FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
COMPLETE SPECIFICATION (See section 10 and rule 13}
1. TITLE OF THE INVENTION
"Integrated Panel Door Interlock Mechanism for a Rotary Type Switching Device"
2.APPUCANT(S)
(a) NAME: Larsen and Toubro Ltd.
(b) NATIONALITY: Indian
(c) ADDRESS: L&T House, Ballard Estate, Mambai - 400 001, India
3. PREAMBLE TO THE DESCRITION COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

Title
Integrated Panel Door Interlock Mechanism for a Rotary Type Switching Device
Field of the invention
The present invention is related to Low Voltage current limiting switching devices such as circuit breakers and the likes, which are commonly used to receive, supply, protect and isolate the current supply in an electrical circuit. More particularly it relates to a safety handle with an integrated mechanism built in the basic switching device complying with standard requirements.
Background of the invention
Circuit breaker typically serves two basic purposes.
1. as a switching device: Switching On/Off during normal operating conditions for the purpose of operation and maintenance; and
2. as a protecting device: Tripping or Isolating by breaking the contacts interrupting the fault current during abnormal conditions such as short-circuit, overload and under voltage.
A circuit breaker, which is an electrical switching device, typically comprises one or more electric poles, and according to the number of poles determined by the application the breaker is called as single pole circuit breaker, two pole circuit breaker, three pole circuit breaker, four pole circuit breaker etc.
Circuit breakers are designed for use in Switchboards, Control Panel, and Combination Starters in separate enclosures for effective single location distribution and control. Safety assumes an utmost importance in an electrical transfer and distribution network. Any lapse of this may prove to be fatal in terms of lives of personnel and damage to electrical installation and equipment.
In the most common type of installation, an operating handle is mounted on the panel door while the switching device is mounted inside the panel door. The mounting device has a shaft coming out that has to be rotated to switch the circuit breaker ON and OFF along with safety interlocking features for added safety of operator. One of the disadvantages of this kind of installation is that, the switching device gets decoupled once the door is opened and can no longer be operable, even if it is required in extreme emergency.
It is one of the standard requirements that in case of switching devices used in emergency like fire, safety alarms etc., provisioning of operations of the switching devices should be made even in conditions where the panel door is open. Additionally

it states that an intent to close a disconnect switch when a control panel is open must first be prevented through an interlocking provision, which can then only be bypassed through a deliberate action. Main disconnect switches equipped with door mounted rotary handles typically have a peculiar design aspect that, with an open control panel door, there no longer is a mechanical linkage established between switch and door. One of the standard requirements for switches used in emergency is that the operating handle must always be permanently connected to the switch. This applies even when the control panel door is open.
Also, with advent in technology, circuit breakers integrated with rotary mechanism are emerging to serve the Rotary handle mechanism purpose as an integrated part when mounted close to the panel door. The present invention relates to a mechanism which is integrated in the rotary mechanism of the breaker which primarily serves as a safety interlocking feature for breaker. This invention can also be applied to add-on mechanisms and like, which may get additionally mounted on such switching devices.
As per standard safety requirements, the operating means should always be coupled to the switches irrespective of the door conditions.
Yet another requirement is to have a door interlock in ON condition of the switch and this interlock to also be defeat able in case of emergency requirement by means of a tool.
Once door is defeated, it should also be possible to restore back to initial conditions normally mainly referred as Auto-restoration.
Yet another requirement is to have an interlock to the operations of the switch in Door open condition which should also be possible to defeat by trained user.
Present invention thus is to integrate the above mentioned requirements within the rotary circuit breaker.
Patent 5493083 provides a door interlocking arrangement in a similar switching device configuration. The design is however too complex and does not clearly address issues of door interlock defeat and its restoration.
Patents 6518526 and 6969813 also cite example of rotary add-on mechanism connected to a switching device but the operational safety aspects of door interlock and its defeat are not mentioned.

Objects of the invention
The main object of the invention is to have added safety feature on an integrated mechanism built in the basic switching device, fulfilling the aforementioned standard requirements.
Another object of the invention is to have the operating handle directly coupled with the Switching device / breaker irrespective of the door location.
Yet another objective of the innovation is to have an interlock to the operating handle once the door is in open condition to prevent accidental switching (with door being in open condition).
A further object is to make this interlock defeatable by trained operators by intentional action thus providing the requisite safety and also meeting the criteria of handle directly coupled to the breaker irrespective of the door position.
Yet another object of the invention is to have a mechanical means of sensing the position of the door which interlocks the operating mechanism in cases the door is open and releases the interlock once it senses the door close situation, mainly referred as Auto-restoration.
Yet another objective of the innovation is to have a door interlock while the breaker is in ON condition which would prevent the door from opening.
Yet another objective is to have a defeat which enables trained technicians with right kind of tool to defeat the said interlock for cases of emergency to open the
Also there is provision of manual defeat to enable the trained user to switch ON the circuit breaker when panel door is opened.
Summary of the invention
In accordance with the above objects, there is provided an integrated panel door interlock mechanism for a rotary type switching device mounted on a panel enclosure having a panel door that sits on the panel enclosure when closed, the mechanism comprising:
a shaft driven by an operating handle protruding out of a cut in the panel door;
a pinion mounted on the shaft;

a door lock hinged on the panel door and having a profile cut thereon, the cut accommodating a tool for rotating the door lock while the switching device is ON; and having a wedge action profile;
a rack lock meshing with the pinion and having a rear end covered by the door lock, the rack lock locking between the panel door and the door lock whenever the switching device is turned on with the operating handle;
a stopper enclosed in a stopper housing and loaded with one or more compression springs, the stopper having one degree of freedom rendering it capable of moving in a downward direction when the panel door sits on the panel enclosure; and
a door sensor having a bend on its rear end operatively connected to the stopper, the bend coming in path of the rack lock till the panel door is open and thereby locking the operating handle.
Brief Description of Drawings
Figure 1 shows a switching device housed inside a panel enclosure.
Figure 2 shows the panel door in open condition. The switching device (1) is mounted on the panel enclosure (4) and the invention forms a part of the switching device.
Figure 3 shows a section of the mechanism where in the switching device is in OFF condition.
Figure 4 shows the mechanical sensing of the door and the consecutive unlocking of the knob.
Figure 5 represents the condition that when the circuit breaker is in ON condition, the panel door is interlocked.
Figure 6 represents the door defeat condition.
Figures 7 and 8 represent the condition of panel door auto-restoration.
List of Components

Component No. Name of the Component
1 Switching device
2 Operating handle

3
Panel door
4 Panel enclosure
5 Door lock
6 Pinion
7 Rack lock
8 Stopper
8a Bend on rear end of door sensor
9 Stopper housing
10 Compression spring
Detailed Description
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 following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and the claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms "a", "an" and "the" include plural referents unless the context clearly indicates otherwise.

By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
An integrated panel door interlock mechanism built in the basic rotary-type switching device complying with standard requirements is provided. The operating handle is directly coupled with the Switching device / breaker irrespective of the door location. An interlock is provided on the operating handle, if the door is in open condition, to prevent accidental switching (with door being in open condition). The Interlock is defeatable for intentional action. A mechanical means of sensing the position of the door is provided, which interlocks the operating mechanism in cases the door is open and releases the interlock once it senses the door close situation. The door is interlocked while the breaker is in ON condition which would prevent the door from opening. Also there is provision of manual defeat to enable a trained user to switch ON the circuit breaker when the panel door is opened.
Figure 1 show a switching device housed inside a panel enclosure. The figure shows the general operating conditions of the switching device. The panel door (3) rests on the panel enclosure (4) with the operating handle (2) protruding out of the cut out for user application. The switching device is generally operated keeping the panel door (3) closed to ensure safety.
Figure 2 shows the panel door in open condition, the switching device {1} is mounted on the panel enclosure (4).
Figure 3 shows a section of the mechanism where in the switching device is in OFF condition. The stopper (8) is enclosed in a housing (9) which is loaded by a compression spring (10). The stopper essentially stops a rack lock (7) which meshes with a pinion (6) which is mounted on the shaft driven by the operating handle. The figure shows the panel door open and shows the knob interlock feature of the mechanism. The stopper (8) is a component which serves the safety purpose of not allowing the switching device to switch on till the panel door is not closed. To ensure this the stopper (8) is fixed in a stopper housing (9). The door sensor further has a bend 8(a) on its rear end. This bend comes in the path of the rack lock (7). Till the door is open, the stopper stays in the position as shown in the figure, and the bend 8(a) does not allow the rack lock to move. Thus, the operating handle (2) cannot be rotated as the stopper locks the motion of the rack lock (7) and so the switching device cannot be switched ON thus ensuring one of the pre requisites of such mechanisms.
Figure 4 shows the mechanical sensing of the door and the consecutive unlocking of the knob. The panel door (3) comes and sits on the panel enclosure (4). As the panel

door comes to rest it pushes the stopper (8) which falls back as it has one degree of freedom in the downward direction by compressing the spring (10). In doing so the bend (8a) uncovers the rack lock such that there is no further obstruction in the path of the rack lock (7) and hence the motion can be easily transmitted from the operating handle to the rack lock by means of the pinion (6) and thus the switching device can be switched ON.
Figure 5 represents the condition when the circuit breaker is in ON condition, the panel door is interlocked. One of the safety requirements suggests that the panel door should be locked when the switching device is turned ON. To ensure this the rack lock moves whenever the operating handle is rotated. On doing this the rack is locked in between the panel door (3) and the door lock (5). The door lock (5) is another component which covers the rear end of the rack and is fixed on to the panel door. Whenever the switching device is turned on the rack is locked between the panel door and the door lock (5) and ensures this safety requirement.
Figure 6 represents the door defeat condition. Another safety requirement suggests that the panel can be opened in emergency condition circuit breaker is in on condition by using a tool defeat. When panel door needs to be opened while the switching device is in on condition, then the door lock can be rotated by means of a tool which can be inserted in a profile cut over the door lock (5). The cut is designed to avoid manual defeat and can be accomplished by a tool by rotating it clockwise.
Figure 8 represents the condition of panel door auto restoration. Another safety requirement suggests that when panel door is open in ON condition of circuit breaker, and again if the panel door is closed the panel door should be automatically interlocked. This feature is called auto restoration. This auto restoration feature is achieved in this invention with the help of door lock (5).The door lock (5) component has wedge action profile as shown in Figure 7. So when panel door is closed, this door lock(5) strikes on the rack lock, and due to wedge action the door lock(5) rotates at some angle and clears the rack and again the rack lock is locked between the panel door and door lock.

We claim:
1. An integrated panel door interlock mechanism for a rotary type switching device
mounted on a panel enclosure having a panel door that sits on the panel enclosure
when closed, the mechanism comprising:
a shaft driven by an operating handle protruding out of a cut in the panel door;
a pinion mounted on the shaft;
a door lock hinged on the panel door and having a profile cut thereon, the cut accommodating a tool for rotating the door lock while the switching device is ON; and having a wedge action profile;
a rack lock meshing with the pinion and having a rear end covered by the door lock, the rack lock locking between the panel door and the door lock whenever the switching device is turned on with the operating handle;
a stopper enclosed in a stopper housing and loaded with one or more compression springs, the stopper having one degree of freedom rendering it capable of moving in a downward direction when the panel door sits on the panel enclosure; and
a door sensor having a bend on its rear end operatively connected to the stopper, the bend coming in path of the rack lock till the panel door is open and thereby locking the operating handle.
2. The mechanism of Claim 1 wherein when the panel door is dosed after being
opened with the tool, the door lock strikes the rack lock and due to the wedge
action profile rotates by an angle to clear the rack lock, rendering back the rack
lock locked between the panel door and the door lock.