Patent Application
20110205005
The present invention relates generally to a plastic cradle. More particularly, the invention encompasses a plastic cradle utilized inside a molded circuit breaker (MCB). The present invention is also directed to a novel nonconductive nonmagnetic cradle that engages a contact arm between a first terminal conductor and a second terminal conductor inside a molded circuit breaker (MCB) in an ON state, and disengages same in an OFF or Neutral state.
Circuit breakers typically have an operating mechanism, and a tripping mechanism, such as, a thermal trip assembly and/or a magnetic trip assembly, which are automatically releasable to effect the tripping operation, and then are manually resettable following the tripping operation.
Such circuit breakers, have commonly been referred to as “miniature” circuit breakers, and have been in use for many years. Their design has been improved upon so as to provide an effective, reliable circuit breaker, which can be easily and economically manufactured on a large scale. In addition, circuit breakers of this type may be utilized in conjunction with are fault and/or ground fault trip mechanisms as well.
Circuit breakers of this type include at least one set of separable contacts disposed within a non-conductive housing. Typically, there is a fixed contact attached to the housing and a movable contact coupled to the operating mechanism. The operating mechanism includes a movable operating handle that extends outside of the housing. The operating mechanism further includes an operating arm, upon which the movable contact is disposed, the trip mechanism, and a cradle. The cradle is coupled to a spring and is pivotally disposed between the trip mechanism and the operating arm. One portion of the cradle pivots with respect to the housing while another portion of the cradle has a latch ledge, which is latched by the trip mechanism.
The operating member or handle has essentially two or three stable positions: (1) ON and OFF; or (2) ON, OFF and TRIPPED. In the latter case, the three positions tell the operator what condition the circuit breaker is operating in when viewed. In normal operation, the handle is maintained in the ON position. Then, once the trip mechanism is automatically released, in order to protect electrical circuitry from damage due to an overcurrent condition, such as, an overload or relatively high level short circuit, the handle automatically moves to the TRIPPED position. The circuit breaker must then be reset, as is well known in the art, by moving the handle beyond the OFF position to a RESET position from which the handle returns to the OFF position when released. The circuit breaker may then be manually operated from the OFF to the ON position, in order to allow the circuit breaker to resume normal operation. In addition, the handle is manually maneuverable from the ON to the OFF position if it is desired to open the protected circuit. A typical circuit breaker is calibrated, for example, to maintain a current flow of 100% of its rated current and to trip within predetermined times at 135% or 200% of such rated current.
The following patents are indicative of the state of the art for miniature circuit breakers: U.S. Pat. No. 6,005,207 (Bernard DiMarco, et al.), U.S. Pat. No. 6,172,586 (James F. Ferree, et al.), U.S. Pat. No. 6,392,512 (James Edward Ferree, et al.), U.S. Pat. No. 6,850,134 (Edward E. Lias, et al.), U.S. Pat. No. 6,894,594 (Joseph P. Fello, et al,), and U.S. Pat. No. 7,800,007 (Narayansamy Soundararajan, et al.).
However, there is room for improvement in circuit breaker operating mechanisms to prevent arcing, magnetic flux physically displacing component, heat degenerating components.
This invention improves on the deficiencies of the prior art, and provides an inventive molded circuit breaker (MCB).
The invention is a novel molded circuit breaker (MCB).
Therefore, one purpose of this invention is to provide a molded circuit breaker (MCB).
Another purpose of this invention is to provide a non-electrically conductive cradle in a molded circuit breaker (MCB).
Yet another purpose of this invention is to provide molded non-electrically conductive cradle for use in a molded circuit breaker (MCB).
Therefore, in one aspect this invention comprises a molded circuit breaker for an electrical circuit, comprising:
In another aspect this invention comprises a molded circuit breaker for an electrical circuit, comprising:
Although the scope of the present invention is much broader than any particular embodiment, a detailed description of the preferred embodiment follows together with drawings. These drawings are for illustration purposes only and are not drawn to scale. Like numbers represent like features and components in the drawings. The invention may best be understood by reference to the ensuing detailed description in conjunction with the drawings in which:
The inventive cradle is one part of the circuit breaker which is used to operate the molded circuit breaker (MCB). It should be appreciated that in the prior art the cradle is a ferrous material, such as, steel or stainless steel materials, which are also electrically conductive materials. The ferrous material is always attracting the arc during fault current, creating a secondary current path. The ferrous material of the cradle of the prior art generates a magnetic field when current flows through the cradle thus causing magnetic attractive forces on the adjacent metal parts thus causing displacement of the adjacent part. However, with a nonconductive and nonmagnetic cradle of this invention, the tracking or attracting of the arc during fault current is prevented. Since, the non-electrically conductive and non-magnetic cradle of this invention cannot conduct an electrical current, no magnetic field is generated, eliminating the magnetic forces on the adjacent components to cause displacement. The nonconductive and nonmagnetic cradle of this invention is composed of a nonconductive, nonferrous material such as a plastic.
As stated earlier the low voltage circuit breaker is designed to protect an electric circuit and its components due to overload and short circuit. Its basic function is to detect a fault condition, by interrupting continuity, to immediately discontinue electrical flow.
Three basic operating conditions must be presented on each circuit breaker, which are close electric circuit, open the electric circuit, and reset if the circuit breaker is tripped by overload and/or short circuit. The cradle is one of the components to accomplish these operations.
As stated earlier, there are several major problems presented by the cradles of the prior art. For example, the steel cradles attract the arc when the contacts open, which results in the arc sugaring and eroding of the operating parts unexpectedly.
Additionally, the electrical conductivity creates a second undesirable current path which is parallel to the main current path. During the current fault the second current path could pass enough current sharing with the main current path, which will heat each part of the second path and anneal some of them. Consequently some of the operating parts are disabled.
Furthermore, an electric sparking and arcing could happen due the difference of the electric potentials between the main and the second current path. In this case the parts could be damaged or even welded to each other and may not be able to function.
Moreover, due to the use of ferrous material the magnetic flux is created during the arc fault which also causes the magnetic field, which in turn also causes the physical displacement of some of the metal parts, such as, for example, the braid, and particularly those parts that are formed of a ferrous material. It has now been discovered that the physical displacement of the metal parts also causes failure in the whole mechanical system. Additionally, the conventional metal cradle is difficult to manufacture in terms of dimensional control under the manufacturing process.
The molded circuit breaker for an electrical circuit of this invention has a line terminal having a stationary contact, an operating mechanism for separating contacts by handle, plastic cradle, a contact arm having a movable contact, and an operating spring, a trip unit for actuating or operating mechanism to latch or de-latch when a fault and or over load current are detected in electrical circuit, which include armature, armature spring, bimetal, load terminal, and a wire connector.
The plastic cradle is a nonconductive, nonmagnetic material, which eliminates the secondary electric path, even though the plastic cradle is physically close to or adjacent the electric circuit or electrically conductive materials, such as, the armature, operating spring, contact arm, movable contact, stationary contact, load terminal, line terminal, etc.
The nonconductive, nonmagnetic cradle of the molded circuit breaker of this invention eliminates the magnetic field generated by the current when overload and/or fault current as in the cradle of the prior art, thus eliminating any physical forces on adjacent parts or parts in close proximity and not causing damage to the adjacent parts.
With the plastic cradle in the place, the elimination of the secondary current path prevents arcing and/or sparking between the cradle of this invention and the braid since no electric potential can exist.
The metallic cradle of the prior art is a stamped part to meet the requirements of the strength and the dimensionality. When the arc occurs during the arc fault, it will erode and heat some parts near the metallic cradle, which further disables the operating system. This also creates the secondary current path white the contacts are closed.
The arc erosion damages the contact arm, operating spring, and the metallic cradle itself thus causing the circuit breaker to potentially malfunction. The failure of the metallic cradle of the prior art within the circuit breaker causes failure of required standard tests.
The secondary current path permits current flow when the contacts are not closed. This in turn heats the parts of the path, such as the operating spring. The overheating of the operating spring anneals and disables the operating spring and ultimately causes failure.
The tolerances of the dimensions during the process in the stamping and the plating of the metallic part are difficult to control in the manufacture of the ferrous metal cradle of the prior art. In the manufacture of the molded non-metallic, nonconductive, nonmagnetic cradle of this invention, the tolerance is easy to control. The nonmetallic nonconductive, nonmagnetic cradle of this invention will not be plated as the ferrous metal cradle of the prior art, thus the nonconductive, nonmagnetic cradle of this invention will be a more environment friendly product and will also result in the cost reduction of the part.
The low voltage molded circuit breaker is packed by several major units which includes the operation mechanism, thermal and magnetic trip unit, terminals and lugs, arc quenching assembly, and a molded plastic case. In the operation mechanism unit it includes four parts which are a handle, an operating spring, a cradle, and a movable contact arm. In this invention a molded plastic cradle is introduced to replace a metallic cradle.
In the switch operation or close and open the electric circuit, the plastic cradle does not rotate. It supports the operating spring while the handle swings between “ON’ and “OFF” positions. When an over load and a fault current are detected in the electric circuit the circuit breaker is de-latched immediately. The plastic cradle is forced to rotate direction rapidly. In this situation the arc is drowned by the movable contact, directed towards the arc chutes, and is not attracted by the plastic cradle. This invention also eliminates the second electric path, prevents annealing of the parts, does not generate sparks, and limits the braids movement to disable the operating system.
Referring now to
The molded circuit breaker 23, comprising of a trip unit connected such that the nonconductive nonmagnetic cradle 30, automatically rotates to disengage the movable contact 42, from the stationary contact 44, to actuate the OFF position in response to a predetermined electrical overload and fault current. It should be understood that the non-electrically conductive cradle 30, is not excited by an electrical current to establish a magnetic field when the trip unit automatically actuates the OFF position in response to a predetermined electrical overload and fault current. Furthermore, the non-electrically conductive cradle 30, prevents a secondary conducting path, while a primary conductive path is created via the second terminal conductor 24, magnet 18, bimetallic strip 29, armature 26, contact arm 40, movable contact 42, stationary contact 44, and the first terminal conductor 14, in an ON position. It should be appreciated that the handle 12, can be used to move the non-electrically conductive cradle 30, from an OFF position to an ON position, and vice versa. For most applications at least a portion of the braid 48, is adjacent the nonconductive, nonmagnetic cradle 30, and wherein there is no arcing and sparking between the braid 48, and the non-electrically conductive cradle 30, when a trip unit automatically actuates the OFF position in response to a predetermined electrical overload and fault current.
It is preferred that the non-electrically conductive cradle 30, is made from a material selected from a group comprising plastic materials, polymer material, polyester material, nonconductive material, non-ferrous material, composite material, to name a few.
While the present invention has been particularly described in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.
The instant patent application claims priority to and the benefit of pending U.S. Provisional Patent Application Ser. No. 61/305,993, filed on Feb. 19, 2010, titled “Plastic Cradle,” the entire disclosure of which provisional application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61305993 | Feb 2010 | US |
