1. Field of the Invention
The invention pertains generally to electrical switching apparatus and, more particularly, to circuit breakers including a limiter having plural trip indicator members. The invention also relates to limiters and to trip indicators therefor.
2. Background Information
Current limiters employ a current interruption device that rapidly and effectively brings the current to a relatively low or zero value upon the occurrence of a line fault or overload condition.
Circuit protection devices protect electrical equipment from damage when excess current flows in a power circuit due to overload or short circuit conditions. Such devices have a relatively low resistivity and, accordingly, a relatively high conductivity under normal current conditions of the power circuit, but are “tripped” or converted to high or complete resistivity when excessive current and/or temperature occurs. When the device is tripped, a reduced or zero current is allowed to pass in the power circuit, thereby protecting the power circuit conductors and load from electrical and thermal damage until the overload or fault is removed.
Conventional circuit protection or current limiting devices include, but are not limited to, circuit breakers, fuses (e.g., expulsion fuses), thermistors (e.g., PTC (Positive Temperature Coefficient) conductive polymer thermistors), and the like. These devices are current rated for the maximum current the device can carry without interruption under a load.
Circuit breakers typically contain a load sensing element (e.g., a bimetal; a hot-wire; a magnetic element) and separable contacts, which open under overload or short circuit conditions. Most circuit breakers have to be reset manually at the circuit breaker site or through a remote switch.
Fuses typically contain a load sensing fusible element (e.g., metal wire), which when exposed to current (I) of fault magnitude rapidly melts and vaporizes through resistive (R) heating (I2R). Formation of an arc in the fuse, in series with the load, can introduce arc resistance into the power circuit to reduce the peak let-through current to a value significantly lower than the fault current. Expulsion fuses may further contain gas-evolving or arc-quenching materials which rapidly quench the arc upon fusing to eliminate current conduction. Fuses generally are not reusable and must be replaced after overload or short circuit conditions because they are damaged inherently when the power circuit opens.
Various fusible elements, gas-evolving materials and fuses are shown for example in U.S. Pat. Nos. 2,526,448; 3,242,291; 3,582,586; 3,761,660; 3,925,745; 4,008,452; 4,035,755; 4,099,153; 4,166,266; 4,167,723; 4,179,677; 4,251,699; 4,307,368; 4,309,684; 4,319,212; 4,339,742; 4,340,790; 4,444,671; 4,520,337; 4,625,195; 4,638,283; 4,778,958; 4,808,963; 4,950,852; 4,952,900; 4,975,551; 4,995,886; and 5,471,185.
Low voltage circuit breakers are often connected in series with so-called limiters, in order to significantly increase the short circuit switching capacity in low voltage electrical networks and to significantly limit the cut-off currents. Such limiters are designed to transition rapidly, in case of a short circuit, from a low-resistance state to a high-resistance state and, thus, provide rapid current limiting and disconnection. Some limiters employ, for example, fuses, such as fusible wire elements to accomplish this function.
It is known to provide a trip indication for a circuit breaker limiter through a button visible at the top surface thereof. The button changes position responsive to a spring when the button is released by a fused wire element. For example, the button “pops” above the surface of the limiter when the fused wire element burns opens during a fault. See, for example, U.S. Patent Application Publication No. 2006/0267720.
There is room for improvement in electrical switching apparatus and in limiters for such apparatus.
There is also room for improvement in indicators for limiters.
These needs and others are met by embodiments of the invention, which provide a limiter including plural current limiters, each of which comprises a first end disposed proximate a first housing surface and being electrically connected to a corresponding first terminal, a second end disposed proximate a second housing surface and being electrically connected to a corresponding second terminal, and an elongated body disposed between the first and second ends. In some embodiments, the corresponding first and second terminals are disposed proximate the first housing surface, and a conductor of the corresponding second terminal is disposed proximate the second housing surface. In other embodiments, indicator members for the current limiters are disposed in different orientations, in order that plural indicators for the current limiters are disposed in a straight or a substantially straight line.
In accordance with one aspect of the invention, a limiter comprises: a housing comprising a first surface, a second surface opposite and distal from the first surface, and a plurality of sides disposed between the first surface and the second surface; a plurality of first terminals disposed proximate the first surface; a plurality of second terminals disposed proximate the first surface, each of the second terminals comprising a conductor disposed proximate the second surface; and a plurality of current limiters, each of the current limiters comprising a first end disposed proximate the first surface and being electrically connected to a corresponding one of the first terminals, a second end disposed proximate the second surface and being electrically connected to the conductor of a corresponding one of the second terminals, and an elongated body disposed between the first end and the second end.
As another aspect of the invention, a limiter comprises: a housing comprising a first surface, a second surface opposite and distal from the first surface, and a plurality of sides disposed between the first surface and the second surface, the second surface including a plurality of openings disposed along a first straight or substantially straight line; a plurality of first terminals; a plurality of second terminals; three current limiters, each of the current limiters comprising a first end disposed proximate the first surface and being electrically connected to a corresponding one of the first terminals, a second end disposed proximate the second surface and being electrically connected to a corresponding one of the second terminals, an elongated body disposed between the first end and the second end, and a plunger, the first end including an aperture, the plunger being disposable through the aperture, the plunger of a first one of the current limiters and the plunger of a second one of the current limiters defining a second straight or substantially straight line, and the plunger of a third one of the current limiters being offset from the second straight or substantially straight line; three indicator members, each of the indicator members comprising a first end, a second end opposite and distal from the last such first end, and an indicator disposed from the last such first end, the last such second end being engaged by the plunger of a corresponding one of the current limiters, the indicator being disposable through a corresponding one of the openings of the second surface of the housing; and three spring members, each of the spring members biasing a corresponding one of the indicator members away from the second surface of the housing, wherein the housing is structured to carry two of the indicator members in a first orientation and another one of the indicator members in a different second orientation, in order that the indicator of each of the indicator members is positioned in a third straight or substantially straight line and is disposable through the corresponding one of the openings of the second surface of the housing.
The housing may further comprise a base and a cover; the cover may include a number of grooves for each of the indicator members; and each of the indicator members may further comprise a number of protrusions carried by the number of grooves.
The cover may include a plurality of grooves for each of the indicator members; each of the indicator members may further comprise a plurality of protrusions carried by a corresponding plurality of the grooves; and the grooves may carry such two of the indicator members in the first orientation and such another one of the indicator members in the different second orientation, in order that the indicators of the three indicator members are positioned in the third straight or substantially straight line and are disposable through the openings of the second surface of the housing.
The protrusions may maintain the first orientation or the different second orientation of the corresponding one of the indicator members when the corresponding one of the indicator members is biased away from the second surface of the housing and when the indicator of the corresponding one of the indicator members is disposed through a corresponding one of the openings of the second surface of the housing.
As another aspect of the invention, a trip indicator member is for a current limiter including a plunger. The trip indicator member comprises: a first end; a second end opposite and distal from the first end; a periphery including a number of alignment protrusions, each of the number of alignment protrusions being slidably engageable by a number of corresponding grooves; and a trip indicator disposed from the first end, the second end being engageable by the plunger of the current limiter, the trip indicator being disposable through an opening of a housing, and the first end being engageable by a spring member.
As another aspect of the invention, an electrical switching apparatus comprises: a circuit interrupter comprising: a housing, a plurality of first terminals, a plurality of second terminals, a plurality of separable contacts, each of the separable contacts being electrically connected between a corresponding pair of the first and second terminals, and an operating mechanism structured to open and close the separable contacts; and a limiter comprising: a housing comprising a first surface, a second surface opposite and distal from the first surface, and a plurality of sides disposed between the first surface and the second surface, the second surface including a plurality of openings disposed along a first straight or substantially straight line, a plurality of third terminals disposed proximate the first surface, a plurality of fourth terminals, each of the fourth terminals comprising a conductor disposed proximate the second surface, three current limiters, each of the current limiters comprising a first end disposed proximate the first surface and being electrically connected to a corresponding one of the third terminals, a second end disposed proximate the second surface and being electrically connected to the conductor of a corresponding one of the fourth terminals, an elongated body disposed between the first end and the second end, and a plunger, the first end including an aperture, the plunger being disposable through the aperture, the plunger of a first one of the current limiters and the plunger of a second one of the current limiters defining a second straight or substantially straight line, and the plunger of a third one of the current limiters being offset from the second straight or substantially straight line, three indicator members, each of the indicator members comprising a first end, a second end opposite and distal from the last such first end, and an indicator disposed from the last such first end, the last such second end being engaged by the plunger of a corresponding one of the current limiters, the indicator being disposable through a corresponding one of the openings of the second surface of the housing, and three spring members, each of the spring members biasing a corresponding one of the indicator members away from the second surface of the housing, wherein the housing is structured to carry two of the indicator members in a first orientation and another one of the indicator members in a different second orientation, in order that the indicator of each of the indicator members is positioned in a third straight or substantially straight line and is disposable through the corresponding one of the openings of the second surface of the housing, and wherein for each pair of the first and second terminals, one of the first and second terminals is electrically connected to a corresponding one of the third and fourth terminals.
A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
Directional phrases used herein, such as, for example, left, right, front, back, top, bottom and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the term “fastener” refers to any suitable connecting or tightening mechanism expressly including, but not limited to, screws, bolts and the combinations of bolts and nuts (e.g., without limitation, lock nuts) and bolts, washers and nuts.
As employed herein, the statement that two or more parts are “connected” or “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are “attached” shall mean that the parts are joined together directly.
The invention is described in association with a limiter for a three-pole circuit breaker including three trip indicator members, although the invention is applicable to a wide range of limiters for electrical switching apparatus, such as, for example, circuit interrupters, having plural poles and to an indicator member for a limiter having one or more poles.
Referring to
A non-limiting example of the current limiters 42,44,46 is a model NB Tri-Pac Limiter 800NBP20 marketed by Eaton Electrical, Inc. of Beaver, Pa.
As shown in
The individual current limiters 42,44,46 preferably each include a plunger 54 disposed from the second end 50 thereof. The plungers 54 of the first and second current limiters 42,44 define a straight or substantially straight line 56, and the plunger 54 of the third current limiter 46 is offset from the straight or substantially straight line 56. The plungers 54 extend away from the current limiter bodies 52 and away from the ends 48,50 in order to indicate to the user what specific pole(s) is(are) open circuit(s) as resulting from short circuit condition(s).
As shown in
Continuing to refer to
Also referring to
As shown in
Referring to
The assembly of
Upon release of the plunger 54 from the corresponding current limiter 42,44,46, which opens during the interruption of a fault, the indicator member 80 is pushed by the plunger 54, which overcomes the bias spring force, toward the housing cover 76 until a portion of the indicator 74 protrudes through (as shown in phantom line drawing in
As shown in
While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
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Number | Date | Country | |
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20080266732 A1 | Oct 2008 | US |