Abstract:
A surge protector for an electrical line is disclosed. The surge protector includes a pair of conductive pins respectively connectable to electrical lines. A first pin is soldered to a lead from a gas tube surge arrester. The lead is further fixed adjacent to the first pin and then attached to the second pin. A ground bracket having an opening is positioned between and connected with the other side of the surge arrester. As an electrical surge travels through the lines, the gas tube surge arrester begins to spark over, shunting overload conditions to the ground bracket. As the temperature begins to build, the solder flows, causing an open condition in which the surge arrester disconnects from the first pin, thereby eliminating the destructive effects of a prolonged electrical surge on the lines.

Description:
FIELD OF THE INVENTION 
     The present invention relates to surge protection in communications systems. More particularly, the present invention relates to a surge protector and a method for protecting against electrical surges in coaxial and other cables. 
     BACKGROUND OF THE INVENTION 
     Surge protectors are in use to protect electronic components from the deleterious effects of electrical surges. Generally, surge protectors function to shunt abnormal surges of electricity away from electronic components. There are three major causes of electrical surges: lightning pulses, ground surges, and power crosses. Lightning pulses are a relatively brief surge of electricity stemming from a strike of lightning on or near an electrical conduit, such as a power line or a communications line. Ground surges are caused when excess voltage, which follows the path of least resistance, does not entirely travel to ground, but instead strays off to another line which is itself connected to ground. Ground surges may be caused by a shorted circuit, a faulty connection to ground, the intensity of the abnormal voltage level, or the duration of an abnormal voltage level. 
     A power cross is potentially the most devastating type of electrical surge. A power cross comes when a pole carrying power lines is toppled, such as by high wind, a tree falling against it, or a car running into it, and falls into another line, for example, a telecommunications cable or line. Upon the pole falling, the various lines may become dislodged and crossed. Crossed lines may remain so for a lengthy time, thus subjecting a line or cable and any electrical components in connection with it to abnormal voltage conditions for a lengthy period of time. Depending upon the intensity of the power cross, as well as its duration, the line or cable may be melted. If the line or cable is running in from an industrial site, such as, for example, a phone company, the amount of line or cable melted may be miles long. The replacement cost, as well as the cost of running new line or cable, is high. 
     Devices have been utilized on so called “twisted pair” telephone lines to protect against electrical surges since the 1920 s. One such device, described in U.S. Pat. No. 4,161,762 (Scheithauer), acts as a fuse. Specifically, the device operates if an excess current flows through the line. Devices such as the one described in Scheithauer are impractical for coaxial communications lines. In particular, placing a fuse in a coaxial communications line changes the characteristics of the coaxial cable by adding impedance to the center conductor. Changing the characteristics alters the signals being transmitted. 
     Surge protectors for cables have been described in U.S. Pat. No. 5,835,326 (Callaway), U.S. Pat. No. 5,751,534 (DeBalko), U.S. Pat. No. 5,726,851 (Knapp), and U.S. Pat. No. 5,508,873 (Knapp et al.). 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for protecting electronic components and signal carrying cables from damage due to electrical line surges. The apparatus has first and second conductors respectively connectable to electrical signal paths, and a first line protection device electrically connected between the first and second conductors. The first line protection device includes a third conductor interconnecting the first and second conductors and being electrically connected to at least one of the first and second conductors through a meltable conductive fixing material, e.g., a solder. The conductive fixing material disrupts electrical connection between the third conductor and at least one of the first and second conductors when predetermined overload electrical signals are present. In one aspect of the invention, the cables are coaxial cables. 
     In a preferred embodiment of the invention, the third conductor is a lead which is soldered to the first conductor at a first point, the lead being further connected to the second conductor, with the solder melting under predetermined electrical overload conditions. The invention may also employ a second line protection device formed by connecting the lead to one electrical side of gas breakdown device, the other electrical side of the gas breakdown device being groundable. 
     These and other features and advantages of the invention will become more apparent from the following detailed description of preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a line protector constructed in accordance with a preferred embodiment of the present invention. 
     FIG. 2 is a perspective view of the coaxial cable and ground bracket of FIG.  1 . 
     FIG. 3 is a side view of a surge arrester constructed in accordance with a preferred embodiment of the present invention. 
     FIG. 4 is a partial cross-sectional view of the line protector of FIG. 1 including the surge arrester of FIG.  3 . 
     FIG. 5 is a schematic view of the line protector of FIG. 1 within an electrical system. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, where like numerals designate like elements, there is shown schematically in FIG. 5 a line protector  10  in use in a typical communications line  140 , for example, a satellite coaxial cable line. Specifically, the line protector  10  may be used to protect electronic equipment  130  in the field, such as the electronics associated with a satellite dish  150 . Further, the line protector may be used to protect electronic equipment (not shown) located, for example, at a terminating location such as in a residence. Although the line protector  10  is shown on the communications line  140  between the satellite dish  150  and the residence, it is to be understood that the line protector  10  of the invention may be used on power lines, or on other signal carrying lines, such as cable television lines and computer, voice and/or data-dedicated lines like ISDN, T-1, T-3, and digital subscriber lines (DSL). 
     With reference to FIG. 1, the line protector  10  includes a groundable bracket  60  positioned between a pair of coaxial cable terminals  20 ,  40 . The terminals  20 ,  40  each include a respective tube portion  22 ,  42 . The tube portions  22 ,  42  each have a first tube portion  24 ,  44  and a second tube portion  26 ,  46 . Preferably, the first tube portions  24 ,  44  each have an end which connects to the ground bracket  60 . The ground bracket  60  provides a good mounting structure for the tube portions  24 ,  44 , and is also a convenient ground wire connection (to be described in detail below). The ends of the first tube portions  24 ,  44  may be soldered or otherwise adhered to the ground bracket  60 . Alternatively, the ends of the first tube portions  24 ,  44  may be female ends having threads and the ground bracket  60  may include complementary threads on a protrusion. In this way the first tube portions  24 ,  44  of respectively the terminals  20 ,  40  may be threaded onto the ground bracket  60 . Alternatively, the ends of the first tube portions  24 ,  44  may have external threads which thread into internal threads in an opening  68  of the bracket  60 . 
     The first tube portions  24 ,  44  are of a greater diameter than the second tube portions  26 ,  46  to accommodate pins  80 ,  84 , FIG. 3 which are described in greater detail below. At an end of the second tube portions  26 ,  46  are threaded ends  30 ,  50  for connection to electronic equipment  120  (FIG. 5) and/or to a line of cable  140 . The threaded ends  30 ,  50  are particularly suitable for connection with the terminal ends of coaxial cables. However, the invention is not limited to use with coaxial cables and any suitable end connector can be employed instead of threads  30 ,  50  for connection with other types of electrical lines, including power lines and communications lines. 
     The ground bracket  60 , which is formed of a conductive material, such as, for example, a metallic material, includes a ring  61  and a base  62 . As shown in FIGS. 2,  3 , the base includes a base bracket  63 . Mounting holes  64  are located through the base bracket  63  and allow the bracket  60  to be mounted to a grounded structure. Ground holes  66  are also located in the base  62 . The ground holes  66  allow for a lead  108  (to be described in more detail below) to be connected to the bracket  60 . Alternatively, the holes  66  may be slots. The ring  61  has a field side  70  and an equipment side  72 , with the ring opening  68  therethrough. The opening  68  allows for a surge arrester  90 , shown in FIGS. 3,  4  and described in more detail below to be positioned therein. 
     FIG. 3 shows the surge arrester  90 , which includes a non-conductive tube  92 . The tube  92  is filled with a gas  110 , such as, for example, argon or neon. The tube  92  is hermetically sealed and has a pair of conductive plates  94 ,  96  on opposite sides thereof. The plates  94 ,  96  may be formed of a metallic material or other like conductive material. A first lead  98  extends from the side plate  94  and a second lead  108  leads from the plate  96 . 
     An important aspect of the present invention is illustrated in FIGS. 3,  4 . A conductive pin  80  including a first end  81  and a second end  82  is positionable within the terminal  20 . A second conductive pin  84  includes a first end  85  and a second end  86  and is positionable within the terminal  40 . Each respective end  81 ,  85  has a female connector for mating with a male pin (not shown) of a coaxial cable when a female collar of the coaxial cable is threaded onto the threads  30 ,  50 . 
     As best shown in FIG. 4, the lead  98  extends to and is connected with the end  82  of the pin  80 . The connection is by solder at solder point  100 . The lead  98  may be further fixed adjacent to a portion of the circumference of the end  82 . A portion  104  of the lead  98  extends from the end  82  and is connected to the end  86  of the second pin  84 . The connection to the second pin  84  of the lead portion  104  may be by solder at a solder point  106 . Alternatively, the lead portion  104  may be mechanically attached, such as by crimping, to the end  86  of the second pin  84 . 
     The second lead  108  of the surge arrester  90  extends from the side plate  96  through the opening  68  in the bracket  60  to the ground hole  66  of the base  62 . Alternatively, the second lead  108  may be solder to an interior surface of the bracket  60  facing the opening  68 . The surge arrester  90  is positioned within the hole  68  of the bracket  60 , as shown in FIG.  4 . 
     The surge arrester  90  is designed to have a defined surge limiting characteristic. Specifically, a voltage limit may be designed into the surge arrester  90  such that once the limit is reached, spark over, or breakdown, occurs within the arrester  90 . For example, a surge arrester  90  having neon as its gas may be designed with a surge limiting characteristic in the range of 70 to 80 volts. If a voltage surge higher than 70 to 80 volts is experienced, the surge arrester  90  begins to glow and conduct electricity by arcing right to the ground  108 . If the voltage surge is of a short duration, such as, for example during a lightening pulse, and the voltage limit is reached, the surge arrester  90  sparks over. The surge arrester  90  acts to prevent surge damage to electric components in the event an abnormal electrical voltage surge of a relatively short duration or of a relatively low magnitude is encountered by shorting such voltage surge to ground. However, the surge arrester  90  is less effective for certain types of electrical surges of longer duration. The surge protector  90  thus serves as one overload protecting device. The solder connection of lead  98  to pin  82  serves as another overload protecting device. The interrelationship of the two overload protecting devices will now be described with reference to an exemplary installation shown in FIG.  5 . 
     The line protector  10  is positioned at the end of an electrical line  140  near the electronic components  130 , which are components for a satellite dish  150 . It should be understood that FIG. 5 is merely exemplary of but one use of the overload protector  10  of the invention and with one exemplary type of line, namely, a coaxial cable. As noted, protector  10  of the invention can be used to protect any type of electrical line and/or components connected to such line. 
     In the presence of a higher than normal current, line protector  10  is able to carry the current through pin  80 , lead  104  and pin  84  as long as the applied voltage is insufficient for the surge arrester  90  to begin to spark over. As noted above, in the event of an electrical surge from a lightening strike or other voltage spike, the surge arrester  90  sparks over in response to the elevated voltage level, sending the electrical surge to ground through the ground line  108  which is connected to the groundable bracket  60 . During the spark over, the tube  92  of the surge arrester  90  will begin to glow. The spark over of the surge arrester  90  continues for the duration of the elevated voltage, which during lightening pulses is a short period of time, or until a circuit breaker in the field is flipped. 
     However, the surge arrester  90  is less effective in instances when an overload condition is of longer than expected duration or of greater intensity than normal, and in instances of other prolonged electrical surges, such as from power crosses and/or ground surges. Such lengthy electrical surges can, if allowed to continue, heat up the cable  140  to the point of destruction. 
     As noted above, the lead  98  of the arrester  90  is soldered to the pin  80  at the solder point  100 . The lead  98  is fixed adjacent to a portion of the circumference of the end  82  of the pin  80 , and the portion  104  of the lead  98  is extended to and connected with the end  86  of the second pin  84 . Through this arrangement, during a prolonged electrical surge, when the surge arrester  90  sparks over the temperature of lead  98  rises due to the heat generated by the glowing tube  92  and the solder at solder point  100  begins to melt. Eventually, the solder will flow to such an extent that the lead  98  will disengage from the pin  80  being only placed adjacent thereto. At that moment, the lead  98  separates from the end  82  of the pin  80 , the spark over of the arrester  90  ends and the electrical surge is contained or isolated on the field side of the cable  140 . 
     The present invention diminishes the likelihood of the destruction of electronic components and large portions of coaxial cable by using the power of the electrical surge to disengage an electrical connection between cables connected by line protector  10 . The present invention provides an apparatus and a method for dampening line surges and preventing damage to electronic components. 
     Although the invention has been described for use with a coaxial cable, for example, an N-type coaxial cable, it is to be understood that any cable, such as, for example, F-type or UHF type, can be used with the invention along with ISDN, T-1, T-3, DSL and other telecommunications cables. The invention may also be employed with power cables. 
     While preferred embodiments of the invention have been described and illustrated, the invention is not limited by the foregoing description as many modifications and substitutions can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the present invention is not to be considered as limited by the specifics of the particular structure which have been described and illustrated, but is only limited by the scope of the appended claims.