Patent Grant
7132616
Embodiments of the invention generally relate to the field of electrical wiring devices and, more particularly, to an electrical wiring device including a switch assembly designed to eliminate contact arcing and welding, and to a method for opening a set of closed switch contacts.
The switch component of an electrical wiring device typically includes a user accessible switch arm, rocker paddle, push button, touch pad, etc. (“switching surface”), a lever arm or suitable linkage attached to the backside of the switching surface, and a line side contact that can be connected/disconnected from a load side contact via operation of the switching surface by the user. A common single switch device for activating a remote receptacle or light, for example, typically presents the switching surface in the center of the electrical wiring device having an on/off motion along the longitudinal axis of the device. When two switches are presented on a single electrical wiring device, or a switch and a receptacle, for example, are presented on a single device, the switching surface(s) operates in a direction that is transverse to the length of the device. Accordingly, switch placement, orientation, size and ergonomics become considerations in modern, functional and aesthetic switch design.
Safety is a further major consideration in the design and operation of electrical wiring devices. For example, a receptacle disposed in an electrical distribution system may supply power through a user attachable plug to a load or to other receptacles. In certain environments where a greater likelihood for an electrical shock hazard exists, such as in a residential bathroom or kitchen, for example, the receptacle may include a circuit protection component, e.g., a ground fault circuit interrupter (GFCI). However, the use of wiring devices having a circuit protection component or capability is in no way limited to this exemplary environment. GFCIs have been known for many years. Their intended purpose is to protect the electrical power user from electrocution when a hazardous ground fault condition is present. Ground fault conditions are an unintended current path from the line conductor having faulty or damaged insulation to ground. The shock hazard occurs when someone contacts ground and the line conductor at the same time. A fire hazard may occur if the ground fault current results in sufficient heating to ignite nearby combustibles. GFCIs configured to prevent fire but not necessarily protect a user from electrocution are known as ground fault equipment protectors (GFEPs.)
Other known protective devices include arc fault circuit interrupters (AFCIs). Their intended purpose is to protect the electrical power user from fire when a hazardous arcing condition is present. Hazardous arc fault conditions (known as series arc faults) may result from a poor electrical connection in the electrical distribution system supplying power to the load. Hazardous arcing conditions (known as parallel arc faults) may occur between a line to line conductor, line to neutral conductor, or line to ground conductor, due to faulty or damaged insulation. The heat associated with the arc fault condition may be sufficient to ignite nearby combustibles.
Known protective devices such as GFCIs, GFEPs, AFCIs or combinations of such devices are configured to protect an electrical distribution system from at least one fault condition. Such devices are typically provided with line terminals for coupling to the supply voltage of the electrical distribution system, and load terminals coupled to the protected portion of the system and a circuit interrupter for disconnection of the load terminals from the line terminals. Load terminals may include plug receptacles for electrical connection of a user attachable load through a plug. Load terminals may include feed-through terminals for attachment to other receptacles. The protective device may be provided with a sensor for sensing the fault, a detector for establishing if the sensed signal represents a true hazardous fault, as opposed to electrical noise, and a switch responsive to the detector sensor, wherein the circuit interrupter comprising the contacts of a relay or trip mechanism are operated by a solenoid responsive to the switch to disconnect the load terminals from the line terminals. The disconnection is also known as tripping. A power supply may be required to furnish power to the sensor, detector, switch or solenoid.
One disadvantage of known combination devices, herein illustrated as a switch in combination with a protection component, is that the user accessible switch toggles in a motion that is parallel to the minor (latitudinal) axis of the device. The user of the device does not find such rocking motion to be ergonomic. Another disadvantage is that such rocking motion is not consistent with other wiring devices whose rocking motion is perpendicular to the minor axis of the device. Another disadvantage of known combination devices is that the user accessible switch portion of the combination device has been limited in number to a single switch.
Another disadvantage of known switch assemblies and combination devices is that the user accessible switch portion may fail to open because the switch contacts permanently remain in the closed position. Such permanent switch closure may occur for the following reasons: The contacts of the switch erode during opening and closing actuations until the contacts metallurgically bond (weld) together. Such erosion is caused by electrical arcing that occurs when the switch is called upon to make or break load current. Arcing during contact mating (contact closure) occurs in the following manner. At the moment of closure one contact strikes the other. Load current is established, but the striking motion causes the contacts to momentarily repel apart (known as contact bounce.) Even though the contacts have separated, load current continues by way of an electrical arc. The temperature of the arc is greater than the melting point of the contact material, causing contact material to melt. The contacts reclose after the bounce energy has dissipated, at which time the electrical arc extinguishes. However, when the contacts reclose, there is a layer of molten contact material between the two contacts that solidifies once the contacts are closed and there is no longer heat generated by the arc. If the bounce is severe enough, the resulting molten material is sufficient to permanently join the contacts together, that is, the switch mechanism is incapable of breaking the weld connection. During contact break (contact opening), load current does not immediately stop flowing the moment that the contacts open. For DC electrical distribution systems, an electrical arc is generated when the contacts open that continues until the contacts have become sufficiently separated from each other. For AC electrical distribution systems, the arc continues until a zero-crossing in the load current occurs or until the contacts become sufficiently separated, whichever happens first. The arc energy during contact opening roughens the surfaces of the contacts that mate with each other during the next closing operation, which exacerbates welding due to contact bounce. In general, the amount of heat generated by an arc increases as the distance between the contacts during the arcing event increases. Another cause of contact erosion includes mechanical abrasion of the contacts during repeated opening and closing operations. Permanent switch closure can also result from contaminants in the vicinity of the switch. Such contaminants can cause the switch contacts to corrode together. Also, contaminants of a particulate nature can impede the motion of the moving parts in the switch assembly, thus preventing the opening of the switch contacts.
In view of the foregoing and other reasons that will be recognized by those skilled in the art, the inventors have recognized a need to provide a compact switch assembly for use in an electrical wiring device that is functional and ergonomic. There is also a recognized need for a combination device (i.e., circuit interrupter and one or more switch assemblies) that is ergonomic and convenient to use. There is a further recognized need for a switch that can be opened and closed reliably under expected use conditions.
Embodiments of the invention are directed to an electrical wiring device including a switch assembly and to an electrical wiring device including one or more of the switch assemblies in combination with a circuit protection component.
A particular embodiment of the invention is directed to an electrical wiring device configured to be disposed in an electrical distribution system including a power source for providing power to a load. The device includes a compact switch assembly comprising a rocker assembly having a user accessible surface responsive to an applied force, a fixed contact assembly having a fixed switch contact and a terminal, and a moveable contact assembly for effecting an open contact position and a closed contact position. The moveable contact assembly includes a pivot member having a lever arm portion and an opposing contact end with a contact. In an aspect, the pivot member has a curved portion intermediate the lever arm portion and the contact end. The pivot member is substantially inflexible in response to any mechanical force applied to operate the switch assembly. By means of the shape and rigidity of the pivot member and the cooperative engagement of selective surfaces of the rocker assembly with the pivot member upon actuation of the user accessible surface, the fixed contact and the pivot member (moveable) contact can be moved from the closed contact position to the open contact position in multiple steps in such a manner that the switch contacts will open, minimizing contact arcing that could otherwise result in a welded contact condition. The pivot member has an operational direction of motion the same as the direction of operational motion of the rocker assembly. In an aspect, the open contact position comprises a first contact separation distance in a first step and a greater second contact separation distance in a further step in response to a typical force applied to the user accessible surface in the operation of the switch. In an aspect, the electrical distribution system is an alternating current (AC) system. In a particular aspect, the pivot member is moved from the closed contact position to no more than the first contact separation distance within a half cycle duration of the current to a load connected to the device. In an aspect, the switch assembly has an operational current handling capacity of 15 amperes (A) or greater. In an aspect, the electrical wiring device includes two or more independent rocker assemblies and corresponding switch assemblies. In an aspect, all of the multiple fixed contacts are located on a common member having a single terminal connectable to a line or a load. In an aspect, the switches are single pole switches.
Another embodiment of the invention is directed to an electrical device as recited in the embodiment immediately above and according to its various aspects, further including a circuit interrupter configured to provide power to a portion of the electrical distribution system in the closed contact position and to interrupt power from a portion of the electrical distribution system in the open contact position in response to a predetermined fault condition in the electrical distribution system. In an aspect, the predetermined fault condition includes a ground fault condition. In an aspect, the predetermined fault condition includes an arc fault condition.
Another embodiment of the invention is directed to a method for opening a set of closed switch contacts in a switch assembly of an electrical device configured to provide the rated current of an AC electrical distribution system to a load. In an aspect, the method involves providing a user accessible surface to move at least one of the contacts of the set of contacts through a progressive plurality of steps from a closed contact position to an open contact position. In an aspect, the progressive steps include applying a force to the user accessible surface so as to urge the switch contacts to separate from each other, continuing to apply force to the user accessible surface so as to separate the contacts to a first contact separation distance and continuing to apply force to the user accessible surface so as to separate the contacts to a second contact separation distance. According to an aspect, applying force to the user accessible surface provides a shearing force or a torque against the closed contacts that is tangentially oriented with respect to the contact surfaces. According to an aspect, the method involves separating the contacts to the first contact separation distance within an half cycle of the current to a load connected to the device.
In each of the embodiments referred to above, the power source may be a hot line or a hot load. In each of the embodiments referred to above, the electrical distribution system is particularly rated at a current of 15 A or greater.
The foregoing and other objects, features, and advantages of embodiments of the present invention will be apparent from the following detailed description of the preferred embodiments, which makes reference to several drawing figures.
A particular embodiment of the invention is directed to an electrical wiring device configured to be disposed in an electrical distribution system including a power source for providing power to a load. The device includes a compact switch assembly. Although the components, design and principles of operation of the switch apply to a single switch, it will be understood that the description is equally applicable to two or more switches adjacently disposed in a housing.
Referring to
The switch assembly 10 also includes a fixed contact assembly 112 having a fixed switch contact 116 and a terminal 114. The switch assembly 10 further includes a moveable contact assembly 118 including a pivot member 120 rotatably mounted on a fulcrum member 124, which is connected to a terminal 128. The pivot member 120 has a lever arm end 200 and a contact end 121 having electrically connected (movable) contact 122. In the illustrated aspect, the pivot member has a curved portion 118 adjacent the lever arm end 200 and a positioning feature 126 to hold the pivot member in a spaced, pivotable relationship to fulcrum member 124. Fulcrum 124 is also referenced to the housing of the wiring device. Fulcrum 124 electrically connects pivot member 120 to terminal 128. The electrical connection may be made by way of a knife edge 125 whose length corresponds to a substantial portion of the width of pivot member 120. Knife edge 125 is configured to distribute heat generated by the electrical connection.
The force of spring 108 urges the actuation surface 132 of post 110 to be in constant contact with the surface of pivot member 120. When the rocker assembly is in a position of contact with stop 130 of the device housing as shown in
In particular, from an open contact position as illustrated in
As this occurs, actuation surface 132 of post 110 slides on the surface of pivot member 120 as shown by directional arrow E, prior to reaching the fulcrum 124. Therefore, post 110 continues to exert downward force on the pivot member 120 that tends to close contacts 122, 116. However, a comparatively stronger force to pivot member 120 is applied by way of user surface 104 to striking surface 202 of the rocker assembly 100, to a lever arm portion 200 on pivot member 120. The force exerted by way of lever arm portion 200 tends to start to open contacts 122, 116 at 204. Since the coupled force from lever arm portion 200 is greater than the force from the actuation surface 132 of post 110, pivot member 120 rotates in the contact opening direction as shown by directional arrow F. In other words, the contact separation is initiated by way of lever arm 200, not by post 110. In particular, contact separation is caused by a force applied to (moveable) contact 122 that is tangential (T) with respect to the mating surface of fixed contact 116. Positioning feature 126 may be configured to permit any necessary tangential motion in pivot member 122.
Although the contacts 122, 116 have separated, electrical connectivity between terminals 114 and 128 continues due to the electrical arc generated between contacts 116, 122 upon separation. For AC power distribution systems, the electrical arc persists until a subsequent zero crossing of the load current occurs. The energy of the arc is minimized if the contacts separate from each other to less than a predetermined first separation distance 206. The switch assembly 10 adheres to the predetermined distance objective even if force is abruptly applied to user surface 104. The predetermined distance is chosen that is suitable for the given source voltage and frequency of the power distribution system. In a switch embodiment intended for a 120VAC, 60 Hz electrical distribution system, for example, a first contact separation distance 206 is less than about 0.03 inches at 0.008 seconds after the contacts have started to separate. In a particular aspect, the first contact separation distance is about 0.02 in.
The force exerted against lever arm 200 by striking surface 202 and the resulting torque exerted at the contact interface will be sufficient to urge contacts 116 and 120 to separate from each other even if they are welded together. It is desirable to prevent the user from being able to tease the contacts into the closed position by applying force to user surface 104. The switch is vulnerable to reclosure due to the separation of the contacts being a small distance, as has been described. Such reclosure, under electrical load, results in excessive arcing that could result in a strong welded condition that even the lever arm 200 is incapable of breaking. The teasing problem is remedied by limiting the angle of rotation of the switch assembly 100 in which the first contact separation distance occurs, to about 5 degrees. It is improbable that the user can maintain the rocker within this angle of rotation to damage the switch contacts.
Referring now to
Now referring to
The presence of curved portion 406 intermediate the lever arm portion 200 and the contact end 121 of pivot member 120 is advantageous for several reasons. Pivot member 120 can be formed as a unitized piece from a malleable and highly conductive material, such as copper. The pivot member is able to occupy a miniature space within the wiring device. The curved portion 406 functionally assists in breaking a welded contact condition.
In an aspect, spring 108 can be configured to ‘bottom out’ when contacts 116, 122 are welded together and force is applied to user surface 104 to cause post surface 132 to slide into curved portion 406. Force applied to user surface 104, no longer limited by spring 108, is directly applied to surface 132. Accordingly, the force applied by surface 132 to curved portion 406 is sufficient to break the welded contacts apart from each other.
In another approach, a distal surface portion 408 of rocker arm striking surface 202 can be configured such that force applied to user surface 104 communicates force by way of distal surface 408 to curved surface 406 to force the welded contacts to break apart from each other, as illustrated in
Electrical distribution circuits are configured to distribute a magnitude of current up to and including a rated current. Residential distribution circuits, for example, are typically rated to at least 15 Amperes. A switch disposed in the wiring device is needed that is configured to repeatably turn on, provide, and turn off such current. According to embodiments of the invention, the pivot member 120 has a thickness that conducts the electrical current without overheating. The given thickness renders pivot member 120 substantially inflexible to applied forces. In contrast to currently available switch cantilever arms, the ability to open and close the switch contacts does not rely on the pivot member (or another member) to substantially flex. Furthermore, a switch mechanism made up of a substantially inflexible member has been found by the inventor to be extremely desirable for a switch included with a protective device, in which the switch is required to switch the rated current of the electrical distribution system.
According to an embodiment of the invention, a protective device is disposed in the wiring device for protecting a portion of the electrical distribution system from a predetermined condition. The protective device portion occupies space that would otherwise be available to the switch. The switch assembly needs to connect and disconnect the current, but must be configured to fit within the available space at the same time.
Referring to
As shown in
In another approach, the device can be configured such that the compact switch assembly is internally connected to either the line terminals or the feed-through terminals of the protection component, in which case terminal 114 can be omitted. Load terminals 128 allow the installer to connect the switch assembly to one or more load, as has been described.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
This application is a continuation-in-part of U.S. Ser. No. 10/994,662 filed on Nov. 22, 2004, which itself claims priority to U.S. Provisional Application Ser. No. 60/553,795 filed on Mar. 16, 2004, and claims the benefit of priority to these prior applications under 35 U.S.C. §119 and §120. These applications are both herein incorporated by reference in their entireties.
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| Number | Date | Country | |
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 10994662 | Nov 2004 | US |
| Child | 11058865 | US |
