FORM 2
THE PATENTS ACT, 1970 COMPLETE SPECIFICATION
(See Section 10)
INTERLOCKING ASSEMBLY FOR MECHANICAL SWITCHING
DEVICE
Numbered as dated
INVENTORS:
a) SHUBHOSANYAL
b) CHANDRAKANTANKUSHPATIL
APPLICANT:
M/s. LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No 278,
Mumbai, 400 001, Maharashtra,
INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
NATURE OF THE INVENTION

INTERLOCKING ASSEMBLY FOR MECHANICAL SWITCHING
DEVICE
A) TECHNICAL FIELD
[0001] The present invention generally relates to a locking assembly used with a mechanical switching device and more particularly to a door interlocking assembly with a panel mounted lock for electrical switching device such as switch gear.
B) BACKGROUND OF THE INVENTION
[0002] Electrical switching devices are used to protect the electrical circuitry and equipment from the damage due to an abnormal condition, such as an overload condition, a relatively high level short circuit or a fault condition. The Electrical switching devices include, for example, circuit switching devices and circuit interrupters such as circuit breakers, contactors, motor starters, motor controllers and other load controllers
[0003] These electrical switching devices typically have two operating handle positions corresponding to the status of the separable contacts. For example, these positions include an ON position, in which the separable contacts are closed and an OFF position in which the contacts are open. Some switching
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devices have a third position which corresponds to a tripped condition in which the contacts are tripped open.
[0004] Switching devices are usually installed in an enclosure so that the entire control and distribution network arranged in the form of metallic sheets and/or cable wires are housed inside the enclosure. All the operating means are arranged outside the enclosure to prevent an access to the high voltage sections to eliminate the generation of a potential hazard. It is often desirable or essential that the settings of the switching devices remain undisturbed in the switching device during a maintenance operation. Unauthorized or inadvertent changing of the position of these breakers could result in unwanted interruptions to service or operations and serious damage to an electrical apparatus, or even serious harm to a person. For example, accidental actuation of a circuit breaker might result in electrocution or shock to a workman performing electrical work or repair on equipment downstream from the circuit breaker.
[0005] Therefore enough safety measures must be taken to prevent another person from inadvertendy returning the circuit breaker handle to the ON position, when a worker is doing electrical work in an area other than the immediate vicinity of the circuit breaker box or electrical panel. One such safety measure is the addition of a locking assembly to the switching device to prevent the displacement of the circuit breaker operating handle.
[0006] The US patents numbered 5,310,969; 5,412,167; 5,500,495; 5,577,599; 5,732,815; 5,817,998; and 5,817,999 disclose handle locking mechanisms
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consisting of an assembly of at least two parts. Each handle lock mechanism employs a padlock to lock the handle of the circuit breaker in a fixed position.
[0007] Another safety measure is to provide an interlocking assembly for the input power supply units. Generally, the industrial electrical systems, in which high-value currents and high power levels are involved, have the switching devices installed in the incoming line from a generator and the grid transformer. In such devices, the incoming power is derived either from a grid transformer or from a generator or from any other alternate power source. Hence, it is also required to interlock the input power devices to avoid potential undesired effect due to inadvertent closing of switching devices from a back-up power system, when the power is derived from a desired alternate source.
[0008] Currentiy several interlocking systems are provided for such switching devices. The EP patent No. 0890181 discloses a cable interlock system for preventing two circuit breakers from being closed at the same time.
[0009] The US patent No. 6329615 discloses an interlocking device using locks to prevent manual actuation of a switch having a handle inlet, and to allow the switch to be actuated manually in a certain sequence of operations determined by using keys for the locks, thereby enabling the switch to move from a first switching position to a second switching position.
[0010] The US pre grant publication No. 2006 0042922 Al discloses a trip component locking assembly for an electrical switching device. The lock
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assembly has a single-piece flexible linkage structured to interconnect pivotal trip lever coupled to a trip component and an extension member coupled to a pivot element of a locking mechanism, so that the single-piece flexible linkage is taut with respect to said pivotal trip lever and said extension member, when the trip component is disposed in first position.
[0011] The US patent No.6192718 discloses a cylinder key lock and locking hasp assembly for use with a stored energy assembly, having a housing and an operator mechanism that may be manually actuated, for use with a circuit breaker assembly. The locking hasp assembly, mounted in the stored energy assembly housing, has a locking hasp receiving member and a locking hasp securing member with an aperture to receive a lifting member so that the lifting member is moved to unsecured and secured positions respectively to allow the movement of locking hasp assembly and to prevent the movement of locking hasp assembly.
[0012] None of the prior art devices provide an interlock mechanism to lock the switch gear in a desired position and to interlock the movement of the door with the movement switching device to prevent the unauthorized access to the switch gear. None of the prior inventions provide a mechanism to prevent the inadvertent or un authorized operation of the switch gear during a maintenance operation to avoid damage to an electrical device and to prevent the generation of potential hazard to the maintenance personnel working on the device.
[0013] Hence, there is a need to provide an interlock mechanism to a switch gear to prevent an inadvertent or unauthorized operation of a circuit breaker during a maintenance operation, to interlock two or more switching devices
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installed in a system and to provide a door interlocking facility to prevent the opening of a door during the switched off condition of the switching device to provide an additional safety measure.
C) OBJECT OF THE INVENTION
[0014] Primary object of the invention is to provide a locking means with a key lock for any mechanical switching device to lock a switching device, in any preferred state i.e. ON or OFF condition,
[0015] Another object of the invention is to provide a mechanism to avoid any unauthorized access for operating the system and to permit only limited number of authorized persons to operate a switching device.
[0016] Another object of this invention is to provide a door interlocking with the switching device using a key lock to permit only the authorized persons to open the door and to access the switch gear device.
[0017] Yet another object of this invention is to provide an interlocking between two or more switching devices.
[0018] These and other objects and advantages of the present invention will become readily apparent from the following summary and detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.
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D) SUMMARY OF THE INVENTION
[0019] According to one embodiment of the invention, an interlocking assembly is provided in a mechanical switching device to lock any mechanical switching device housed in an enclosure, in ON or OFF condition and also to interlock the selected switching condition of the switching device with the switching operation of an enclosure door. A universal interlocking device is provided to lock the switching device either in the OFF condition or in the ON condition, whichever is preferred, to prevent the access of the switching device to any unauthorized person. The invention provides a means to prevent the accidental or intentional non-intended operation of the switching device which is installed in a distribution and control system. The invention also provides a means to interlock two or more switching devices installed in the system. The invention provides an additional safety feature by preventing the operation of door when the switching device is locked in a desired position.
[0020] According to one embodiment of the invention, a switching device provided with a shaft assembly is housed inside an enclosure. An operating means such as an operating handle or an operating knob is connected to one end of the shaft and the other end of the shaft is connected to a switching device, so that the handle is arranged outside the enclosure to operate the switching device and the handle is installed at the outer surface of the enclosure. The shaft assembly has a square shaft with a profile which is obtained by riveting two U-shaped clips along the shaft to form a locking pad on the shaft. A locking assembly is mounted along with the operating handle at the outer side of the enclosure, on a door panel which is hinged to the
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enclosure at one end. The locking assembly has a slidable fork with a square shaped cut so that the fork is moved up and down to hold the profile (locking pad) of the shaft of the shaft assembly in the square shaped cut to hold the entire shaft assembly in a desired locking condition. The operating handle or knob is freely operated to move the switching device to any position, when the fork of the locking assembly does not hold the profile (locking pad) of the shaft in the shaft assembly.
[0021] According to another embodiment of this invention, a key lock assembly is provided for a switching device. The key lock assembly consists of a housing inside which a pinion gear is meshed with a driven gear and is mounted on a key lock. The driven gear is coupled to a sliding link called fork through a cam like profile so that the fork is reciprocatably moved by the rotation operation of the key lock to engage the profile (locking pad) of the shaft in the shaft assembly to prevent the rotation of the shaft to prohibit the switching of the device from OFF condition into ON condition. The entire key lock assembly housing storing the key lock gears and rollers is fixed to a mounting plate. The mounting plate is fitted from the back of enclosure door panel along with the operating handle so that the mounting screws of both the switching device and the key lock assembly are arranged behind the door of the enclosure to ensure that the removal of the mounting plates of key lock assembly and the operating handle are prevented to avoid an unauthorized access to the switching device in a locked condition. The entire key lock assembly is further covered by a back plate.
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[0022] Other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiments and the accompanying drawings.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 shows a perspective view of a switching device according to one embodiment of the invention and mounted with a key lock assembly of the invention, with the key in an unlocked condition.
[0024] FIG. 2 shows a perspective view of a switching device according to one embodiment of the invention and mounted with a key lock assembly of this invention, with the key in a locked condition.
[0025] FIG. 3 shows an exploded perspective view of a key lock assembly according to one embodiment of the invention.
[0026] Although the specific features of the invention are shown in some drawings and not others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention.
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F) DETAILED DESCRIPTION OF THE INVENTION
[0027] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof and in which the specific embodiments that may be practiced are 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 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.
[0028] Various embodiments of the invention provide a switching device and an interlocking key lock assembly for a switching device. However, the embodiments are not limited and may be implemented in connection with mechanical or electrical switching devices.
[0029] According to one embodiment of the invention, a switching device with an interlock assembly is provided. The switching device has an enclosure to accommodate a switching unit. A shaft assembly having a rectangular shaft is coupled with the switching unit so that the switching unit is operated from the exterior of the enclosure through the shaft assembly. An operating means such as an operating handle or knob is mounted at one end of the shaft in the shaft assembly so that the operating means is installed at the exterior of the enclosure on a door panel. The door panel is hinged at one end to the enclosure and the door is opened by swiveling the door alone the hinge, while
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the switching unit and the shaft assembly are arranged inside the enclosure. The shaft assembly has a rectangular shaft with a head with a profile which is achieved by riveting two U - shaped clips along the shaft. A locking assembly is mounted along with the operating handle on the door panel. The locking assembly has a key lock and a fork which reciprocates up and down slidably by using the key lock. The fork has a slot to hold the profile of the shaft in the shaft assembly so that the fork is moved up to hold the profile in the slot to prevent the rotation of the shaft to hold the shaft in a desired ON or OFF condition or moved down to release the profile of the shaft from the slot to permit the movement of the shaft to move the switching unit to any desired position or condition. The engagement of the fork with the shaft assembly also prevents the opening of the door. The riveted head opposes the fork, during the opening of the door in, a locked condition of the key lock, thereby achieving a door interlocking facility.
[0030] According to another embodiment of the invention, a key lock assembly is provided for a switching device. The key lock assembly mounted along with an operating handle or knob is installed on a door panel which is hinged to an enclosure housing a shaft assembly and a switching unit. The key lock assembly consists of a housing to accommodate a pinion gear, a driven gear, a roller, a sliding link such as a fork and a key lock. A pinion gear is meshed with the driven gear and is mounted on a key lock. The driven gear is coupled to the fork having square slotls through a cam like profile so that the fork is moved by using the key lock to hold or release the profile of a head in the shaft of the shaft assembly to prevent or permit the rotation of the shaft to prevent or
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permit the rotation of the switching unit from any desired ON or OFF condition.
[0031] The key lock is inserted in to the housing. The pinion gear is mounted on the key lock and tightened with a nut. The driven gear is inserted into the housing and is engaged with the pinion gear. A cam like profile of the driven gear is engaged with the fork. When a rotary motion is given to the key lock for locking or unlocking, it is transmitted to the fork through the gears. Thus rotary motion is converted into the linear motion and fork moves linearly along a slot formed in the housing. The pinion and driven gears are designed to get the maximum possible movement of the fork. The engagement of the fork with the shaft assembly is possible only when the switching unit inside the panel or enclosure is in OFF condition. Hence the switching ON of the switching unit is prevented when the shaft is held by the fork and locked by the key lock in the OFF condition.
[0032] The entire key lock assembly housing accommodating the key lock, the gears and rollers is fixed to a mounting plate. The mounting plate of the operating handle and that of the key lock assembly are fitted from the back of enclosure through the screws so that the removal of the mounting plates of key lock assembly and the operating handle are prevented to avoid an unauthorized access to the switching device in a locked condition. The entire key lock assembly is further covered by a back plate.
[0033] FIG. 1 shows a perspective view of a switching device 1 provided with a key lock assembly 4 according to one embodiment of this invention, with the
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key lock unit in an unlocked condition. The switching device 1 is mounted with a shaft assembly 2 which is used for operating of the switching device 1 from the exterior face of an enclosure 5 provided to house a switching device 1. An operating means such as an operating handle or an operating knob 3 is attached to a square shaft in the shaft assembly 2 and is mounted on the exterior face of the enclosure 5 on a door panel hinged to the enclosure. The switching device 1 and the shaft assembly 2 are mounted inside the enclosure 5. The shaft assembly 2 has a square shaft with a profile which is achieved by attaching two U- shaped clips 7 along the length of the shaft with the rivet heads 8.
[0034] The locking assembly 4 is mounted along with the operating handle 3 on the door panel. The operating knob 3 and the locking assembly 4 are mounted on a panel door which is hinged at one edge and is opened by swiveling the door along the hinge. The locking assembly 4 has a fork 6 which is slidably moved upwardly or downwardly and is provided with a square cut that is adapted to engage the profile of in the shaft at the shaft assembly 2.
[0035] The key lock unit is unlocked and the operating handle 3 is free to operate the switching device 1 through the shaft assembly 2.
[0036] FIG. 2 shows a perspective view of a switching device with a key lock assembly according to one embodiment of this invention, with the key lock in a locked condition. With reference to FIG.2, an operating knob 3 is mounted at one end of a shaft assembly coupled to a switching device 1. A locking assembly 4 is mounted along with the operating knob 3 at the exterior of an
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enclosure housing the switching device 1 and the shaft assembly. The fork 6 provided in the key lock assembly 4 is pushed up to engage with the profile 7 of the shaft in the shaft assembly to hold the shaft thereby preventing the rotation of the operating handle 3. Since the profile 7 is formed by attaching two U- shaped clips along the length of the shaft in the shaft assembly using riveted heads 8, the opening of a door is also prevented during the locked condition of shaft in any desired condition.
[0037] The Key lock assembly 4 is mounted on the panel door in such a way that when the fork 6 is in extreme out state, it engages with the shaft assembly mounted on the switching device 1. The C-shaped fork 6 engages with the rectangular shaft, the rotation of the shaft and hence the switching ON or OFF operation of the switching device 1 are prohibited. The engagement of the fork 6 with the shaft assembly also prevents the opening of the door. The riveted head 8 opposes the fork, when one attempts to open the door during the locked condition of the key lock unit, thereby achieving the door interlocking operation.
[0038] FIG.3 shows an exploded perspective view of a key lock assembly according to one embodiment of this invention. The key lock assembly consists of a housing 10, a pinion gear 11, a driven gear 12, a sliding link called fork 6, a roller 13 and a key lock 14. The entire key lock assembly housing with key lock gears and rollers are fixed to a mounting plate 15.The mounting plate 15 is fitted from the back of enclosure along with the mounting of the operating handle through the mounting screws so that the removal of the mounting plates of both the switching device and the key lock assembly are prevented to
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prohibit an unauthorized access to the switching device in an OFF condition. The entire assembly is further covered by the back plate 16.
[0039] The key lock 14 is inserted into the housing 10. The pinion gear 11 is mounted on the key lock 14 and tightened with the nuts. The driven gear 12 is inserted into the housing 10 and is engaged with the pinion gear 11. A cam like profile of the driven gear 12 is engaged with the fork 6. When a rotary motion is given to the key lock 14 during the locking or unlocking operations, it is transmitted to the fork 6 through the gears. Thus rotary motion is converted in to the linear motion and the fork 6 is moved linearly along the slot in the housing 10. The pinion and the driven gears 11, 12 are designed to get the maximum possible displacement of the fork. The fork is engaged with the shaft assembly, only when the switching device inside the panel or enclosure is in OFF state. Thus the switching ON of the device is prevented when the switching device is locked with the key lock in OFF state.
[0040] The arrangement of gears and fork provided in the preferred embodiments is to achieve a reciprocatable moving mechanism which is used to hold the locking pad of the shaft in the shaft assembly at the switching unit. However any mechanism which gives reciprocating movement as an output can be used to get the desired function of the invention. The use of gear arrangement and roller is to improve the performance of the assembly mechanically.
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[0041] Thus various embodiments of the present invention provide a switching device with a lock assembly and an interlocking key lock assembly for a switching device.
[0042] It will be obvious for a person of skilled in the art to practice the invention with several modifications. However, all those modifications will be deemed to be covered within the scope of the invention as covered in the claims mentioned hereunder.
G) ADVANTAGES OF THE INVENTION
[0043] The present invention provides a key lock assembly for any mechanical switching device to hold the switching device in any preferred condition like ON or OFF condition. As a key lock is provided, only limited numbers of authorized persons are allowed to operate the switching device. The door interlocking operation is provided using a key lock assembly so that only authorized person is allowed to open the door and access the switchgear device. An interlocking between two or more switching devices is also provided. The door interlocking is possible in ON/OFF or in both state of device by reorienting the U- shaped clips.
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CLAIMS
What is claimed is:
1. A switching device, comprising:
a) an enclosure;
b) a switching unit housed inside the enclosure;
c) a shaft assembly coupled to switching unit and housed in side the enclosure;
d) an operating means attached at one end of a shaft in the shaft assembly and arranged at the exterior of the enclosure;
e) a locking assembly mounted along with operating means at the exterior of the enclosure;
f) Wherein the locking assembly consists of a fork with a slot to hold the shaft in the shaft assembly attached to the switching unit to hold the switching unit in any desired operating condition.
2. Switching device according to claim 1 wherein the said shaft assembly
has a rectangular shaft.
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3. Switching device according to claim 1 wherein the said rectangular shaft has a profile formed by riveting two U-shaped clips along the said shaft using riveting heads.
4. Switching device according to claim 1 wherein the said fork is moved up slidably to hold the profile of the shaft in the slot to prevent the rotation of the shaft from any desired operating condition of the switching unit.
5. Switching device according to claim 1 wherein the said fork is slidably moved down to release the shaft from the slot to permit the rotation of the shaft to allow the switching operation of the switching unit.
6. Switching device according to claim 1 wherein the desired operating condition of the switching unit is a switched ON condition.
7. Switching device according to claim 1 wherein the desired operating condition of the switching unit is a switched OFF condition.
8. Switching device according to claim 1 wherein the operating means is actuated to rotate the shaft to move the switching unit to either ON or OFF condition.
9. Switching device according to claim 1 wherein the operating means is an operating knob.
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10. Switching device according to claim 1 wherein the operating means is an operating handle.
11. A key lock assembly for a switching device having a switching unit provided with a shaft assembly, comprising:

a) a housing
b) a key lock unit inserted into the housing;
c) a pinion gear arranged inside a housing and mounted on the key lock unit;
d) a driven gear engaged with the pinion gear and arranged inside the housing;
e) a fork coupled to the driven gear and arranged out side the housing;
f) Back plate which covers the housing;
g) Wherein the key lock unit is locked or opened to move the fork up or down to hold a shaft in a shaft assembly of a switching unit in a desired operating condition or to release shaft to permit switching operation in the switching unit.
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12. A key lock assembly for a switching device according to claim 11 wherein the said fork is coupled to the driven gear through a cam like profile.
13. A key lock assembly for a switching device according to claim 11 wherein the said key lock unit is locked to rotate the pinion gear to move the driven gear to move the fork to hold the shaft.
14. A key lock assembly for a switching device according to claim 11 wherein the said fork has a C-shaped slot to hold the shaft in the shaft assembly.
Dated this the 13TH day of March, 2007

Rakesh Prabhu,
Patent Agent, ALMT Legal,
No.2, Lavelle Road, Bangalore-560 001, INDIA
To,
The Controller of Patents,
The Patent office,
At Mumbai
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ABSTRACT
The present invention provides a switching device with a lock assembly. An operating means is provided at one end of a shaft in the shaft assembly attached to a switching unit to move the switching unit to an ON or OFF condition. The operating means is provided at the outer surface of an enclosure housing the shaft assembly and the switching unit. A lock assembly mounted along with the operating means at the outer surface of the enclosure has a fork which is moved up or down to hold or release the shaft to prevent or permit rotation of shaft to hold switching unit in any desired operating condition or to move switching unit to ON /OFF condition. In another embodiment of the invention, an interlocking key assembly for the switching device is provided.
14 claims, 3 drawing sheets
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