Patent Publication Number: US-7217147-B2

Title: Power source outlet device

Description:
TECHNICAL FIELD 
   The present invention relates to a power source outlet device which detects a spark discharge occurring before tracking occurrence to prevent occurrence of tracking. 
   BACKGROUND ART 
   Conventionally, there is a device shown in Patent Literature 1 as a power source outlet device having a function of preventing tracking. In a technique of Patent Literature 1, an electrically conductive plate is disposed in plug insertion holes on a front face of a power source outlet device, one end thereof being protruded from a surface while another end thereof being connected to a ground terminal, so that a leakage current occurring between plug blades is led to flow to the ground terminal via the electrically conductive plate before tracking occurs and a cable run is disconnected by letting a leakage breaker detect the leaked current. 
   However, in the above-described conventional power source outlet device, since an electrically conductive plate serving as a sensor is exposed to a surface of a cover of the power source outlet device, malfunction may occur when an electrically conductive material comes in contact with the electrically conductive plate. Further, a user&#39;s hand or the like may touch the sensor, and such exposure is not desirable. 
   In view of these circumstances, the present applicant has proposed a power source outlet device where a through-hole is provided without exposing a sensor to a surface of a cover of the power source outlet device so that a spark discharge (scintillation) between plug blades which causes a tracking phenomenon can be detected inside the cover in Patent Literature 2. In the power source outlet device, such a method is adopted that a sensor is disposed on a back face of the cover as a sensor mounting structure, and the sensor is fixed being covered its back portion with insulator such as resin. 
   [Patent Literature] JP-A-2001-35599 
   [Patent Literature] JP-A-2004-327247 
   DISCLOSURE OF THE INVENTION 
   [Problem to be Solved by the Invention] 
   However, in a constitution of the above-described Patent Literature 2, since fine manipulation must be conducted in a small space, there is such a drawback that workability deteriorates. Further, since connection between the sensor and the circuit board is made through a lead wire, it is necessary to perform soldering, which results in troublesome work. 
   Further, for preventing water or dusts from entering in the through-hole and reducing an output current from the sensor to reduce a load on an amplifying circuit, the smaller the through-hole is, the more excellent it is. In the power source outlet device of Patent Literature 2, however, a diameter limit of the through-hole is approximate 0.5 mm due to property of moldability of a cover produced from insulating material such as synthetic resin. Therefore, there is such a problem that moldability and productivity deteriorates when the through-hole is downsized. 
   In order to solve the above problem, an object of the present invention is to provide a power source outlet device to which a sensor can be mounted easily and which implements an excellent discharge detecting behavior without downsizing of a through-hole to a limit. 
   [Means for Solving the Problem] 
   In order to solve the above problem, the invention described in claim  1  is a power source outlet device which is provided on a front face of an outlet case formed from insulating material with at least one pair of plug insertion holes, and receiving blades paired which pinch plug blades of a plug being disposed inside the plug insertion holes, and the power source outlet device having a through-hole between the plug insertion holes on the front face of the outlet case, and a sensor which detects a spark discharge occurring between the plug blades being disposed internally of the through-hole, characterized in that a partition wall made from insulator is disposed between the receiving blades in a standing manner, the sensor is received in the partition wall, and the sensor is disposed such that a portion thereof faces in the through-hole. 
   With the constitution, the sensor can be mounted without adhesion operation so that mounting can be conducted easily. 
   The invention of claim  2  is characterized in that the outlet case comprises an intermediate base body which has a receiving blade mounting portion and the partition wall and which holds the sensor, a main body which holds a circuit board and the intermediate base body, and a cover body which covers a front face of the main body and has the plug insertion holes in the invention described in claim  1 . With the constitution, assembling workability can be improved. 
   The invention of claim  3  is characterized in that the sensor is received in the partition wall by insertion molding in the invention described in claim  1 . With the constitution, a mounting work of the sensor can be eliminated. 
   The invention of claim  4  is characterized in that the sensor is received in the partition wall by insertion molding in the invention described in claim  2 . With the constitution, a mounting work of the sensor can be eliminated. 
   The invention of claim  5  is characterized in that a sensor insertion hole is formed in the partition wall and the sensor is fittingly inserted in the sensor insertion hole to be received therein in the invention described in claim  1 . With the constitution, the sensor can be mounted by the fitting-insertion, so that mounting of the sensor can be performed easily. 
   The invention of claim  6  is characterized in that a sensor insertion hole is formed in the partition wall and the sensor is fittingly inserted in the sensor insertion hole to be received therein in the invention described in claim  2 . With the constitution, the sensor can be mounted by the fitting-insertion, so that mounting of the sensor can be performed easily. 
   The invention of claim  7  is characterized in that the sensor is made of a metal plate and the circuit board is disposed behind the partition wall, a rear end of the sensor is extended so as to reach the circuit board, and electrical connection is achieved by inserting the rear end into an insertion hole provided in the circuit board in the invention described in claim  2 . With the constitution, connection between the sensor and the circuit board can be performed easily. 
   The invention of claim  8  is characterized in that the sensor is made of a metal plate and the circuit board is disposed behind the partition wall, a rear end of the sensor is extended so as to reach the circuit board, and electrical connection is achieved by inserting the rear end into an insertion hole provided in the circuit board in the invention described in claim  3 . With the constitution, connection between the sensor and the circuit board can be performed easily. 
   The invention of claim  9  is characterized in that the sensor is made of a metal plate and the circuit board is disposed behind the partition wall, a rear end of the sensor is extended so as to reach the circuit board, and electrical connection is achieved by inserting the rear end into an insertion hole provided in the circuit board in the invention described in claim  4 . With the constitution, connection between the sensor and the circuit board can be performed easily. 
   The invention of claim  10  is characterized in that the sensor is made of a metal plate and the circuit board is disposed behind the partition wall, a rear end of the sensor is extended so as to reach the circuit board, and electrical connection is achieved by inserting the rear end into an insertion hole provided in the circuit board in the invention described in claim  5 . With the constitution, connection between the sensor and the circuit board can be performed easily. 
   The invention of claim  11  is characterized in that the sensor is made of a metal plate and the circuit board is disposed behind the partition wall, a rear end of the sensor is extended so as to reach the circuit board, and electrical connection is achieved by inserting the rear end into an insertion hole provided in the circuit board in the invention described in claim  6 . With the constitution, connection between the sensor and the circuit board can be performed easily. 
   The invention of claim  12  is characterized in that the sensor is made of a metal plate and the circuit board is disposed behind the partition wall, a rear end of the sensor is extended so as to reach the circuit board, at least one of the rear end of the sensor and a sensor connection portion of the circuit board is formed to be elastically deformable, and both of the rear end of the sensor and the sensor connection portion are brought in contact with each other to be electrically connected to each other in the invention described in claim  2 . With the constitution, connection between the sensor and the circuit board can be performed easily. 
   The invention of claim  13  is characterized in that the sensor is made of a metal plate and the circuit board is disposed behind the partition wall, a rear end of the sensor is extended so as to reach the circuit board, at least one of the rear end of the sensor and a sensor connection portion of the circuit board is formed to be elastically deformable, and both of the rear end of the sensor and the sensor connection portion are brought in contact with each other to be electrically connected to each other in the invention described in claim  3 . With the constitution, connection between the sensor and the circuit board can be performed easily. 
   The invention of claim  14  is characterized in that the sensor is made of a metal plate and the circuit board is disposed behind the partition wall, a rear end of the sensor is extended so as to reach the circuit board, at least one of the rear end of the sensor and a sensor connection portion of the circuit board is formed to be elastically deformable, and both of the rear end of the sensor and the sensor connection portion are brought in contact with each other to be electrically connected to each other in the invention described in claim  4 . With the constitution, connection between the sensor and the circuit board can be performed easily. 
   The invention of claim  15  is characterized in that the sensor is made of a metal plate and the circuit board is disposed behind the partition wall, a rear end of the sensor is extended so as to reach the circuit board, at least one of the rear end of the sensor and a sensor connection portion of the circuit board is formed to be elastically deformable, and both of the rear end of the sensor and the sensor connection portion are brought in contact with each other to be electrically connected to each other in the invention described in claim  5 . With the constitution, connection between the sensor and the circuit board can be performed easily. 
   The invention of claim  16  is characterized in that the sensor is made of a metal plate and the circuit board is disposed behind the partition wall, a rear end of the sensor is extended so as to reach the circuit board, at least one of the rear end of the sensor and a sensor connection portion of the circuit board is formed to be elastically deformable, and both of the rear end of the sensor and the sensor connection portion are brought in contact with each other to be electrically connected to each other in the invention described in claim  6 . With the constitution, connection between the sensor and the circuit board can be performed easily. 
   The invention of claim  17  is a power source outlet device which is provided on a front face of an outlet case formed from insulating material with at least one pair of plug insertion holes, and receiving blades paired which pinch plug blades of a plug being disposed inside the plug insertion holes, and the power source outlet device having a through-hole between the plug insertion holes on the front face of the outlet case, and a sensor which detects a spark discharge occurring between the plug blades being disposed internally of the through-hole, characterized in that a bushing with elasticity made from insulating material is pressure-fitted into the through-hole and the bushing has at least one through-hole extending in a pressure-fitting direction, and a surface of the outlet case and the sensor are caused to communicate with each other through the at least one through-hole so that the sensor can detect a spark discharge. 
   With the constitution, since it is unnecessary to form the through-hole down to the limit in a small size, moldability of the outlet case is excellent and productivity is improved. Further, a hole diameter of a detection hole can be made small and since the bushing has the elasticity, cleaning of the detection hole is easy. Furthermore, when many detection holes are formed in the bushing, it is possible to expand a detection range for a spark discharge. 
   The invention of claim  18  is a power source outlet device which is provided on a front face of an outlet case formed from insulating material with at least one pair of plug insertion holes, and receiving blades paired which pinch plug blades of a plug being disposed inside the plug insertion holes, and the power source outlet device having a through-hole between the plug insertion holes on the front face of the outlet case, and a sensor which detects a spark discharge occurring between the plug blades being disposed internally of the through-hole, characterized in that a bushing with elasticity made from insulator is pressure-fitted into the through-hole and a gap is provided at at least one portion of a contacting face between the bushing and the through-hole, a surface of the outlet case and the sensor are caused to communicate with each other through the gap so that the sensor can detect a spark discharge. 
   With the constitution, since it is unnecessary to downsize the through-hole to the limit, moldability of the outlet case is excellent and productivity is improved. Further, a gap for detecting a spark discharge can be made small, and since the bushing has elasticity, cleaning to the gap is facilitated. 
   The invention of claim  19  is a power source outlet device which is provided on a front face of an outlet case formed from insulating material with at least one pair of plug insertion holes, and receiving blades paired which pinch plug blades of a plug being disposed inside the plug insertion holes, and the power source device having a through-hole between the plug insertion holes on the front face of the outlet case, and a sensor which detects a spark discharge occurring between the plug blades being disposed internally of the through-hole, characterized in that a bushing made of an insulating permeable body is embedded in the through-hole. 
   With the constitution, since it is unnecessary to downsize the through-hole to the limit, moldability of the outlet case is excellent and productivity is improved. Further, a detection range for a spark discharge can be expanded since detection is conducted on the surface of an area, and even if the surface is wiped, clogging does not occur, so that cleaning is easy. 
   [Effect of the Invention] 
   Thus, according to the inventions of claims  1  to  16 , mounting of a sensor for detecting a spark discharge and connection between the sensor and a circuit board are easy and assembling easiness is improved. Further, according to the inventions of claims  17  to  19 , since it is unnecessary to downsize a through-hole to a limit, moldability of an outlet case is excellent and productivity is improved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view of a power source outlet device showing a first embodiment of the present invention; 
       FIG. 2  is a sectional view of the power source outlet device taken along line A—A in  FIG. 1 ; 
       FIG. 3  is a perspective view showing an intermediate base body shown in  FIG. 1 ; 
       FIG. 4  is a sectional view of a main portion of a power source outlet device showing a modification of a constitution of a sensor mounting portion; 
       FIG. 5  shows a perspective view of an intermediate base body shown in  FIG. 1  and shows a modification of a sensor; 
       FIG. 6  is a sectional view of a main portion of a power source outlet device showing a mounting structure of a sensor shown in  FIG. 5 ; 
       FIG. 7  is a sectional view of a main portion of a power source outlet device showing a modification of a constitution of a sensor mounting portion; 
       FIG. 8  is a sectional view of a main portion of a power source outlet device showing a modification of a constitution of a sensor mounting portion; 
       FIG. 9  is a front view of a power source outlet device showing a second embodiment of the present invention; 
       FIG. 10  is a sectional view of the power source outlet device taken along line B—B shown in  FIG. 9 ; 
       FIG. 11  is a perspective view of a bushing shown in  FIG. 9 ; 
       FIG. 12  is a sectional view of a power source outlet device showing modifications of a through-hole and a bushing; 
       FIG. 13  shows a third embodiment of the present invention, (a) being a front view of a power source outlet device and (b) being an enlarged view of a portion J indicated in (a); 
       FIG. 14  shows a fourth embodiment of the present invention, (a) being a front view of a power source outlet device and (b) being an enlarged view of a portion F indicated in (a); 
       FIG. 15(   a ) is a sectional view of the power source outlet device taken along line C—C shown in  FIGS. 14 and 15(   b ) is an enlarged view of a portion G shown in  FIG. 15(   a ); 
       FIG. 16  is a perspective view of a bushing shown in  FIG. 14 ; 
       FIG. 17  shows a fifth embodiment of the present invention, (a) being a front view of a power source outlet device and (b) being an enlarged view of a portion H indicated in (a); 
       FIG. 18(   a ) is a sectional view of the power source outlet device taken along line D—D shown in  FIGS. 17  and  18 ( b ) is an enlarged view of a portion I shown in  FIG. 18(   a ); 
       FIG. 19  is a perspective view of a bushing shown in  FIG. 17 ; 
       FIG. 20  is a front view of a power source outlet device showing a sixth embodiment of the present invention; and 
       FIG. 21  is a sectional view of the power source outlet device taken along line E—E shown in  FIG. 20 . 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   Embodiments of the present invention will be explained below in detail with reference to the drawings. 
   First Embodiment 
     FIG. 1  is a front view showing a first embodiment of a power source outlet device according to the present invention and  FIG. 2  is a sectional view of the power source outlet device taken along line A—A. An outlet case  2  of a power source outlet device  1  is constituted of a main body  3  with a front face opened, a cover body  4  mounted so as to close the front face opening of the main body  3 , and an intermediate base body  5  accommodated in an inner space formed by the main body  3  and the cover body  4 . The outlet case  2  is formed from insulating material such as synthetic resin, and it is assembled internally with a leakage current detecting circuit, a breaker for breaking a cable run, and the like. 
   The cover body  4  is formed on its front face with a pair of plug insertion holes  6 ,  6  for inserting plug blades (not shown) of a plug at each of two positions of a central portion and a lower portion, and a through-hole  7  is formed at an intermediate position between plug insertion holes of each pair. The cover body  4  is provided on its upper portion with an operation handle  8  for performing return operation of the breaker which has performed breaking behavior at a tracking time, display lamps  9  which display leakage occurrence, tracking occurrence and the like, and a test button  10  which tests leakage breaking behavior. 
   The intermediate base body  5  is formed such as shown with a perspective view in  FIG. 3 . It is formed with a standing portion  12  over an entire periphery of a rectangular plate portion  11  and a partition wall  13  extending to a back face of the cover body  4  at an intermediate position in a shorter size direction thereof. Holes  14  are formed on a front end of the partition wall  13  at positions opposed to the through-holes  7  of the cover body  4 , and sensor insertion holes  15  continuous to the holes  14  are formed at a rear end of the partition wall  13 . A sensor  16  made of a metal plate is fittingly inserted into the sensor insertion hole  15 , and the sensor  16  is mounted such that its front end faces the hole  14 . The sensor  16  is provided such that its rear end is exposed from a back face of the intermediate base body  5 . Thus, such arrangement is performed that one portion of the sensor  16  faces the through-hole  7  via the hole  14 , so that a spark discharge occurring between the plug blades of the plug can be detected. 
   Further, receiving blades  17  pinching plug blades of a plug are positioned and disposed on both left and right sides regarding the partition wall  13  by the standing portion  12  and the partition wall  13 . Since upper and lower receiving blades  17  have the same polarity, they are coupled by a coupling portion  18 . The receiving blade  17  is connected with a wire  21  connected to an insertion terminal  20  of the main body  3  connected with a cable  19  extending from a cabinet panel or the like, and a wire  23  for a power source whose one end is connected to a circuit board  23  described later. 
   Incidentally, when the sensor  16  is insert-molded to the partition wall  13 , the time-consuming work for mounting can be avoided. It should be noted that the sensor  16  may be formed from an electrically conductive member instead of the metal plate. 
   On the other hand, the circuit board  22  mounted with various circuits, such as a tracking detecting circuit and a power source circuit, is accommodated in a space behind the intermediate base body  5  in parallel with the rectangular plate portion  11  of the intermediate base  5 . The circuit board  22  is connected with one end of the lead wire  24  whose other end is connected to the sensor  16 , and it is electrically connected with the tracking detecting circuit and the sensor  16 . Further, a breaker (not shown) is accommodated in a space above the intermediate base body  5 . 
   The power source outlet device  1  with the above constitution performs a tracking detecting behavior in the following manner. When dusts are accumulated between the plug blades of the plug connected to the receiving blades  17 ,  17  and the dusts absorb air moisture, a minute current flows between the plug blades via the moisture. When moisture thus charged with the minute current evaporates, a spark discharge occurs. Then, when the spark discharge which has occurred enters through the through-hole  7  and contacts with the sensor  16 , a minute current flows in the sensor  16 . The tracking detecting circuit detects tracking (correctly speaking, detects occurrence of a spark discharge causing tracking) from an output current of the sensor  16  to cause the breaker to behave and perform displaying with the display lamp  9 . 
   Thus, a spark discharge occurring before tracking occurrence is detected and outlet output is stopped. The sensor can be mounted by simple insertion to the partition wall of the intermediate base body, so that mounting of the sensor can be implemented easily. An insulating distance between the sensor and the receiving blade can be secured reliably. 
   Incidentally, in the embodiment, although formation is made such that a distal end of the sensor does not project from the partition wall  13 , formation can be performed such that the distal end of the sensor  16  projects from the partition wall  13 , as shown with a sectional view in  FIG. 4 . 
     FIG. 5  shows a modification of the sensor  16 , and  FIG. 6  is a sectional view of a power source outlet device for explaining a mounting structure of the sensor  16  shown in  FIG. 5 . The sensor  16  is formed with a metal plate punched in a generally U shape and it is formed integrally so as to correspond to two sensor pieces. The sensor  16  is provided at a rear portion thereof with a terminal  16   a  projecting from a rear face of the intermediate base body  5 . 
   On the other hand, an insertion terminal  27  is provided on a front face of the circuit board  22  at a position corresponding to the terminal  16   a  of the sensor  16 , so that it is made possible to conduct electrical connection with the circuit board  22  by only performing inserting work of the terminal  16   a  of the sensor  16  into the insertion terminal  27 . Incidentally, same constituent elements as those in  FIG. 2  and  FIG. 3  are attached with same reference numerals, and explanation thereof is omitted. 
   By adopting such a terminal structure, the sensor and the circuit board can be connected by only insertion operation, so that connection operation becomes easy. 
   Incidentally, since the sensor  16  is formed integrally to correspond to two sensor pieces, only one insertion hole  27  can be provided in  FIG. 5 , but sensors  16  are provided to respective receiving blades  17  one-by-one, the insertion terminals  27  are required by the number corresponding to the number of the sensors  16 . 
   A sectional view of a power source outlet device shown in  FIG. 7  shows a modification of the sensor mounting portion. In  FIG. 7 , the sensor  16  is provided such that its rear end projects from the back face of the intermediate base body  5 , and an elastically deformable connection terminal  28  of a leaf spring type is provided at a position of the circuit board  22  opposed to the rear end of the sensor  16 . Incidentally, same constituent elements as those in  FIG. 2  and  FIG. 3  are attached with same reference numerals, and explanation thereof is omitted. 
   Accordingly, when the power source outlet device  1  is assembled, the rear end of the sensor  16  comes in contact with the connection terminal  28  to be electrically connected to the circuit board  22 , so that connection operation between the sensor and the circuit board is easy. Incidentally, such a constitution may be adopted that the rear end of the sensor  16  is formed to be elastically deformable and the rear end is brought in contact with the connection terminal  28  of the circuit board  22  so that the both are connected to each other, or the both are elastically deformed to be connected to each other. 
   A sectional view of a power source outlet device shown in  FIG. 8  shows a modification of the sensor mounting portion. In  FIG. 8 , a partition wall  30  is integrally formed on a back face of the cover body  4 . Further, a through-hole  31  is provided at an intermediate position of the intermediate base plate  5  in its shorter side direction, and the partition wall  30  penetrates the through-hole  31  at an assembling time. Incidentally, same constituent elements as those in  FIG. 6  are attached with same reference numerals, and explanation thereof is omitted. Therefore, the hole of the partition wall and through-hole of the cover body are prevented from deviating from each other. 
   Incidentally, although the embodiment is directed to a two port power source outlet device to which two plugs can be connected, the present invention may be directed to a one port power source outlet device, an extension tap to which a plurality of plugs can be connected, or the like. Further, although the embodiment is constituted to house the breaker therein to break the cable run, the present invention is not limited regarding behavior at a tracking detecting time. Furthermore, it is possible to modify the shape, structure, function, and the like of the power source outlet device such as forming the intermediate base integrally with the main body properly without departing from the spirit and scope of the invention to perform implementation. 
   Second Embodiment 
     FIG. 9  and  FIG. 10  show a second embodiment of a power source outlet device of the invention,  FIG. 9  being a front view of the second embodiment and  FIG. 10  being a sectional view thereof taken along line B—B shown in  FIG. 9 . An outlet case  52  of a power source outlet device  1  is constituted of a main body  53  with a front face opened, a cover body  54  mounted so as to close the front face opening of the main body  53 , and an intermediate base body  55  accommodated in an inner space formed by the main body  53  and the cover body  54 . The outlet case  52  is formed from insulating material such as synthetic resin, and it is assembled internally thereof with a leakage current detecting circuit, a breaker for breaking a cable run and the like. 
   The cover body  54  is formed on a front face thereof with a pair of plug insertion holes  56 ,  56  for inserting plug blades (not shown) of a plug at each of two positions of a central portion and a lower portion thereof, and a through-hole  57  is formed at an intermediate position between plug insertion holes of each pair. The cover body  54  is provided on its upper portion with an operation handle  58  for performing return operation of the breaker which has performed breaking behavior at a tracking time, display lamps  59  which display leakage occurrence, tracking occurrence and the like, and a test button  60  which tests leakage breaking behavior. 
   A receiving blade  62  pinches a plug blade of a plug inside the plug insertion hole  56 , and a bushing  63  shown with a perspective view in  FIG. 11  is mounted to the through-hole  57 . The bushing  63  is formed from soft resin material or rubber material having elasticity such that its outer shape is slightly larger than the shape of the through-hole  57 . Then, the bushing  63  is formed in a cylindrical shape coincident with the through-hole  57 , and it has a detection hole  64  formed on a center axis thereof in a penetrating manner. Further, flange portions  63   a  are provided such that upper and lower ends of the bushing comes in close contact with the through-hole  57  reliably. 
   The bushing  63  is pressure-fitted into the through-hole  57  and mounted thereto such that a surface of the outlet case  52  and a sensor  67  described later are caused to communicate with each other via the detection hole  64 . 
   The sensor  67  is disposed inside the through-hole  57  internally of the outlet case  52 . The sensor  67  is formed of an electrically conductive member such as a metal piece, and it is connected to a tracking detecting circuit of a circuit board  68  disposed internally of the outlet case  52 . 
   The power source outlet device  1  with the above constitution performs a tracking detecting behavior in the following manner. When dusts are accumulated between the plug blades of the plug connected to the receiving blades  62 ,  62  and the dusts absorb air moisture, a minute current flows between the plug blades via the moisture. When moisture thus charged evaporates, a spark discharge occurs. Then, when the spark discharge which has occurred enters from the detection hole  64  of the bushing  63  provided in the through-hole  57  to come in contact with the sensor  67 , a minute current flows in the sensor  67 . The tracking detecting circuit detects tracking from an output current of the sensor  67  to cause the breaker to behave and break the cable run, and perform displaying by the display lamp  59 . 
   Since the bushing having the detection hole is mounted to the through-hole in this manner, it is unnecessary to downsize the through-hole to the limit, so that moldability of the outlet case can be improved and the productivity is improved. Further, a hole diameter of the detection hole can be made small easily. For example, the hole diameter can be set to about 0.1 mm by utilizing shrinkage of an contour of the bushing due to pressure-fitting mounting. In addition, since the bushing has elasticity, even if the detection hole clogs up due to dusts, the detection hole can be cleaned easily by using a needle with a diameter slightly larger than the hole diameter of the detection hole or the like. 
   Third Embodiment 
     FIG. 13  shows a power source outlet device showing a third embodiment of the invention, in which (a) is a front view of the power source outlet device and (b) is an enlarged view of a portion J indicated in (a). This embodiment is different from the second embodiment shown in  FIG. 9  in that a plurality of detection holes  64  are formed in the bushing  63 . Incidentally, same constituent elements as those in the second embodiment are attached with same reference numerals, and explanation thereof is omitted. 
   When many detection holes are formed in the bushing in this manner, a spark discharge can be detected on the surface of an area, so that a detection range can be expanded. 
   Incidentally, in the second and third embodiments, although the through-hole  57  is formed in a circular shape and the bushing  63  is formed in a cylindrical shape, the through-hole  57  and the bushing  63  may be formed to have one ends diameter-expanded, for example, as shown in  FIG. 12 . Further, the through-hole  57  and the bushing  63  may be formed in a rectangular shape or they may have a long hole shape. Shapes of the through-hole and the bushing of the outlet case  52  are not limited. 
   Fourth Embodiment 
     FIG. 14  and  FIG. 15  show a fourth embodiment of the invention, in which  FIG. 14(   a ) is a front view of a power source outlet device,  FIG. 14(   b ) is an enlarge view of a portion F indicated in  FIG. 14(   a ),  FIG. 15(   a ) is a sectional view taken along line C—C shown in  FIG. 14(   a ), and  FIG. 15(   b ) is an enlarged view of a portion G indicated in  FIG. 15(   a ). The embodiment is different from the second embodiment shown in  FIG. 9  in constitutions of the through-hole  57  and a bushing  70 , and shape of a sensor  72 . The bushing  70  is formed from insulating material to have an outer shape slightly smaller than a shape of the through-hole  57 .  FIG. 16  is a perspective view of the bushing  70 , the bushing  70  is formed in a cylindrical shape so as to match with the through-hole  57 , and it has engagement projections  70   a  formed around upper and lower end portions thereof. When the bushing  70  is inserted into the through-hole  57 , the engagement projections  70   a  are engaged with end edges of the through-hole  57 , so that mounting can be achieved. Incidentally, same constituent elements as those in the second embodiment shown in  FIGS. 9 ,  10  are attached with same reference numerals, and explanation thereof is omitted. 
   By forming the bushing  70  in this manner, a gap  71  causing an outer face of the outlet case  52  and an inner face of the outlet case  52  to communicate with each other can be formed between the through-hole  57  positioned around the bushing  70  and the bushing  70 , so that the gap  71  can be utilized as a hole when a sensor  67  described later detects a spark discharge. Incidentally, a distal end of the sensor  72  facing the bushing  70  is formed in a flat shape to match with a shape of the gap  71 , so that a spark discharge can be detected on an area. 
   With this constitution, tracking detection is performed by the power source outlet device  1  in the following manner. A spark discharge causing tracking occurs due to dusts built up between the plug blades of the plug connected to the receiving blades  62 ,  62  and moisture. Then, when the spark discharge enters from the gap  71  between the through-hole  57  and the bushing  70  to come in contact with the sensor  72 , a minute current flows. The tracking detecting circuit detects tracking from an output current from the sensor  72  and causes a breaker housed in the outlet case  52  to behave to break a cable run and perform display by the display lamps  59 . 
   Since it is made unnecessary to reduce a hole diameter of the through-hole by mounting the bushing in the through-hole in this manner, moldability of the outlet case is excellent and productivity is improved. Further, the gap between the through-hole utilized as a hole of a sensor for detection and the bushing can be formed in a small size easily. 
   Fifth Embodiment 
     FIG. 17  and  FIG. 18  show a fifth embodiment of the invention, in which  FIG. 17(   a ) is a front view of a power source outlet device,  FIG. 17(   b ) is an enlarged view of a portion F indicated in  FIG. 17(   a ),  FIG. 18(   a ) is a sectional view taken along line D—D shown in  FIG. 17(   a ), and  FIG. 18(   b ) is an enlarged view of a portion I indicated in  FIG. 18(   a ). The embodiment is mainly different from the fourth embodiment shown in  FIG. 14 , in shape of a bushing  74 . Incidentally, same constituent elements as those in the fourth embodiment shown in  FIG. 14  are attached with same reference numerals, and explanation thereof is omitted. 
   The bushing  74  is formed from insulating material, and it has a shape as shown in a perspective view in  FIG. 19 . The bushing  74  is formed to have substantially the same shape as the through-hole  57 , and a plurality of grooves  74   b  extending in an insertion direction are formed on a face of the bushing  74  coming in contact with the through-hole  57 . 
   Gaps  71  are formed on a contact face between the bushing  74  and the through-hole  57  by the grooves  74   b , and when a spark discharge enters from the gaps  71  to come in contact with the sensor  72 , a minute current flows. The tracking detecting circuit detects tracking from an output current from the sensor  72  and causes a breaker housed in the outlet case  52  to behave to break the cable run and perform display by the display lamps  59 . 
   Since it is made unnecessary to reduce the hole diameter of the through-hole by mounting the bushing in the through-hole in this manner, moldability of the outlet case is excellent and productivity is improved. Further, the gap between the through-hole utilized as a hole of a sensor for detection and the bushing can be formed in a small size easily. 
   Incidentally, the groove  74   b  may be formed on a face of the through-hole  57  coming in contact with the bushing  74  instead of the bushing  74 . Further, the number of grooves  74   b  may be one. However, when a plurality of grooves  74   b  are formed, a detection range of the sensor  72  can be expanded. 
   Furthermore, in the fourth and fifth embodiments, though the through-hole  57  has been formed in a circular shape, it may be formed in a rectangular shape or it may be formed in an elongated hole shape, for example. If a gap between of the through-hole  57  and the bushing  74  is formed, shapes of the through-hole  57  and the bushing  74  are not limited to specific ones. Further, regarding the mounting structure of the bushing  74 , adhesion mounting may be adopted or pressure-fitting mounting may be adopted. 
   Sixth Embodiment 
     FIG. 20  and  FIG. 21  show a sixth embodiment of the invention,  FIG. 20  being a front view of a power source outlet device and  FIG. 21  is a sectional view of the power source outlet device taken along line E—E in  FIG. 20 . An outlet case  82  of a power source outlet device  1  is constituted of a main body  83  with a front face opened, a cover body  84  mounted so as to close the front face opening of the main body  83 , and an intermediate base body  85  accommodated in an inner space formed by the main body  83  and the cover body  84 . The outlet case  82  is formed from insulating material such as synthetic resin, and it is assembled internally thereof with a leakage current detecting circuit, a breaker for breaking a cable run and the like. 
   The cover body  84  is formed on a front face thereof with a pair of plug insertion holes  86 ,  86  for inserting plug blades (not shown) of a plug at each of two positions of a central portion and a lower portion, and a through-hole  87  is formed at an intermediate position between the plug insertion holes of each pair. The cover body  84  is provided on its upper portion with an operation handle  88  for performing return operation of the breaker which has performed breaking behavior at a tracking time, display lamps  89  which display leakage occurrence, tracking occurrence and the like, and a test button  90  which tests leakage breaking behavior. 
   A receiving blade  92  pinching a plug blade of a plug is disposed internally of the plug insertion hole  86 , and the through-hole  87  is formed to extend long in parallel to a longitudinal direction of the receiving blade  92 . Then, an insulating permeable body  93  shown with a perspective view in  FIG. 11  is attached to the through-hole  87 . The permeable body  93  is formed such that its outer shape is slightly larger than a shape of the through-hole  87  and it matches with the through-hole  87 . For example, wood, sponge, fiber or the like can be used as the permeable body. The permeable body  93  is pressure-fitted into the through-hole and mounted thereto. 
   A sensor  97  is disposed on a back face of the permeable body  93  which is the inside of the through-hole  87  internally of the outlet case  82 . The sensor  97  is formed of an electrically conductive member such as a metal piece, and it is connected to a tracking detecting circuit of a circuit board  98  disposed internally of the outlet case  82 . 
   With the constitution, tracking detection is performed by the power source outlet device  1  in the following manner. When a spark discharge causing tracking occurs between the plug blades of the plug connected to the receiving blades  92 ,  92  due to dusts and moisture, the spark discharge comes in contact with the permeable body  93 . At this time, since the permeable body  93  also becomes moist to have electrical conductivity, a current flows to the sensor  97  via the permeable body  93 . The tracking detecting circuit detects tracking from an output current from the sensor  92  and causes a breaker housed in the outlet case  82  to behave to break a cable run and perform display by the display lamps  89 . 
   Since the permeable body is mounted in the through-hole in this manner, it is unnecessary to downsize the hole diameter of the through-hole, so that moldability of the outlet case is excellent and productivity is improved. Further, a spark discharge can be detected over the whole through-hole, a detection range of a spark discharge can be expanded, cleaning can be performed by only wiping a surface of the permeable body and cleaning can be performed easily. 
   Incidentally, in the above sixth embodiment, though the through-hole has been formed in a vertically long elongated hole shape, it may be formed in a circular or rectangular shape, for example. Further, in the above embodiment, a wall face outlet structure provided on a wall face has been shown, but a shape of a table tap to which a plurality of plugs can be connected or the like can be adopted. Furthermore, such a constitution has been adopted that a breaker is built in to break a cable run, but behavior at a tracking detecting time is not limited. 
   REFERENCE NUMERALS 
   
       
         2  . . . outlet case,  3  . . . main body,  4  . . . cover body,  5  . . . intermediate base body,  6  . . . plug insertion hole,  7  . . . through-hole,  13  . . . partition wall,  14  . . . hole,  15  . . . sensor insertion hole,  16  . . . sensor,  17  . . . receiving blade,  30  . . . partition wall,  52  . . . outlet case,  56  . . . plug insertion hole,  57  . . . through-hole,  62  . . . receiving blade,  63  . . . bushing,  64  . . . detection hole,  67  . . . sensor,  70  . . . bushing,  71  . . . gap,  72  . . . sensor,  74  . . . bushing,  82  . . . outlet case,  86  . . . plug insertion hole,  87  . . . through-hole,  92  . . . receiving blade,  93  . . . permeable body, and  97  . . . sensor.