Patent Publication Number: US-9852869-B2

Title: Switch module with a built-in structure of anti-surge and dual disconnection

Description:
This patent application is a continuation-in-part of Ser. No. 14/950,069 filed on Nov. 24, 2015, currently pending. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a switch module with a built-in structure of anti-surge and dual disconnection, particularly to one that has conductive plates disconnecting a series connection and an anti-surge structure disconnecting a parallel connection by insulation elements. 
     2. Description of the Related Art 
       FIGS. 1A and 1B  disclose a conventional overcurrent protection switch  10  that has plural connecting points arranged in the middle part and comprises a housing  11  with a press button  12  on the top, a first terminal  12   a,  a second terminal  12   b,  a third terminal  12   c  separately arranged at the bottom, and a moving element  14 . The first terminal  12   a  has a bimetal plate  13  and a first contact  131 ; the second terminal  12   b  has a second contact  121  corresponding to the first contact  131 . The moving element  14  has one end linking the bottom of the press button  12  and the other linking the moving terminal of the bimetal plate  13 , whereby the pressing of the press button  12  actuates the first contact  131  connecting to the second contact  121  and therefore turns on the device; while overcurrent occurs, the bimetal plate  13  deforms due to high degree of temperature and disconnects the first and second contact  131 ,  121 , turning off the device so as to form an overcurrent protection switch  10 . Such structure can be found in Taiwan patent applications No. 540811, 367091, 320335, 262168, and 208384. However, the structure disclosed above aims at protection from overcurrent situation but is not able to protect the device when sudden overvoltage such as lightning strike occurs. 
     Therefore, for safety concern, a usual solution to the defect is to parallel connect to a metal oxide varistor, and to connect to a thermal fuse in series. 
       FIG. 2A  is the invention of U.S. Pat. No. 8,643,462. It discloses an anti-surge switch module applied in an electric system. The switch module comprises a power switch  105 , an insulating member  106 , a surge absorber  107  and a pyrocondensation belt  108 . The insulating member  106  engages with the power switch  105  that abutting against the surge absorber  107 ; and the pyrocondensation belt  108  ties the surge absorber  107  and the insulating member  106  together so that it could contract when receiving the heat from the surge absorber  107  and thus turn off the power switch  105  under certain degree of contracting. However, the insulating member  106 , the surge absorber  107  and the pyrocondensation belt  108  are not disposed inside the power switch  105  but are connected outside, failing to form a complete device with the power switch  105 . 
     In short, the structures disclosed above have shortcomings as uncertain quality, possible exceeding heat due to external connection of components, slow reaction, large volumes, and complicated composition, and they require more constructing space and procedures. Besides, the protection device has to be connected independently outside instead of having one inside. 
     In UL 1449 3 rd  Edition (2009) Type 4 was added to Surge Protective Devices (SPDs) requirements. The 3 rd  Edition also includes the Low voltage Surge Arresters under 1000V in the requirements, and the title is also altered from Transient Voltage Surge Suppressors into Surge Protective Devices. This shows the importance of integrating the components and the surge arresters function of the device. 
     Hence, the inventor has an invention in U.S. patent application Ser. No. 14/617,000 filed on Feb. 9, 2015 which has an anti-surge disconnection structure built inside a heat-resisting and fireproof housing of an overcurrent protection switch so that the disconnection could be operated successfully and instantly when an overload occurs. Features of the invention disclosed are illustrated in  FIG. 2B . A band  74  having a first end  741  and a second end  742  fixedly adhered on a surface of a metal oxide varistor  71  by a thermo-sensitive piece  72  to have the band  74  tightly compressing a spring  73  by wrapping it up. When overvoltage occurs, the metal oxide varistor  71  heats up and melts down the thermo-sensitive piece  72  instantly and therefore loosens the band  74  for the spring  73  to eject upwards to push a pushing rod  75  and disconnect the circuit. 
     Still, the inventor has continued to develop such feature and further designed a switch module disclosed in U.S. patent application Ser. No. 14/950,069 filed on Nov. 24, 2015. The switch module has provides the same effect in operation as the previous one. The invention also has a built-in structure that can melt down a thermo-sensitive piece by a heating metal oxide varistor for a spring element to be loosened and has an outer periphery thereof displacing a pushing rod, so as to detach a first contacting point from a second contacting point, thus disconnecting the circuit. However, both inventions can only disconnect the circuit of series connection, but cannot ensure the structure therein is completely disconnected. That is, the outer periphery of the spring element would still contacting surfaces of the metal oxide varistor; and if the entire structure cannot be disconnected thoroughly, the circuit may still be working and keep heating up, resulting in a dangerous situation. 
     On the other hand, metal oxide varistors are prone to operate function less effectively after in use for a period. To overcome such issue, manufacturers usually have a fuse connected to a metal oxide varistor for safety concerns, and the inventor therefore tries to improve such structure with a simpler and easier manufacturing process and better effectiveness based on structures of the previous inventions mentioned above. 
     SUMMARY OF THE INVENTION 
     A primary object of the present invention is to provide a switch module with a built-in structure of anti-surge and dual disconnection that has the original function of overcurrent protection and further includes dual disconnection structure for anti-surge to ensure more of electricity safety. The switch module has a conductive colloid thermo-sensitive piece fixedly compressing a conductive spring element and an insulating element for complete disconnection. 
     Another object of the present invention is to ensure a complete disconnection even when conductive plates fail to disconnect a circuit within the switch. 
     Yet another object of the present invention is to accomplish qualifications of the surge standards in UL 1449 3 rd  edition. 
     To achieve the objects mentioned above, the present invention comprises a housing having a press button arranged atop thereof, and a first conductive plate, a second conductive plate and a third conductive plate arranged at a lower section thereof; said first conductive plate being connected to a binary alloy conductive plate having a first connecting point, and the second conductive plate having a second connecting point on the surface of an upper section thereof corresponding to the first connecting point; a moving rod linking up the bottom of the press button with one end and the binary alloy conductive plate with the other end for the first connecting point to contact the second connecting point, consequently turning on the switch, and for the first connecting point to detach from the second connecting point when current overload occurs and the binary alloy conductive plate is deformed due to high temperature, consequently turning off the switch, so as to form an overcurrent protection switch; 
     Wherein a structure of anti-surge and dual disconnection is built inside the housing, including: at least one metal oxide varistor being disposed under a plate and having a first surface and an opposite second surface; at least one insulating element having a through hole arranged at a center thereof, an upper surface and a lower surface, said upper surface arranged correspondingly to the first surface of the metal oxide varistor; at least one conductive spring element having an outer periphery with an extended portion connecting the first surface of the metal oxide varistor with the second conductive plate, and a springy section being compressed by the first surface of the metal oxide varistor in the through hole of the insulating element; at least one thermo-sensitive piece which is conductive and solid colloid to be disposed in the through hole of the insulating element for the springy section of the spring element to be adhered between the lower surface of the insulating element and the first surface of the metal oxide varistor for electrical connection and for the spring element to be conductive and ready for ejection; and a pushing element having a first end thereof arranged correspondingly to the metal oxide varistor, the insulating element and the springy section of the spring element, and a second end thereof arranged correspondingly to the binary alloy conductive plate for pushing; 
     Whereby when the first connecting point is contacting the second connecting point and an overvoltage occurs, temperature of the metal oxide varistor would instantly rise up to a degree higher than the melting point thereof, therefore melting the thermo-sensitive piece, loosening the springy section of the spring element and displacing the pushing element to force the first connecting point detaching from the second connecting point and turn off the switch; meanwhile, the insulating element also disconnects the circuit structure simultaneously. 
     With structures disclosed above, the present invention complements the defect of a conventional overcurrent protection switch that it has to connect to a metal oxide varistor from the outside by having the anti-surge disconnection structure ingeniously built inside the heat-resisting and fireproof housing. When receiving exceedingly high voltages, the heating metal oxide varistor would instantly melt down the thermo-sensitive piece, loosening the springy section of the conductive spring element for ejection and further displacing the pushing element, therefore forcing the first connecting point detaching from the second connecting point and turning off the switch immediately. Therefore, the present invention is not only overcurrent protective but also overvoltage protective and surge absorbing; also, the insulating element is able to completely disconnect the thermo-sensitive piece and the spring element from the metal oxide varistor by insulation, ensuring more electricity safety and conveniences in using. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of an overcurrent protection switch according to the prior art; 
         FIG. 1B  is a section view of an overcurrent protection switch according to the prior art; 
         FIG. 2A  is a perspective view of an anti-surge disconnection structure according to U.S. Pat. No. 8,643,462; 
         FIG. 2B  is a perspective view of a major structure according to U.S. Ser. No. 14/617,000; 
         FIG. 3  is a sectional view of the present invention in a first embodiment in an OFF status; 
         FIG. 4  is a sectional view of the present invention in the first embodiment in an ON status; 
         FIG. 5  is an application example of the present invention in the first embodiment, illustrating the thermo-sensitive piece melting, loosening the spring element, displacing the pushing element and further turning the switch off; 
         FIG. 6  is an exploded view of major components of the present invention in the first embodiment; 
         FIG. 6A  is an exploded view of partial components of the present invention in the first embodiment; 
         FIG. 7  is a sectional view of the present invention in a second embodiment with two metal dioxide varistors; 
         FIG. 8  is another sectional view of  FIG. 7 , illustrating the thermo-sensitive piece melting, loosening the spring element, displacing the pushing element and further turning the switch off; 
         FIG. 9  is an exploded view of major components of the present invention in the second embodiment; 
         FIG. 10  a sectional view of the present invention in a third embodiment with three metal oxide varistors; 
         FIG. 11  is another sectional view of  FIG. 10 , illustrating the thermo-sensitive pieces melting, loosening the spring element, displacing the pushing element, and further turning the switch off; 
         FIG. 12  is an exploded view of major components of the present invention in the third embodiment; 
         FIG. 13  is an exploded view of the present invention in the third embodiment; and 
         FIG. 14  is a perspective view of  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 3-6 , in a first embodiment, the present invention mainly includes a housing  31 , a moving rod  33 , and an anti-surge disconnection structure  70 . 
     The housing  31  has a press button  32  arranged atop thereof, and a first conductive plate  40  as a positive electrode, a second conductive plate  50  as another positive electrode and a third conductive plate  60  as a negative electrode arranged at a lower section thereof. The first conductive plate  40  is connected to a binary alloy conductive plate  41  that has a spring leaf  42  and a first connecting point  421 , and the second conductive plate  50  has a second connecting point  511  corresponding to the first connecting point  421 . 
     The moving rod  33  has a top end arranged at the bottom of the press button  32  and a bottom end connecting to a movable end  411  of the binary alloy conductive plate  41 . With reference to  FIG. 4 , when pressing the press button  32 , the binary alloy conductive plate  41  ejects upwards and the spring leaf  42  ejects downwards to make the first connecting point  421  contacting the second connecting point  511  and thus turn on the switch; when current overload occurs, the binary alloy conductive plate  41  deforms due to high temperature and detach the first connecting point  421  from the second connecting point  511  to turn the switch off back to the original status as shown in  FIG. 3 , so as to form a switch module  30  with an overcurrent protection switch. 
     The arrangement of the binary alloy conductive plate  41  and the press button  32  is different in various switch modules. In this embodiment, the binary alloy conductive plate  41  has the first connecting point  421  arranged on the spring leaf  42  but it is not limited to such application. The binary alloy conductive plate  41  can eject without the spring leaf  42  and the first connecting point  421  can be arranged aside the binary alloy conductive plate  41 . Also, theis is a positive electrode for output and a negative electrode for input; in the embodiment, the first conductive plate  40  is arranged to be the positive electrode input and the second conductive plate  50  is arranged to be the positive electrode output. 
     The features of the present invention lies in that the anti-surge disconnection structure  70  is built inside the housing  31  and includes at least one metal oxide varistor  71 , at least one insulating element  76 , at least one conductive spring element  73 , at least one thermo-sensitive piece  72 , and at least one pushing element  75 . 
     The metal oxide varistor  71  is disposed under a plate  74  and has a first surface  711  and an opposite second surface  712 . In this embodiment, the first surface  711  is the positive electrode and the second surface  712  is the negative electrode; they are electrically connected to the second conductive plate  50  and the third conductive plate  60  by a connector which can be a conductive wire, a conductive plate, or a conductive element extended from the surface of the metal oxide varistor  71 . 
     The insulating element  76  has a through hole  763  arranged at a center thereof, an upper surface  761  and a lower surface  762 . The upper surface  761  is arranged correspondingly to the first surface  711  of the metal oxide varistor  71  to ensure melting liquid would not spill out. Size of the through hole  763  and positions of insulation and adherence on the insulting element  76  is adaptable according to different needs. In this embodiment, the insulating element  76  is arranged in a shape in correspondence to the shape of the metal oxide varistor  71 , and it has a surrounding protrusion  764  on both the upper surface  761  and the lower surface  762 , individually forming a space thereon. 
     The conductive spring element  73  has an outer periphery  731  and a springy section  732  compressed in the through hole  763  of the insulating element  76  on the first surface  711  of the metal oxide varistor  71 . In this embodiment, there is one spring element  73  and one metal oxide varistor  71 . The second surface  712  of the metal oxide varistor  71  is arranged under the plate  74  which is arranged to have a fixed surface for ejection; therefore, it can be a conductive plate, a positioning plate formed in one-piece together with the housing  31 , or an extended portion from the third conductive plate  60 . The spring element  73  is abutting on the lower surface  762  of the insulating element  76  and the outer periphery  731  of the spring element  73  further has an extended portion  733  that is arranged as a bended portion  734  and connects the first surface  711  of the metal oxide varistor  71  with the second conductive plate  50 . As shown in  FIG. 6 , the second surface  712  of the metal oxide varistor  71  is connected to the third conductive plate  60  by the plate  74  and a conductive wire  741 ; in this embodiment, the plate  74  and conductive wire  741  are formed in one-piece extended from the third conductive plate  60  and the extended portion  733 , the outer periphery  731  and the springy section  732  of the spring element  73  are formed in one-piece. 
     The thermo-sensitive piece  72  is conductive and solid colloid to be disposed in the through hole  763  of the insulating element  76  for the springy section  732  of the spring element  73  to be adhered between the lower surface  762  of the insulating element  76  and the first surface  711  of the metal oxide varistor  71  for electrical connection and for the spring element  73  to be ready for ejection. In this embodiment, the thermos-sensitive piece  72  is made of metal compounds which are conductive and fast-acting in low temperature that would melt at a pre-determined degree before temperature of the metal oxide varistor  71  rises up to a dangerously high number. 
     The pushing element  75  has a first end  751  arranged correspondingly to the metal oxide varistor  71 , the insulating element  76  and the springy section  732  of the spring element  73 , and a second end  752  arranged correspondingly to the binary alloy conductive plate  41  for pushing. 
     In this embodiment, the pushing element  75  is an isolated pushing rod and the first end  751  thereof is contacting the springy section  732  of the spring element  73 , and the second end  752  thereof is arranged as a protruding portion to contact the binary alloy conductive plate  41 . Furthermore, the first end  751  is arranged in a shape in accordance with shapes of the insulating element  76  and the spring element  73 , and it has a positioning hole  753  for the springy section  732  of the spring element  73  to engage therein; whereby the first connecting point  421  on the binary alloy conductive plate  41  would be forced to detach from the second connecting point  511  when the spring element  73  is ejected. 
     Further referring to  FIG. 5 , when the first connecting point  421  is contacting the second connecting point  511  and overvoltage occurs, temperature of the metal oxide varistor  71  would instantly rise up to a degree higher than melting point of the thermo-sensitive piece  72 , melting the thermo-sensitive piece  72 , counterbalancing the compressing force on the spring element  73  and further displacing the pushing element  75 , therefore forcing the first connecting point  421  detaching from the second connecting point  511  for disconnection and turning off the switch without causing the first conductive plate  40  deformed due to high degree of temperature; meanwhile, the insulating element  76  further ensures the disconnection of the metal oxide varistor  71  from the spring element  73  by insulation. The metal oxide varistor  71  stops heating up and supplying electricity power for the device due to the disconnection as a result. 
       FIGS. 7-9  illustrate elements of the present invention in a second embodiment. In this embodiment, the anti-surge disconnection structure  70  mainly comprises a first metal oxide varistor  71   a,  a second metal oxide varistor  71   b,  a first thermo-sensitive piece  72   a,  a second thermo-sensitive piece  72   b,  a first insulating element  76   a,  a second insulating element  76   b,  a conductive spring element  73   a,  an electrical connector  73   c,  and a pushing element  75 . 
     The first metal oxide varistor  71   a  is disposed under a plate  74  and has a first surface  711  and an opposite second surface  712 . The first insulating element  76   a  has a through hole  763  arranged at a center thereof, an upper surface  761  and a lower surface  762 . The spring element  73   a  has an a springy section  732  compressed in the through hole  763  by the first surface  711  of the first metal oxide varistor  71   a  and an outer periphery  731  having a first extended portion  733   a  connecting to the first surface  711  of the first metal oxide varistor  73   a  with the second conductive plate  50 . The first thermo-sensitive piece  72   a  is conductive and solid colloid to be disposed in the through hole  763  of the first insulating element  76   a  for the springy section  732  of the spring element  73  to be compressed and adhered between the lower surface  762  of the first insulating element  76   a  and the first surface  711  of the first metal oxide varistor  71   a  for electrical connection, and the spring element  73   a  to be ready for ejection. 
     The second metal oxide varistors  71   b  also has a first surface  711  compressing the spring element  73   a.  The second insulating element  76   b  has a through hole  763  arranged at a center thereof, an upper surface  761  and a lower surface  762 . The electrical connector  73   c  is disposed under the second insulating element  76   b  and a second surface  712  of the second metal oxide varistor  71   b  with a second extended portion  733   b  arranged aside for electrical connection between the second surface  712  of the second metal oxide varistor  71   b  and the third conductive plate  60 . In this embodiment, the first extended portion  733   a  and the second extended portion  733   b  are arranged as bended portions for respectively engaging the second conductive plate  50  and the third conductive plate  60 . The second thermo-sensitive piece  72   b  is conductive and solid colloid to be disposed in the through hole  763  of the second insulating element  76   b,  electrically connecting the springy section  732  of the electrical connector  73   c  and the second surface  712  of the second metal oxide varistor  71   b;  and the springy section  732  of the electrical connector  73   c  is compressed and adhered on the second surface  712  of the second metal oxide varistor  71   b  for the electrical connector  73   c  to be ready for ejection. 
     The pushing element  75  has a first end  751  arranged correspondingly under the second surface  712  of the second metal oxide varistor  71   b,  the second insulating element  76   b  and the electrical connector  73   c,  and a second end  752  arranged correspondingly to the binary alloy conductive plate  41  for pushing. In this embodiment, the electric connector  73   c  is made of a spring and has an outer periphery  731  and a springy section  732  compressed by the second surface  712  of the second metal oxide varistor  71   b  corresponding to the through hole  763  of the second insulating element  76   b.  The second end  752  of the pushing element  75  is arranged close to the binary alloy conductive plate  41  so that when either of the first spring element  73   a  or the electrical connector  73   c  ejects the pushing element  75  would displace and force the first contacting point  421  on the binary alloy conductive plate  41  detaching from the second contacting point  422  and therefore stop the heating operation of the first and second metal oxide varistors  71   a,    71   b  to cease the power supply operation. 
       FIG. 8  is a schematic diagram illustrating the first thermo-sensitive piece  72   a  melting, loosening the spring element  73   a,  displacing the pushing element  75 , and further turning the switch off. In this embodiment, the plate  74  does not have to be parallel connected to the third conductive plate  60 ; it is also applicable to connect the second extended portion  733   b  with the third conductive plate  60  and to have the plate  74  being the ground for connection. In the embodiment, the melting of either of the thermo-sensitive pieces  72   a,    72   b  would cause ejection of either the spring element  73   a  or the electrical connector  73   c  and disconnect the device without damaging structure of the other thermo-sensitive piece for disconnection. 
       FIGS. 10-12  illustrate a third embodiment of the present invention. In this embodiment, the anti-surge disconnection structure  70  mainly comprises a first metal oxide varistor  71   a,  a second metal oxide varistor  71   b,  a third metal oxide varistor  71   c,  a first thermo-sensitive piece  72   a,  a second thermo-sensitive piece  72   b,  a third thermo-sensitive piece  72   c,  a first insulating element  76   a,  a second insulating element  76   b,  a third insulating element  76   c,  a first spring element  73   a,  a second spring element  73   b,  an electrical connector  73   c  and a pushing element  75 . 
     The first insulating element  76   a  has a through hole  763  arranged at a center thereof, an upper surface  761  and a lower surface  762 . The upper surface  761  is arranged correspondingly to the first surface  711  of the first metal oxide varistor  71   a.  The first thermo-sensitive piece  72   a  is conductive and solid colloid to be disposed in the through hole  763  of the first insulating element  76   a  for a springy section  732  of the first spring element  73   a  to be compressed and adhered between the lower surface  762  of the first insulating element  76   a  and the first surface  711  of the first metal oxide varistor  71   a  for electrical connection and for the first spring element  73   a  to be ready for ejection. The first spring element  73   a  further has an outer periphery  731  with a first extended portion  733   a  connecting the first surface  711  of the first metal oxide varistor  71   a  with the second conductive plate  50 . 
     The second insulating element  76   b  has a through hole  763  arranged at a center thereof, an upper surface  761  and a lower surface  762 ; the upper surface  761  is arranged correspondingly to the second surface  712  of the second metal oxide varistor  71   b.  The second metal oxide varistor  71   b  has a first surface  711  and an opposite second surface  712 ; the first surface  711  thereof is compressing the first spring element  73   a.  The second thermo-sensitive piece  72   b  is conductive and solid colloid to be disposed in the through hole  763  of the second insulating element  76   b  for a springy section  732  of the second spring element  73   b  to be compressed and adhered between the lower surface  762  of the second insulating element  76   b  and the second surface  712  of the second metal oxide varistor  71   b  for electrical connection and for the second spring element  73   b  to be ready for ejection. The second spring element  73   b  further has an outer periphery  731  with a second extended portion  733   b  connecting the second surface  712  of the second metal oxide varistor  71   b  with the third conductive plate  60 . 
     The third insulating element  76   c  has a through hole  763  arranged at a center thereof, an upper surface  761  and a lower surface  762 ; the upper surface  761  is arranged correspondingly to the first surface  711  of the third metal oxide varistor  71   c.  The electrical connector  73   c  abuts on the third insulating element  76   c  and has an outer periphery  731  with a third extended portion  733   c  electrically connecting to the first surface  711  of the third metal oxide varistor  71   c  and to the plate  74 . The plate  74  is also electrically connected to the second surface  712  of the first metal oxide varistor  71   a.    
     The third metal oxide varistor  72   c  is conductive and solid colloid to be disposed in the through hole  763  of the third insulating element  76   c  for a springy section  732  of the electrical connector  73   c  to be electrically connected to the first surface  711  of the third metal oxide varistor  71   c  and to be compressed and adhered between the lower surface  762  of the third insulating element  76   c  and the first surface  711  of the third metal oxide varistor  71   c  for electrical connection and for the electrical connector  73   c  to be ready for ejection. 
     The pushing element  75  has a first end  751  disposed under the electrical connector  73   c  and arranged correspondingly to a middle of the electrical connector  73   c  and the first surface  711  of the third metal oxide varistor  71   c , and a second end  752  arranged correspondingly to the binary alloy conductive plate  41  for pushing. In the embodiment, the melting of either of the thermo-sensitive pieces  72   a,    72   b  would cause ejection of either of the first or second spring elements  73   a,    73   b  and disconnect the device without damaging structure of other thermo-sensitive pieces for disconnection. 
     In this embodiment, the electrical connector  73   c  is made of a spring that has an outer periphery  731  with a third extended portion  733   c  electrically connecting to the third metal oxide varistor  71   c,  and a springy section  732  compressed under the third insulating element  76   c  and the first surface  711  of the third metal oxide varistor  71   c;  the plate  74  further has a conductive element  742  to be electrically connected to the third extended portion  733   c  of the electrical connector  73   c  and a fourth conductive plate  743  disposed aside and extended to outside of the housing  31  as shown in  FIG. 14 . 
     With structures disclosed above, the present invention complements the defect of a conventional overcurrent protection switch that it has to connect to a metal oxide varistor and a thermal fuse from the outside by having an anti-surge disconnection structure  70  including at least one metal oxide varistor, at least one thermo-sensitive pieces, at least one insulating element, and at least one conductive spring element ingeniously built inside so that when receiving exceedingly high voltages, the heating metal oxide varistor would instantly melt at least one thermo-sensitive piece, counterbalancing the compressing force on a spring element and further displacing the pushing element, therefore forcing the connecting points to detach and turning off the switch immediately; meanwhile, a corresponding insulating element would further ensure the disconnection is performed completely and safely. Hence, the present invention has the original function of overcurrent protection and further has the overvoltage protection and anti-surge disconnection structures built inside, ensuring more electricity safety and conveniences in using. 
     Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.