FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE SPECIFICATION (Section 10)
'AN IMPROVED CONTACT BRIDGE ASSEMBLY"
LARSEN & TOUBRO LIMITED
L & T House,
Ballard Estate,
MUMBAI-400 001. Maharashtra State, India
The following specification particularly describes the nature of this invention and the manner in which if is to be performed-

The present invention relates to an improved Contact Bridge Assembly in an Electromagnetic Contactor. More particularly it relates to a contact bridge assembly, which houses the moving contacts, in an electromechanical switching device such as an Electromagnetic contactor.
In prior art, an electromagnetic contactor consists of a set of fixed and moving contacts. The fixed contacts are connected to the front housing & the moving contacts are supported in the contact bridge. This contact bridge is connected to the moving magnet (armature). It is actually coupled to the magnet.
When the electromagnet is energized, the fixed & moving contacts close, thereby conducting electrical power to the load. The springs housed in the contact bridge guarantee the requisite contact pressure between the fixed & the moving contacts. This ensures that the contactor carries the rated current without getting unduly heated.
These fixed & moving contacts in the electromagnetic contactor undergo erosion due to arcing and therefore are required to be replaced during the life span of the electromagnetic contactor The contacts are also inspected regularly for preventive maintenance. To ensure proper functioning, it is recommended that all the fixed contacts and moving contacts should be replaced simultaneously;
The fixed contacts, which are housed in the front housing, can be replaced either by unscrewing or detaching it from the front housing. However, the replacement of moving contacts is difficult since contact spring force always keeps it pressed against the bridge. Replacement of moving contacts may even call for removal of the contact springs and/or spring guide from the contact bridge.
The present invention aims at modifying the contact bridge so as to enable easy replacement and inspection of the moving contacts. Therefore the contact bridge supporting the moving contacts and the armature is improved as a, contact bridge assembly. This contact bridge assembly consists of two parts -


(1) A front bridge assembly comprising of a front bridge, three moving contacts, contact springs and two latches; the said front bridge assembly is made up of plastic having higher Comparative Tracking Index, high arc resistance and high ampere arc ignition to boost the electrical life.
(2) A rear bridge; the said rear bridge is made up of more resilient material like Poly Amide 66 and glass fiber.
In order to inspect or replace the moving contacts, the two latches in the front bridge, when moved, disengage the front bridge from the rear bridge and the entire front bridge assembly consisting of the three moving contacts, contact springs and the two latches can then be slid out from the rear bridge. Thus not only the moving contacts but also the entire front bridge assembly can be replaces by a new front bridge assembly.
Therefore the present invention is an improved contact bridge assembly in an electromagnetic contactor comprising a front bridge assembly and a rear bridge, characterized in that the said front bridge assembly houses moving contacts, contact springs, two latches which are spring loaded, the said springs being provided to keep the latches pushed towards outer edge of the said front assembly, the said rear bridge is connected to a moving magnet by means of a steel strap and consists of two arms with two slots, the said latches of the front bridge assembly having profiles, which are so designed that when the said front assembly is inserted inside the said rear bridge, the two latches move apart and then eventually get engaged in the said two slots provided in the said two arms of the said rear bridge.
The invention will now be described with reference to drawings. The drawings contain 5 figures.
Fig. I: Shows the perspective view of the contact bridge assembly and the armature of a 3 pole electromagnetic contractor showing the moving contacts, contact springs, front bridge & rear bridge and latches.
Fig. II: Shows the side view of the contact bridge assembly.


Fig HI. Shows how the front bridge can be de-coupled from the rear bridge for inspection & replacement of contacts.
Fig IV: Shows the perspective view of the rear bridge.
Fig V: Shows the perspective view of the front bridge assembly.
Description of the invention:
The present invention, i.e. an improved contact bridge assembly is divided into two parts- front bridge assembly (I) & rear bridge (2) - Please refer fig I.
The Key for the figures is as follows:
Front Bridge (1)
RearBridge (2)
Moving contacts (3a, 3b & 3c)
Contact springs (4a, 4b & 4c)
Larches (5a & 5b)
Springs (6a & 6b)
Arms of rear bridge (7a & 7b)
Slots of these arms (8a & 8b)
Moving magnet (9)
Slits of Front Bridge (10a & 10b)
Refer to Fig.I
This figure shows the perspective view of the contact bridge assembly and the armature of a 3 pole electromagnetic contactor showing the moving contacts, contact springs, front bridge Sc rear bridge and latches. The rear bridge (2) consists of two arms (7a & 7b) with two slots (8a and 8b). It is connected to the moving magnet (9) by means


of a steel strap whereas the f^6& bridge (1) houses the three moving contacts (3a, 3b & 3c) (for 3 pole contactor) and the contact springs (4a, 4b & 4c). The front bridge (1) contains two latches (5a & 5b), which are spring loaded. These latches can slide in the direction as shown by the arrows. The springs (6a & 6b) provided wilt always keep the latches pushed towards outer edge of the front bridge (l).
Refer Fig, n
The front bridge (1) & the rear bridge (2) are coupled together by means of the two latches (5a & 5b) of the front bridge (1), which gets engaged in the slots (8a & 8b) of the rear bridge (2)
The front bridge has got two slits (10a & 10b) (shown in fig V) in which the two arms (7a &7b) of the rear bridge get guided during insertion. The profiles of the latches (5a & 5b) of the front bridge (1) are so designed that when the ^6^ bridge is inserted inside the rear bridge, the two latches move apart and then eventually get engaged in the slots (8a &' 8b) provided in the two arms (7a & 7b) of the rear bridge (2)
Refer to Fig, m
In order to inspect/ replace the moving contacts, the two latches (5a & 5b) in the front bridge (1) should be moved in the direction of the arrow as shown in fig I. This disengages the front bridge (1) from the rear bridge (2) and the entire front bridge assembly consisting of the three moving contacts (3a, 3b & 3c), contact springs (4a, 4b & 4c) and the two latches (5a & 5b) can then be slid out from the rear bridge as shown in fig. in.
Refer to Fig. IV
This figure shows the perspective view of the rear bridge The rear bridge (2) consists of two arms (7a & 7b) with two slots (8a and 8b).


Refer to figV
It shows the perspective view of the front bridge assembly: The front bridge assembly (1) houses the three moving contacts (3a, 3b & 3c) (for 3 pole contactor) and the contact springs (4a, 4b & 4c). The front bridge (1) contains two latches (5a & 5b), which are spring loaded. These latches can slide in the direction as shown by the arrows. The springs (6a & 6b) provided will always keep the latches pushed towards outer edge of the front bridge (1).
The front bridge (I) with moving contacts (3a, 3b & 3c) & die contact springs (4a, 4b & 4c) can then be easily replaced / inspected if required.
Advantages of the present invention:
1. Replacement and inspection of moving contacts becomes easier by removing the front bridge which is "Gick-fitted" with the rear bridge by two sliding latches.
2. The conscruction of the contact bridge makes it possible to use two different materials for the contact bridge. While front bridge, which is in the arcing zone can be made of a material with high Comparative Tracking Index, high arc resistance and high ampere arc ignition to boost the electrical life and the rear bridge is made up of more resilient material like Poly Amide 66 and glass fibre, which can improve the mechanical durability.
3. When the front bridge assembly is replaced not only the moving contacts get replaced but the entire front bridge assembly can be replaced by a new front bridge assembly


We claim .
1. An improved contact bridge assembly in an electromagnetic contactor comprising a front bridge assembly and a rear bridge, characterised in that the said front bridge assembly houses moving contacts, contact springs, two latches which are spring loaded, the said springs being provided to keep the latches pushed towards outer edge of the said front bridge assembly, the said rear bridge is connected to a moving magnet by means of a steel strap and consists of two arms with two slots, the said latches of the front bridge assembly having profiles, which are so designed that when the said front bridge assembly is inserted inside the said rear bridge, the two latches move apart and then eventually get engaged in the said two slots provided in the said two arms of the said rear bridge
2. An improved contact bridge assembly as claimed in claim 1, wherein the said two latches in the front bridge assembly can be moved so as to disengage die said front bridge assembly from the said rear bridge and the entire front bridge assembly can be slid out from the rear bridge for the purpose of inspection or replacement.
3. An improved contact bridge assembly as claimed in claim 1, wherein the said front bridge is made up of plastic having higher Comparative Tracking Index, high arc resistance and high ampere arc ignition to boost the electrical life and the said rear bridge is made up of more resilient material like Poly Amide 66 and glass fibre.
4 An improved contact bridge assembly as ciaimed in claims 1 to 3 substantially as herein described with reference to the accompanying specification and drawings.
Dated this 22nd Day of March, 2004
(M.D. BHATE) AGENT FOR APPLICANT