condition of the moulded case circuit breaker.
As shown in figures 8 -11, upon assembling the front cover (20) to the housing (40), the first member (12) of the knob (10) protrudes though the slot (22) of the front cover (20). Thereafter, when the second member (14) is secured to the first member (12), the second member (14) arrest movement of the front cover (20) by locking the front cover (20) against the ribs (24a, 24b) thereby restricting the front cover (20) to come out from the housing (40) in ON and OFF conditions of the moulded case circuit breaker.
When the front cover (20) needs to be removed from the housing (40) in ON and OFF conditions of the moulded case circuit breaker, the second member (14) of the knob (10) has tc be removed from the first member (12) by releasing the screw. Without the second member (14) of the knob (10), there is no interlock to the front cover (20) and the front cover (20) can also be removed in ON/OFF

conditions of the moulded case circuit breaker, and when, the front cover (20) is removed, the operating mechanism (30) components are accessible.
Advantages of the invention
1. The interlock mechanism (100) provides interlock to the front cover and
restricts its removal in ON and OFF condition, thereby offering mechanical and
electrical safety for the operator.
2. The interlock mechanism (100) allows the front cover to be removed in only
TRIP condition of the moulded case circuit breaker.
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. An interlocking mechanism for use in moulded case circuit breaker, the moulded case circuit breaker having a contact system assembly, an operating mechanism assembly, a release and sensor assembly, housing and a knob protruding from the operating mechanism through a front cover of the housing for changing state of the moulded case circuit breaker to any one of ON, OFF and TRIP condition, characterised in that the interlock mechanism comprises:
the knob having a first member secured to a fork of the operating mechanism and a second member capable of removably securing to the first member; and
the front cover having a elongated slot from which the first member of the knob protrudes outside the housing when the front cover is assembled to the housing, the elongated slot having ribs configured along either side of a first end at which the knob defines ON position of the moulded case circuit breaker and either side of a second end at which the knob defines OFF position of the moulded case circuit breaker, wherein the elongated slot has width less than the second member of the knob,
wherein when the front cover is assembled to the housing, the first member of the knob protrudes though the slot of the front cover, and when the second member is secured to the first member, the second member arrest movement of the front cover by locking the front cover against the ribs thereby restricting the front cover to come out from the housing in ON and OFF conditions of the moulded case circuit breaker.
2. The interlock mechanism as claimed in claim 1, wherein a cut is provided on either side of the elongated slot of the front cover in between the ribs configured on the first end and the second end of the elongated slot member which allows the second member of the knob to pass through elongated slot when the knob is in trip condition.