Circuit protection device

Abstract

A voltage suppression device for suppressing voltage surges in an electrical circuit, comprised of a voltage sensitive element having a predetermined voltage rating, the voltage sensitive element increasing in temperature as voltage applied across the voltage sensitive element exceeds the voltage rating. Terminals are provided for electrically connecting the voltage sensitive element between a power line of an electrical circuit and a ground or neutral line of the electrical circuit. A normally closed, thermal switch is electrically connected in series with the voltage sensitive element between the power line and the voltage sensitive element, the thermal switch being thermally coupled to the voltage sensitive element wherein the thermal switch moves from a normally closed position to an open position to form a gap between the thermal switch and the voltage sensitive element when the temperature of the voltage sensitive element reaches a level indicating an over-voltage condition. A non-conductive barrier that is operable to move into the gap when the thermal switch moves to an open position, the barrier preventing line voltage surges from arcing between the thermal switch and the voltage sensitive element.

1. A disposable voltage suppression device for suppressing voltage surges in an electrical circuit, said device comprised of:
 a voltage sensitive element having a first surface and a second surface and a predetermined voltage rating across said first and second surfaces, said voltage sensitive element increasing in temperature as voltage applied across said first and second surfaces exceeds said voltage rating; 
 a first terminal having one end electrically connected to said first surface of said voltage sensitive element and another end connectable to a ground or neutral line of an electrical circuit; 
 a thermal element electrically connected to said second surface of said voltage sensitive element, said thermal element being an electrically conductive solid at room temperature and having a predetermined softening temperature; 
 a second terminal having one end in electrical connection with said second surface of said voltage sensitive element and another end connectable to an electrical power line of an electrical circuit, said voltage sensitive element sensing the voltage drop between said electrical power line and ground or neutral line, said second terminal being maintained in electrical contact with said voltage sensitive element by said thermal element and being biased away therefrom, wherein said second terminal moves away from electrical contact with said voltage sensitive element and breaks said electrical current path if an over-voltage condition sensed by said voltage sensitive element exceeds the voltage rating of said voltage sensitive element and causes said voltage sensitive element to heat said thermal element beyond its softening point; 
 an arc shield movable from a first position wherein said arc shield allows contact between said second terminal and said voltage sensitive element to a second position wherein said shield is disposed between said second terminal and said voltage sensitive element when said second terminal moves from electrical contact with said voltage sensitive element; and 
 a housing enclosing said voltage sensitive element, said one ends of said first and second terminals, said thermal element and said arc shield; and 
 a wall contained within the housing for separating the voltage sensitive element from the arc shield over a substantial portion of the length of the arc shield. 
 
     
     
       2. A voltage suppression device as defined in  claim 1 , wherein said voltage sensitive element is a metal oxide varistor (MOV); and
 the arc shield is movable along the wall that separates it from the voltage sensitive element. 
 
     
     
       3. A voltage suppression device as defined in  claim 2 , wherein said metal oxide varistor (MOV) is rectangular in shape. 
     
     
       4. A voltage suppression device as defined in  claim 1 , wherein said thermal element is a metal solder comprised of a fusible alloy; and
 the arc shield moves along the wall and passes through at least a portion of a gap that is formed when said one of said terminals moves out of contact with the voltage sensitive element. 
 
     
     
       5. A voltage suppression device as defined in  claim 4 , wherein said metal solder has a melting point of about 95° C. 
     
     
       6. A voltage suppression device as defined in  claim 1 , wherein said thermal element is an electrically conductive polymer. 
     
     
       7. A voltage suppression device as defined in  claim 1 , wherein said the wall has an opening that is aligned with the thermal element, and the arc shield is supported in said a first position by to provide access to said thermal element for passage of said second terminal. 
     
     
       8. A voltage suppression device as defined in  claim 1 , further comprising a third terminal having one end in electrical connection with said second surface of said voltage sensitive element and another end connectable to an indicator device for indicating whether said second terminal is in electrical connection with said thermal element. 
     
     
       9. A voltage suppression device as defined in  claim 8 , wherein said indicator device is a light emitting device. 
     
     
       10. A voltage suppression device as defined in  claim 8 , wherein said indicator device is mounted to said housing. 
     
     
       11. A voltage suppression device as defined in  claim 1 , wherein said arc shield is biased toward said second position and it moves along a path that is substantially parallel to the wall. 
     
     
       12. A voltage suppression device as defined in  claim 11 , wherein said arc shield is biased by gravity. 
     
     
       13. A voltage suppression device as defined in  claim 11 , wherein said arc shield is biased by a spring element. 
     
     
       14. A voltage suppression device as defined in  claim 13 , wherein said arc shield is maintained in said first position by said second terminal when said second terminal is in contact with said thermal element. 
     
     
       15. A voltage suppression device as defined in  claim 1 , further comprising indication means for indicating the condition of said voltage suppression device. 
     
     
       16. A voltage suppression device as defined in  claim 15 , wherein said indication means is an electrical switch. 
     
     
       17. A voltage suppression device as defined in  claim 15 , wherein said indication means is a mechanical indicator. 
     
     
       18. A voltage suppression device for suppressing voltage surges in an electrical circuit, said device comprised of:
 a voltage sensitive element having a predetermined voltage rating, said voltage sensitive element increasing in temperature as voltage applied across said voltage sensitive element exceeds said voltage rating; 
 terminals for electrically connecting said voltage sensitive element between a power line of an electrical circuit and a ground or neutral line of said electrical circuit; 
 a normally closed, thermal switch comprised of one end of one of said terminals, a surface of said voltage sensitive element and a thermal element, said one end of one of said terminals being maintained in electrical contact with said surface of said voltage sensitive element by said thermal element, said thermal switch being electrically connected in series with said voltage sensitive element between said power line and said voltage sensitive element, said thermal switch being thermally coupled to said voltage sensitive element wherein said one of said terminals moves from a normally closed position wherein said one of said terminals is maintained in electrical contact with said surface of said voltage sensitive element to an open position wherein said one of said terminals moves out of electrical contact with said surface of said voltage sensitive element to form a gap between said one of said terminals and said voltage sensitive element when the temperature of said voltage sensitive element reaches a level causing said thermal element to melt; 
 said one of said terminals including a contact portion and a second portion that extends away from the contact portion; 
 a non-conductive barrier operable to move into said gap when said one of said terminals moves to an open position, said barrier preventing line voltage surges from arcing between said one of said terminals and said voltage sensitive element, 
 the second portion of said one of said terminals extends over at least a portion of the non-conductive barrier and bends toward the thermal element so that the contact portion is held by the thermal element until said thermal element begins to melt, and 
 said non-conductive barrier being biased toward the thermal element, but being constrained from movement toward the thermal element by contact with the second portion of said one of said terminals at a location that is spaced away from the contact portion, until said thermal element begins to melt. 
 
     
     
       19. A voltage suppression device as defined in  claim 18 , wherein said voltage sensitive element is a metal oxide varistor (MOV), said voltage suppression device further including:
 a housing having walls, a top member and a base member, connected to one another to form an enclosure; 
 a partition within said enclosure separating a first portion of the enclosure from a second portion thereof; 
 the voltage sensitive element being located in the first portion of the enclosure; 
 an opening in the partition providing access to said thermal element on the voltage sensitive element for the passage of one of said terminals; 
 the non-conductive barrier being located in the second portion of the enclosure adjacent the partition; and 
 said non-conductive barrier operating to move along the partition to pass into said gap so as to intercept an arc in the gap between the voltage sensitive element and said one of said terminals. 
 
     
     
       20. A voltage suppression device as defined in  claim 18 , further comprising an indicator device for indicating the condition of said voltage suppression device claim 19, wherein the non-conductive barrier is a generally flat plate that is located along a path that is generally parallel to the partition that separates the first portion of the enclosure from the second portion of the enclosure; and
 the second portion of said one of said terminals is located along a path that intercepts the path of the non-conductive barrier. 
 
     
     
       21. A voltage suppression device as defined in  claim 20 , wherein said indicator device is actuated by movement of said barrier the non-conductive barrier is located between the partition and said one of said terminals before passing into the gap between said one of said terminals and said voltage sensitive element. 
     
     
       22. A voltage suppression device as defined in  claim 21 , wherein said indicator device is an electrical switch the partition has an opening adjacent the thermal element,
 the non-conductive barrier has an opening at least a portion of which is in line with the opening in the partition. 
 
     
     
       23. A voltage suppression device as defined in  claim 21 , wherein said indicator device is a mechanical device said one of said terminals passes along the non-conductive barrier and bends toward the thermal element to pass through the opening in the partition, to connect to the thermal element. 
     
     
       24. A voltage suppression device as defined in  claim 18 , wherein said thermal switch is comprised of a contact element held in electrical contact with said voltage sensitive element by a said thermal element, said contact element being biased away from said voltage sensitive element. 
     
     
       25. A voltage suppression device as defined in  claim 24 , wherein said thermal element is a low melting temperature solder material. 
     
     
       26. A voltage suppression device as defined in  claim 18 , further comprising a detachable base section attachable to said ground or neutral line and said power line of said electrical circuit, said voltage suppression device being received by said base section with said terminals connecting said voltage sensitive element between said power line of said electrical circuit and said ground or neutral line of said electrical circuit. 
     
     
       27. A voltage suppression device as defined in  claim 26 , wherein said voltage suppression device is received by said base section in snap-lock fashion. 
     
     
       28. A voltage suppression device as defined in  claim 26 , wherein said voltage suppression device and said base section include matching identification markings claim 18, wherein the non-conductive barrier is in a stationary state adjacent the partition before the thermal element softens and, when the thermal element softens, the non-conductive barrier passes along the partition to the location of the thermal element to intercept an arc that exists between said voltage sensitive element and said one of said terminals. 
     
     
       29. A voltage suppression device for suppressing voltage surges in an electrical circuit, said device comprised of:
 a voltage sensitive element having a first surface and a second surface and a predetermined voltage rating across said first and second surfaces, said voltage sensitive element increasing in temperature as voltage applied across said first and second surfaces exceeds said voltage rating; 
 a first terminal having one end electrically connected to said first surface of said voltage sensitive element and another end connectable to a ground or neutral line of an electrical circuit; 
 a thermal element electrically connected to said second surface of said voltage sensitive element, said thermal element being an electrically conductive solid at room temperature and having a predetermined softening temperature; 
 a second terminal formed of a spring metal having one end in electrical connection with said second surface of said voltage sensitive element and another end connectable to an electrical power line of an electrical circuit, said voltage sensitive element sensing the voltage drop between said electrical power line and ground or neutral line, said second terminal being bent from a normal and relaxed configuration maintained in contact with said voltage sensitive element by said thermal element, said second terminal being inherently biased away from said voltage sensitive element toward said normal and relaxed configuration, wherein said second terminal springs away from electrical contact with said voltage sensitive element and breaks said electrical current path if an over-voltage condition sensed by said voltage sensitive element exceeds the voltage rating of said voltage sensitive element and causes said voltage sensitive element to heat said thermal element beyond its softening point; 
 an arc shield movable from a first position wherein said arc shield allows contact between said second terminal and said voltage sensitive element to a second position wherein said arc shield is disposed between said second terminal and said voltage sensitive element when said second terminal moves from electrical contact with said voltage sensitive element; and 
 the second terminal having a contact portion for making electrical contact with the thermal element and a second portion, the second portion extending through the path of the arc shield and blocking the movement of the arc shield until the thermal element reaches its softening point; and 
 a housing enclosing said voltage sensitive element, said one ends one end of each of said first and second terminals, said thermal element and said arc shield. 
 
     
     
       30. A voltage suppression device as defined in  claim 29 , wherein said arc shield includes an indicator portion that provides a visual indication external to said housing of movement of said arc shield. 
     
     
       31. A disposable voltage suppression device as in claim 1, wherein
 said second terminal has a contact portion and a second portion that extends away from the contact portion, at least the second portion of said second terminal being flexible and being located over at least a portion of the arc shield and being bent into a bent condition toward the thermal element,   said contact portion of said second terminal being held in electrical contact with the voltage sensitive element by the thermal element before the thermal element softens,   said second terminal flexing outward away from the thermal element when the thermal element softens, and   the arc shield being biased toward the thermal element before the thermal element softens, but being constrained from movement toward the thermal element by the second portion of said second terminal at a location along the second portion that is spaced away from the contact portion, until the thermal element softens and said second terminal flexes outward away from the thermal element.   
     
     
       32. A disposable voltage suppression device as in claim 31., wherein said second terminal is released from said bent condition and it flexes outward to a more straightened condition, when the thermal element softens. 
     
     
       33. A disposable voltage suppression device as in claim 31, wherein
 the second terminal flexes outward to a position spaced from the thermal element when the thermal element softens, and   at least a portion of the arc shield passes between the thermal element and said second terminal when the voltage across the voltage sensitive element exceeds the voltage rating of the voltage sensitive element and heats up the voltage sensitive element so as to soften the thermal element.   
     
     
       34. A disposable voltage suppression device as in claim 1, wherein
 in the normal a operation of the voltage sensitive element the thermal element is solid, but when the voltage across the voltage sensitive element increases beyond the voltage rating of the voltage sensitive element, the voltage sensitive element heats up to a temperature at or above said predetermined softening temperature and the increased heat causes the thermal element to soften,   said second terminal has a contact portion and a second portion that extends away from the contact portion,   the contact portion of said second terminal is held in electrical contact with the voltage sensitive element solely by the thermal element and the second portion of said second terminal is positioned to block the path of the arc shield prior to the time that the thermal element softens, and the contact portion of the second terminal is released from the thermal element when the thermal element softens, and   the second terminal moves away from the thermal element, when the thermal element softens, and releases the arc shield to pass along a path in close proximity to the thermal element.   
     
     
       35. A disposable voltage suppression device as in claim 1, wherein
 said second terminal has a contact portion and a second portion, said contact portion being held in electrical contact with the voltage sensitive element by the thermal element, and being biased away from the voltage sensitive element by internal mechanical forces in said second terminal,   said arc shield is located between the voltage sensitive element and the second portion of said second terminal while the contact portion of said second terminal is held by the thermal element,   the second portion of said second terminal extending through the path of the arc shield to constrain the movement of the arc shield prior to the softening of the thermal element, and   said arc shield traversing a path substantially parallel to the voltage sensitive element once the thermal element softens and releases the contact portion of said second terminal.   
     
     
       36. A voltage suppression device as in claim 18, wherein
 at least the second portion of said one of said terminals is flexible and is located over at least a portion of the non-conductive barrier and is bent toward the thermal element,   said contact portion of said one of said terminals is held in electrical contact with the voltage sensitive element by the thermal element before the thermal element softens,   said second portion of said one of said terminals flexes outwardly away from the thermal element when the thermal element softens, and   the non-conductive barrier is biased toward the thermal element before the thermal element softens, but is constrained from movement toward the thermal element by the second portion of said one of said terminals at a location along the second portion that is spaced away from the contact portion, until said one of said terminals flexes outward away from the thermal element.   
     
     
       37. A voltage suppression device as in claim 18, wherein
 said one of said terminals is flexible and, when released from said thermal element, it flexes outward away from said thermal element to a more straightened condition.   
     
     
       38. A voltage suppression device as in claim 18, wherein
 said non-conductive barrier is positioned with its forward edge in close proximity to the second portion of said one of said terminals,   said second portion of said one of said terminals is positioned to block the path of the non-conductive barrier prior to the softening of the thermal element.   
     
     
       39. A voltage suppression device as in claim 18, wherein
 said thermal element is formed of an electrically conductive solder,   said second portion of said one of said terminals being biased away from the thermal element by its internal mechanical forces, but its contact portion is held in electrical contact with the voltage sensitive element by the thermal element,   said second portion of said one of said terminals extends over at least a portion of the non-conductive barrier and the second portion bends toward the thermal element while the contact portion is held by the thermal element,   the non-conductive barrier is biased toward the thermal element, but is constrained from movement toward the thermal element by a region along the length of said second portion of said one of said terminals, spaced away from the contact portion, while the contact portion of said one of said terminals is held by the thermal element.   
     
     
       40. A voltage suppression device as in claim 39, further including:
 a molded plastic housing for retaining the voltage sensitive element,   at least two cavities formed in the housing, the cavities being generally cylindrical, at least two springs, one extending along the length of each of the cavities,   the springs biasing the non-conductive barrier toward the thermal element along a path that is substantially parallel to the voltage sensitive element, but the movement of the non-conductive barrier being constrained by the second portion of said one of said terminals, and   the springs advancing the non-conductive barrier toward the thermal element when the thermal element softens and the contact portion of said one of said terminals moves away from the thermal element.   
     
     
       41. A voltage suppression device as in claim 40, further including
 at least one slot along the length of the molded plastic housing, and   at least one extension from the non-conductive barrier that extends into the slot in order to guide movement of the non-conductive barrier when the thermal element softens.   
     
     
       42. A modular voltage suppression device for suppressing voltage surges in an electrical circuit, said device comprised of:
 a housing made of molded plastic having two side walls, two end walls, a top and an open end;   a base member made of molded plastic forming a base that covers the open end of the housing;   a voltage sensitive element having a predetermined voltage rating, said voltage sensitive element increasing in temperature as voltage applied across said voltage sensitive element exceeds said voltage rating;   a compartment supported by the base member and located in the housing for holding the voltage sensitive element;   terminals for electrically connecting said voltage sensitive element between a power line of an electrical circuit and a ground or neutral line of said electrical circuit;   a normally closed thermal switch comprised of one end of one of said terminals, a surface of said voltage sensitive element and a thermal element, said one end of one of said terminals being maintained in electrical contact with said surface of said voltage sensitive element by said thermal element, said thermal switch being electrically connected in series with said voltage sensitive element between said power line and said voltage sensitive element, said thermal switch being thermally coupled to said voltage sensitive element wherein said one of said terminals moves from a normally closed position wherein said one of said terminals is maintained in electrical contact with said surface of said voltage sensitive element to an open position wherein said one of said terminals moves out of electrical contact with said surface of said voltage sensitive element to form a gap between said one of said terminals and said voltage sensitive element when the temperature of said voltage sensitive element reaches a level causing said thermal element to melt;   a non-conductive barrier operable to move into said gap when said one of said terminals moves to an open position, said barrier preventing line voltage surges from arcing between said one of said terminals and said voltage sensitive element;   each of said terminals including a plug-in portion that extends from the bottom surface of said base member for plugging in the voltage suppression device and removing it from its plug-in condition; and   the compartment being supported by the base member and including a wall for separating the voltage sensitive element from the non-conductive barrier over a substantial portion of the length of the barrier.   
     
     
       43. A voltage suppressor device as defined in claim 42, further including:
 columnar channels along the wall that separates the voltage sensitive element from the non-conductive barrier;   the non-conductive barrier being movable along the wall that separates the voltage sensitive element from the non-conductive barrier.   
     
     
       44. A voltage suppressor device as defined in claim 43, further including:
 a plurality of springs in alignment with a portion of the non-conductive barrier, at least one of said springs being located in each of the channels;   the springs causing the non-conductive barrier to pass along the gap between said one of said terminals and said voltage sensitive element when the thermal element melts.   
     
     
       45. A voltage suppressor device as defined in claim 42, wherein
 said wall extends adjacent one surface of the voltage sensitive element,   an aperture in said wall provides access to the thermal element,   said one of said terminals passes over a portion of the barrier and extends through said aperture to contact the thermal element before said one of said terminals moves out of electrical contact with the voltage sensitive element; and   the non-conductive barrier moves along the wall and passes through at least a portion of the gap when said one of said terminals moves out of contact with the voltage sensitive element.   
     
     
       46. A voltage suppressor device as defined in claim 45, wherein:
 the non-conductive barrier moves along the wall and passes into the gap, between said one of said terminals and said voltage sensitive element, when said one of said terminals moves out of contact with the voltage sensitive element.   
     
     
       47. A modular voltage suppression device for suppressing voltage surges in an electrical circuit, said device comprised of:
 a housing having surrounding surfaces including walls, a top and a base, all being joined together to form an enclosure;   a compartment wall within the enclosure;   a voltage sensitive element having a predetermined voltage rating, said voltage sensitive element increasing in temperature as voltage applied across said voltage sensitive element exceeds said voltage rating;   the wall in the enclosure supported by at least one of said surfaces of the enclosure;   the voltage sensitive element being located within the enclosure;   terminals for electrically connecting said voltage sensitive element between a power line of an electrical circuit and a ground or neutral line of said circuit;   a normally closed thermal switch comprised of one end of one of said terminals, a surface of said voltage sensitive element and a thermal element;   said one end of one of said terminals being maintained in electrical contact with said surface of said voltage sensitive element by said thermal element;   said thermal switch being electrically connected in series with said voltage sensitive element and between said power line and said voltage sensitive element, said thermal switch being thermally coupled to said voltage sensitive element, wherein said one of said terminals moves from a normally closed position wherein said one of said terminals is maintained in electrical contact with said surface of said voltage sensitive element to an open position wherein said one of said terminals moves out of electrical contact with said surface of said voltage sensitive element to form a gap between said one of said terminals and said voltage sensitive element, when the temperature of said voltage sensitive element reaches a level causing said thermal element to melt;   a non-conductive barrier being urged to move toward said gap and being operable to move into said gap when said one of said terminals moves to an open position, said barrier preventing line voltage surges from arcing between said one of said terminals said voltage sensitive element;   the non-conductive barrier being located in a first position where it is stationary and located adjacent the compartment wall, and being movable generally parallel to the compartment wall to the location of the gap; and   the compartment wall being supported from at least one of the surfaces of the enclosure and separating the voltage sensitive element from the non-conductive barrier over a substantial portion of the length of the barrier at least when the non-conductive barrier is in its first position.