1. Technical Field
This disclosure relates generally to the field of electrical circuit breakers and more particularly to a mechanical interlock feature that engages upon circuit breaker tripping.
2. Description of the Related Art
In general, circuit breakers are employed to selectively engage a branch circuit to an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are several ways by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism; or auxiliary devices can be used to trip the circuit breaker thereby move the movable contact. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.
When an overload condition occurs, the trip bar is rotated away allowing the trip bar latch to disengage the auxiliary latch. With the auxiliary latch free, the cradle is able to pivot thereby disengaging the breaker contacts. This sequence of event is referred to as the breaker tripping. In order for the breaker to be safely reset, the auxiliary latch must be held open until the cradle is first reset. According to the prior art, a variety of heavy springs and dampers are used to keep the auxiliary latch from resetting prematurely. In addition a push to trip button could be used to trip the mechanism again.
The disadvantage of the prior art systems are that there is no guarantee that the auxiliary latch will not reset after the breaker is tripped. In addition, using some type of damper will add extra cost to the mechanism. Using a heavier torsion spring could make the auxiliary latch rebound thereby allowing itself to reset with the trip bar latch. The cradle could not be reset in this case as it would strike the top of the auxiliary latch.
Accordingly, there is a need for a secure feature that will prevent the auxiliary latch from resetting prematurely.
An apparatus for restricting auxiliary latch movement within a tripped circuit breaker having an auxiliary latch held in a closed state and being biased into an open state. A cradle disengages the breaker contact when the auxiliary latch moves into the open state. An interlock limits the auxiliary latch from exiting the open state until the cradle is properly reset. The interlock comprises complementary interfering parts on the auxiliary latch and the cradle which physically prevent the auxiliary latch from exiting the open state when the cradle is disengaged. One interfering part is an auxiliary latch tab which is disposed on said auxiliary latch. Another interfering part is a cradle tab which is disposed on said cradle.
The cradle pivots to a disengaged position where the cradle tab is disposed at a radial distance R from the auxiliary latch axis, corresponding to the radial location of the auxiliary latch tab, thereby preventing the auxiliary latch from pivoting out of its open state. The cradle synchronously pivots with an auxiliary latch surface for selective meshing and unmeshing, with the auxiliary latch tab and the cradle tab cooperatively interlocking in the unmeshed state to maintain said auxiliary latch in proper rotational alignment for subsequent meshing upon cradle resetting. A trip bar latch holds said auxiliary latch in a closed state until the breaker trips. The interlock restricts said auxiliary latch from pivoting back into the closed state thereby avoiding accidental trip bar reset.
Another embodiment of the invention includes a method of restricting auxiliary latch movement within a tripped circuit breaker, including selectively meshing an auxiliary latch with a cradle via synchronous pivoting on respective parallel axes. Next, the auxiliary latch pivots out of mesh with the cradle allowing it to disengage the breaker contact. The auxiliary latch and the cradle are interlocked to prevent the auxiliary latch from exiting the open state until the cradle is reset.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.
This disclosure will present in detail the following description of preferred embodiments with reference to the following figures wherein:
The present invention provides devices and methods relating to an interlock feature which prevents the auxiliary latch from improperly reengaging the trip bar latch. It is used in a breaker mechanism to restrict the auxiliary latch from reengaging after the breaker has been tripped, i.e. to prevent a nuisance relatch. If the auxiliary latch is reengaged before the cradle is in place, then the breaker cannot be reset. In
The present principles will be described in terms of single pole circuit breakers employed for residential applications. However, the embodiments described are not limited to the illustrative example and may be employed in other configurations for other applications. For example, the present principles are equally applicable to two or more pole mechanisms, breakers that include push to test features, any size breakers, multiple breaker systems in a single housing, etc. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. For example, reference to clockwise and counter clockwise are provided for explanatory purposes and are non-limiting. The alternate or opposite directions are intended to be included within the concepts and mechanisms described herein. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure).
Thus, for example, it will be appreciated by those skilled in the art that the drawings presented herein represent conceptual views of illustrative system components embodying the principles of the invention. Referring now in specific detail to the drawings in which like reference numerals identify similar or identical elements throughout the several views, and initially to
In general, all breakers have mechanisms that engage and disengage the electrical contacts when operated by the handle. In addition to those two functions, the mechanism must be able to trip automatically when an overload condition occurs. The part called the cradle engages with the auxiliary latch. The auxiliary latch in turn engages a trip bar latch. When the trip bar is rotated in a first direction the trip bar latch disengages the auxiliary latch allowing the cradle to push the auxiliary latch in a second direction and disengage the breaker contacts. This action is referred to as the breaker tripping.
When the breaker is reset after being tripped the operator moves the handle which is attached to the cradle. The cradle than engages the auxiliary latch moving it in the first direction to the reset position allowing the trip bar latch to engage the auxiliary latch thus locking the cradle in place. Once the cradle is locked in place the breaker can be turned to the on position reengaging the electrical contacts. The function of the invention is to keep the auxiliary latch from resetting against the trip bar latch before the cradle is reset.
If the auxiliary latch is reset before the cradle is reset then the cradle will run into the auxiliary latch, and the breaker will not be able to be reset. In prior art devices, a variety of heavy springs and dampers are used to keep the auxiliary latch from resetting. In addition a push to trip button could be used to trip the mechanism again. The disadvantages of the prior art systems are that there is no guarantee that the auxiliary latch will not reset after the breaker is tripped. In addition using some type of damper will add extra cost to the mechanism. Using a heavier spring could make the auxiliary latch rebound thereby allowing itself to reset with the trip bar latch. The cradle could not be reset in this case as it would strike the top of the auxiliary latch.
The advantage of the invention is that there is no physical way the auxiliary latch can reset while the breaker is tripped. The tab on the auxiliary latch engages a tab on the cradle. The cradle has to be reset before it is possible for the auxiliary latch to be reset. In addition to preventing reset, the tab on the auxiliary latch is bent with a radius which improves the trip characteristics of the mechanism by removing the sharp edge off of the auxiliary latch.
By way of comparison there is shown schematically several components that interact when a breaker transitions from the on or reset position to the tripped position. The “on” position is shown in
Typically, a reset occurs by manual movement of a handle which is connected to cradle 160 and extends outside of the circuit breaker 148 housing. Starting from the orientation of
Since axles 162 and 102 are parallel, the respectively mounted cradle 160 and auxiliary latch 100 interact via synchronous meshing, like gears. The free end of cradle 160 functions like one gear tooth, while auxiliary latch tab 110 and lower plate 114 function like two gear teeth. The teeth-like portions of the cradle and the auxiliary latch will selectively mesh (
The interlock 130 according to an embodiment of the invention is shown in
An exemplary, cross-sectional view of the back half of auxiliary latch 100 is shown in
The disadvantage of lip 108 is clearly shown in
As can be seen in
Having described preferred embodiments for cradle and auxiliary latch interlocks for circuit breakers (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.
This application claims priority to provisional application Ser. No. 61/029,588 filed on Feb. 19, 2008 the contents of which are incorporated herein by reference thereto.
Number | Date | Country | |
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61029588 | Feb 2008 | US |