Patent Publication Number: US-6991495-B1

Title: Power strip with self-contained ground fault circuit interrupter module

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to a power strip and more particularly to a power strip which provides ground fault protection. 
   Power strips are well-known and are commonly used in the art to provide a plurality of ancillary outlets for a single conventional wall outlet. 
   Power strips are typically constructed to include an plastic or metal casing which is at least partially hollowed out so as to form an interior cavity. The casing is mounted onto a first end of a power cable, said power cable including a hot line, a neutral line and a ground line which are all wrapped together by an outer protective sheath. The second end of the power cable is typically in the form of plug which is adapted to connect with a conventional wall outlet. 
   Each outlet in the power strip includes a first female contact receptacle which is electrically connected to the hot line of the power cable and a second female contact receptacle which is electrically connected to the neutral line of the power cable. Each of the first and second female contact receptacles is disposed within the interior cavity and is accessible through an associated slotted opening formed in the top of the casing. Optionally, each outlet in the power strip may include a third female contact receptacle which is electrically connected to the ground line of the power cable, the third female contact receptacle being disposed within the interior cavity and accessed through an associated opening formed in the top of the casing. 
   As such, each outlet is adapted to receive the plug of a device, such as an electrical appliance, which receives current from a power source. Specifically, each contact receptacle of an outlet is adapted to receive an associated contact terminal of the plug. As a result, a current path is established between the outlet and the plug, thereby providing the device with the necessary power to operate. 
   A power switch is commonly mounted onto the casing and electrically connects the hot and neutral lines of the power cord with each of the individual outlets. As such, the power switch allows for manual regulation of the flow of current between the power cord and each of the individual outlets. The power switch may be provided with an internal circuit breaker which monitors the amount of current passing into and traveling out from the individual outlets. Whenever the amounts of incoming and outgoing current passing into and traveling out from a load connected to the power strip exceeds the current rating of the circuit breaker (thereby signifying a dangerous overcurrent condition) or if there is an accidental short circuit in the load, the circuit breaker opens, or trips, thereby instantaneously cutting off the flow of electricity to the load, which is highly desirable. 
   Power strips are also commonly provided with surge protection capabilities. Specifically, a surge protector is often disposed within the interior cavity of the casing and electrically connects the hot and neutral lines of the power cord with each of the individual outlets. Connected in this manner, the surge protector protects any load connected to the power strip from a power surge occurring at the wall outlet. A power surge (also commonly referred to as transient voltage) is an increase in the voltage at the wall outlet which is above the standard level (e.g., 120 volts). As can be appreciated, subjecting a load to a power surge can potentially damage and/or destroy the load, which is highly undesirable. 
   Although widely used in commerce, conventional power strips of the type described above suffer from a notable drawback. Specifically, although conventional power strips provide protection from power surges and overcurrent conditions, conventional power strips do not provide protection from ground fault conditions. 
   A ground fault condition occurs if the current in the hot line and the current in the neutral line have unequal values (e.g., if the hot line connects directly to ground). As will be described further below, a ground fault condition can be extremely dangerous to a person who is in contact with the load. Specifically, if someone accidentally touches (i.e., grounds) the hot line, the current level in the hot line will immediately become less than the current level in the neutral line. However, because the current path from the wall outlet to the load effectively functions as a closed circuit, the current level in the hot line will always adjust to the current level in the neutral line. As a result, once the hot line is grounded, the current level in the hot line will quickly surge to the current level in the neutral line. This surge in current in the hot line can potentially electrocute the person contacting the load, which is highly undesirable. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a new and improved power strip. 
   It is another object of the present invention to provide a power strip which provides ground fault protection. 
   It is yet another object of the present invention to provide a power strip as described above which includes a readily detectable indicator for notifying the user that the power strip has tripped in response to a ground fault condition. 
   It is still another object of the present invention to provide a power strip as described above which can be manually reset after the power strip has tripped in response to a ground fault condition. 
   It is yet still another object of the present invention to provide a power strip as described above which can be manually tripped for testing purposes. 
   It is yet another object of the present invention to provide a power strip as described above which may be mass produced, has a minimal number of parts, includes modular components, and can be easily assembled. 
   Accordingly, as one feature of the present invention, there is provided a power strip comprising a power cord comprising a hot line and a neutral line, a casing mounted onto said power cord, a plurality of outlets disposed in said casing, and a ground fault circuit interrupter (GFCI) disposed in said casing, said GFCI electrically connecting said power cord to each of said plurality of outlets, said GFCI regulating the flow of current between said power cord and said plurality of outlets. 
   As another feature of the present invention, there is provided a ground fault circuit interrupter (GFCI) for regulating the flow of current between a power source and a load, said GFCI comprising an outlet-free housing, and GFCI circuitry disposed in said outlet-free housing. 
   Additional objects, as well as features and advantages, of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. In the description, reference is made to the accompanying drawings which form a part thereof and in which is shown by way of illustration specific embodiments for practicing the invention. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are hereby incorporated into and constitute a part of this specification, illustrate various embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings wherein like reference numerals represent like parts: 
       FIG. 1  is a top perspective view of a power strip constructed according to the teachings of the present invention; 
       FIG. 2  is a top perspective view, broken away in part, of the power strip shown in  FIG. 1 ; 
       FIG. 3  is a side perspective view of the ground fault circuit interrupter shown in  FIG. 2 ; 
       FIG. 4  is a top perspective view of the ground fault circuit interrupter shown in  FIG. 2 ; 
       FIG. 5  is an end perspective view of the ground fault circuit interrupter shown in  FIG. 2 ; 
       FIG. 6  is an exploded perspective view of the ground fault circuit interrupter shown in  FIG. 2 ; 
       FIG. 7  is a top perspective view of the bottom member of the ground fault circuit interrupter shown in  FIG. 3 ; 
       FIG. 8  is a bottom perspective view of the bottom member of the ground fault circuit interrupter shown in  FIG. 3 ; 
       FIG. 9  is a top perspective view of the ground fault circuit interrupter shown in  FIG. 3 , the ground fault circuit interrupter being shown with its top member removed therefrom; 
       FIG. 10  is bottom perspective view of the top member of the ground fault circuit interrupter shown in  FIG. 3 ; 
       FIG. 11  is an end perspective view of the outlet-free housing for the ground fault circuit interrupter shown in  FIG. 3 ; and 
       FIG. 12  is a fragmentary plan view of a device for receiving electrical power, said device being constructed according to the teachings of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring now to  FIGS. 1 and 2 , there is shown a power strip constructed according to the teachings of the present invention, the power strip being represented generally by reference numeral  11 . As will be described further in detail below, power strip  11  is constructed to provide ground fault protection. 
   Power strip  11  comprises a power cord  13 . Power cord  13  is conventional in construction and includes a hot line  15 , a neutral line  17  and a ground line  19  which are all wrapped together by an outer protective sheath  21  constructed of an insulated material. 
   A plastic casing  23  is mounted onto one end of power cord  13 . The other end of power cord  13  is preferably in the form of a male plug (not shown) which can be inserted into a conventional electrical outlet. With the plug inserted into a conventional electrical outlet, electricity delivered into the electrical outlet travels through the plug, along the power cord  13  and into the various outlets of the power strip, as will be described further below. 
   Casing  23  comprises a bottom portion  25  and a top portion  27  which can be fixedly secured together by any conventional means (e.g., using screws, through snap-fit engagement between portions  25  and  27 , etc.). Secured together, bottom portion  25  and top portion  27  together define an interior cavity  29  into which the primary electric components for power strip  11  are disposed. 
   Power strip  11  comprises a plurality of outlets  31  disposed in a side-by-side relationship, each outlet  31  being adapted to receive a conventional, three-terminal electric plug. Specifically, each outlet  31  includes a hot line female contact receptacle  33  which is electrically connected to hot line  15 . Receptacle  33  is sized and shaped to conductively receive the hot line conductor blade of a standard electrical plug, receptacle  33  being accessed through a vertical, slot-shaped opening  35  formed in top portion  27  of casing  23 . In addition, each outlet  31  includes a neutral line female contact receptacle  37  which is electrically connected to neutral line  17 . Receptacle  37  is sized and shaped to conductively receive the neutral line conductor blade of a standard electrical plug, receptacle  37  being accessed through a vertical, slot-shaped opening  39  formed in the top portion  27  of casing  23 . Furthermore, each outlet  31  includes a ground line female contact receptacle  41  which is electrically connected to ground line  19 . Receptacle  41  is sized and shaped to conductively receive the ground pin of a standard electrical plug, receptacle  41  being accessed through a rounded opening  43  formed in the top portion  27  of casing  23 . As can be appreciated, due to its connection to hot line  15 , neutral line  17  and ground line  19 , each outlet  31  is provided with the necessary current to power a load connected thereto. 
   It should be noted that the particular construction of each outlet  31  does not serve as a principal feature of the present invention. Rather, outlets  31  serve to represent any conventional outlet which is well known and widely used in the art. As such, outlets  31  could be replaced with any other type of conventional outlet without departing from the spirit of the present invention. For example, outlets  31  could be in the form of a conventional two-prong outlet (which does not include a receptacle for receiving a ground pin). 
   As seen most clearly in  FIG. 2 , a ground fault circuit interrupter (GFCI)  45  is disposed within casing  23 . As will be described further in detail below, GFCI  45  connects hot and neutral lines  15  and  17  with each of the individual outlets  31 . In this manner, GFCI  45  serves to interrupt the flow of current from power cord  13  and into each of the individual outlets  31  upon detecting a ground fault or grounded neutral condition in lines  15  and  17 , which is highly desirable. 
   As will be described further in detail below, two novel features of power strip  11  relate to (1) the implementation of ground fault circuit interrupter  45  in power strip  11 , and (2) the self-contained, modular construction of ground fault circuit interrupter  45 . 
   Referring now to  FIGS. 3–11 , GFCI  45  comprises a outlet-free housing  47  and GFCI circuitry  49  disposed within housing  47 . 
   Housing  47  is constructed of a durable and insulated material, such as plastic, and includes a bottom member  51  and a top member  53  which are releasably secured together using screws  55  or other suitable means (e.g., rivets or snap-in feature). Together, bottom member  51  and top member  53  define an interior cavity  56  which is sized and shaped to receive GFCI circuitry  49 . 
   As seen most clearly in  FIGS. 7 and 8 , bottom member  51  is an integral piece which includes a substantially flat bottom panel  57  and a pair of sidewalls  59 - 1  and  59 - 2  which extend orthogonally up from opposite sides of bottom panel  57 , thereby providing bottom member  51  with a generally U-shaped configuration in lateral cross-section. Bottom member  51  is shaped to include a pair of openings  60 , one opening  60 - 1  being formed at one end  61 - 1  of bottom panel  57  and the other opening  60 - 2  being formed at the other end  61 - 2  of bottom panel  57 . It should be noted that the outer surface of bottom panel  57  is countersunk around each opening  60  to receive the head of a screw. 
   A first mounting bracket  62 - 1  is formed onto bottom panel  57  at end  61 - 1  and a second mounting bracket  62 - 2  is formed onto bottom panel  57  at end  61 - 2 , each bracket  62  being positioned at the approximate midpoint between sidewalls  59 . Each bracket  62  includes a flat support surface  63  which is spaced slightly up from and lies parallel with bottom panel  57 , surface  63 - 1  extending out and away from end  61 - 1  and surface  63 - 2  extending out and away from end  61 - 2 . Each support surface  63  is shaped to define a pair of spaced apart mounting holes  65  which are sized and shaped to receive a device (e.g., a screw, nail, bolt, etc.) for fixedly mounting GFCI  45  onto casing  23 . 
   Each bracket  62  is also shaped to include a pair of spaced apart support arms  67 , each support arm  67  projecting orthogonally up from bottom panel  57  and extending at an angle parallel with sidewalls  59 . As will be described further below, support arms  67  help retain circuitry  49  in place on bottom member  51 . A pair of shortened end walls  69  project orthogonally up from bottom panel  57  on opposite sides of each bracket  62 , each end wall  69  extending at a right angle relative to sidewalls  59 . 
   As seen most clearly in  FIG. 10 , top member  53  is an integral piece which includes a substantially flat top panel  71 . Top panel  71  is shaped to include a first circular opening  73 , a second circular opening  74  and a third circular opening  75 . As will be described further below, each of openings  73 ,  74  and  75  is sized and shaped to fittingly receive an associated component of GFCI circuitry  49 . 
   A pair of sidewalls  76  extend orthogonally down from opposite sides of top panel  71 , thereby providing top member  53  with a generally U-shaped configuration in lateral cross-section. A pair of spaced apart tabs  77  are formed onto the inner surface of each sidewall  73  and project downward away from top panel  71 . Each tab  75  includes a longitudinally extending rib  78  which is substantially circular in lateral cross-section. 
   A pair of end walls  79  extend orthogonally down from opposite ends of top panel  71 , thereby providing top member  53  with a generally U-shaped configuration in longitudinal cross-section. A threaded boss  81  is formed onto the inner surface of each end wall  79 , the free end of each boss  81  projecting downward away from top panel  71 . 
   It should be noted that, with top member  53  mounted onto bottom member  51 , top member  53  and bottom member  51  together define a pair of lateral slots  83  on opposite sides of each bracket  61 , as seen most clearly in  FIG. 11 . As will be described further below, each slot  83  is sized and shaped to receive an associated contact terminal of GFCI circuitry  49 . 
   GFCI circuitry  49  represents any conventional GFCI circuitry. As an example, GFCI circuitry  49  may be of the type disclosed in U.S. Pat. No. 5,757,598, which is incorporated herein by reference. 
   As seen most clearly in  FIG. 6 , GFCI circuitry  49  includes a main printed circuit board  85  onto which various circuit components are mounted. Each side of main printed circuit board  85  is shaped to include a pair of semi-circular notches  87 , each notch  87  being sized and shaped to fittingly receive an associated rib  78  from top member  53 . Furthermore, each end of main printed circuit board  85  is shaped to include a pair of longitudinally-extending slots  89 , each slot  89  being sized and shaped to fittingly receive an associated support arm  67 . 
   As such, with GFCI  45  assembled together, arms  67  project into slots  89  to secure GFCI circuitry  49  securely in place on bottom member  51 , as seen most clearly in  FIG. 9 . Furthermore, with GFCI  45  assembled together, tabs  77  abut against the inner surface of sidewalls  59  to secure top member  53  in place on bottom member  51  and ribs  78  project into notches  87  to secure main printed circuit board  85  fixed in place in relation to top member  53 . 
   GFCI circuitry  49  also includes an indicator light  91  which is sized and shaped to fittingly protrude through opening  73  in top member  53  when GFCI  45  is in its assembled form. In use, GFCI circuitry  49  is designed in such a manner so that indicator light  91  will illuminate when circuitry  49  detects a ground fault or grounded neutral condition. Preferably, indicator light  91  is in the form of a light emitting diode. However, it is to be understood that indicator light  91  could be in the form of an alternative illuminating device which is well-known in the art without departing from the spirit of the present invention. 
   GFCI circuitry  49  also includes a test button  93  which is sized and shaped to fittingly protrude through opening  74  in top member  53  when GFCI  45  is in its assembled form. In use, the depression of test button  93  allows the user to trip circuitry  49  in ensure that GFCI  45  is providing proper ground fault protection. 
   GFCI circuitry  49  further includes a reset button  95  which is sized and shaped to fittingly protrude through opening  75  in top member  53  when GFCI  45  is in its assembled form. In use, the depression of reset button  95  serves to reset circuitry  49  after a trip condition is experienced. 
   GFCI circuitry  49  additionally includes four, blade-shaped, terminal contacts  97 , each contact  97  being sized and shaped to fittingly protrude through an associated lateral slot  83  formed between top member  53  and bottom member  51 . Terminal contact  97 - 1  is designated for electrical connection with the hot line  15  of the power source (i.e., power cord  13 ). Terminal contact  97 - 2  is designated for electrical connection to the neutral line  17  of the power source (i.e., power cord  13 ). Terminal contact  97 - 3  is designated for electrical connection to the hot line of the load (i.e., each outlet  31 ). Terminal contact  97 - 4  is designated for electrical connection to the neutral line of the load (i.e., each outlet  31 ). 
   As can be seen most clearly in  FIG. 1 , top portion  25  of casing  23  includes a first circular opening  99 , a second circular opening  101  and a third circular opening  103 . With power strip  11  constructed into its assembled form, GFCI  45  is disposed between top portion  25  and bottom portion  27  of casing  23  in such a manner so that light  91  protrudes through opening  99 , test button  93  protrudes through opening  101 , and reset button  95  protrudes through opening  103 , thereby providing the consumer with suitable access to the necessary components of GFCI  45 . 
   A combination power switch and circuit breaker  105  is preferably disposed within casing  23 . Combination power switch/circuit breaker  105  is preferably disposed in the current path between GFCI  45  and each of individual outlets  31 . In this manner, power switch/circuit breaker  105  can be used to: (1) manually regulate the flow of current between power cord  13  and outlets  31  (by means of the power switch) and (2) automatically interrupt current passing into outlets  31  when the current levels passing into and traveling out from outlets  31  exceeds a predetermined current rating (by means of the circuit breaker). As can be appreciated, the inclusion of combination power switch/circuit breaker  105  does not serve as a novel feature of the present invention. Accordingly, it is to be understood that any conventional combination power switch and circuit breaker could be used in power strip  11  without departing from the spirit of the present invention. 
   As can be appreciated, the self-contained, modular construction of GFCI  45  provides a number of significant advantages. 
   As a first advantage, due to its self-contained, modular construction, GFCI  45  does not need to be manufactured in conjunction with the device into which it is disposed (i.e., remainder of power strip  11 ). Rather, GFCI  45  could be manufactured independently of the remainder of power strip  11 . As a result, it is to be understood that GFCI  45  could be inexpensively and efficiently mass produced and subsequently sold to the manufacturer of any electric device that requires ground fault protection, thereby increasing the range of its potential applications, which is highly desirable. 
   As a second advantage, due to its self-contained, modular construction, GFCI  45  can provide open neutral protection (i.e., circuit protection when the neutral line is cut or otherwise opened) whereas traditional GFCIs do not provide open neutral protection. 
   As a third advantage, due to its self-contained modular construction, GFCI  45  can be constructed without a relay circuit whereas traditional GFCIs require a relay circuit. The ability to eliminate the relay circuit from circuitry  49  of GFCI  45  simplifies the manufacturing process and reduces costs, which is highly desirable. 
   As noted briefly above, the modular, self-contained construction of GFCI  45  allows it to be used in a wide variety of potential applications. In particular, GFCI  45  can be individually manufactured and sold for use in conjunction with any device that receives current from a power source. 
   Specifically, referring now to  FIG. 12 , there is shown a fragmentary plan view of a device for receiving electrical power (such as a stake light), said device being constructed according to the teachings of the present invention and identified generally by reference numeral  111 . Device  111  comprises a protective housing  113  which is at least partially hollowed to allow GFCI  45  to be disposed therewithin. Preferably, housing  113  includes a first circular opening  115  which is sized and shaped to enable light  91  of GFCI  45  to fittingly project therethrough, a second circular opening  117  which is sized and shaped to enable test button  93  of GFCI  45  to fittingly project therethrough and a third circular opening  119  which is sized and shaped to enable reset button  95  of GFCI  45  to fittingly project therethrough. As such, the consumer is provided with the necessary access to the buttons and displays of GFCI, which is highly desirable. In use, GFCI  45  connects the load  121  of device  111  with a power source  123 . 
   The versions of the present invention described above are intended to be merely exemplary and those skilled in the art shall be able to make numerous variations and modifications to it without departing from the spirit of the present invention. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims. For example, it should be noted that the particular components which make up the aforementioned embodiments may be interchanged or combined to form additional embodiments.