FORM-2
THE PATENTSACT.1970
(39 of 1970)


COMPLETE SPECIFICATION
(Section 10)

'AN ELECTROMAGNETIC CONTACTOR WITH A LOCKABLE ARRANGEMENT IN "OFF1 STATE,"
LARSON & TOUBRO LIMITED,
L&T House, Ballard Estate, MUMBAT-400 001. Maharashtra State, India An Indian Company registered under the provisions of the Company's Act 1956
The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed ;-


Present invention relates to an electromagnetic contactor with a lockable arrangement in ''off' state. More particularly present invention concerns an electromagnetic contactor comprising of a moving bridge which carries a moving contact. An arc shield is fastened to the arc shield by way of sliding fit. A transparent lid is pressed fitted to the top cover which is generally provided whh a rectangular opening Rectangular opening provides an access to the key.
The electromagnetic contactor comprises of a front housing which holds the moving bridge. The fixed terminals are fastened to the front housing. The contact bridge carries the moving contacts. The arc shield is removable and is secured to the front housing with the help of screws. The removable feature of the arc shield enables removal and replacement of the fixed and moving contacts as and when desired by the user -
Contact replacement is a maintenance-enabling feature desired by the user as it helps in prolonging the useful life of the contactor.
Objection of the present invention aims at devising an electromagnetic contactor with a lockable arrangement in "off" state.
Thus, according to this invention, therefore, an electromagnetic contactor with a lockable arrangement in "off state comprises of a front housing (3) which houses a moving bridge (1), the said moving bridge carries moving contacts and the fixed contacts in turn are secured to the said front housing, a removable arc shield (2) fastened to the said front housing by means of screws (4), a top cover (5) is provided, which shrouds the screws, characterized in that a transparent lid (6) with a opening in the middle is provided, which allows insertion of the key for locking and unlocking of the moving bridge, the locking of the moving bridge prevents closing of the contacts even when an electrical closing command is impressed upon on the coil; the electromagnetic contactor allows for the locking of the moving bridge with the help of a key in the "OFF" state of the contactor; the electromagnetic contactor disallows
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inadvertent closing of the contacts once the bridge has been locked by the key; the electromagnetic contactor wherein the transparent lid has a rectangular shaped opening in the middle.
Our invention relates to a novel maintenance-enabling feature which helps in locking the contactor in 'OFF' state. Once the contactor is locked in 'OFF' state with the help of a key, it is possible to close the contact even if the electromagnet of the contactor receives a closing command. Such a feature helps in preventing inadvertent closing of the contact if desired by the user during inspection of control panel, testing of control panel and maintenance of the control panel.
The electromagnetic contactor comprises a top cover which is shaped in such a way that it shrouds the screws. The top cover and the arc shield are shaped in such a way that they are enclosed between the sidewalls of the front housing. The front contour of the top cover matches with that of the front contour provided on the front housing. The railing provided on the top cover allows for unidirectional insertion to the arc shield. The construction of the railing inside the top cover does not allow bi¬directional insertion to the arc shield .
According to this invention, a transparent lid is press fitted to the top cover. The said transparent lid is provided with an opening usually rectangular . This opening is dimensioned to provide access to another component key.
During usage of the contactor, some times it is necessary to avoid inadvertent closing of the contactor. Whenever such a function is desired, lockable feature in "OFF' state helps in preventing closing of the contactor even if the electromagnet receives a closing command. Whenever inadvertent closing of the contact need to be prevented, the key is to be inserted in the opening which is generally rectangular provided on the transparent lid after inserting the key it has to be turned in the clockwise direction through 90°. Now the key will not allow farther movement of the moving bridge even if the electromagnet receives a closing command. As the
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moving contacts are attached to the moving bridge, the moving contacts are prevented from touching the fixed contacts. Thus, any unintentional closing of the contactor is avoided.
If desired, to disable the locking of the moving bridge, the key needs to be rotated through 90° anti-clockwise direction. Only then it is possible to take out the key from the contactor.
The invention will now be described with the help of a drawing accompanying this specification wherein the salient features have been shown by suitable numerals and referred to appropriately in the following description :
Drawing comprises 3 figures.
Fig.l shows exploded view of the electromagnetic contactor.
Fig.2 shows frontal view of the key.
Fig.3 shows frontal view of contactor with the key position in front.
According to this invention the arc shield (2) is provided with a biasing projection, which ensures that the arc shield (2) can be fastened to the front housing (3) only in a predetermined orientation. The predetermined orientation of the arc shield (2) ensures that the top cover (5) also remains oriented in a predetermined orientation. Construction of the front housing (3) is made to result in a click fit fastening to the rear housing (11). The construction of the rear housing (11) and front housing (3) allow only for predetermined orientation. The novelty of the design allows for predetermined orientation for the top cover (5) with respect to the arc shield (2), arc shield with respect to the front housing, and front housing with respect to the rear housing (11).
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Details of the components in the figures :

Moving Bridge - 1
Arc Shield 2
Front Housing 3
Screws 4
Top Cover 5
Transparent Lid - 6
Key 7
Opening 8
Fixed Terminals - 9
Moving Contacts - 10
Rear Housing 11
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WE CLAIM:
An electromagnetic contactor comprising of a front housing (3) which
houses a moving bridge (1), the said moving bridge carries moving contacts

and the fixed contacts in turn are secured to the said front housing a

removable arc shield (2) fastened to the said front housing ,by means of
screws (4), a top cover (5) is provided, which shrpuds. the screws,

characterized in that a transparent lid (6) with a opening the middle is
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provided, which allows insertion of the key for locking and unlocking of the

moving bridge, the locking of the moving bridge prevents closing bf the

contacts even when an electrical closing command is impressed upon on the
coil; .
2. The electromagnetic contactor according to claim 1, which allows for the
locking of the moving bridge with the help of a key in the "OFF" state of the contactor;

3 The electromagnetic' contactor according to claim 1, which disallows
inadvertent closing of the contacts once the bridge has been locked by the key,
4. The electromagnetic contactor according to claiml, wherein the transparent lid has a rectangular shaped opening in the middle.


Dated this 01st Day of June, 2002

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