Electrical switching apparatus and retention system therefor

A retention system is for an electrical switching apparatus. The electrical switching apparatus includes a frame having a number of slots, a cover coupled to the frame, an electrical component enclosed by the frame and the cover, separable contacts enclosed by the frame and the cover, and an operating mechanism to open and close the separable contacts. The retention system includes: at least one bundle of wires having a plurality of individual wires extending through a corresponding one of the number of slots to be electrically connected to the electrical component; and at least one restriction mechanism each including an insulative sleeve surrounding a corresponding one of the at least one bundle of wires, and a blocking member connected to the insulative sleeve. The blocking member engages the frame to prevent undesired movement of the individual wires with respect to the corresponding one of the number of slots.

BACKGROUND

Field

The disclosed concept pertains generally to electrical switching apparatus, such as for example, circuit breakers. The disclosed concept also pertains to retention systems for electrical switching apparatus.

Background Information

Electrical switching apparatus are used to protect electrical circuitry from damage due to a trip condition, such as, for example, an overcurrent condition, an overload condition, an undervoltage condition, a relatively high level short circuit or fault condition, a ground fault or arc fault condition. Molded case circuit breakers, for example, include at least one pair of separable contacts which are operated either manually by way of a handle located on the outside of the case, or automatically by way of a trip unit in response to the trip condition.

Some molded case circuit breakers have wires that attach to internal components and exit the circuit breaker for use with external systems. In order for the circuit breaker to be properly certified, such as, for example and without limitation, to be properly certified by Underwriters Laboratories Inc., headquartered in Northbrook, Ill., the wiring configuration must pass a pull test. The pull test generally involves disconnecting the wires from the internal components and applying a pull force to the wires external the circuit breaker for one minute. During the test, there can be no displacement within the wire routing.

Due to advancements in technology, more features have been added internally to circuit breakers. As a result, wires having different diameters (i.e., gauges) have been employed to accommodate the internal changes. A significant drawback caused by employing the different wires is that the pull test is not always satisfied. More specifically, pull testing the different wires results in undesirable displacement of the individual wires, thereby failing the test and the ability to get the appropriate certification.

There is, therefore, room for improvement in electrical switching apparatus and in retention systems therefor.

SUMMARY

These needs and others are met by embodiments of the disclosed concept, which are directed to an electrical switching apparatus and retention system therefor, in which a restriction mechanism prevents undesired movement of individual wires.

As one aspect of the disclosed concept, a retention system for an electrical switching apparatus is provided. The electrical switching apparatus includes a frame having a number of slots, a cover coupled to the frame, an electrical component enclosed by the frame and the cover, separable contacts enclosed by the frame and the cover, and an operating mechanism to open and close the separable contacts. The retention system comprises: at least one bundle of wires comprising a plurality of individual wires structured extending through a corresponding one of the number of slots to be electrically connected to the electrical component; and at least one restriction mechanism each comprising an insulative sleeve surrounding a corresponding one of the bundle of wires, and a blocking member connected to the insulative sleeve. The blocking member is structured to engage the frame in order to prevent undesired movement of the individual wires with respect to the corresponding one of the number of slots.

As another aspect of the disclosed concept, an electrical switching apparatus is provided. The electrical switching apparatus comprises: a frame having a number of slots; a cover coupled to the frame; an electrical component enclosed by the frame and the cover; separable contacts enclosed by the frame and the cover; an operating mechanism to open and close the separable contacts; and a retention system comprising: at least one bundle of wires comprising a plurality of individual wires extending through a corresponding one of the number of slots to be electrically connected to the electrical component, and at least one restriction mechanism each comprising an insulative sleeve surrounding a corresponding one of the bundle of wires, and a blocking member connected to the insulative sleeve. The blocking member engages the frame in order to prevent undesired movement of the individual wires with respect to the corresponding one of the number of slots.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

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.

As employed herein, the statement that two or more parts or components “engage” one another shall mean that the parts touch and/or exert a force against one another either directly or through one or more intermediate parts or components.

FIG. 1shows an electrical switching apparatus (e.g., molded case circuit breaker2) in accordance with a non-limiting embodiment of the disclosed concept. The example circuit breaker2includes a frame4and a cover6coupled to the frame4. The circuit breaker2further includes an electrical component (e.g., without limitation, main printed circuit board8, shown in simplified form) enclosed by the frame4and the cover6. Also enclosed by the frame4and the cover6are a pair of separable contacts10(shown in simplified form) and an operating mechanism12(shown in simplified form) for opening and closing the separable contacts10.

Referring toFIG. 2, the circuit breaker2further includes a retention system100located on the frame4. The retention system100includes a number of bundles of wires (see, for example, three bundles of wires110,140,170) extending through the frame4. Each of the bundles of wires110,140,170has a plurality of individual wires (see, for example, individual wires112,114, shown in hidden line drawing inFIG. 3) that are each electrically connected to the main printed circuit board8(FIG. 1). Although the disclosed concept is being described in association with the two individual wires112,114, it will be appreciated that a suitable alternative bundle of wires (not shown) may also have any known number of individual wires (not shown) greater than two. The retention system100further includes a number of restriction mechanisms (see, for example, three restriction mechanisms120,150,180) that advantageously prevent undesired movement of the individual wires112,114(and the respective individual wires of the bundles of wires140,170) with respect to the frame4and with respect to each other.

Each of the respective restriction mechanisms120,150,180is secured to a respective one of the bundle of wires110,140,170. The restriction mechanisms120,150,180each include a respective insulative sleeve (see, for example, three heat shrink tubes122,152,182) and a respective blocking member (see, for example, three cable ties124,154,184) connected to a respective one of the heat shrink tubes122,152,182. Each of the respective heat shrink tubes122,152,182surrounds a respective one of the bundles of wires110,140,170. When each of the respective heat shrink tubes122,152,182is heated, such as for example, by a heat gun, the respective heat shrink tube122,152,182contracts in a manner well known in the art.

Furthermore, each of the heat shrink tubes122,152,182is adhesively bonded to a respective one of the bundles of wires110,140,170. More specifically,FIG. 4shows a simplified section view of the bundle of wires110and the heat shrink tube122. The heat shrink tube122includes an external portion126and an internal portion128. The internal portion128has an adhesive coating130that is bonded to the bundle of wires110. In this manner and as will be described below, during pull testing, the individual wires112,114(and the respective individual wires of the bundles of wires140,170) cannot move independently with respect to the respective heat shrink tubes122,152,182. Stated differently, the adhesive coating130fixes (i.e., retains) each of the individual wires112,114in the same position with respect to the external portion126.

The cable tie124is wrapped around the external portion126of the heat shrink tube122and is fastened securely. In this manner, the cable tie124advantageously applies a clamp force to the heat shrink tube122, which results in the individual wires112,114being clamped together. It will be appreciated that the respective cable ties154,184are likewise wrapped around the respective external portions of the heat shrink tubes152,182and are fastened securely. The cable ties124,154,184are each spaced from each other (i.e., the cable tie124is spaced from each of the cable ties154,184, and the cable tie154is spaced from the cable tie184). Moreover, the cable ties124,154,184are fastened securely to the respective heat shrink tubes122,152,182so as not to move independently with respect to the respective heat shrink tube122,152,182or the individual wires112,114(and the respective individual wires of the bundles of wires140,170). In other words, the heat shrink tubes122,152,182are fixed with respect to the respective cable ties124,154,184.

As shown inFIG. 5, the frame4has a number of slots (see, for example, three individual slots14,16,18) that are each spaced from each other (i.e., the slot14is spaced from the slots16,18, and the slot16is spaced from the slot18). The respective bundle of wires110,140,170each extend through a corresponding one of the slots14,16,18in order to be electrically connected to the main printed circuit board8(FIG. 1). Additionally, with reference toFIG. 1andFIG. 5, it will be appreciated that the respective cable ties124,154,184are located on the respective bundles of wires110,140,170between the respective slots14,16,18and the main printed circuit board8(FIG. 1). When the cable ties124,154,184are fastened securely to the respective bundles of wires110,140,170, the cable ties124,154,184cannot be pulled (such as for example, during pull testing) through the respective slots14,16,18.

FIG. 6shows another section view of the circuit breaker2. As shown, the frame4and the cover6are coupled to each other at a junction15. It will be appreciated that the cable tie124is located on the bundle of wires110between the junction15and the main printed circuit board8(FIG. 1). Similarly, it will be appreciated that the cable ties154,184are likewise located on the respective bundles of wires140,170between the junction15and the main printed circuit board8(FIG. 1). The cable tie124has a first distal end portion132and a second distal end portion134located opposite and distal from the first distal end portion132. The first distal end portion132of the cable tie124engages the cover6at a first location20on the cover6. The cable tie124engages the frame4at a second location22on the frame4. The second location22is located between the second distal end portion134and the first location20. Additionally, the first location20is spaced a first distance24from the second location22. The first distal end portion132is spaced a second distance136from the second distal end portion134. As shown, the second distance136is greater than the first distance24.

As a result, the cable tie124cannot fit between (i.e., cannot be pulled through, such as for example, during pull testing) the frame4and the cover6. Stated differently, when the cable tie124is fastened securely to the heat shrink tube122, the size of the cable tie124(i.e., see for example, the distance or width136) advantageously prevents the cable tie124from being pulled through the gap between the frame4and the cover6(i.e., between the first location20and the second location22) through which the bundle of wires110extends, such as for example, during pull testing. That is, the cable tie124blocks or otherwise suitably prohibits undesired movement of the bundle of wires110and the individual wires112,114thereof.

Together, the heat shrink tubes122,152,182and the cable ties124,154,184advantageously prevent undesired movement of the individual wires112,114(and the individual wires of the bundles of wires140,170). More specifically, during pull testing for Underwriters Laboratories Inc., headquartered in Northbrook, Ill., the individual wires112,114(and the individual wires of the bundles of wires140,170) are disconnected internally from the main printed circuit board8(FIG. 1) and a pull force is applied to each of the individual wires112,114(and the individual wires of the bundles of wires140,170) for a minimum of one minute. Referring toFIG. 5andFIG. 6, the cable ties124,154,184engage the frame4and the cover6and cannot be pulled through the respective slots14,16,18. In this manner, because each of the cable ties124,154,184is fastened securely to the external portion126(and the external portions of the respective heat shrink tubes122,152,182), each of the heat shrink tubes122,152,182advantageously remains fixed with respect to the frame4and the cover6during pull testing.

Furthermore, because the heat shrink tubes122,152,182are adhesively bonded to the respective bundles of wires110,140,170, and because the respective cable ties124,154,184clamp the individual wires112,114(and the individual wires of the bundles of wires140,170) together, the individual wires112,114(and the individual wires of the bundles of wires140,170) advantageously remain fixed with respect to the respective heat shrink tubes122,152,182during pull testing. Thus, when a pull force is applied longitudinally to any one of the individual wires112,114(or the individual wires of the bundles of wires140,170), the pull force is translated to the respective heat shrink tubes122,152,182as a result of the clamp force from the respective cable ties124,154,184, and the adhesive bond (i.e., by way of the adhesive coating130(and the adhesive coating of the heat shrink tubes152,182)) between the heat shrink tubes122,152,182and the respective individual wires112,114(and the individual wires of the bundles of wires140,170).

The pull force is further translated to respective cable ties124,154,184as a result of the secure connection between the cable ties124,154,184and the respective external portions126(and the external portions of the heat shrink tubes122,152,182). However, because the cable ties124,154,184engage the frame4and the cover6and cannot be pulled through the frame4and the cover6(i.e., because the cable ties124,154,184are fixed with respect to the frame4and the cover6), undesired movement (i.e., displacement) of the individual wires112,114(and the individual wires of the bundles of wires110,140,170) is advantageously avoided. The restriction mechanisms120,150,180thus prevent longitudinal movement of the individual wires112,114(and the individual wires of the bundles of wires140,170) with respect to each other and with respect to the frame4. As a result, the pull test is advantageously able to be satisfied.

Although the disclosed concept has been described in association with the cable ties124,154,184, it will be appreciated that a restriction mechanism (not shown) may employ any known or suitable alternative blocking member (not shown) in order to perform the desired function of fixing the respective heat shrink tubes122,152,182with respect to the frame4and the cover6, and applying a clamp force to the individual wires112,114(and the respective wires of the bundles of wires140,170). Additionally, although the disclosed concept has been described in conjunction with advantages associated with passing the pull test, it will be appreciated that other advantages, such as, for example, additional insulation provided by the heat shrink tubes122,152,182, are also realized.

Accordingly, it will be appreciated that the disclosed concept provides for an improved (e.g., without limitation, able to pass testing requirements, relatively low cost, can be employed with existing designs without modification) electrical switching apparatus2and retention system100therefor, which prevents undesired movement of individual wires112,114through a frame4of the electrical switching apparatus2.