Patent Publication Number: US-6215082-B1

Title: Load break interrupter having vented muffler assembly on arc-suppressing tube

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The following copending applications assigned to the same assignee as this application disclose related subject matter: 
     (1) Ser. No. 09/454,575, filed Dec. 7, 1999, entitled “Load Break Interrupter Having Diagonally Split Case With Component Mounting Elements” by Brad W. Davis. 
     (2) Ser. No. 09/454,572, filed Dec. 7, 1999, entitled “Load Break Interrupter Having Shunt Circuit Break Actuating Mechanism” by Brad W. Davis. 
     (3) Ser. No. 09/454,574, filed, Dec. 7, 1999, entitled “Load Break Interrupter Having Arc-Suppressing Tube With Mechanically Interlocked Inner Quench Liner” by Brad W. Davis. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a load break interrupter for suppressing arcing during opening of a blade-type disconnect switch and, more particularly, is concerned with such an interrupter having a vented muffler assembly on an arc-suppressing tube. 
     2. Description of the Prior Art 
     In the use of high voltage electrical transmission and distribution equipment, it is common practice to provide manually operable blade-type switches which can be opened as needed to break the flow of current in order that linemen can work on such equipment. These switches employ a pivotally movable blade-like contact electrically connected between a pair of fixed switch terminal contacts. When the movable contact of the switch is swung open by means of a conventional hot-line tool or the like, the circuit between the fixed terminal contacts is broken and the flow of current is interrupted. The fixed and movable contacts are in proximal relationship during opening and closing of the movable contact and the swinging movement of the movable contact away from the fixed contacts is slow relative to the current flow. 
     Because transmission and distribution lines carrying high voltages on the order of 15,000 volts or more will produce arcing which is damaging to the blade-type switch as the movable contact is swung away from the fixed contacts, it is also common practice to employ load break interrupters with such blade-type switches. One load break interrupter marketed under the trademark DuoGap by Hubbell Power Systems, Inc. of Centralia, Mo., a subsidiary of Hubbell Incorporated, is designed to overcome the problems associated with arcing across switch contacts. The Hubbell DuoGap interrupter is illustrated and described in detail in U.S. Pat. No. 4,013,852 to Roberts et al. The Hubbell DuoGap interrupter basically includes a case, an arc-suppressing tube supported on the housing, a reciprocal shunt circuit rod slidably supported in the tube, electrical contacts spaced apart from one another on the rod and tube, and a spring-loaded trip mechanism disposed in the housing and coupled with the rod. Actuation of the trip mechanism pushes the rod through and relative to the tube to break an electrical shunt circuit between the electrical contacts on the rod and on the tube after the movable contact of the blade-type switch has separated from the fixed contacts thereof. Any arcing between the spaced apart electrical contacts on the interrupter rod and tube is confined to and suppressed inside the tube due to the presence of arc-suppressing material therein. The interrupter also includes a mechanism for resetting the interrupter to re-establish the shunt circuit through the interrupter after each actuation thereof. 
     The above-described Hubbell interrupter has performed highly satisfactorily over a prolonged period of commercial use. However, as with any successful product, the need arises from time to time to make improvements which will enhance its overall manufacture and operation. 
     SUMMARY OF THE INVENTION 
     The present invention provides a load break interrupter incorporating improved features that satisfies the aforementioned need. These features are a diagonally split case having component mounting elements, a shunt circuit break actuating mechanism, an arc-suppressing tube having a mechanically interlocked inner quench liner, and a vented muffler assembly on the arc-suppressing tube. One of these features, a vented muffler assembly on the arc-suppressing tube, constitutes the present invention of this application. This feature along with the other features constituting the inventions of the applications cross-referenced above increase reliability of the interrupter and simplify the manner of assembly and reduce the cost of the interrupter. 
     Accordingly, the present invention is directed to a load break interrupter which comprises: (a) a case defining an interior chamber; (b) an arc-suppressing tube supported on and extending outwardly from the case; (c) a vented muffler assembly supported on a terminal end of the arc-suppressing tube; (d) a shunt circuit rod slidably supported in the tube for making and breaking a shunt circuit upon sliding of the rod into and from the tube; and (e) a shunt circuit break actuating mechanism disposed in the interior chamber of the case and coupled with the rod such that tripping of the actuating mechanism from a shunt circuit-defining position to a shunt circuit-breaking position causes the rod to at least partially extend into the case from the tube thereby breaking the shunt circuit such that any arcing that occurs upon breaking of the shunt circuit is confined and suppressed inside the tube and vented through the muffler. 
     These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following detailed description, reference will be made to the attached drawings in which: 
     FIG. 1 is a plan view of a load break interrupter having the improvements constituting the present invention and the inventions of the applications cross-referenced above, with an external lever shown mounted on a housing of a case of the interrupter and adapted to be pivoted by a switch blade or contact of an external blade-type switch as described in the background hereinbefore. 
     FIG. 2 is a side elevational view of the interrupter as seen along line  2 — 2  of FIG.  1 . 
     FIG. 3 is another plan view of the interrupter similar to that shown in FIG. 1 now showing the external lever mounted on a cover of the case of the interrupter. 
     FIG. 4 is a side elevational view of the interrupter as seen along line  4 — 4  of FIG.  3 . 
     FIG. 5 is a plan view similar to that of FIG. 1 but with the cover of the case removed showing a shunt circuit break actuating mechanism disposed within the housing of the case. 
     FIG. 6 is a longitudinal sectional view of the interrupter taken along line  6 — 6  of FIG.  5 . 
     FIG. 7 is a plan view similar to that of FIG. 5 but with the actuating mechanism removed from the housing of the case. 
     FIG. 8 is an end view of the housing of the case as seen along line  8 — 8  of FIG.  7 . 
     FIG. 9 is a fragmentary cross-sectional view taken along line  9 — 9  of FIG. 7 showing a spring anchor post formed on the housing about which is hooked an end of a reset spring employed by the interrupter. 
     FIG. 10 is a fragmentary cross-sectional view taken along line  10 — 10  of FIG. 7 showing a collar formed on the housing defining a hole for receiving and mounting a rotatable shaft of the actuating mechanism. 
     FIG. 11 is an enlarged plan view of the cover of the interrupter case. 
     FIG. 12 is a cross-sectional view of the cover taken along line  12 — 12  of FIG.  11 . 
     FIG. 13 is an enlarged side elevational view of a latch of the interrupter actuating mechanism. 
     FIG. 14 is an end elevational view of the latch as seen along line  14 — 14  of FIG.  13 . 
     FIG. 15 is an enlarged side elevational view of a drive assembly of the interrupter actuating mechanism. 
     FIG. 16 is an end elevational view of the drive assembly as seen along line  16 — 16  of FIG.  15 . 
     FIG. 17 is an enlarged plan view of a latch backup spring of the interrupter actuating mechanism. 
     FIG. 18 is a side elevational view of the latch backup spring as seen along line  18 — 18  of FIG.  17 . 
     FIG. 19 is an enlarged plan view of a lever of the interrupter actuating mechanism. 
     FIG. 20 is a side elevational view of the lever as seen along line  20 — 20  of FIG.  19 . 
     FIG. 21 is a longitudinal sectional view of a drive shaft of the drive assembly of FIG.  15 . 
     FIG. 22 is an end elevational view of the drive shaft as seen along line  22 — 22  of FIG.  21 . 
     FIG. 23 is an opposite end elevational view of the drive shaft as seen along line  23 — 23  of FIG.  21 . 
     FIG. 24 is an enlarged side elevational view of a shunt circuit rod of the interrupter. 
     FIG. 25 is an end elevational view as seen along line  25 — 25  of FIG. 24 showing a connector on a shunt cable attached to a leading end of the shunt circuit rod. 
     FIG. 26 is an enlarged end elevational view of an arc quench liner of the arc suppressing tube of the interrupter. 
     FIG. 27 is a longitudinal sectional view of the liner taken along line  27 — 27  of FIG.  26 . 
     FIG. 28 is a plan view the same as that of FIG. 5, showing the interrupter in its relaxed shunt-circuit defining position, the external lever being shown in a rest position before being engaged by a movable switch blade contact of a blade-type switch. 
     FIG. 29 is a longitudinal sectional view taken along line  29 — 29  of FIG.  28 . 
     FIG. 30 is a cross-sectional view taken along line  30 — 30  of FIG.  28 . 
     FIG. 31 is a plan view similar to that of FIG. 28, now showing the interrupter in its loaded shunt-circuit defining position prior to tripping of the actuating mechanism of the interrupter, the external lever being shown in a partially displaced position after being engaged and moved relative to the interrupter by the movement of the movable switch blade contact of the blade-type switch out of electrical connection with the fixed contacts of the switch. 
     FIG. 32 is a longitudinal sectional view taken along line  32 — 32  of FIG.  31 . 
     FIG. 33 is a cross-sectional view taken along line  33 — 33  of FIG.  31 . 
     FIG. 34 is a plan view similar to that of FIG. 32, now showing the interrupter in its actuated shunt circuit-breaking position after tripping of the actuating mechanism of the interrupter, the external lever being shown in a fully displaced position after the shunt circuit rod has been pulled into the case from the arc-suppressing tube. 
     FIG. 35 is a longitudinal sectional view taken along line  35 — 35  of FIG.  34 . 
     FIG. 36 is a cross-sectional view taken along line  36 — 36  of FIG.  34 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as “forward”, “rearward”, “left”, “right”, “upwardly”, “downwardly”, and the like are words of convenience and are not to be construed as limiting terms. 
     Load Break Interrupter—In General 
     Referring to the drawings and particularly to FIGS. 1 to  6 , there is illustrated a load break interrupter, generally designated  10 , incorporating several improved features. These improved features are a diagonally split case with component mounting elements, a shunt circuit break actuating mechanism, an arc-suppressing tube having a mechanically interlocked inner quench liner, and a vented muffler assembly on the arc-suppressing tube. Only one of these features, the vented muffler assembly on the arc-suppressing tube, is the subject of the present invention. However, all such features are described hereinafter to facilitate an overall understanding of the interrupter  10 . 
     The load break interrupter  10  basically includes a case  12 , an arc-suppressing tube  14 , a shunt circuit rod  16 , a shunt circuit break actuating mechanism  18  and a reset element  20 . The tube  14  is mounted on and projects outwardly from the case  12 . The shunt circuit rod  16  is slidably supported in the tube  14  with the tube  14  and rod  16  having respective electrical contacts  22 ,  24  attached thereto and convertible between make and break conditions upon sliding of the rod  16  into and from the tube  14 . The shunt circuit break actuating mechanism  18  is disposed in the case  12  and coupled with a leading end  16 A of the rod  16  which extends into the case  12  such that upon tripping the actuating mechanism  18  from a shunt circuit-defining position (FIG. 28) to a shunt circuit-breaking position (FIG. 34) the rod  16  is pulled partially into the case  12  from the tube  14  thereby breaking a shunt circuit through the rod  16  and between the electrical contacts  22 ,  24  on the tube  14  and rod  16  with any arcing that occurs upon breaking the shunt circuit at the contacts  22 ,  24  being confined and suppressed inside the tube  14 . The reset element  20  coupled between the case  12  and the actuating mechanism  18  is adapted to return the actuating mechanism  18  to the shunt circuit-defining position (FIG. 28) after each tripping thereof to the shunt circuit-breaking position (FIG.  34 ). 
     Diagonally Split Case with Component Mounting Elements 
     Referring to FIGS. 1 to  12 , the case  12  of the interrupter  10  is split diagonally and includes a housing  26  to which the arc-suppressing tube  14  is attached and a cover  28  adapted to attach to and forms a closed interior chamber  30  with the housing  26  in which the shunt circuit break actuating mechanism  18  is disposed. The housing  26  has a generally flat main wall  32  and a side wall  34  integrally attached to, projecting transversely outwardly from, and encompassing the periphery of the main wall  32 . The side wall  34  of the housing  26  has a first end portion  34 A located adjacent to and preferably integrally connected to the tube  14  and an opposite second end portion  34 B located remote from the tube  14 . As can be seen in FIG. 2, the first end portion  34 A is greater in height from the main wall than the second end portion  34 B such that opposite side portions  34 C extending between and interconnecting the first and second end portions  34 A,  34 B taper from the first end portion  34 A to the second end portion  34 B. 
     The cover  28  has a generally flat main wall  36  and a side wall  38  integrally attached to, projecting transversely outwardly from, and encompassing the periphery of the main wall  36 . The side wall  38  of the cover  28  has a first end portion  38 A located adjacent to the tube  14  and the first end portion  34 A of the housing  26  and an opposite second end portion  38 B located remote from the tube  14  and adjacent to the second end portion  34 B of the housing  26 . As can be seen in FIG. 2, the first end portion  38 A of the cover side wall  38  is smaller in height from the main wall  36  thereof than the second end portion  38 B thereof such that opposite side portions  38 C of the cover  38  extending between and interconnecting the first and second end portions  38 A,  38 B taper from the second end portion  38 B to the first end portion  38 A. Furthermore, the first end portion  38 A of the side wall  38  of the cover  28  is smaller in height than the first end portion  34 A of the side wall  34  of the housing  26  whereas the second end portion  38 B of the side wall  38  of the cover  28  is larger in height than the second end portion  34 B of the side wall  34  of the housing  26 . 
     The actuating mechanism  18  is disposed in the interior chamber  30  of the case  12  formed by the housing  26  and cover  28 . The housing  26  and cover  28  have respective elements formed thereon and extending into the interior chamber  30  which cooperate together to mount and retain the components of the actuating mechanism  18  and the reset element  20  and to guide movement of the shunt circuit rod  16  into and from the interior chamber  30  of the case  12 . As best seen in FIG. 7, the elements formed on the main wall  32  of the housing  26  which mount the components of the actuating mechanism  18  include an annular collar  40  extending in opposite directions from the main wall  32  of the housing  26  and defining a hole  42  therethrough, posts  44  spaced in one direction from the annular collar  40 , and a first boss  46  disposed between and spaced from the annular collar  40  and the posts  44 . The element formed on the main wall  32  of the housing  26  which mounts the reset element  20  is a second boss  48  spaced in the opposite direction from the annular collar  40 . As best seen in FIG. 7, the elements formed on the main wall  36  of the cover  28  which retain the components of the actuating mechanism  18  mounted on their respective housing elements are an annular bearing  50  aligned with and disposed adjacent to the annular collar  40  on the housing  26 , a first protuberance  52  aligned with and disposed adjacent to the posts  44  on the housing  26 , and a second protuberance  54  aligned with the reset element  20  and disposed adjacent to but offset from the second boss  48  on the housing  26 . The elements formed on the main walls  32 ,  36  of the housing  26  and cover  28  which guide movement of the rod  16  are two pairs of laterally-spaced apart generally parallel rails  56 ,  58  aligned with and extending toward one another. The pair of rails  56  on the main wall  32  of the housing  26  at their first ends  56 A are interconnected by an arcuate-shaped bight  60  disposed adjacent to the first end portion  34 A of the side wall  34  of the housing  26 . The pair of rails  56  at their second ends  56 B together with the second end portion  34 B of the side wall  34  of the housing  26  form a pocket  62  disposed adjacent to the second end portion  34 B of the side wall  34  of the housing  26 . A resilient impact bumper  63  (see FIG. 6) is disposed in the pocket  62  at the second ends  56 B of the rails for receiving the impact of the leading end  16 A of the rod  16  when pulled into the case  12  by tripping of the actuating mechanism  18 . 
     The pair of rails  58  on the main wall  36  of the cover  28  at their first ends  58 A are interconnected by an arcuate bight  64  disposed adjacent to the first end portion  38 A of the side wall  38  of the cover  28 . The pair of rails  58  at their second ends  58 B are spaced apart from one another and disposed adjacent to the second end portion  38 B of the side wall  38  of the cover  28 . 
     The outer edges of the side walls  34 ,  38  of the housing  26  and cover  28  define respective annular rims  34 D,  38 D where they mate with one another. The housing  26  has a plurality of bosses  66  spaced apart from one another and formed on and protruding outwardly from its annular rim  34 D. The cover  28  has a like plurality of lugs  68  spaced apart from one another and formed on and protruding outwardly from its annular rim  38 D and aligned over the bosses  66  of the housing  26  when the cover  28  is mated on the housing  26 . A plurality of fasteners  70 , such as screws, are inserted through openings  72  in the cover lugs  68  and threaded into holes  74  in the housing bosses  66  to securely attach the cover  28  to the housing  26 . Also, an annular gasket  76  is provided between the mated rims  34 D,  38 D so as to provide a seal therebetween. 
     The housing  26  and cover  28  of the case  12 , including the above-described respective elements thereof, and the tube  14  are preferably made of a suitable plastic material and fabricated by a suitable conventional injection molding process. The housing  26  and tube  14  are molded as a single unit and the cover  28  is molded as a separate unit removably securable to the housing  26  by means of the fasteners  70  as described above. 
     Shunt Circuit Break Actuating Mechanism 
     Referring to FIGS. 5 to  24 , the shunt circuit break actuating mechanism  18  of the interrupter  10  includes a drive shaft  78 , a trip lever  80 , an elongated link  82 , a power spring  84 , a latch  86  and a latch backup spring  88 . The drive shaft  78  is rotatably supported between the annular collar  40  on the housing  26  and the annular bearing  50  on the cover  28  with an end  78 A of the drive shaft  78  extending through the hole  42  where the external lever L is fixedly attached to the shaft  78 . The trip lever  80  is fixedly attached on the drive shaft  78  and has first and second ends  80 A,  80 B extending in opposite directions therefrom. A shunt cable  89  is attached to and extends between the trip lever  80  and the leading end  16 A of the rod  16  so as to provide the portion of the shunt circuit extending between the external lever L and the rod  16 . The elongated link  82  at a first end  82 A is rotatable journalled on the drive shaft  78  between the annular bearing  50  and trip lever  80  and at an opposite second end  82 B has a slot  90  where it is slidably coupled to the leading end  16 A of the shunt circuit rod  16  by a pin  92 . The power spring  84  extends between and resiliently yieldably interconnects the first end  80 A of the trip lever  80  and an intermediate location on the link  82  through an aperture  94  spaced from its first and second ends  82 A,  82 B. The latch  86  is pivotally mounted to the housing  26  by the first boss  46  thereon and disposed adjacent to the first end  82 A of the link  82  where a pin  96  spaced a short distance from the first end  82 A protrudes from the link  82  and extends into a notch  98  formed in a side of the latch  86 . The latch backup spring  88  is mounted at one end between the posts  44  formed on the housing  26  and retained in such mounted position by the first protuberance  52  formed on the cover  28  extending toward the posts  44 . The latch backup spring  88  can be a leaf spring which engages the latch  86  on a side thereof opposite from the notch  98  in the latch  86  which receives the pin  96  protruding from the side of the link  82  adjacent to the latch  86 . The latch backup spring  88  biases the latch  86  toward the pin  96  such that the link  82  is retained by the latch  86  in the relaxed shunt circuit defining position of the actuating mechanism  18 , as seen in FIG.  28 . 
     The drive shaft  78  and trip lever  80  therewith are rotated counterclockwise from the relaxed shunt circuit defining position shown in FIG. 28 by counterclockwise movement of the external lever L and in response thereto the power spring  84  is expanded until the drive shaft  78  and trip lever  80  therewith reach a loaded shunt circuit defining position of the actuating mechanism  18 , as seen in FIG.  31 . As the drive shaft  78  and trip lever  80  therewith rotate past the loaded shunt circuit defining position of FIG. 31 with continued rotation of the external lever L, the second end  80 B of the trip lever  80  engages a free end  86 A of the latch  86  located adjacent to the notch  98  and lifts the latch  86  away from the pin  96  releasing the link  82  and thereby tripping the actuation mechanism  18  allowing it to move abruptly to its shunt circuit breaking position, as seen in FIG.  34 . The released link  82  is now free to rotate abruptly in response to a force imposed thereon by the expanded power spring  84 . Due to the imposed force of the expanded power spring  84 , the link  82  abruptly rotates about the drive shaft  78  and pulls the shunt circuit rod  16  into the interior chamber  30  of the case  12  partially from the tube  14  breaking the shunt circuit. 
     The reset spring  20  at one end  20 A is hooked about the second boss  48  formed on the housing  26  and at an opposite end  20 B is hooked to the second end  80 B of the trip lever  80  on the drive shaft  78 . As the trip lever  80  is rotated counterclockwise with the drive shaft  78  in response to the external lever L, the reset spring  20  expands and imposes a return force on the trip lever  80 . Then, once the external switch blade (not shown) is completely open and the actuating mechanism  18  has tripped as described above, in response to the external lever L disengaging from the external switch blade, the expanded reset spring  20  causes reverse or clockwise rotation of the drive shaft  78  and trip lever  80  and link  82  therewith which brings the pin  96  on the link  82  into engagement with the latch  86 , lifting the latch  86  against its backup spring  88  until the pin  96  is again received in the notch  98  in the latch  86 . At this point the actuating mechanism  18  has returned to its relaxed shunt circuit defining position wherein the contacts  22 ,  24  on the tube  14  and shunt circuit rod  16  are again in electrical contact with one another. The pin  96  engages and holds the latch  86  and thereby the link  82  at the initial untripped condition wherein the rod  16  is withdrawn from the interior chamber  30  of the case  12  into the tube  14 . 
     FIGS. 28 to  36  show the respective positions of the actuating mechanism  18  and the shunt circuit rod  16  of the interrupter  10  at three successive stages of its operation. FIGS. 28 to  30  show a first stage of operation wherein the actuating mechanism  18  is in the relaxed shunt-circuit defining position and the rod  16  is substantially fully disposed in the tube  14  with their contacts  22 ,  24  electrically contacting one another in response to the external lever L connected to the actuating mechanism  18  being disposed in a rest position before being engaged by an external switch blade (not shown) upon movement of the latter in a known manner by a linesman in the process of breaking an electrical connection of a known blade-type switch as discussed in the background hereinabove. FIGS. 31 to  33  show a second stage of operation wherein the actuating mechanism  18  has moved into the loaded shunt-circuit defining position with the rod  16  still fully in the tube  14  and the contacts  22 ,  24  of the tube  14  and rod  16  still electrically connected with one another, prior to the actuating mechanism  18  and rod  16  being tripped as described above, in response to the external lever L assuming a partially displaced position due to being engaged and moved by the external switch blade as the latter is moved and breaks electrical connection with the fixed contacts of the blade-type switch so that line current is then fully transferred through the shunt circuit of the interrupter  10  before the electrical connection is broken through the blade-type switch. And FIGS. 34 to  36  show a third stage of operation wherein the actuating mechanism  18  is moved into the shunt circuit-breaking position, the rod  16  partially pulled from the tube  14 , and the contacts  22 ,  24  of the tube  14  and rod  16  disconnected from one another after tripping of the actuating mechanism  18  as described above, in response to the external lever L assuming a fully displaced position due to being further moved by the external switch blade. 
     Mechanically Interlocked Inner Quench Liner 
     Referring to FIGS. 6,  26  and  27 , the arc-suppressing tube  14  includes an outer protective sleeve  100  and an inner quench liner  102  mechanically interlocked with the outer sleeve  100 . The outer sleeve  100  includes a pair of annular ridges  104  spaced apart from one another and defined on an interior annular surface  100 A of the sleeve  100  so as to project radially inwardly therefrom. The inner liner  102  includes a pair of annular grooves  106  spaced apart from one another, disposed adjacent to opposite ends of the liner  102  and defined in an exterior annular surface  102 A of the liner  102  so as to project radially inwardly therefrom and receive in an interlocking fashion the annular ridges  104  on the sleeve  100 . The inner liner  102  preferably is molded into the outer sleeve  100  and is made of acetal material. 
     The shunt circuit rod  16  which extends through the tube  14  includes an elongated plunger portion  108  disposed through and inwardly spaced from the liner  102  when the rod  16  is substantially fully withdrawn into the tube  14  and an arc quenching trailing end portion  110  connected to one end of the plunger portion  108 . The trailing end portion  110  is substantially shorter in length than the plunger portion  108  and preferably is made of acetal. The rod  16  has the annular electrical contact  24  surrounding and attached on the plunger portion  108  adjacent to the trailing end portion  110 . The tube  14  has the electrical contact  22  supported therein adjacent to the one end  102 B of the liner  102  and surrounding and electrically contacting the electrical contact  24  on the rod  16  when the rod  16  is substantially fully withdrawn into (or disposed within) the tube  14 . 
     Vented Muffler Assembly 
     Referring again to FIGS. 1 to  6 , the interrupter  10  further includes a vented muffler assembly  112  mounted on a terminal end  14 A of the arc-suppressing tube  14 . The muffler assembly  112  includes a tubular body  114  having opposite inner and outer ends  114 A,  114 B and a central cavity  116  extending between the opposite ends  114 A,  114 B. The tubular body  114  is adapted to slidably fit at its inner end  114 A over the terminal end  14 A of the tube  14  and to be secured thereto by means of screws  118 . 
     The muffler assembly  112  further includes an end cap  120  and complementary exterior threads  122  on the outer end  114 B of the tubular body  114  and interior threads  124  on the end cap  120  for removably securing the end cap  120  on the outer end  114 B of the tubular body  114 . A disc  126  made of stainless steel material is disposed between the end cap  120  and the outer end  114 B of the tubular body  114  for shielding the end cap  120  from contact with the arc generated gases in the tube  14 . 
     The muffler assembly  112  still further includes an annular wall  128  and an annular ring  130  attached on the annular wall  128 . The annular wall  128  is disposed inside the tubular body  124 , extending transversely to the tubular body  114  and partially across the central cavity  116  thereof. The annular wall  128  defines an opening  132  through it. The annular ring  130  is spaced from the end cap  120  and attached on the annular wall  128 , surrounding the opening  132  therein and spaced inwardly from the tubular body  114 . The tubular body  114  has spaced side openings  134  defined therein outwardly from the annular ring  130  such that a path for escape of gases from the tube  14  into the muffler assembly  112  proceeds through the cavity  116  of the tubular body  114 , through the opening  132  of the annular wall  128 , past the annular ring  130  and then radially outwardly through the cavity  116  of the tubular body  114  to the side openings  134  therein. Finally, the muffler assembly  112  includes a roll  136  of porous mesh disposed in the cavity  116  between the annular wall  128  and the end cap  120  and surrounding the annular ring  130  such that the escape path of gases also goes through the roll  136  of porous mesh. The porous mesh  136  is preferably a stainless steel material and in the form of a continuous coiled roll. Preferably, the coiled mesh roll  136  is formed by wrapping a length of continuous mesh material onto a non-circular (hex) shaft (not shown) in forming a coiled roll. Since the mesh material retains a spring action due to its memory, when the coiled roll  136  is slide into the muffler  112 , it springs radially outwardly against the inner diameter of the tubular body  114  resulting in a slight separation of the layers of mesh material so as to provide a desired gas flow rate through the porous mesh roll  136 . The muffler assembly  112  having the foregoing construction creates a back pressure providing the proper balance of gas pressure between the muffler cavity  116  and the interior chamber  30  and enhances the life of the inner liner  102  of the tube  14 . The side openings  134  on the tubular body  114  while allowing passage of vented gases substantially prevents entry of water into the tube  14  via the muffler assembly  112 . 
     It is thought that the present invention and its advantages will be understood from the foregoing description and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely preferred or exemplary embodiment thereof.