TITLE: AN ARCING CONTACT FOR CIRCUIT BREAKER. TECHNICAL FIELD OF THE INVENTION:
The present invention relates to electrical switching devices and more particularly to an improved arcing contact for a Molded Case Circuit Breaker (MCCB). BACKGROUND OF THE INVENTION :
An electrical switching device may be defined as a switch designed to protect an electrical circuit from damage caused by overload or short circuit. A circuit breaker is a commonly used electrical switching device. The circuit breaker may be classified as a high voltage type and a low voltage type. The commonly used low voltage type circuit breaker may be a Moulded Case Circuit Breaker (MCCB). The circuit breaker may include a main contact and an arcing contact. The main contact may comprise of an upper contact and a lower contact. The arcing contact is generally provided to protect the main contact from wear and damage caused by arcing. The arcing contact protects the main contact by providing a high resistance parallel path to the current.
The arcing contact may close before the main contact to eliminate the arc formation in the main contact. In the closed position, the main contact may conduct current through the circuit. The arcing contact may provide a high resistance alternate path to the current in the closed position.
Various arcing contacts are known in the prior art. A typical arcing contact existing in the prior art has a spring at the base of the lower contact or in the upper contact which means pin joints are present in the contacts. This increases the resistance of the electrical circuit and temperature rise in these areas will be more.
Therefore, there exist requirements for an arcing contact that can obviate the above-mentioned problems and enhance the life of the electrical switching device.
SUMMARY OF EMBODIMENT OF THE INVENTION:

An object of the present invention is to provide an improved arcing contact for enhancing the life of an electrical switching device.
According to one embodiment of the present invention the improved arcing contact comprises two main contacts including a fixed contact and a moving contact. Each contact has a contact button. A stack of plates is arranged over the fixed contact and an arcing contact adapted between the plates for providing high resistance to current. The arcing contact closes before the main contacts are closed for eliminating arc formation during closed state of the moving and the fixed contact, thereby saving the contact buttons in the main contact from arcs and increasing the life time of the circuit breaker.
Details of the instant invention and further objects thereof will become evident as the description proceeds and from an examination of the accompanying drawings, which illustrate preferred embodiment of the invention.
DRAWINGS OF EMBODIMENTS OF THE INVENTION:
Figure 1 shows the three dimensional schematic of the improved arcing contact according
to an embodiment herein.
Figure 2 shows the two-dimensional schematic of the improved arcing contact according
to an embodiment herein.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION:
The present invention describes in conjunction with the accompanying drawing an
improved arcing contact for an electrical switching device such as a molded case circuit
breaker.
Referring now to the figures including Figure 1 and Figure 2, the like numerals assigned to the parts shown in various figures indicate the like parts.
Figure 1 shows the three dimensional schematic of the improved arcing contact according to an embodiment herein. The improved arcing contact comprises a stack of plates 120

arranged in a stack. Contact buttons 110 and a special spring 100 can be seen in the figure
that holds the first plate of the stack.
Figure 2 shows the two-dimensional schematic of the improved arcing contact according
to an embodiment herein.
According to one embodiment of the present invention the improved arcing contact comprises plurality of plates 120 arranged between a fixed contact 270 and a moving contact 220 of the electrical switching device. The electrical switching device may be a circuit breaker such as a Molded Case Circuit Breaker (MCCB). The upper (moving) contact 220 and lower (fixed) contact 270 can be collectively termed as main contact. The main contact 220, 270 of the circuit breaker conduct current in the electrical power driven circuit. The main contact 220, 270 is made of copper. The main contact 220, 270 may be in open or closed state. The main contact 220, 270 may be provided with slots for keeping a contact button 110. The contact buttons 110 are placed in Upper contact 220 , Lower contact 270 and in the first connector of the arcing contact.
Contact buttons 110 establishes contacts when the main contacts 220, 270 close i.e., when the upper contact 220 moves down to make contact with the lower contact 270, also between the upper contact 220 and the arcing contact.
The moving contact 220 may be contained by a holder or a cup 200 that may execute vertical motion. The moving contact 220 may be connected to the first plate of the arcing contact through a movable hand 250. The movable hand 250 may be riveted to the first plate of the arcing contact. There may be an upper and a lower projection/stopper 210 provided on the upper and the lower portion of the holder 200 respectively. The holder 200 carries the movable hand 250 while executing vertical motion through the projection/ stopper 210. The movable hand 250 may be free to move sideways. A special spring 100

may provide the necessary contact pressure to the movable hand 250 and the contact button (sliding path provided at the side of the upper contact for electrical connection with the arcing contact) of the main contact. Therefore, even if the contact button in the sliding path of the main contact or that of the movable hand 250 erodes, the spring 100 may provide the necessary connection between the moving contact 220 and the first plate of the arcing contact.
When the main contact 220. 270 closes to supply current in the electrical power driven circuit, there may be formation of arc. The formation of arc may be eliminated or reduced by providing a high resistance parallel or alternate path to the current. The high resistance parallel or alternate path may be provided by the arcing contact. The arcing contact may be included between the moving contact 220 and the fixed contact 270 of the circuit breaker. When the main contact closes, there may be arc formation. However, the arcing contact may close before the main contact to prevent arc formation in the main contact. Closing of the arcing contact means the plates 120 are placed over one another and it remains as a solid block. When the main contact 220. 270 closes i.e., when the upper contact 220 moves down towards the lower contact 270, the upper stopper pushes the movable hand 250 downwards, so the plates 120 becomes as a solid block making the electrical connection before the main contact 220, 270 do. The movable hand 250 will be always in connection with the upper contact 220 through that movable hand 250 no matter whether the upper contact 220 is in top (OFF position) or down (ON position). Thus, the arcing contact provides the high resistance parallel or alternate path to the current.. The plates 120 may be de ion plates 260 made up of mild steel in order to provide high resistance due to the material property as mild steel has relatively higher resistance when compared to copper. Not only that de ion plates have higher specific heat capacity and melting point than copper and hence it can withstand arc better for a

relatively longer duration. Therefore, lesser current may flow through the arcing contact as compared to the main contact during the closed state of the main contact.
When the main contact opens, the plates 120 of the arcing contact remains as a solid block till the upper contact opens up to a certain height (16 mm here) which means 16 mm of air is in between the main contacts (between upper and lower contact). As the contacts opens equivalent amount of air is introduced between the upper 220 and lower contact 270 which increases the resistance drastically. But the alternate current path (Arcing contact) though initially it had relatively higher resistance (as mild steel has a higher resistance than copper), it decreases as the main contact opens (as air has a higher electrical resistance than mild steel). Therefore, the arcing contact remains closed while the main contact opens.. Therefore, high resistance may be introduced in the main contact and the current starts flowing through the arcing contact. When current starts flowing through the arcing contact, and only when it starts opening after 16 mm movement of upper contact, an arc is formed between the plates 250. The plates 250 may be designed in such a way that when it opens for 14mm, the anode cathode drop and the voltage drop in air sum up to the electric power driven circuit voltage. Therefore, the flow of current may be stopped.
The invention therefore, provides an improved arcing contact with an effective arcing mechanism for an electrical switching device. The invention therefore provides the electrical switching device with enhanced life and performance.
The opening of the plates can be explained as follows. When the upper contact is moved up (when OFF signal or Trip command is given), it moves along with its holder (Cup). This holder has two projections called Stoppers. One is placed at the top and another at the bottom of the Holder. The lower stopper gets connected with the movable hand on its way of opening. So the first plate opens along with the holder

as it is connected to it through the movable hand. The overall movement of the upper contact is 30 mm in this case. It carries the first connector from 16 mm to 30 mm (14 mm). The plates are connected to one another with a bellow like material. So when the plates are stacked over one another like a solid block, this plate connector protrudes out between the plates giving the appearance of a bellow. When the stopper lifts the movable hand, the first plate of the arc contact moves up along with the first connector. The part of the plate holder between the first and second plate will straighten itself, and once it straightens the force will be implied in the second plate. The distance between the first and second late is determined by the length of plate holder between them. Similar pattern is followed in successive plates.
Once the upper contact closes the lower stopper along with the upper contact moves down. The movable hand falls down due to gravity. Thus the plates form a solid block. As the solid length of the plates together after forming the solid block is 16 mm, the arcing contacts closes much earlier than the main contact closing as the upper contact has to move 30 mm to come into contact with the lower contact. Even if the plates gets struck in between, the upper stopper in the holder (Cup) while moving down comes into contact with the first plate connector and pushes it down to its solid length position.
The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof

WE CLAIM:
1.) An improved arcing contact for a molded case circuit breaker operable in an open and close state, comprising:
two main contacts including a fixed contact and a moving contact, each contact having a contact button;
stack of plates arranged over the fixed contact; and
an arcing contact adapted between the plates for providing high resistance to current; wherein the arcing contact closes before the main contacts are closed for eliminating arc formation during closed state of the moving and the fixed contact, thereby saving the contact buttons in the main contact from arcs and increasing the life time of the circuit breaker.
2.) An improved arcing contact as claimed in claim 1, wherein the main contacts are provided with slots to keep contact buttons.
3.) An improved arcing contact as claimed in claim 1, wherein a movable hand connects the first plate of the stack to the moving contact.
4.) An improved arcing contact as claimed in claim 3 further comprises a projection for engaging the movable hand to the first plate. 5.) An improved arcing contact as claimed in claim 3, further comprises a spring to give
contact pressure to the movable hand.
7.) An improved arcing contact as claimed in claim 1, wherein the plates assemble by
compressing vertically to form the stack of plates.
8.) An improved arcing contact as claimed in claim 1, wherein the plates dissemble by
opening up between the plates..