Abstract:
An electrical enclosure includes a re-usable cover of electrically insulative material surrounding a portion of a screw-type electrical terminal of an electric device mounted in an access panel of the enclosure. The reusable protective cover includes an integral clamp for attaching the cover to the terminal and also includes an opening for passage of a wire through the cover to the terminal. A test probe access hole is disclosed for passage of a test probe through the cover and into contact with the terminal when the cover is installed on the terminal. Embodiments of enclosures compliant with Underwriter&#39;s Laboratory Standard 508 are disclosed.

Description:
FIELD OF THE INVENTION 
     My invention is directed to enclosures for electrical equipment utilizing devices having screw-type electrical terminals. 
     BACKGROUND OF THE INVENTION 
     It has long been common practice in the design of enclosures for electrical equipment to equip the enclosure with an access panel attached to a chassis of the enclosure by hinges or fasteners in such a manner that the access panel may be opened or removed to facilitate manufacture, maintenance, and repair of the enclosure and equipment included as part of the enclosure. It has also long been a practice to mount electrical devices such as push-buttons, switches, or indicator lights in such access panels so that the electrical devices can be actuated or viewed from outside of the enclosure. 
     Electrical devices mounted in access panels are often equipped with screw-type wire terminals for connecting the electrical device to a wire extending out of the enclosure when the access panel is opened or removed. During assembly, maintenance, or repair of the enclosure, it is sometimes necessary to operate the enclosure with the access panel open and electrical current or voltage applied to the screw-type terminal of an electrical device mounted in the access panel. 
     In the past, electrical codes applicable to such enclosures did not require screw-type terminals of electrical devices mounted in access panels to be electrically insulated. During the year 2001, however, Underwriters Laboratories Standard 508 will become effective requiring that screw-type terminals on electrical devices mounted in access panels must include some sort of electrically insulative protection against inadvertent electrical contact by personnel who might come into contact with the terminals while the access panel is open. 
     Traditional methods of providing electrical insulation of such screw-type terminal has been accomplished by wrapping exposed metal surfaces of the terminal with electrician&#39;s tape, or encapsulating exposed metal surfaces of the terminal in an electrically insulative coating such as glyptol or RTV. These traditional methods suffer from a number of drawbacks. Applying electrical tape or such coatings is also time consuming and labor intensive, thereby driving up the cost of initial manufacture and repair or maintenance of the enclosure. Taping and coatings are also undesirable in that they provide no access to the electrical terminal for test probes of diagnostic or trouble shooting equipment, thereby making it necessary to destroy or compromise the protective covering of the terminal during troubleshooting and repair operations. Because the taping and coating cannot be removed without destroying its effectiveness, it cannot be reused, thereby necessitating a complete re-application of tape or coating after troubleshooting or repair-operations to ensure that electrical insulation protection of the terminal is maintained. 
     What is needed, therefore, is an improved electrical enclosure capable of meeting the requirements of UL Standard 508 and solving one or more of the drawbacks and problems recited above associated with the prior methods of insulating screwed-type terminals in enclosures subject to the requirements of UL 508. 
     SUMMARY OF THE INVENTION 
     My invention provides such an improved electrical enclosure through the use of a reusable cover of electrically insulative material for surrounding a portion of a screw-type electrical terminal of an electric device mounted in an access panel of the enclosure. My protective cover includes an integral clamp for attaching the cover to the terminal and also includes an opening for passage of a wire through the cover to the terminal. 
     According to one aspect of my invention, the cover is adapted to be removed or installed on the terminal regardless of whether a wire is attached to the terminal. 
     In some embodiments of my invention, a test probe access hole is provided for passage of a test probe through the cover and into contact with the terminal when the cover is installed on the terminal. 
     Some embodiments of my invention include a cover configured to cover two or more terminals. In some embodiments, the integral clamp for attaching the cover to the terminal is provided by snap tabs that grip a portion of the terminal. In other embodiments, the cover is formed of a first and a second part which clamp together to surround the terminal. Some embodiments of my invention include a cover having a flexible hinge to facilitate installation and removal of the cover. 
     In a preferred embodiment of my invention, the cover is formed of two or more parts capable of providing electrical protection for two or more terminals, with one of the parts of the cover being configured so that it may be cut in pieces, and the pieces interlocked to form a cover for a single terminal. 
     Other aspects and advantages of my invention will be apparent to those having skill in the art upon review of the attached drawings and the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts an exemplary embodiment of an electrical enclosure according to my invention assembled to a terminal; and 
     FIGS. 2 a - 8   b  depict exemplary embodiments of a cover according to my invention for a screw-type terminal, some assembled to a terminal and some not so assembled. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 depicts an exemplary embodiment of an electrical enclosure  10  having a removable access panel  12  attached to a chassis  11 . An electric device  14  having a pushbutton  15  is installed through an opening  13  in the access panel  12  in such a manner that a screw-type electrical terminal  16  of the electric device  14  is located within the enclosure  10  when the pushbutton  15  is located to be accessible from outside of the enclosure  10 . The terminal  16  includes a fixed element in the form of a terminal blade  18  threaded to receive a screw  20 , and a movable element in the form of a washer  22  for clamping a wire  24  between the fixed and movable elements  18 ,  22 , with the screw  20  clamping the washer  22  and wire  24  against the blade  18 . The movable element  22  can be provided in many forms including a simple round washer, or various shaped parts known in industry as pressure plates or saddle clamps. 
     A cover  26  that is in the form of a housing  27  surrounds a portion of the electric wire terminal  16 . The cover  26  is formed of a generally rigid but somewhat resilient insulating material such as NYLON, or any of the many plastics conventionally used in the art. The cover  26  is configured to provide an integral clamp, generally indicated by reference numeral  28 , for attaching the cover  26  to the terminal  16 . The cover  26  also includes openings  30 ,  31  for passage of the wire  24  and the blade  18  respectively through cover  26  to the terminal  16 . 
     All of the embodiments depicted in FIGS. 2 a - 2   d  show a cover  26  defining a cavity  32  for receipt of the screw  20 , washer  22  and a portion of the blade  18  of the terminal  16 . Each of the embodiments of a cover  26  depicted in FIGS. 2 a - 2   d  includes one or more side resilient walls  34  projecting from the cavity  32  with a protruding snap tab  36  at a distal end of the side wall  34  for gripping the fixed element  18  to retain the cover  26  on the terminal  16 . As shown in FIGS. 1 and 2 a - 2   c,  the snap tabs  36  have hook-like ends  37  adapted to grip the non-wire engaging surface  40  opposite a wire engaging surface  38  of the blade  18  of the terminal  16 . As shown in FIGS. 2 a - 2   c,  the snap tab ends  37  also have a canted cam surface  39  to engage the surface  38  and cam the associated side wall  34  away from the blade  18  to allow the end  37  to move past the same to engage the surface  40 . The snap tabs  36  in conjunction with the side walls  34  and the remainder of the cover  26  collectively provide the integral clamp  28  for attaching the cover  26  to the terminal  16 . 
     All of the cover embodiments depicted in FIGS. 1 and 2 a - 2   d  include a test probe access hole  42  positioned for passage of a test probe through the cover  26  and into electrical contact with the terminal  16  when the cover  26  is installed on the terminal  16 . The test probe access hole  42  therefore greatly facilitates initial manufacture, maintenance and repair of the electrical enclosure, in comparison with prior enclosures utilizing electrician&#39;s tape or insulative coatings on screw-type electrical terminal  16 . 
     Each of the cover embodiments  26  depicted in FIGS. 1 and 2 a - 2   c  include one or more openings  30  in the form of a slot or a hole for passage of a wire through the cover for attachment to the terminal  16 . Where the opening  30  is provided by an open-ended slot as depicted in FIGS. 2 a - 2   c,  the cover  26  may be installed on or completely removed from the terminal  16  regardless of whether or not a wire  24  is attached to the terminal  16 . When the openings  30  for the wires  24  are provided in the form of holes  30  as depicted in FIG. 2 d,  rather than by open-ended slots  30  as shown in FIGS. 2 a - 2   c , the cover  26  may still be installed or completely removed from a terminal to which a wire is not attached. The embodiment depicted in FIG. 2 d  cannot, however, be completely removed from the terminal  16  if a wire  24  is attached, but provides a potential advantage in some situations by ensuring that the cover  26  will be retained with the wire  24  because the wire  24  extends through the hole  30  in the cover  26 . With such an arrangement as depicted in FIG. 2 d,  the cover  26  may be slid back onto the wire  24  for access to the screw  20  of the terminal  16  during installation or removal of the electric device  14 , and is automatically retained on the wire  24 , for reinstallation of the cover  26  following replacement of the electric device  14 . 
     As depicted in FIGS. 2 a - 2   d,  I contemplate that there may be considerable variation within the scope of my invention in the configuration of the side walls  34 , holes  30 , and features of the integral clamp  28  such as the snap tabs  36 . FIGS. 3 a  and  3   b  depict alternate embodiments of a cover  26  according to my invention as viewed along line  3   a,   3   b — 3   a,   3   b  of FIG. 2 a.  FIGS. 3 a  and  3   b  illustrate that an end wall  44  of the cover  26  disposed adjacent the panel  12  may also be configured to suit the needs of a particular installation and electrical device  14  or terminal  16 . For example, the end wall  44  may serve to provide additional electrical isolation of the washer  22  from the panel  12  as illustrated in FIG.  1 . The end wall may also be configured to include an opening  31  shaped to match the profile of a particular terminal blade  18 . 
     FIGS. 4 a  and  4   b  depict an embodiment of my invention in which a cover  26  defines a cavity  32  configured for receiving the screws  20  and washers  22  of two terminals  16  disposed side-by-side with their respective non-wire engaging surfaces  40  lying substantially in a common plane  46 , with the cover  26  including two snap tabs  36  gripping the non-wire engaging surfaces  40  of the two terminals  16 . First and second test probe access holes  42  are included to allow passage of a test probe through the cover  26  and into electrical contact with either of the terminals  16 . 
     FIG. 7 depicts an embodiment of a cover  26  having an integral clamp  28  including a hinged side wall  48  projecting from a cavity  32  formed by a main body  50  of the cover  26 . The hinged side wall  48  is attached to the main body  50  by a resiliently flexible hinge  49  formed integrally with the main body  50  and hinged side wall  48  by thinning the insulative material of the cover  26  along the intersection of the hinged wall  48  with the main body  50  of the cover  26 . The hinge  49  allows the side wall  48  to be movable between an open and a closed position so that the cover may be installed or removed from the terminal  16 . The integral clamp  28  of the cover  26  further includes an integral latch having complementary snap lock tabs  52 , 54  located on a distal end of the hinged side wall  48  and main body  50  of the cover  26 , respectively. 
     FIG. 6 depicts an embodiment of a cover  26  for protecting two screw-type terminals disposed in a side-by-side relationship similar to that depicted in FIG. 4 a.  As depicted in FIG. 6, the cover  26  includes an upper first part  86  and a lower second part  88  of a main body  50 . The first and second parts  86 ,  88  of the cover  26  are joined at one end by a resiliently flexible hinge  58  integrally formed in the main body  50  by locally reducing the thickness of the main body  50  along a line formed by the intersection of the first and second parts  86 , 88  of the main body  50  of the cover  26 . The hinge  58  allows the first and second parts  86 , 88  of the cover  26  to be spread apart during installation of the cover on or removal of the cover  26  from the side-by-side terminals  16 . The end of the cover  26  opposite the hinge  58  is closed by a hinged side wall  48  extending from the first part  86  and including a snap tab  52  for engaging a complementary tab  54  extending from the second part  88  to lock the cover  26  in place on the terminals  16 . 
     The main body  50  is further configured such that the first part  86  includes a first housing half  90  and a second housing half  92  joined by a web  94 . In similar fashion, the second part  88  of the main body  50  is configured to include a first housing half  96  and second housing half  98  joined by a web  100 . When the cover  26  is in a closed position, the hinge  58  aligns the first and second parts of the main body  50  in such a manner that the first housing halves  90 , 96  of the first and second parts  86 , 88  respectively are aligned to form a first cavity  32  for receipt of one of the two terminals  16 , and second housing halves  92 , 98  are aligned to form a second cavity  33  for receiving a second terminal  16 . The webs  94 , 100  include a complementary male and female halves (not shown) of a conventional snap stake latch  56  forming part of the integral clamp  28  and facilitating alignment of the first and second parts  86 , 88  of the cover  26 . 
     FIGS. 8 a  and  8   b  depict an embodiment of a cover  26  according to my invention having first and second cover members  60 , 62  connected by flexible segments  64  configured for allowing the first and second cover members  60 , 62  to be flexed apart during installation of the cover  26  on or removal of the cover  26  from the terminal  16 . Integral lever wings  66  that may be gripped between the finger and thumb facilitate flexing of the first and second members  60 , 62  by applying pressure to the lever wings  66  as indicated by arrows  68 . A screw clearance hole  70  is provided in the second member  62 . 
     FIGS. 5 a - 5   c  depict an embodiment of my invention in which a cover  26  is provided for two screw terminals  16  arranged in a side-by-side fashion through utilization of identical first and second parts  72 , 74  to form the cover  26 . The first and second parts  72 , 74  include interlocking snap tabs  76  and slots  78  as part of the integral clamp formed by the cover  26 . The first and second parts  72 , 74  each include a first housing half  102  and a second housing half  104  joined by a web  106 . The outer ends of the first and second housing halves  102 , 104  are respectively configured as a long wall  108  and a short wall  110  so that when the first and second parts  72 , 74  are assembled about the two terminals  16  in an offset nested fashion as depicted in FIG. 5 b,  the first and second parts  72 , 74  can be offset by a distance equal to approximately one wall thickness of the short and long walls  108 , 110  and nested together to form the clamp  26  and provide a first cavity  32  about one of the terminals  16  and a second cavity  33  about the second terminal  16 . 
     The distal ends of the snap tabs  76  are configured to form a locking barb  112  having angled faces  114  and  116  to facilitate alignment and passage of the snap tabs  76  through the slots  78 . In a preferred embodiment of a cover  26 , the snap tabs  76  and slots  78  are configured to be resiliently flexible enough to withstand multiple engagements and disengagement so that the cover  26  is reusable. 
     As shown in FIG. 5 c,  the embodiment depicted in FIGS. 5 a  and  5   b  provides an additional advantage in that either the first or second part  72 , 74  of the cover  26  may be cut into a first and second piece  82 , 84  along a line as indicated at  80 , in FIG. 5 a,  between the snap tab  76  and slot  78 , and the first and second pieces  82 , 84  interlocked together to provide a cover for a single terminal  16 . 
     Although I have described certain exemplary embodiments of my invention in the description above and attached drawings, those having skill in the art will recognize that many other alternate embodiments of my invention are possible and contemplated by me within the scope of the appended claims.