FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
Contact System in draw-out type assemblies
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
*Compiete 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

Contact System in draw-out type assemblies Field of invention
The present invention relates to primary contact system used in draw-out type assemblies. This electrical contact system is used for giving main power supply to the draw-out type of apparatus. The contact device is intended for use in electrical switchgear assemblies Viz. Motor Control Center for operating voltages upto 1000 volts. Background of the invention
Primary contact systems are typically used in Motor control center units which are generally draw-out types and racked-in and racked-out of the control center enclosure to facilitate maintenance, testing and installation. The protective device, which may be fusible disconnect switch or circuit breaker, is typically mounted on a carriage or chassis or trolley assembly which can be racked-out and put racked-in the control center housing. This requires making and breaking of contact between the protective device mechanism itself and current carrying conductors in the enclosure. A contact device or stab assembly or jaw assembly is used to make the connection between the draw-out protective device and the bus-bars. A draw-out primary contact device mainly consists of two parts, a contact assembly and contact housing.
Object of the invention
An object of the present invention is to provide a contact device / connecting
terminal which is convenient, reliable and efficient for draw-out type
assemblies.
Another object of the present invention is to make an assembly of contact
system modular in nature, i.e. a single contact assembly can be used for

different nominal current ratings, only by changing the thickness of the
contact fingers.
The present invention further aims at solving the problem due to lack of
space inside Modules/trolleys (draw-out assemblies] used in switchgear &
control gear assemblies. The modularity of the contact system would save the
space.
The invention at hand further provides a rigid structure/design of the contact
assembly including the side brackets and other components making the
contact device more safe and reliable from electrical & mechanical
perspectives.
Summary of the invention
The primary contact system in draw-out type assembly consists primarily of two
parts, viz. a contact assembly and the contact housing. The contact assembly
consists of contact fingers, contact connection block and brackets, which enables a
proficient, hassle-free, and compact connection module for draw-out assemblies.
The contact housing consists of contact assembly fixing and rest area locator for
housing. This entire structural assembly is providing better connecting and
operating procedures for draw out type assemblies used in Motor Control
Centre(MCC) units, also known as bucket or module or feeder or draw-out unit.
Following is the list of components: Withdraw-able unit or module (1) Bus-bars (2]
Bus-bar fixed contact (3) Outgoing bus-bar contact (4] Draw-out contact device (5] Contact Assembly (51) Contact Fingers (51A]

Contact Connection Block (51B]
Rod (51C)
Spacer (51D)
Spring Holder (51E)
Spring (51F)
RHS Bracket (51G)
LHS Bracket (51H)
Contact Housing (52)
Housing Mounting Fixing Screw Location (52 A)
Contact Assembly Fixing (52B]
Rest Area locator for Housing (52C]
Support for Contact Connection Block (52D)
Description of drawings:
Fig. 1 to Fig. 5 shows different views of an Motor Control Center(MCC) assembly. Fig. 6 & Fig. 7 show the contact device (5] with 2 sub-parts (51 & 52].
Fig. 8 is a disassembled view of the contact device.
Fig. 9 shows the isolated contact assembly.
Fig. 10,11 & 12 shows disassembled view of the isolated contact assembly. Fig. 13 shows the special cross-section of the contact fingers. Fig. 14 & 15 shows the details of contact housing.
Fig. 16 shows the details of special brackets.
Detail description:
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and

obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.
The Contact system for draw-out type assemblies (5) can be characterized as
consisting of two parts; Contact assembly (51) and contact housing [52).
Motor control center unit (1) also called as bucket or module or feeder or
draw-out unit. Motor control center unit (1) is a movable component and is
racked-in and racked-out of the MCC compartment using guides or rails
mounted on the sides.
Motor control center unit [1) generally contains electrical components such as one or more circuit breakers, starters, overload protectors, indicating lamps, auxiliary devices.
Motor control center unit (1) has a horizontal frame known as chassis on which draw-out contact device (5) are mounted for giving incoming electrical supply to the unit. Motor control center unit (1) also has a vertical frame member on which the same draw-out contact device (5) are mounted for giving outgoing electrical supply to the load side of the units.
Incoming electrical supply to the unit is fed through as bus bars (2) (vertical or horizontal). From these bus bars the supply is fed through bus bar fixed contact (3). When the withdraw able unit is racked-in and racked-out the said contact device (5) makes and breaks the supply with this fixed contact(3).

In a similar way on the outgoing side the supply is given out through the bus bar fixed contact (4). When the withdraw able unit is racked-in and racked-out the said contact device (5) fixed on the vertical frame of the unit makes and breaks the supply with this outgoing fixed contact(4).
The special cross-section (Fig-13] of contact fingers allows the optimization of expensive conducting material, to achieve an economic benefit. Also the shape of the contact fingers enables very simple manufacture by extrusion and sectioning of a single block of conducting material, preferably copper.
Each contact finger (51A) has a curvature surface (c 1 and c2) at the ends to provide a larger opening to make the contact with the bus bars easier. This will eliminate the need for precise alignment of the fingers. The contact assembly is supported by 2 sheet metal brackets (51G and 51H) on the right side and left side respectively to strengthen the assembly.
Detailed features of special brackets (51G and 51H] are:
Holes (hi) through which non-magnetic material rods (51C) pass to hold the
contact fingers in its place. A special circlip or riveting procedure is used to
tighten these rods.
The brackets (51G and 51H) have special bend structure (bl) to give an extra
strength and rigidity to an entire contact assembly.
The brackets enable the proper placement of the contact connection block
(51B). The holes (h2) provided on this bend (bl) is used to mount the contact
assembly (51) into the contact housing (52) through the holes (52B) provided
in housing.
The detailed embodiments of the contact housing (52) consist of:
52A: Housing mounting Fixing Screw locations. Housing mounting fixing screw location wall (52A) is constructed in such a way that the conducting

contact (51A) does not see the screw in turn increasing the electrical creepage distance. The wall also helps in easy fixing of the screws. 52B: Contact assembly fixing. Contact assembly (51) is mounted on the housing (52) using screws through the special groove and projections (52B) provided on the housing at 2 locations (right & left), so that the movement of the contact assembly is secured.
52C: Rest area locator for housing. A special projection surface (52C) is provided on the contact housing for properly resting the contact device assembly onto the chassis frame of draw-out unit. This projection ensures a fool proof ("poka-yoke") assembly method.
52D: Support for contact connection block. Rigid surface (52D) provided on the housing will reduce the pressure exerted by external links, lugs, and cables to be mounted on the connection block (51B).

We claim,
1. A contact system for draw-out units comprising,
a contact housing(52); the contact housing (52) having plurality of slots for
mounting contact [51];
a plurality of contact fingers(51A) of varying cross-section (tl and t2), the
contact fingers[51A) curved(cl and c2) at its ends and mounting the said
contact fingers(51A) in the said contact housing(52] wherein adjacent
contacts fingers(51A) are connected using pin;
a contact connection block(51B]; the contact connection block mounted in the
curved (cl and c2] end of the said contact fingers(51A) and a support(52D)
for the contact connection block, the said support(52D] holding the contact
connection block(51B] into the contact housing(52);
a spring element(51F), the spring element[51F) integrating the two sets of
contact fingers(51A) and sustains the contact pressure between the said
contact fingers(51A]; and
a pair of bent brackets(51G and 51H) enclosing the said contact fingers(51A]
on the two sides.
2. A contact system for draw-out assemblies of claim 1 wherein; the cross-section [tl and t2) of the contact fingers (51A) is proportional to current rating.
3. A contact system for draw-out assemblies of claim 1 wherein; the curves (cl and c2) at the ends of the contact fingers [51A] result in a mix of a line contact joint and a point contact joint between the contact connection block (51B) and the contact surface.
4. A contact system for draw-out assemblies of claim 1 wherein; the plurality of contact fingers (51A] increases the number of contact points resulting in decrease of electrical resistance and dissipated power at the point of contact.

5. A contact system for draw-out assemblies of claim 1 wherein; the plurality of contact fingers (51A) of varying cross-section (tl and t2) allows reduction in use of expensive conducting material.
6. A contact system for draw-out assemblies of claim 1 wherein; the contact housing (52] is made up of an insulating material preferably sheet molded polyester glass filled compound.