FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
Draw-out type contact engagement measuring instrument
2. APPLICANT(S)
(a) NAME : Larsen and Toubro Ltd.
(b) NATIONALITY: Indian
(c)ADDRESS : L&T House, Ballard Estate, Mumbai-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
4. DESCRIPTION (Description shall start from next page)
5. CLAIMS (not applicable for provisional specification. Claims should start with the preamble -"I/We claim" on separate page)
6. DATE AND SIGNATURE (to be given on the last page of specification)
7. ABSTRACT OF THE INVENTION (to be given along with complete specification on the separate page)
Note:
*Repeat boxes in case of more than one entry
*To be signed by the applicant(s)or the authorized registered patent agent
*Name of the applicant should be given in full, family name in the beginning
*Complete address of the applicant should be given stating with postal index no. / code, state and
country
*Strike out the column which is/are not applicable

Draw-out type contact engagement measuring arrangement. Field of the invention
The present invention relates to a contact engagement measuring arrangement used for measuring male and female contact engagement in draw out module type of switchboard. This is used to determine the exact contact engagement when the contacts are out of reach to check the exact overlapping of fixed and moving contacts in electrical devices like circuit breakers.
Background of the invention
Switchboard, being an essential part of the distribution system, has to supply continuous power to various segments like power sector, building and construction sites, big restaurant etc. The foremost requirement of any switchgear product is to work safely and efficiently for long time. Switchboard consists of many cubicles having number of feeders with electrical equipments assembled in it. These provided feeders are of two types: Fixed & Draw out type. Fixed type feeders are directly fed from droppers which are connected to main bus-bars whereas draw out type feeders have a separate mechanism to isolate it from incoming droppers. Thereby, draw out type feeder has fixed and moving contacts to make and break the circuit while drawing out module. This type of feeders facilitates the maintenance work without switching off the main circuit.
The draw out type feeder can be switched on after inserting module in the service position and at the same time, exact overlapping or engagement of both moving and fixed contact should be ensured. Any misalignment of these contacts can lead to low pressure contact and thereby creating condition of arcing at the incoming of feeder. Therefore, the foremost requirement of contact is to get engaged properly while inserting the module from isolation position to service position. The overlap area of both male and female contact engagement should be sufficient to carry rated thermal current without over heating the contacts. Otherwise the failure of contact system would lead to flashover in the system which can also affect the performance of nearby modules. After considering the above factor, a device was required to measure or to ensure adequate overlapping of fixed and moving contacts. In the case of switchboard, there are many constraints for designing such an instrument as follows:

Space constraints: The incoming contacts are assembled at the rear side of the module where many other terminals are also connected, so available space for measuring contact engagement is very less.
Limited area for displacement: The measuring instrument has one fixed and one moving part and it should have adequate space for displacement of scale pointer or the moving part. Available area to allow the pointer to move depends only on the length of incoming contacts which is very less almost 40-50 mm.
Mechanical strength: The dimension of pointer, which shows the displacement, should be strong enough to bear the forces acting on it and it should transfer the linear force of racking module to linear displacement of pointer without interfering with the other components of assembly present in its vicinity. So the dimension of pointer should be accurately matching with the distance between current carrying contacts fingers.
Friction: The friction of moving pointer and fixed parts should be less to avoid any collision of mechanism which may cause damage to contact assembly also.
Object of the invention:
One object of the present invention is to provide contact engagement measuring arrangement for electrical devices like circuit breakers where the contacts are out of reach to check the exact overlapping of fixed and moving contacts.
Another object of the present invention is to provide a contact measuring arrangement which , occupies lesser space compared to prior art methods, easy to operate and has higher mechanical strength.
Yet another object of the present invention is to provide a displacement measurement arrangement where dimension of the pointer, which shows the displacement, should be strong enough to bear the forces acting on it and it should transfer the linear force of racking module to linear displacement of pointer without interfering with the other components of assembly present in its vicinity.

Summary of the invention:
An arrangement for measuring engagement of fixed contact with moving contact consists of a hollow rectangular housing having a linear slot on its surface. The edges along the slot are marked with measuring scale. The rectangular housing is mounted over moving contacts using mounting pillars. An "L" shaped sliding pointer, one arm of the sliding pointer slides through the slot on the rectangular housing and another arm of the "L" shaped pointer passes through the space between moving contacts and coincides with the end of the moving contact. When moving contact starts engaging with the fixed contact, it displaces the pointer in opposite direction which indicates distance travelled by moving contact on measuring scale.
Description of the Drawings:
Fig. 1: shows L shaped sliding pointer
Fig. 2: shows side view of rectangular housing
Fig. 3: shows front view of the rectangular housing
Fig. 4: shows L shaped sliding pointer engaged in rectangular housing
Fig. 5: shows L shaped sliding pointer projecting out from rectangular housing
Fig.6: shows scale on the rectangular housing
Fig.7: shows rectangular housing mounted on the contact housing and L shaped slider positioned between the gap in moving contacts
Fig.8: shows displacement of L shaped pointer when moving contact engages with fixed contact

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 contact engagement instrument part has two parts:
1. Sliding pointer
2. Fixed housing
"L" shaped sliding pointer has designed in such manner that it will transfer linear force acting at the bottom L shape link (1), into linear displacement of pointer and will shows the actual engagements at any racking position of module i.e. service-test etc.
Sliding pointer has straight marker line (2) to show the displacement of pointer and it is also provided with stopper screw/bolt (4) which has two functions, first, to restrict the pointer to come out of the housing and second, It will set the initial position of pointer i.e. while taking out the sliding pointer, the position from which screw/bolt will not allow further movement, will be the initial set position of sliding pointer. This is achieved by providing slot (10) so screw/bolt (4) can easily move in the slot and will halt at the surface (12) of slot (10).
The profile of sliding pointer is designed in order to offer less friction during linear displacement of pointer. This profile has six edges (5) which provide less friction along a line instead of friction over the whole surface and therefore total surface friction is reduced to line friction without disturbing the lateral movement of pointer. The edge rib (6) in pointer is given to strengthen the L shape link (1) which helps to transfer the linear force acting on it, to link (7) of pointer.
Fixed housing is designed in such manner that it can be easily mounted in the main contact housing. It has two mounting pillars (8) which will be inserted in the contact housing. To avoid any additional movement of fixed housing semi-oval shape (9) on both mounting pillars are provided which facilitates a lock feature to housing. Once this semi-oval shape will get inserted in the contact housing blocks (17), it will not allow any further movement of mechanism and will provide more accuracy for measurements.

Due to space constraint for displacement of pointer, a cut slot (15) on the front of fixed housing is also given to allow more displacement space for pointer, even it can move till pointer touches the cut slot (10) surface without disturbing the housing position and contact finger of contact assembly. The cut profile or linear slot in the housing is designed to accommodated moving pointer with less friction and the upper extended projection (11) of the cut profile will restrict the upward movement of pointer while displacement.
Fixed housing also has measuring scale (13) on the top surface of it which allow user to read actual displacement of pointer and so the actual overlapping of contacts. There is no need of any external scale or means to measure the contact engagement. Addition slot (10) is made in the fixed housing to extend the range of measuring engagement without interference with assembly parts and thereby sliding pointer can be easily moved more in the mechanism. The assembly of sliding pointer in the fixed housing is made such that it can be easily moved in between the two contact fingers (16) and pointer will slide in from its initial position, when fixed contact (18) will push the link (7) and at the same time, The circular edge (19) of contact (18) will apply linear force on the surface (14) of the sliding pointer.

We claim,
1) Draw-out type contact engagement measuring arrangement in electrical devices
comprising;
a rectangular housing having a linear slot along its length and the linear slot having scale
marked along its length,
an L shaped movable pointer, one arm of the L shaped moving pointer slides through the
said linear slot in the rectangular housing,
pair of moving contacts of the electrical device separated by gap, the contacts mounted in
the contact housing and the second arm of the said L shaped arm passing through the gap
between moving contacts,
a fixed contact of the electrical device, the fixed contact when engaged with the said
moving contact pushes the L shaped pointer and length of engagement of fixed contact
with moving contact is indicated on the scale along the linear slot.
2) Draw-out type contact engagement measuring arrangement in electrical devices of the claim 1 wherein, the rectangular housing has mounting pillars for mounting over moving contacts.
3) Draw-out type contact engagement measuring arrangement in electrical devices of the claim 1 wherein, the L shaped pointer has a line marked on its surface corresponding to zero mark on the measuring scale.
4) Draw-out type contact engagement measuring arrangement in electrical devices of the claim 1, wherein, the edge of the second arm of the L shaped pointer coincides with the edge of the moving contact.
5) Draw-out type contact engagement measuring arrangement in electrical devices of the claim 1. wherein, the engagement of moving contact with fixed contact causes movement of the second arm of the L shaped pointer in the gap between moving contacts and first arm of the L shaped pointer slides through the linear slot in the housing and indicates length of engagement.