Patent Application
20110094863
The present disclosure relates to circuit breakers, and, more particularly, to a flexible amperage flag in a circuit breaker.
Amperage flags are used in some circuit breakers to indicate the amperage rating of a circuit breaker. The rating is typically printed on an exposed, visible surface of the flag that protrudes from an auxiliary cover of the circuit breaker. These flags must be visible from an exterior of the circuit breaker and also through the panelboard trim when installed into a panelboard. The auxiliary cover of the circuit breaker is also visible through an opening in the panelboard trim. The visible nature of the amperage flag allows visual inspection of the panelboard by an operator to ascertain the amperage rating of the circuit breaker by reading the rating printed on the amperage flag.
An amperage flag 106 is attached to a wall 116 of the trip unit 102 via an attachment member 114. A cutaway portion of an auxiliary cover 104 that houses components of the circuit breaker 100 is shown in phantom lines to show the amperage flag 106 in clear detail. The amperage flag 106 can include ribs to strengthen the attachment of the amperage flag 106 to the wall 116 of the trip unit 102.
When certain electrical faults occur, such as a short circuit that produces high electrical current, large arcs can be created generating high gas pressure inside the circuit breaker 100. The gas pressure expands in all directions, causing high stresses in the plastic housings of the circuit breaker 100.
During interruption of the current, the gas pressure pushes the trip unit 102 and the auxiliary cover 104 in opposite directions from one another, creating a stress point at the interface between the trip unit 102 and the auxiliary cover 104. As a result, the amperage flag 106 undesirably cracks or breaks at this interface, even with the stiffening ribs 112. The flag 106 can fall inside the circuit breaker 100 when it breaks, disappearing from view and potentially interfering with the operation of the circuit breaker. It would be desirable to have an amperage flag that does not crack or break (i.e., is non-frangible) during interruption of the circuit breaker.
During assembly of some circuit breakers, a hammer is installed in the trip unit. A solenoid activates this hammer in response to detection of an electrical fault, and the hammer rotates to engage a trip mechanism of the circuit breaker, which causes a sequence of mechanical actions to trip the circuit breaker by separating the movable contacts and severing the electrical connections between the circuit breaker and the loads being protected. During assembly of such circuit breakers, the hammer can pop out of its position in the trip unit. It would be desirable to provide a way of ensuring that the hammer stays in its pre-assembled position during assembly of the trip unit so that it does not pop out of that position.
Compared to the prior-art amperage flags, which sought to reinforce the amperage flag to a trip unit of a circuit breaker, the amperage flag disclosed herein is attached more flexibly to the trip unit, allowing it to flex with excursions of the auxiliary cover through which the flag protrudes during circuit interruptions. As the contacts of the circuit breaker separate from one another, explosive gasses are produced, creating sudden, internal pressure inside the circuit breaker's housing. The auxiliary cover abuts against a trip unit housing, and the internal pressure causes the auxiliary cover to move away from the trip unit housing, taking with it the amperage flag. In prior-art designs, this flag was reinforced by adding ribs or making the flag thicker, in an effort to make the flag stronger and thus more resistant to excursions by the auxiliary cover away from the trip unit housing. But the flags were still subject to cracking or breaking, causing the top of the flag that bore the amperage rating for the trip unit to fall or break off, sometimes into the circuit breaker, taking with it the only visible indication of the amperage rating readily apparent to the operator. Because the trip units can be designed to be interchangeable among different circuit breaker housings or frames, losing the amperage rating flag is undesirable.
The amperage flag disclosed herein is made more flexible, by thinning its walls, making it of a flexible material like plastic, and positioning it a distance away from the trip unit by an attachment member. The top surface member indicates the amperage rating and is attached to a flexible leg that is attached to the attachment member. The entire trip unit housing together with the amperage flag can be molded from a single mold to form a single piece. This ensures that the proper amperage flag always stays with the trip unit housing. The flexibility of the amperage flag allows it to flex like a spring during circuit interruptions and to move with the auxiliary cover as it is force away from the trip unit, then return to its original position and form when the interruption has completed. Thus, by making the amperage flag more flexible instead of trying to reinforce it and make it stronger, the disclosed amperage flag is more resistant to breakage or cracking.
In some electronic circuit breakers that include a solenoid-actuated hammer that engages a trip mechanism for tripping the circuit breaker, the amperage flag can also include a leg member that is positioned and dimensioned to keep the hammer from popping out of its pre-assembled position during assembly of the circuit breaker. The leg member acts like a finger keeping the hammer in position during assembly, because it has a tendency to pop out of position and when installed incorrectly can lead to incorrect trip unit operation or trip unit malfunction. Because the hammer is needed to engage the trip mechanism, which ultimately causes the movable contacts of the circuit breaker to separate from one another, it is important for the hammer to be correctly positioned within the trip unit during assembly of the circuit breaker and prior to operational deployment of the circuit breaker.
The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings.
While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
The flexible amperage flag 206 can be an integrated component made of molded plastic, or it can comprise multiple components secured together to form the amperage flag 206. The leg 220 is flexible and has a thickness 228 sufficient to permit them to flex without breaking or cracking in response to excursions of the auxiliary cover 204 away from the trip unit 202 at the interface 218. In a specific example, the flexible leg 220 has a thickness of 0.06 inches. When flexed, the amperage flag 206 operates like a spring, springing back to its original position and form after being displaced. It has been found that the flexible arrangement of the amperage flag 206 eliminates the cracking and breaking that occurred in prior-art amperage flags. The leg 220 also has a length that is longer than its width, as shown in
The trip unit 202 includes a molded plastic housing 230, which includes the wall 216 and the amperage flag 206. The molded plastic housing is molded as a single component or piece of plastic. Attaching the flag 206 to the trip unit 202 ensures that the amperage flag 206 travels with the trip unit 202 when the trip unit 202 is removed from the circuit breaker 200 and installed into a different circuit breaker. Alternately, the amperage flag 206 can be formed as a separate component and attached to the wall 216 of the trip unit 202 in any conventional manner. Although the amperage flag 206 is preferably made of plastic, it can be made of metal, such as steel, or any other material that is flexible.
The amperage flag 206 further includes a second leg 222, which keeps a hammer 224 of the trip unit 202 from moving out of position during assembly of the circuit breaker 200. If the hammer 224 moves in an upward direction during assembly, the circuit breaker 200 will be assembled incorrectly. The second leg 222 has a length that is operable to keep the hammer 224 from moving out of its pre-assembled position during assembly of the circuit breaker 200. Note that only the first leg 220 is needed for preventing the amperage flag 206 from breaking or cracking during a circuit interruption. The second leg 222 is operable to keep the hammer from moving out of position during assembly. Note that the second leg 222 does not prevent the hammer from rotating, as the hammer needs to rotate counterclockwise when activated by a plunger of a solenoid 226 in the trip unit 202, and engage a conventional trip mechanism (not shown) of the circuit breaker 200 that causes the movable contacts to separate, interrupting current to the load(s) that the circuit breaker 200 is protecting. Rather, the second leg 222 ensures that the hammer 224 does not pop out of place during assembly of the circuit breaker 200, yet does not prevent the normal operation of the hammer 224 during operation of the circuit breaker 200.
The second leg 222 also has a length longer than its width, and the length of the second leg 222 is generally parallel to the first flexible leg 220 and extends away from the top surface member 210 toward the hammer 224. The length of the second leg 222 has a dimension that extends from the top surface member 210 to the hammer 224. In a non-limiting example, the second leg 222 has a thickness slightly smaller than that of the first leg 220. In this example, the second leg 222 has a thickness of 0.05 inches, and is made of a flexible material. The second leg 222 has a length sufficient to prevent the hammer 224 from popping out of its pre-assembled position in the trip unit 202 during assembly of the circuit breaker 200.
The top surface member 210 is visible through the auxiliary cover 204, as shown in
While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations can be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.
