Patent Publication Number: US-6340926-B1

Title: Power plug with circuit breaker

Description:
The present invention relates to a power plug incorporating a built-in circuit breaker. 
     BACKGROUND OF THE INVENTION 
     Power plugs incorporating a built-in circuit breaker are generally known, in that the circuit breaker has a reset button for, after the clearance of a circuit fault, resetting the circuit breaker back to the normal switched-on condition. The reset button is usually provided on one side of the power plug and its relative position (raised or lowered) indicates the operating condition of the circuit breaker. 
     The invention introduces an improved power plug of this type, which can provide a more noticeable indication of the circuit breaker condition. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided a power plug comprising a body having opposite sides and an end, a plurality of terminal prongs extending from the end of the plug body, and a built-in circuit breaker operable between a normal condition enabling the power plug to connect a load to a mains power source and a tripped condition disconnecting the load upon the detection of a circuit fault, said circuit breaker including at least two members provided at the opposite sides of the plug body respectively, which members are simultaneously movable between a first position corresponding to the said normal condition and a second position corresponding to the said tripped condition, thereby providing an indication of the operating condition of the circuit breaker on either side of the plug body irrespective of the position of the plug body in use. 
     In a first preferred embodiment, one of the members is movable between a lowered position on the plug body corresponding to the said normal condition and a raised position corresponding to the said tripped condition 
     More preferably, said one member is a reset button for resetting the circuit breaker to the normal condition. 
     In a second preferred embodiment, one of the members is movable between a hidden position within the plug body corresponding to the said normal condition and an exposed position corresponding to the said tripped condition. 
     More preferably, the corresponding side of the plug body is formed with a recessed opening for exposing a lateral side of said one member extending into it from inside the plug body. 
     It is preferred that the circuit breaker includes at least one resiliently biassed movable contact for contacting one of the terminal prongs in the said normal condition and an actuator for moving the contact into contact with the terminal prong, and said one member is movable by the actuator. 
     More preferably, said one member is provided by a part fixed to the actuator. 
     Further more preferably, said one member is provided by an integral part of the actuator. 
     Advantageously, said one member is of a distinctive color. 
     In the second preferred embodiment, the other member is movable between a lowered position on the plug body corresponding to the said normal condition and a raised position corresponding to the said tripped condition. 
     More preferably, the two members are movable in opposite directions. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings in which: 
     FIG. 1 is a top perspective view of an embodiment of a power plug in accordance with the invention; 
     FIG. 2 is a bottom perspective view of the power plug of FIG. 1; 
     FIG. 3 is an exploded perspective view showing the components of a built-in circuit breaker and related parts of the power plug of FIG. 1; 
     FIG. 4 is a perspective view showing the circuit breaker components and related parts of FIG. 3, showing how they are assembled together; 
     FIGS. 5A to  5 D are cross-sectional side views of the power plug of FIG. 1, illustrating the operation of the circuit breaker components and related parts of FIGS. 3 and 4; and 
     FIG. 6 is a bottom perspective view of another embodiment of a power plug in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring initially to FIGS. 1 to  5 D of the drawings, there is shown a power plug  100  embodying the invention, which power plug  100  has a generally rectangular box-like body  10  and a pair of live and neutral terminal prongs  20  extending out from a front end  11  of the body  10 . The plug body  10  includes a rear end  12  for the entrance of a power cable  9  connected to a load, top and bottom sides  13  and  14 , and left and right sides  15  and  16  for gripping. The power plug  100  incorporates a built-in circuit breaker  30  which has a test button  31  and a reset button  32  both provided on the body top side  13 . The body bottom side  14  is formed with a recessed slot opening  17  at a position corresponding to that of the reset button  32  on opposite side. 
     The circuit breaker  30  incorporates an electronic operating circuit (not shown) provided on a circuit board  70  for, inter alia, detecting the occurrence of a circuit fault, such as an earth leakage of over-current, in the load circuit. The circuit breaker  30  further includes a solenoid  36  controlled by the operating circuit, an L-shaped slider  40  movable by a spring-loaded plunger  37  of the solenoid  36 , an actuator  50  co-operable with the slider  40 , and a pair of resilient contact levers  60  provided on opposite sides of these components which are aligned along a horizontal central axis of the plug body  10 . 
     The levers  60  have respective rear ends  62  which are fixed and connected to the corresponding cores of the power cable  9  and respective front ends  64  which are resiliently pivotable upwards and downwards. Rear ends  22  of the terminal prongs  20  are positioned directly above the front ends  64  of the respective levers  60 , for contact by them to complete the circuit between the terminal prongs  20  and the power cable  9  via the levers  60 . 
     The slider  40  has a vertical panel  42  which is formed with a vertical slot  44  in engagement with a free end  38  of the plunger  37 , and includes a horizontal panel  46  which is formed with a horizontal slot  48 . 
     The actuator  50  has a body  52  which has a vertical hollow passage  53  of a rectangular cross-section and includes a pair of horizontal integral arms  54  on opposite outer sides in engagement from below with and for pivoting the front ends  64  of the respective levers  60  upwards to come into contact with the rear ends  22  of the corresponding terminal prongs  20 . In reaction, the actuator  50  is resiliently biased by the levers  60  to move downwards. 
     The actuator body  52  is formed with a horizontal gap  56 , right below the lower end of the passage  53 , for slidably receiving the horizontal panel  46  of the slider  40  such that the actuator  50  and slider  40  are inter-engaged for simultaneous vertical movement. The slot  48  of the panel  46  is generally aligned with the lower end of the passage  53 . Lowermost end  58  of the actuator body  52  is planar and in vertical alignment with the opening  17  on the bottom side  14  of the plug body  10 , for extending outwards through the opening  17 . The actuator  52  or in particular its lowermost end  58  is of a distinctive color, such as red, which is different from the color of the plug body  10 . 
     The reset button  32  has a vertical shaft  33  of a rectangular cross-section, which extends downwards through the circuit board  70  and then the passage  53  for co-operation with the actuator  50  and also the slider  40 . The lowermost end of the shaft  33  is in the form of a side hook  34  facing the solenoid plunger  37  and including an inclined outer surface  35  for latching engagement with the horizontal panel  46  of the slider  40  through the slot  48 . 
     The slider panel  46  passes completely through the gap  56  and extends out on the opposite side of the actuator body  52 . A compression coil spring  49  is used within the exposed end of the slot  48  to resiliently bias the panel  46  further outwards for two actions. The first action is to resiliently bias the opposite end of the slot  48  into latching engagement with the hook  34 . The second action is to, in turn via the other panel  42  of the slider  40 , resiliently bias the plunger  37  to extend outwards from the coil of the solenoid  36 . 
     Another, relatively larger, compression coil spring is disposed on the shaft  33 , which co-acts between the reset button  32  and the circuit board  70  for resiliently biasing the reset button  33  upwards. The latching engagement between the hook  34  and the slider panel  46  will keep the reset button  32  downwards against the action of the spring  39 . 
     The circuit breaker  30  may be in either one of the following operating conditions: (1) a normal condition enabling the power plug  100  to connect the load to the mains power source and (2) a tripped condition disconnecting the load upon the detection of a circuit fault by the operating circuit. 
     In the normal condition (FIG.  5 C), the solenoid  36  is not energised to have its plunger  37  free to extend outwards, which permits the spring  49  to perform the aforesaid two actions. The latching of the reset button hook  34  with the slider panel  46  results in vertical engagement of the actuator  50  with the reset button  32  (via the shaft  33 ). The spring  39  moves the reset button  32  upwards (to a limited extent) into a normal or lower/lowered position and also moves the actuator  50  upwards causing the levers  60  to come into contact with the corresponding terminal prongs  20  (FIG.  5 D). In the upward position, the lowermost end  58  of the actuator  50  stays off the opening  17  and is hidden within the plug body  10 . 
     The reset button  32  being lowered and the actuator end  58  being invisible provide two indications on opposite top and bottom sides  13  and  14  of the plug body  10  that the circuit breaker  30  is in the normal condition (FIG.  5 C). 
     Upon the detection of a circuit fault, the solenoid  36  is energised to retract its plunger  37  inwards against the action of the spring  49 , thereby causing the plunger  37  to withdraw the slider  40  from the actuator  50 . This results in disengagement of the slider panel  46  from the reset button hook  34 , which in turn releases the vertical engagement between the actuator  50  and the reset button  32 . Consequently, the spring  39  will move the reset button  32  further upwards into a raised position. Also, the levers  60  will flex, by virtue of their resilient nature, downwards off the corresponding terminal prongs  20 , thereby cutting off the mains power previously supplied to the load and circuit breaker  30 , and at the same time moving the actuator  50  downwards, Downward movement of the actuator  50  causes its lowermost end  58  to extend outwards through the opening  17  and have the lateral side of its extreme end exposed in the recess of the opening  17  (see FIG.  2 ). 
     The reset button  32  being raised and the actuator end  58  being visible provide two indications on opposite top and bottom sides  13  and  14  of the plug body  10  that the circuit breaker  30  in the tripped condition (FIG.  5 A). 
     After the circuit fault has been cleared, depression of the reset button  32  will return the circuit breaker  30  back to the normal condition. When the reset button  32  is initially depressed fully downwards against the action of the spring  39 , its hook  34  will re-engage with the slider panel  46  (FIG. 5B) by reason of its inclined surface  35  through a latch action enabled by the spring  49 . This results in vertical engagement of the actuator  50  with the reset button  32 . Upon release, the reset button  32  will be moved upwards by the spring  39  into the lowered position (FIG.  5 C). The actuator  50  will simultaneously moved upwards by the spring  39  to pivot the levers  60  into contact with the corresponding terminal prongs  20  (FIG. 5D) and to withdraw its lowermost end  58  from sight. 
     The reset button  32  and the actuator end  58  provide, on opposite top and bottom sides  13  and  14  of the plug body  10 , duplicate indication of the operating condition of the circuit breaker  30 . In practice, irrespective of the position (whether normal or upside-down) the power plug  100  is inserted into a mains power socket on the wall, and/or the orientation of the power socket fixed on the wall, the circuit breaker condition could easily or conveniently be determined by a person by looking at either indication. 
     Referring now to FIG. 6 of the drawings, there is shown another power plug  10 A embodying the invention, which has the same general construction as the earlier power plug  100 , with like parts designated by like reference numerals suffixed by letter “A”, and operates in essentially the same way. 
     The present power plug  100 A has two major differences. First, there is a third, earth terminal prong  26  in addition to the live and neutral prongs  20 A, which necessitates the formation of a central ridge  14 A′ (extra space) on the bottom side  14 A of the plug body  10 A. Second, the internal actuator (not shown but equivalent to the earlier actuator  50 ) has a pair of lowermost ends  58 A which are extendable in and out through respective holes  17 A formed in the bottom side  14 A on opposite sides of the ridge  14 A′. Apart from these two ends  58 A, the present actuator is constructed and works in the same manner. 
     In operation, the actuator is movable downwards to protrude its ends  58 A out from the bottom side  14 A (raised position) for indicating the tripped condition of the built-in circuit breaker and movable upwards to retract its ends  58 A into the plug body  10 A (hidden position or lowered position if desired) for indicating the normal condition. Two ends  58 A are employed to ensure that at least one of them will not be blocked from sight by the ridge  14 A′. 
     The two actuator ends  58 A and the reset button (not shown but equivalent to the earlier reset button  32 ) provide, on opposite top and bottom sides of the plug body  10 A, duplicate indication of the operating condition of the built-in circuit breaker for easy/convenient viewing by a person irrespective of the position/orientation of the power plug  100 A and/or wall socket. 
     The invention has been given by way of example only, and various other modifications of and/or alterations to the described embodiment may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.