Abstract:
An enclosed motor protector has a housing formed by a base ( 10 ) and a cover ( 12 ) received on the base and enclosing a recess ( 10   a ) formed in the base. A first terminal ( 14 ) extends through an opening in the housing and mounts a stationary contact ( 14   c ) within the recess. An elongated movable contact arm ( 18 ) is cantilever mounted at one end in the recess and mounts a second movable contact ( 18   a ) on a free end of the arm which is adapted to move into and out of engagement with the stationary contact. A heater ( 20 ) is mounted in the recess in heat transfer relation with a snap acting thermostatic disc ( 22 ) disposed adjacent to the movable contact arm so that upon reaching a preselected temperature the disc will snap from one dished configuration to an opposite dished configuration with its motion transferred to the movable contact arm to move the contacts out of engagement. The cover is formed with a first multiple wall barrier ( 122 ) in the form of a triangular body when seen in a lateral cross section closing a first terminal receiving opening and a second multiple wall barrier ( 124 ) closing a second terminal receiving opening to interrupt the travel of arcs and the inlet of explosive gas to the enclosure. These features also diminish air supply in the enclosure to thereby weaken any combustion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Benefit is claimed under 35 U.S.C. Section 119(e) (1) of Provisional Application No. 60/618,083, filed Oct. 12, 2004. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to motor protectors and more particularly to electrical enclosed break devices. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 4,706,152, assigned to Texas Instruments Incorporated, relates to an enclosed break device known as the 4TM and the 5TM. An enclosed break device, according to the International Electrotechnical Commission (IEC) Standard 60079-15 second edition 2001-02, is a “device incorporating electrical contacts that are made and broken and that will withstand an internal explosion of the flammable gas or vapor which may enter it without suffering damage and without communicating the internal explosion to the external flammable gas or vapor.” The 4TM and 5TM devices which have been made in accordance with the referenced patent comply with the first edition of the IEC standard 60079-15 which requires that enclosed break devices pass a make-and-break test 3 times without communicating an internal explosion to external flammable gas or vapor. 
     However, such devices may not meet the requirement of the second edition IEC Standard 60079-15, which requires that an enclosed break device pass a make-and-break test 10 times. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a 4TM/5TM type device that complies with the second edition (2001-02) IEC Standard 60079-15. 
     Another object of the invention is the provision of an internal break device that can be subjected to a make-and-break test ten times without communicating an internal explosion to external flammable gas or vapor. 
     A conventional 4TM/5TM type device comprises a base of electrically insulative material in which an elongated recess is formed. A first terminal is mounted at a first end and provided with a contact mounting portion disposed within the recess with a stationary contact mounted thereon. An elongated movable contact arm has a first end fixedly mounted on a mounting portion connected to another terminal. A movable contact is mounted on a free end of the movable contact arm and is arranged to move into and out of engagement with the stationary contact. A well is formed intermediate to the ends of the elongated recess and a heater is disposed therein in heat transfer relation to a thermostatic disc seated in the base over the well. The disc is adapted to snap from one dished configuration to an opposite dished configuration upon being heated to a preselected temperature. When the disc snaps it transfers motion to the movable contact arm causing the movable contact to move out of engagement with the stationary contact thereby interrupting the circuit path therethrough. A cover of electrically insulative material is received on the base to enclose the switch mechanism. However, there are two paths leading from the electrical contacts to openings at locations between the cover and base where the cover side wall is not interdigitated with the base, or closed, with a notched seating ledge of the base or comparable blocking protrusions of the cover. These locations allow flammable gas outside the protector housing to enter into the housing and enable internal arcing to ignite the flammable gas outside the device. The first path is shown by lines  2   a  of  FIGS. 3 and 6  which extend directly from the contacts through slots/openings between the first terminal blade portion and the side walls of the slots/openings of the base and the cover. The second path is shown by lines  2   b  ( FIG. 3 ) which extends from the contacts over the wall at the back portion of the contact receiving end of the recess. 
     According to a preferred embodiment of the invention, the cover is modified by forming first and second multiple wall barriers to impede the travel of arcs from the make-and-break contacts. The first multiple wall barrier comprises spaced apart wall portions which are received on the mounting portion of the first terminal closely adjacent to the stationary and movable contacts. According to a feature of the invention, the wall portions form a generally triangular configuration with respect to a cross section taken parallel to the bottom wall of the base. This structure also serves to decrease the volume of space between the base and cover thereby minimizing the supply of fuel to an internal explosion. According to another modification of the cover a vertically extending notch is formed in the walls which interfit with a corner portion of a corresponding side wall of the base to further inhibit arc travel. The second multiple wall barrier comprises another set of spaced apart wall portions along the perimeter of the base at a side of the first end of the recess to limit travel of arcing from the contacts and to further decrease excess volume of space. In another preferred embodiment of the invention, the various openings formed in the housing of the device are sealed by epoxy to prevent propagation of any internal explosion from external flammable gas. The sealing can be utilized by itself or along with the cover modifications noted above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and features of the invention will become apparent by reference to the following detailed description of preferred embodiments when considered in connection with the accompanying drawings in which like reference characters refer to like components or structural features throughout the several views wherein: 
         FIG. 1  is a perspective view of a 4TM/5TM device taken from above the device; 
         FIG. 2  is a perspective view of the  FIG. 1  device taken from the same position but with the device rotated half a turn upwardly into the paper as seen in  FIG. 1 ; 
         FIG. 3   a  is a top plan view of the base of the device prior to the installation of components therein and  FIG. 3   b  is a view similar to  FIG. 3   a  shown at a slight angle relative to the position of  FIG. 3   a  to better illustrate the relative heights of the various surfaces of the base; 
         FIG. 4  is a perspective view of the cover of the  FIG. 1  device as it existed prior to the instant invention taken generally in the  FIG. 2  orientation; 
         FIG. 5   a  is a top plan view of the  FIG. 1  device as it existed prior to the instant invention with the cover removed;  FIG. 5   b  is the same as  FIG. 5   a  but with the snap acting disc removed for purposes of illustration; and  FIG. 5   c  is the same as  FIG. 5   a  but with the disc and heater element removed for purposes of illustration; 
         FIG. 6  is a broken away cross section in the direction of a front elevational view of  FIGS. 5   a - 5   c  device taken through the make-and-break contacts; 
         FIG. 7  is a view similar to  FIG. 4  of a cover made in accordance with a preferred embodiment of the invention; 
         FIG. 8  is a view similar to  FIG. 5   a  but is shown with a cover in a horizontal cross section, the cover incorporating the preferred embodiment shown in  FIG. 7 ; 
         FIG. 9  is a top plan view of a 4TM and 5TM device made in accordance with the preferred embodiment of  FIGS. 7 and 8 ; 
         FIG. 10  is an elevational cross section taken on line  10 - 10  of  FIG. 9 ; 
         FIG. 11  is an elevational cross section taken on line  11 - 11  of  FIG. 9 ; 
         FIG. 12  is an elevational cross section taken on line  12 - 12  of  FIG. 9 ; 
         FIG. 13  is a view similar to  FIG. 8  but showing an alternative preferred embodiment of the invention; 
         FIG. 14  is a perspective view, similar to  FIG. 1  of a device made in accordance with the  FIG. 13  preferred embodiment; 
         FIG. 15  is a perspective view, similar to  FIGS. 8 and 13  showing another alternative preferred embodiment of the invention; and 
         FIG. 16  is a view similar to  FIG. 15  of a device made according to the  FIG. 15  embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following description references made to top, bottom, side and the like relate to the orientation of the device as shown in  FIGS. 3 ,  5 ,  8 ,  9 ,  13  and  15 . 
     With reference to  FIGS. 1-5 , the 4TM and 5TM devices referenced above comprise a housing having a generally rectangular base  10  having a major length along the front of the device and a minor length from front to back of the device. A recess  10   a  is formed in the base and a cover  12  is received thereon closing the recess. First and second guide pin holes  10   t ,  10   u  are formed in the bottom wall for reception of cover guide pins  12   d ,  12   e , respectively, to be discussed. With particular reference to  FIG. 3 , recess  10   a  is generally elongated in the direction of the major length having a contact receiving end  10   b , an opposite movable contact arm mounting end  10   c  and a central heater receiving portion  10   d  intermediate to the two ends. Contact receiving end  10   b  of the recess is defined by side wall portions  10   e  on the front, and  10   e  and  10   e   1  tapered downwardly from line  10   g   1  on the left side of the base as seen in  FIG. 3  with an offset lower seating ledge  10   f  contiguous with these portions on the front and left sides. The back side of the contact receiving end of the recess is defined by wall portion  10   e  with a downward tapered portion extending from line  10   g  on to the right extreme of that wall portion as viewed in  FIG. 3 . As will be discussed below, there is no seating ledge along the back portion of the contact receiving end of the recess. Outboard of the back side of the contact receiving end of the recess defining wall is a downwardly spaced terminal receiving ledge  10   h . Central heater receiving portion  10   d  is defined on the front by a downwardly offset portion  10   k  along with an outer downwardly further offset ledge  10   m  and on the back side by wall portion  10   f . Outboard of wall portion  10   f  defining the central heater receiving portion  10   d  of the recess is another terminal receiving ledge  10   n  offset further downwardly than terminal receiving ledge  10   h , i.e., ledge  10   n  is closer to the bottom wall of the base than is ledge  10   h . The movable contact arm mounting end  10   c  of the recess is defined by side wall  10   e  with outer wall portion  10   f  serving as a seating ledge. 
     With particular reference to  FIGS. 3 and 5   a , a slot  10   o  is formed in side wall  10   e  defining the left side of contact receiving end  10   b  of the recess for reception of a first terminal  14  to be discussed. A second terminal  16  has a base portion  16   a  received on ledge  10   n  and has a transversely extending step portion  16   b  extending up to a higher level to a body portion  16   c . A separate electrically conductive terminal strip  16   d  is received on terminal receiving ledge  10   h  and is provided with a transversely extending step portion  16   e  extending down to the bottom of the central heater receiving recess portion in a space  10   r  between wall portion  10   f  defining the back of the central heater receiving portion of the recess and the central heater receiving portion of the recess  10   d  with the end  16   f  of strip portion  16   d  serving as a connection location for one end  20   a  of a heater  20 , to be discussed, disposed in an annular well  10   q  in the recess. The body portion  16   c  of the second terminal  16  is fixedly and electrically connected to terminal strip  16   d  on ledge portion  10   h , as by welding. 
     First terminal  14  has a first, generally flat mounting portion  14   a  disposed at the contact receiving end  10   b  of recess  10   a , an arm  14   d  which projects downwardly through an opening  10   w  in the bottom wall of the base and formed with a pair of clamping fingers  14   e  which are spread apart after being received through opening  10   w  to secure the mounting portion. First terminal  14  has a second portion  14   b  that includes an interconnection blade portion extending out of an opening in the side wall of the housing. 
     An electrically conductive movable contact arm mounting platform  17 , see  FIGS. 5   a  and  11 , received in movable contact arm mounting end  10   c  of recess  10   a , is provided with an arm that steps down to an end portion  17   a  at a location in annular well  10   q  on the opposite side of a vertically extending rib  10   s  of wall  10   f  from end  16   f  of strip portion  16   d . End portion  17   a  of the arm of platform  17  serves as a connection point for the second end  20   b  of heater  20 . Platform  17  is fixedly and electrically connected to an end  18   b  of an elongated movable contact arm  18  which extends in the direction of the major length of recess  10   a . A movable contact  18   a  is mounted on the bottom surface of movable contact arm  18  at its free end and is arranged to move into and out of electrical engagement with a stationary contact  14   c  mounted on mounting portion  14   a  of the first terminal. 
     A third pin receiving terminal  24  ( FIG. 1 ) has a body portion  24   a  received on the top surface of cover  12  with pin receiving portion  24   b  aligned with the space between ears  12   p  of the cover. Terminal  24  has an arm  24   c  which extends over to the blade portion  14   b  of first terminal  14  and is electrically connected thereto, as by welding. 
     As noted above, heater  20  (see  FIG. 5   b ) is disposed in well  10   q  of central heater receiving portion  10   d  of recess  10   a  and a thermostatic, snap acting disc  22  (see  FIG. 5   a ) is received on a disc seat formed in that portion of recess  10   d  so that the disc is above the heater in heat transfer relation therewith. Disc  22  is arranged so that at normal ambient temperature the disc is in a first dished shape configuration out of engagement with movable contact arm  18  however, upon reaching a predetermined actuation temperature, the disc snaps to a second, opposite dished configuration engaging dimple  18   c  of movable contact arm  18  and moves the movable contact  18   a  out of engagement with stationary contact  14   c  thereby opening the electrical path between terminals  16  and  18 . 
     Cover  12 , shown best in  FIG. 4  and shown inverted relative to  FIG. 1 , is formed with a recess closing wall  12   a  and side walls  12   b  formed generally around the outer perimeter of recess closing wall  12   a  and extend orthogonally therefrom side walls  12   b  are alignable with seating ledge portion  10   f  of side walls  10   e  of base  10 . A slot or opening  12   c  formed in side wall  12   b , extends into recess closing wall  12   a  and is alignable with slot or opening  10   o  in the base, to provide access for blade portion  14   b  of terminal  14 . First and second alignment posts  12   d ,  12   e , respectively, extend orthogonally from recess closing wall  12   a  and are adapted to be received in matching bores  10   t ,  10   u , respectively, in base  10 . Side wall  12   b  is extended in height at central front portion  12   f  and is adapted to be received on seating ledge  10   m  of the base, i.e., extending beyond wall portion  10   k  to provide an interdigitated or closed fit with wall portion  12   f  received in a step between wall portion  10   k  and  10   m . Also shown in  FIG. 4  are first and second disc retaining pins  12   g  disposed at opposed locations alignable with outer peripheral portions of the disc seat. First and second elongated blocks  12   h  are formed on wall  12   a  extending along the major wall length contiguous with side wall  12   b  on either side of one of the disc retaining pins and extending in height beyond side wall  12   b.    
     Although protectors made as shown in  FIGS. 1-5  have performed extremely well and have been widely used in various industries, certain aspects of the devices need to be modified to ensure that the devices comply with recent changes in the requirements of the International Electrotechnical Commission Standard relating to “enclosed break devices” discussed above. With particular reference to  FIGS. 3 ,  5   a - 5   c  and  6 , there are two paths leading from contacts  18   a ,  14   c  to openings at locations between the cover and the base where the cover side wall is not interdigitated with the base, or closed, with a notched seating ledge of the base, or the like. These locations allow flammable gas outside the protector housing to enter into the housing and enable internal arcing to ignite the flammable gas outside the device. The first path is shown by lines  2   a  ( FIGS. 3 and 6 ) which extend directly from the contacts through slots/openings  10   o  of the base and  12   c  of the cover between terminal blade portion  14   b  and the side walls of slots/openings  10   o  of base  10  and  12   c  of cover  12 . The second path is shown by lines  2   b  ( FIG. 3 ) which extends from the contacts over wall  10   e  and  10   e   1  at the back portion of contact portion end  10   b  of recess  10   a  and wall  10   f  of the central heater receiving recess  10   d.    
     A modified cover  120  (see  FIG. 7 ) made in accordance with a first feature of a preferred embodiment of the invention comprises a first multiple wall barrier  122  extending from recess closing wall  12   a  comprising a first wall  122   a  orthogonally from wall  12   a  and disposed so that it is essentially flush with the inner surface of terminal receiving slot  10   o  and extends from the recess closing wall  12   a  generally to horizontally extending flat portion  14   b  of terminal  14  when the cover is received on the base (see  FIG. 10 ). Extending generally normal to wall  122   a  at a side of slot  10   o  closest to ears  12   p  is a second wall  122   b  which extends over to guide pin  12   e  and then a third wall  122   c  extends between the extremity of wall  122   a  and post  12   e  generally forming a triangular barrier wall that extends normally from recess closing wall  12   a  that not only serves to interrupt arc travel but also reduces the volume of free space between the cover and the base, that is, it reduces the amount of fuel for supporting combustion. Preferably, a notch  122   d  ( FIG. 8 ), extending in a normal direction to recess closing wall  12   a  is formed in walls  122   a  and  122   c  at their intersection that is adapted to receive the side wall  10   e  of the base to further impede arc travel. Preferably, a portion of wall barrier  122  along wall  122   c  that forms notch  122   d  is extended at  122   e  a distance essentially the same as the thickness of a mounting portion  14   a  of terminal  14 . When the cover is in plan, this extension, or knob is received in a small open space next to mounting portion  14   a  extending toward opening  10   t . This triangular feature essentially closes off the first path  2   a  of arc travel. 
     A second multiple wall barrier  124  is formed in the cover so that when placed on the base the barrier is at the first end of the housing adjacent to contacts  14   c ,  18   a  along the outer periphery. The second barrier adds wall  124   a  which extends normal to recess closing wall  12   a  and generally parallel to side wall  12   b  relative to the major length of the elongated base and spaced therefrom. Wall  124   a  extends away from recess closing wall  12   a  a distance essentially the same as outer wall  12   b . Wall  124   a  at its extremity away from side wall  12   b  on the minor length end of the cover is joined to side wall  12   b  on the major length side by wall  124   b  of the same height. Contiguous to barrier  124  and extending along side wall  12   b  in the direction of its longitudinal axis, i.e., major length, is a block  124   c , preferably formed of the same material as the cover, the block extending vertically a distance greater than that of side wall  12   b . Block  124   c  serves as an arc barrier filling in the space  10   r  between wall portion  10   e ,  10   e   1  adjacent to stop  16   e  of conductive strip  16   d  defined by the back part of the contact receiving recess and wall portion  10   f  in back of the central heater receiving portion of the recess. 
     According to an alternative embodiment, terminal portion  14   b  can be moved inwardly away from the outer periphery of the housing as seen in  FIGS. 13 and 14  with side wall portions  10   e ′ and  12   b ′ being continuous, that is, without slot  10   o  and  12   c  being formed in the side walls with wall  122   a  of the first barrier  122  essentially butted up against side wall  10   e  just beyond slot  10   o . In this case, barrier  122 , if desired, could be formed without notch  122   d  with barrier wall  122   a  butted up against sidewall  10   e  just beyond slot  10   o.    
     According to another alternative embodiment shown in  FIGS. 15 and 16 , the  FIG. 1  structure can be modified by forming side wall portion  126  to extend across slot  10   o  externally thereof. The location of terminal  14  can remain as shown in  FIG. 8  with a side wall  126  covering the slot  10   o ,  12   c  in side walls  10   e  of the base and  12   b  of the cover, respectively. 
     With reference to  FIGS. 1 and 2  a number of openings are formed through the housing for various purposes, comprising openings at dashed lined locations  3  and  4  for terminals  14  and  16 ,  5  for guide pins  12   d ,  12   e  and  6  for clamping elements in the base and  7  for providing access to the movable contact arm mounting portion. In accordance with another embodiment of the invention, each of these openings, once the device is assembled, can be sealed with suitable epoxy. This can be done along with the above embodiments or in place of them, as desired. 
     Although the invention has been described with regard to specific embodiments thereof, many variation and modifications will become apparent to those of ordinary skill in the art. It is therefore, the intent that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.