FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION :
Earth switch contact sub-assembly.
APPLICANTS:
Crompton Greaves Limited, CG House, 6lh House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company.
INVENTORS:
Sathe Mahesh of Crompton Greaves Ltd, Industrial Design Centre, Global R&D, Crompton Greaves, Kanjurmarg (East), Mumbai- 400042, Maharashtra, India and More Sachin Vasant of Crompton Greaves Ltd, Engineering Department, CG Global R&D Centre, Kanjur (E), Mumbai 400042, Maharashtra, India; both Indian Nationals.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

Field of the Invention:
This invention relates to the field of electro-mechanical assemblies.
Particularly, this invention relates to the field of earth switch contact sub-assembly.
Background of the Invention:
Isolator switch is used to make sure that an electrical circuit can be completely de-energized for service or maintenance. Such switches are often found in electrical distribution and industrial applications where machinery must have its source of driving power removed for adjustment or repair. High-voltage isolation switches are used in electrical substations to allow isolation of apparatus such as circuit breakers and transformers, and transmission lines, for maintenance.
In order to ground all the residual voltage, an earth switch with finger contacts is provided. This isolator finger contacts receive an operating rod, connected to ground (earth), which grounds the charge. Typically, there are provided a pair of finger contacts with faces opposite to each other, and the operating rod is adapted to slide in between said two finger contacts. The contacts include a stopper element, in between its faces, in a position placed posterior to said contacts, in order to stop the operating rod motion from its operative resting position to its operative active position in between said faces of contacts so as to mate with the contact faces, for transfer of charge from said contact faces to operating rod.

Present Isolator Contact where flexibility to get proper face to face contact between operating rod and contact is provided by adjustment of contact gap and spring loading on moving contact do not offer perfect face to face contact and on line adjustment of contact is cumbersome and not accurate.
A continuous process of operating rod being inserted and withdrawn from said contacts, leads to the contacts being spaced apart, thereby not providing the required contact.
According to the prior art contact mechanism, line or point contact elimination is a cumbersome process. Line and point contact due to localized force accumulation are likely to lead to wear problems due to friction.
In order to bring the contacts faces to their original position, according to the prior art design, adjustment was possible off-line, by contact finger and its support bending or by addition of shim packings; which is a cumbersome process.
All isolator manufacturers in India have used conventional design where contact live faces in open condition are perfectly horizontal and do become inclined when operating rod gets inserted between fixed and moving contact finger live faces. This leads to achieving improper contact.
These designs being outdoor product designs, never had thrown light on contact heat problems and such development was just overlooked by others.

In light of US Patent US4490595 ('595 patent), it is observed that the invention is an electric disconnect or grounding switch. The switch includes a switch blade and a fixed blade with a slot therein to receive the switch blade. During open position of the switch, the switch blade is parallel or at an angle with the fixed blade and, during closing of the switch, the switch blade is introduced into the slot of the fixed blade, accordingly, is guided to the vicinity of the current contacts. In light of GB Patent GB1287502 ('502 patent) it is observed that, the invention is an isolator or an earthing switch for high voltage. The isolator includes an isolating or earthing knife contact adapted to pivot through approximately 90° and to perform an additional sliding motion in a zone where the contact is made. The '502 patent also discloses reliable contact making.
There is a need to overcome the limitations of the prior art.
Objects of the Invention:
An object of the invention is to eliminate the cumbersome process of eliminating problems relating to face contact in an earthing assembly.
Another object of the invention is to reduce the material cost of earthing assemblies.
Yet another object of the invention is to reduce wear and tear of earthing assemblies.
Still another object of the invention is to provide proper face contact in earthing assemblies, for full earthing.

Summary of the Invention:
According to this invention, there is provided an earth switch contact sub-assembly adapted to provide earthing contact between an earth metal plate and finger contacts, said assembly comprises:
a. a pair of finger contacts with its mating faces facing each other in a spaced
apart configuration;
b. earth plate adapted to be slid into the spaced apart configuration of the finger
contacts in order to mate with said mating faces of said finger contact in
order to transfer charge from said finger contact to said earth plate for
purposes of earthing;
c. stopper element adapted to be placed operatively posterior to said face
contacts in order to stop the movement of said earth plate so that it mates
perfectly with said mating surfaces of said finger contacts
characterized in that,
said stopper element includes a slit through its operative proximal lateral sides, so that it provides a play for the finger contacts to operate such that the gap due to the slit eliminates stress on to the finger contacts.
Typically, said sub-assembly includes an earth switch tandem adapted to swivel said plate from its inoperative position to its operating position wherein it mates.
Typically, said sub-assembly includes a tightening element can be effected onto the stopper element so that the finger contacts in communication with the stopper element retain their original position

Brief Description of the Accompanying Drawings:
The invention will now be described in relation to the accompanying drawings, in which:
Figure 1 illustrates an isometric view of the isolator with earth switch open condition;
Figure 2 illustrates a front view of the isolator with earth switch open condition;
Figure 3 illustrates a top view of the isolator with earth switch open condition;
Figure 4 illustrates a side view of the isolator with earth switch open condition;
Figure 5 illustrates a earth switch contact sub-assembly, according to the prior art;
Figure 6 illustrates a side view of the isolator with earth switch closed condition;
Figure 7 illustrates a top view of the isolator with earth switch closed condition;
Figure 8 illustrates a front view of the isolator with earth switch closed condition;
Figure 9 illustrates an isometric view of the isolator with earth switch closed condition;

Figure 10 illustrates an earth switch contact sub-assembly, according to this invention;
Figure 11 illustrates an isometric view of the earth switch contact sub-assembly, according to the prior art; and
Figure 12 illustrates an isometric view of the earth switch contact sub-assembly, according to this invention;
Detailed Description of the Accompanying Drawings:
Figure 1 illustrates an isometric view of the isolator with earth switch open condition. Figure 2 illustrates a front view of the isolator with earth switch open condition. Figure 3 illustrates a top view of the isolator with earth switch open condition. Figure 4 illustrates a side view of the isolator with earth switch open condition.
Figure 6 illustrates a side view of the isolator with earth switch closed condition. Figure 7 illustrates a top view of the isolator with earth switch closed condition. Figure 8 illustrates a front view of the isolator with earth switch closed condition. Figure 9 illustrates an isometric view of the isolator with earth switch closed condition.
An isolator comprises bushing (10), a turn and twist mechanism (12), a turn and twist mechanism stopper (14). At one of the extreme ends of the isolator, an earth switch contact assembly is installed. It comprises isolator finger contact support

(16) and a terminal pad (18) for isolator contacts. It further comprises earth switch finger contacts (20) which are a pair of spaced apart contact plates supported by earth switch finger contact support (22) in order to maintain their operative configuration. The earth switch finger contacts are adapted to receive, in the spaced apart region, an earth copper plate (24) such that it mates with the spaced apart contacts. Typically, the spaced apart measurement is equal to the thickness of the plate. An earth switch tandem bracket (26) swivels the plate from its inoperative position to its operating position wherein it mates. The contacts are mounted, extending, from a terminal or stopper (28) for earth copper plate in a manner such that the stopper sits in a posterior position within the gap defined by said contacts. The contacts sandwich the stopper, in that the stopper is posteriorly displaced with respect to said contacts facing each other, thereby leaving a gap between said contacts and an opening, proximal to said contacts, in order to receive said plate. Reference numeral 30 refers to earth switch bracket. Reference numeral 32 refers to brass bush with square hole accommodating square bar. Reference numeral 34 refers to split pin for holding brass bush.
In the prior art, the stopper is a solid element. Upon continuous entry and exit of the earth plate, the finger contacts tend to get spaced apart. This renders inappropriate contact between the faces of said earth plate and said finger contacts. According to the prior art, a person has to reach to the finger contacts and bend the contacts in place so as to achieve its initial position. This bending is not only dangerous, but also leads to failure of the contacts due to stress upon it. Reference numeral 100 refers to earth switching assembly of the prior art.

Figure 5 illustrates an earth switch contact sub-assembly, according to the prior art. Figure 11 illustrates an isometric view of the earth switch contact sub-assembly, according to the prior art.
Reference numeral 200 refers to earth switching assembly in accordance with this invention.
Figure 10 illustrates an earth switch contact sub-assembly(200), according to this invention. Figure 12 illustrates an isometric view of the earth switch contact subassembly, according to this invention.
According to this invention, there is provided an earth switch contact sub-assembly adapted to provide earthing contact between an earth metal plate and finger contacts.
In accordance with an embodiment of this invention, there is provided a pair of finger contacts with its mating faces facing each other in a spaced apart configuration.
In accordance with another embodiment of this invention, there is provided a earth plate adapted to be slid into the spaced apart configuration of the finger contacts in order to mate with said mating faces of said finger contact in order to transfer charge from aid finger contact to said earth plate for purposes of earthing.
In accordance with yet another embodiment of this invention, there is provided a stopper element (50) adapted to be placed operatively posterior to said face

contacts in order to stop the movement of said earth plate so that it mates perfectly with said mating surfaces of said finger contacts, in that, said stopper element includes a slit through its operative proximal lateral sides, so that it provides a play for the finger contacts to operate. This play is provided such that the gap does not cause stress on to the finger contacts. Moreover, due to repeated use, if the finger contacts are spaced apart more than usually required, the tightening element can be effected onto the stopper element so that the finger contacts in communication with the stopper element retain their original position. This slit thus provides the play for such movement.
Thus, on-line contact gap adjustment may be achieved. With due respect to proven spring design for required electrical contact, this invention offers just the required adjustment, thereby eliminating need of heavy finger and finger support bending devices. Further, fatigue based permanent bending related problems possible with design of the prior art are taken care of.
Such a device can be adopted for other contacts used in indoor devices.

We claim,
1. An earth switch contact sub-assembly adapted to provide earthing contact between an earth metal plate and finger contacts, said assembly comprising:
a. a pair of finger contacts with its mating faces facing each other in a spaced
apart configuration;
b. earth plate adapted to be slid into the spaced apart configuration of the finger
contacts in order to mate with said mating faces of said finger contact in
order to transfer charge from said finger contact to said earth plate for
purposes of earthing;
c. stopper element adapted to be placed operatively posterior to said face
contacts in order to stop the movement of said earth plate so that it mates
perfectly with said mating surfaces of said finger contacts
characterized in that,
said stopper element includes a slit through its operative proximal lateral sides, so that it provides a play for the finger contacts to operate such that the gap due to the slit eliminates stress on to the finger contacts.
2. An earth switch contact sub-assembly as claimed in claim 1 wherein, said subassembly includes an earth switch tandem adapted to swivel said plate from its inoperative position to its operating position wherein it mates.

3. An earth switch contact sub-assembly as claimed in claim 1 wherein, said sub-assembly includes a tightening element that can be effected onto the stopper element so that the finger contacts in communication with the stopper element retain their original position.