Abstract:
A telecommunications protection unit includes a voltage unit having an electrically insulating base configured to house a diode module assembly and a voltage limiting cell therein. The voltage limiting cell and diode module assembly are retained within the housing by a bus clip. The housing includes structure for preventing damage to the voltage limiting cell and diode module assembly during placement of the bus clip thereon. The diode module assembly is a one-piece article including a bus bar and several diodes and terminals which can be used by itself or in a voltage unit to provide desired electrical effects and facilitate assembly of an electrical system such as a telecommunications protection unit. The terminals of the diode module are highly flexible to respond to excessive voltage and sneak current events encountered by telecommunications protection equipment, and the bus clip is constructed to provide a plurality of independently yieldable segments to accommodate diode stacks of variable heights and reduce manufacturing costs.

Description:
RELATED APPLICATIONS 
     This application is related to U.S. application Ser. No. 09/097,251 filed Jun. 12, 1998, entitled DIODE MODULE ASSEMBLY,now U.S. Pat. No. 6,034,862; U.S. application Ser. No. 09/096,688 filed Jun. 12, 1998 entitled VOLTAGE UNIT HOUSING, now U.S. Pat. No. 6,067,221; and U.S. application Ser. No. 09/097,315 filed Jun. 12, 1998, entitled FLEXIBLE VOLTAGE UNIT TERMINAL, abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the protection of communication equipment, and more particularly to improved arrangements for current and voltage overload protection. 
     BACKGROUND OF THE INVENTION 
     Protecting telecommunications equipment in telephone central offices or other locations against voltage surges and sneak currents is well known. For example, U.S. Pat. No. 4,796,150 discloses a solid state protector for insertion in a telephone line having tip and ring conductors. The protector comprises a current unit, a voltage unit and a pair of springs assembled within a housing structure. The voltage unit includes solid state devices that respond instantaneously to spurious voltage surges on the telephone line in the tip conductor, the ring conductor, or both tip and ring conductors. When a voltage surge exceeds a predetermined threshold, the voltage device operates to ground the telephone line thereby insuring that the spurious voltage bypasses the telephone equipment in the central office. 
     Conventional voltage units including that disclosed in U.S. Pat. No. 4,796,150 often include one or more metal clips for retaining the various diodes and terminals of the voltage unit in a desired assembled state. However, the clips used in these devices are quite narrow relative to the length of the voltage unit housing to which they are attached. Thus, the clips often pivot out of proper alignment and become dislodged during placement onto the housing. As a result, the clip(s) may become dislodged and one or more of the electrical components of the voltage unit may become loose, lost or damaged both during or after assembly. Additionally, in certain existing voltage unit assemblies, the clip may fail to retain the electrical components within the housing if one or more of the diodes becomes damaged during operation and its thickness is reduced. Either of these eventualities may hinder the assembly process or the reliability of the voltage unit. 
     SUMMARY OF THE INVENTION 
     The present invention provides a voltage unit for use in a telecommunications protection unit having an electrically insulating housing configured to house a diode module assembly and a voltage limiting cell therein. The voltage limiting cell and the diode module assembly are retained within the housing by a bus clip. 
     To overcome the problems of parts loss or damage resulting from the improper placement of narrow, retaining clips, the present invention provides a relatively long bus clip including multiple, independently yieldable diode stack contacting segments designed for reliable placement and operation which eases assembly and increases performance of the voltage unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is an exploded, isometric view of an existing voltage unit adapted for use in a telecommunications protection unit; 
     FIG. 1B is a plan view of the assembled voltage unit of FIG. 1A; 
     FIG. 1C is a partially cut side view of the assembled voltage unit of FIG. 1A; 
     FIG. 1D is a sectional view of the assembled voltage unit of FIG. 1A taken along line D—D of FIG. 1C; 
     FIG. 2 is an exploded, isometric view of an embodiment of a voltage unit in accordance with the present invention; 
     FIG. 3 is an isometric view of the assembled voltage unit depicted in FIG. 2; 
     FIG. 4 is a sectional view of the assembled voltage unit depicted in FIG. 3; 
     FIG. 5 is an exploded, isometric view of an embodiment of a diode module assembly in accordance with the present invention; 
     FIG. 6 is an isometric view of the assembled diode module assembly depicted in FIG. 5; 
     FIG. 7 is an electrical schematic diagram of the assembled diode module assembly depicted in FIG. 6; 
     FIG. 8 is an electrical schematic diagram of the assembled voltage unit depicted in FIG. 3; 
     FIG. 9 is an exploded, isometric view of an embodiment of a telecommunications protection unit employing a voltage unit in accordance with the present invention; 
     FIG. 10A is an isometric view of a further embodiment of an assembled voltage unit in accordance with the present invention; 
     FIG. 10B is a view of the voltage unit depicted in FIG. 10A fastened to a printed circuit board; 
     FIG. 11 is an isometric view of a further embodiment of an assembled voltage unit in accordance with the present invention; 
     FIG. 12A is an isometric view of a preferred embodiment of a bus clip adapted for use with a voltage unit in accordance with the present invention; 
     FIG. 12B is an elevation view of the bus clip depicted in FIG. 12A; 
     FIG. 13 is an elevational cross-section view taken through a central region of a preferred embodiment of a voltage unit housing adapted for use with a voltage unit in accordance with the present invention; and 
     FIG. 14 is a plan view of a preferred embodiment of a contact adapted for use in a voltage unit in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Collectively referring to FIGS. 1A,  1 B,  1 C and  1 D, there is shown a voltage unit manufactured by Lucent Technologies, Inc., adapted for use in a telecommunications protection unit. The voltage unit, identified generally by reference numeral  100 , typically includes an electrically insulating base or housing  102  which may be formed from polybutylene terephthalate (PBT) or other suitable moldable material. Voltage unit  100  further currently includes a self-triggering surge suppressor (or surgistor or voltage limiter)  104  constructed as a cell or disc package. Voltage limiter  104  is preferably a unidirectional type P 247  manufactured by Teccor Electronics. The voltage limiter  104  is sandwiched between two metallic plates  106  having outwardly extending elongate wing segments. Four diodes  108 , two on either side of the voltage limiter  104 , are sandwiched between the elongate wing segments of plates  106 . Diodes  108  are preferably PR 4  type diodes manufactured by General Instrument. A metallic terminal  110  (either a tip or a ring terminal) is disposed between each of the two sets of diodes  108  and one of a pair of additional diodes  112 , which are preferably of the same or similar type as diodes  108 , is positioned exteriorly of a central region of each of the metallic plates  106 . 
     The operative electrical components of unit  100  are disposed within housing  102  in the manner most clearly depicted in FIGS. 1B,  1 C and  1 D and are retained therein by a narrow (relative to the length of housing  102 ) generally C-shaped metallic clip  114 . Clip  114  electrically contacts the diodes  112  and compressively maintains the unit  110  in assembled condition. Additionally, each of the terminals  110  of voltage unit  100  incorporates a notch  116  (FIG. 1B) generally in a mid-region of each of its side edges to engagingly retain the terminals within the housing. 
     Although effective for its intended purpose, voltage unit  100  is costly to manufacture and rather difficult to assemble. Specifically, all of the electrical components of unit  100  are discrete elements which are not affixed to one another, yet must assume and maintain specific dispositions in the final assembly. If constant compressive force is not exerted against diodes  112  as clip  114  is placed thereon, or if clip  114  is improperly positioned on the diodes  112 , e.g., it pivots out of proper placement alignment, the unit  100  may literally fall apart during the manufacturing process. Hence, as many as thirteen parts may have to be recovered and realigned (both structurally and electrically) before the assembly may be reassembled. Further, because of their small size and delicate construction, one or more of the voltage limiters  104 , metallic plates  106 , paddle terminals  110  and/or diodes  108 ,  112  may become lost or damaged if the assembly process fails. Moreover, even if assembly proceeds without apparent incident, the construction of housing  102  is such that it affords limited protection of the diodes  112  from crushing, chipping or similar damage which may occur as a result of the compressive and/or shear forces exerted by the clip  114  as it is positioned on diodes  112 . The clip  114  may also fail to retain the electrical components within the housing if one or more of the diodes  108 ,  112  becomes damaged and reduces its thickness during operation. 
     The voltage limiter  104 , metallic plates  106 , diodes  108 ,  112  and terminals  110  have utility separate and distinct from one another as a surge suppressor, simple conductor or diode, as the case may be. However, the cooperation of the several components to provide sophisticated voltage surge protection is possible only if clip  114  is present. Moreover, their individual constructions do not render either the diodes  108 ,  112 , terminals  110  or clip  114  readily adaptable to other installation applications. For instance, unless considerably modified, the various electrical components of voltage unit  100  are incapable of attachment to a printed circuit board or individual wire conductors. 
     A typical telecommunications protection unit for which voltage unit  100  is adapted for use contains two heat coils for sneak current overload protection of the tip and ring circuits. One heat coil is in operative contact with the tip terminal of the pair of terminals  110  as well as a first office pin and a first line pin of the protection assembly. The other heat coil is in operative contact with the ring terminal of the pair of terminals  110  as well as a second office pin and second line pin of the protection assembly. The term “office” and words of similar import as used herein refer to components connected to the central office telecommunications equipment (e.g., switching, transmission equipment, telephone, modem or computer) whereas the term “line” and the like refer to the outside telecommunications lines which transport signals to and from the central office equipment. 
     Each of the terminals  110  make mechanical and electrical contact with a respective one of the heat coils. Either or both of the heat coils must move during a power surge or sneak current event. For the protection unit to function properly, each terminal  110  must also move and maintain electrical contact with its associated heat coil. Otherwise, protection is lost and the damaging power is transmitted to the office telecommunications equipment. The elongate wing segments of plates  106  impart a yieldable spring force against diodes  108  which permits limited motion of the terminals  110  and diodes  108 . To augment movement of the affected terminal(s)  110  during a power surge or a sneak current event, the side of each of terminals  110  opposite the heat coils is in contact with a compressed compression spring. The force exerted by the compression springs against the terminals  110  is intended to assure constant contact of either or both of terminals with the appropriate heat coil. 
     While generally useful to effectuate terminal movement under power surge or sneak current events, voltage unit  100  may be susceptible to failure in the event of exposure to certain voltage surges or sneak currents. That is, the limited movement afforded to the terminals  110  may be insufficient to provide rapid and reliable response to sudden movements of the heat coil(s) which might cause momentary breaches in contact between the affected terminal(s)  110  and the heat coil(s). 
     Referring to FIG. 2, there is shown an exploded, isometric view of an embodiment of a voltage unit of the present invention, which finds beneficial use, inter alia, in a telecommunications protection unit, generally referred to as  200 . The voltage unit  200  includes an electrically insulating base or housing  202 . The housing is preferably molded using a polybutylene terephthalate (PBT) or other suitable material. Housing  202  includes a central region  202   a  bounded by a pair of end plates  202   b ,  202   c  and is configured with various receptacle areas and slots of suitable dimensions to house a diode module assembly  204  and a voltage limiter  206 . The voltage limiter  206  is preferably a type IEL limiter manufactured by Texas Instruments. An electrically conductive clip  208  described in greater detail with reference to FIGS. 12A and 12B retains the diode module assembly  204  and the voltage limiter  206  within the housing  202  as shown in FIGS. 3 and 4. The material of the clip  208  is preferably a beryllium copper alloy. When assembled, as depicted in FIG. 3, the voltage unit  200  establishes an electrical circuit as schematically depicted in FIG.  8  and results in a completed assembly consisting of four parts as opposed to the fourteen elements required to produce the voltage unit disclosed in U.S. Pat. No. 4,796,150. 
     An exploded, isometric view of the diode module assembly  204  is depicted in FIG.  5 . The diode module assembly  204  includes an electrically conductive bus bar  502 . The material of the bus bar is preferably a copper alloy. A first terminal  504 , a second terminal  506  and a ground terminal  508  are each sandwiched between diodes  510  and  512 . Either first terminal  504  or second terminal  506  may serve as a ring terminal while the other may serve as a tip terminal. For purpose of illustration only, terminal  504  may be considered a tip terminal and terminal  506  may be considered a ring terminal. The diodes  510 ,  512  are preferably type PR 4  diodes manufactured by Texas Instruments and the material of the terminals  504 ,  506  and  508  is preferably an annealed copper alloy. The diodes  510  are each sandwiched between a respective terminal  504 ,  506  and  508 , and a terminal cap  514 . The material of the terminal caps  514  is preferably an annealed copper alloy. The bus bar  502 , terminals  504 ,  506  and  508 , diodes  510  and  512  and terminal caps  514  are preferably soldered or otherwise electrically and mechanically affixed together to form the unitary assembled diode module  204  as shown in FIG.  6 . When assembled, the diode module establishes an electrical circuit as schematically depicted in FIG.  7 . 
     Among the advantages arising from the integral or unitary construction of the diode module assembly  204  of the present invention is that it simplifies assembly of the voltage unit  200 . For instance, the diode module assembly  204  is a single piece assemblage comprising several diode and conductor sub-components which can be easily and reliably placed as a unit in a correspondingly shaped receptacle in housing  202 . By contrast, the various diodes, terminals and plates of the voltage unit  100  shown in FIGS. 1A-1D are “loose” items not integrally connected to one another. If not carefully placed individually into specific positions within housing  100 , and maintained in those positions under the influence of continuous compression until proper placement of clip  114 , one or more of these components may become misaligned or separated from the others. Consequently, the proper arrangement of parts must be carefully maintained before assembly of the voltage unit  100  may be completed. As will be appreciated, improper placement of any of the electrical components of voltage unit  100  requires reassembly of the unit and raises manufacturing costs. 
     The peripheral dimensions of bus bar  502 , terminals  504 ,  506  and  508  and terminal caps  514  of diode module assembly  204  are desirably greater than the peripheral dimensions of diodes  510 ,  512  with which they are in contact. With the diode module assembly  204  so constructed, the diodes  510 ,  512  are effectively protected from physical trauma before, during and after placement of the diode module assembly into housing  202 . 
     Moreover, the modular nature of the diode module assembly  204  enables it to be manufactured and stored in inventory. Thereafter, it may be used, either by itself or as a component of a voltage unit (as will be described in greater detail and in connection with the discussion of FIGS. 10A,  10 B and  11 ), in an in-line telecommunications protection unit and other applications to produce electrical circuitry functions far more sophisticated, for example, than the individual diodes  108 ,  112  of voltage unit  100 . Also, the diode module assembly  204  may be used with voltage limiters other than voltage limiter  206  to achieve differing levels of telecommunications equipment protection. 
     Referring to FIG. 9, there is shown an exploded, isometric view of a telecommunications equipment protection unit, generally designated  900 , which employs a voltage unit  200  in accordance with the present invention. The protection unit  900  incorporates many of the structural features of the protection unit described in U.S. Pat. No. 4,796,150, the disclosure of which is incorporated herein by reference. 
     A presently preferred protection unit  900  includes a protector housing  902  formed from any suitable non-conductive material which may be molded and cured into a hollow, rugged and substantially rigid casing-type configuration. Protection unit  900  further includes a voltage unit, preferably unit  200  described above, a right coil assembly  904 , and a left coil assembly  906 . In a manner known in the art, each of the left and right coil assemblies  904 ,  906  includes a housing formed from suitable non-conductive material which retains a central office pin  908  communicable with the telecommunications equipment to be protected and a line pin  910  communicable with the outside telecommunications lines which transport signals to and from the central office equipment. Rearward projections of each of the line pins  910  are mechanically soldered and electrically connected to metallic, e.g., copper, sleeves  912 . Surrounding each of the sleeves  912  is a heat coil  914 , one end of which is secured to the sleeve and the other end of which is secured to a rearward projection of an appropriate central office pin  908 . As is conventional, the heat coils  914  function as the sneak current limiters for protection unit  900 . The housings of each of the left and right coil assemblies  904 ,  906  are preferably provided with a groove  916  adapted to accommodate approximately one-half of the circumference of a metallic ground pin  918  of a grounding assembly  920 . Grounding assembly  920  further includes a metallic leaf-type ground spring  922  integrally connected to ground pin  918  and adapted for abutting contact with the ground terminal  508  of voltage unit  200 . 
     Protection unit  900  additionally includes a pair of metallic compression springs  924 , only one of which is shown in FIG. 9. A first end of each spring  924  contacts one of the tip and ring terminals  504 ,  506  of voltage unit  200  and a second end receives a metallic ball-like cap  926  which normally abuts against the interior surface of a rear wall  928  of housing  902 . Rear wall  928  further preferably comprises a pair of openings  930  only one of which is shown in FIG.  9 . Each opening  930  is in alignment with a respective one of the caps  926  to permit testing for continuity of the line. 
     As known in the art, springs  924  exert compressive spring force against tip and ring terminals  504 ,  506 . Springs  924  are provided to maintain contact between the tip and ring terminals and sleeves  912  during periods of normal operation and during voltage and/or current overload events. The operation of springs  924 , which itself does not form a part of the present invention, is described more fully hereinafter. 
     FIGS. 10A and 10B reveal a further embodiment of a voltage unit in accordance with the present invention. The voltage unit, identified generally by reference numeral  300 , is constructed and functions substantially similarly to previously described voltage unit  200 . Accordingly, only those elements of voltage unit  300  which materially differ from voltage unit  200  or are otherwise necessary for a proper understanding of the invention will be described in detail herein. 
     One difference between voltage unit  300  and voltage unit  200  lies in the construction of their terminals. For example, the tip and ring terminals  504 ,  506  of voltage unit  200  lie in a common plane throughout their lengths (FIGS.  2 - 6 ). Ground terminal  508 , however, lies in part in the plane established by tip and ring terminals  504 ,  506  and in part deviates from that plane. Indeed, at its distal end, ground terminal  508  curves away from the common plane of tip and ring terminals  504 ,  506  to an extent that it extends substantially perpendicular to such plane. It is this distal end of ground terminal  508  which abuts the ground spring  922  (FIG. 9) when the protection unit  900  is in assembled condition. 
     In contrast, the three terminals of voltage unit  300 , respectively identified by reference numerals  304 ,  306  and  308 , lie substantially in a common plane through their lengths. So constructed, terminals  304 ,  306 ,  308  may be inserted into appropriately sized and spaced slots or holes provided in a suitable substrate  310  such as a printed circuit board or the like and fixedly connected thereto by solder joints  312  or similar fastening means. It will also be understood that, although not illustrated, a diode module assembly similar to the diode module assembly  204  described hereinabove may also be affixed to a printed circuit board or similar substrate if provided with terminals constructed substantially similarly to terminals  304 ,  306 ,  308  of voltage unit  300 . 
     Referring to FIG. 11, there is shown a further embodiment of voltage unit according to the present, identified generally by reference numeral  400 . Like voltage unit  300  discussed immediately hereinabove, voltage unit  400  is substantially similar to voltage unit  200  and only material differences therebetween will be emphasized herein. Additionally, like voltage unit  300 , a difference between voltage unit  400  and voltage unit  200  is in the construction of their terminals. More specifically, the terminals  404 ,  406  and  408  of voltage unit  400  lie substantially in a common plane throughout their lengths and are bifurcated at their distal ends to form slots  410 . Slots  410  are desirably of suitable width to receive individual insulated wire conductors, one of which is represented by reference numeral  412 , and sever the insulation of such conductors so as to establish an insulation displacement connection (IDC) with such wires. And, although not illustrated, it will be appreciated that a diode module assembly similar to diode module assembly  204  may be affixed to wire conductors if provided with terminals constructed substantially similarly to terminals  404 ,  406 ,  408  of voltage unit  400 . 
     It will be understood that other diode module assemblies and/or voltage unit constructions consistent with the spirit of the present invention may be envisioned by those of ordinary skill in the subject art. For instance, the terminals of any of the diode module assemblies and/or voltage units of the present invention may be modified so as to accommodate wire wrapping or fitted with any suitable male or female connection elements so as to permit their connection to virtually any presently available circuitry, terminals or conductors. 
     FIGS. 12A and 12B respectively depict enlarged isometric and front views of a presently preferred embodiment of a bus clip  208  suitable for use in assembling any of the voltage units herein described. Clip  208  is substantially C-shaped in cross-section and has a length L spanning a majority or, more preferably, substantially the entire length of housing  202  between end plates  202   b ,  202   c  (FIG.  2 ). A benefit arising from bus clip  208  extending for most and preferably nearly the entire distance between end plates  202   b ,  202   c  is that it is difficult to misalign the clip during placement. That is, end plates  202   b ,  202   c  function as lateral guides which effectively prevent undesirable rotation of the bus clip  208  about axis A (FIG. 12A) during placement into housing  202 . 
     Clip  208  may be formed from any suitable metal stamping and/or bending techniques to produce a substantially stiff yet slightly yieldable member having flange portions  210 ,  212  joined by a web portion  214 . Flange portions  210 ,  212  preferably include contiguous longitudinal inward and outward bends which together define opposed inwardly protruding elongate contact ridges  216  and  218 . Upon assembly of voltage unit  200 , for example, contact ridges  216 ,  218  compressively contact the outer surfaces of the voltage limiter  206  and diode module assembly  204 , respectively, to retain and electrically connect the several electrical components within the housing  202 . 
     A pair of spaced-apart, substantially parallel slots  220  extend generally transverse to the length L of clip  208  and preferably divide a substantial portion of web portion  214  and all of flange portion  212  into three independently yieldable segments  222   a ,  222   b  and  222   c . The contact ridge  218  of segment  222   a  is adapted to contact the diode stack, specifically, the terminal cap  514 , associated with terminal  506  (FIGS.  5  and  6 ). Similarly, the contact ridge  218  of segment  222   b  is adapted to contact the diode stack (specifically, the terminal cap  514 ) associated with terminal  508 , and the contact ridge  218  of segment  222   c  is adapted to contact the diode stack (specifically, the terminal cap  514 ) associated with terminal  504 . 
     An advantage to segmentation of the bus clip  208  is that each segment  222   a ,  222   b ,  222   c  may operate independently to produce an essentially uniform contact force on each stack of diodes and provide reliable retention of the voltage unit assembly. Hence, if one stack of diodes becomes damaged and its thickness is reduced, the appropriate independently yieldable segment  222   a ,  222   b ,  222   c  moves accordingly to ensure contact with the damaged diode stack. Moreover, since each segment  222   a ,  222   b ,  222   c  independently moves to accommodate the height of its corresponding diode stack, precise manufacturing tolerances are not required for either the diode stacks or the bus clip  208  which reduces manufacturing costs and simplifies assembly of the voltage unit. 
     As mentioned previously, housing  202  of voltage unit  200  is formed with various receptacle and slot areas to accommodate the diode module assembly  204  and voltage limiter  206 . One of those areas, identified by reference numeral  224  is shown in FIG.  13 . Area  224  is of sufficient size to receive both the diode module assembly  204  and voltage limiter  206  in the manner shown in FIG.  4 . In existing voltage unit designs such as, for example, voltage unit  100  (FIGS.  1 A- 1 D), the exposed edges of diodes  112  may experience crushing, chipping and related damage as a result of the compressive and/or shear forces exerted by the clip  114  during assembly of the voltage unit. Such trauma may require replacement of one or more of the diodes thereby increasing manufacturing time and cost. 
     Housing  202  is desirably constructed to overcome this problem. More particularly, housing  202  is desirably configured with structure for preventing direct contact of the contact ridges  216 ,  218  of bus clip  208  with anything other than the exposed oppositely facing surfaces of the voltage limiter  206  and the diode stacks (specifically the terminal caps  514  shown in FIGS.  5  and  6 ). 
     As seen in FIG. 13, a presently preferred structure for protecting the diode module assembly  204  and voltage limiter  206  from damage during placement of bus clip  208  is at least one, or more preferably, a pair of guide members  226  and  228  provided along first and second opposite edges of a longitudinal housing wall  230  connecting and extending substantially perpendicular to end plates  202   b ,  202   c . Guide members  226 ,  228  each preferably include an outwardly inclined first portion  226   a  and  228   a , respectively. The first portions  226   a ,  228   a  urge outward separation of the contact ridges  216 ,  218  of the first and second flange portions  210 ,  212  of the bus clip  208  with respect to the housing  202  as the clip is moved onto the housing (i.e., as the clip is moved from right to left with respect to housing when the housing is disposed in the orientation shown in FIG.  13 ). Adjacent and preferably contiguous with outwardly inclined first portions  226   a ,  228   a , guide members  226 ,  228  further preferably include substantially uninclined second portions  226   b  and  228   b , respectively, for maintaining the first and second webs  210 ,  212  in an outwardly urged or expanded condition and out of contact with the exposed corners and outwardly facing surfaces of the voltage limiter  206  and voltage diode assembly  204  as the bus continues leftwardly with respect to the housing  202  in FIG.  13 . 
     Optionally, guide members  226 ,  228  further comprise inwardly inclined third portions  226   c  and  228   c , respectively. Third portions  226   c ,  228   c  are disposed adjacent and preferably contiguous with the second portions  226   b ,  228   b  and permit somewhat controlled inward movement or contraction of the first and second flange portions  210 ,  212  with respect to the housing  202  as the bus clip continues leftward onto the housing. Upon passing the guide members  226 ,  228  the contact ridges  216 ,  218  of bus clip  208  come to rest directly upon the oppositely directed faces of the voltage limiter  206  and the diode stacks, specifically, the terminal caps  514 , of the diode module assembly  204  as reflected in FIG.  4 . As such, The fragile edges of the voltage limiter  206  and diode module assembly  204  are protected from harm from the bus clip  208  during assembly. 
     FIG. 14 illustrates a presently preferred construction of the terminals  504 ,  506 ,  508  described above in connection with FIGS. 5 and 6. As mentioned previously, it is known to use compression springs in telecommunications protection units such as unit  900  (FIG. 9) to enhance contact between the terminals of the voltage unit and the protection unit&#39;s heat coil sleeves. Under the influence of an excessive power surge or sneak current, the affected heat coil(s) heat up and the solder which connects a particular heat coil to its associated line pin melts. The sleeve about which the heat coil is wrapped is then urged to slide toward under the influence of the compression spring and contact the grounding assembly, thereby diverting the damaging voltage and/or current to ground. 
     As the sleeve slides, it carries its associated heat coil. If the tip and/or ring terminal of the voltage unit loses contact with the moving sleeve, the damaging power is sent to the telecommunications equipment rather than to ground. The paddle or terminal portions of contacts  110  (FIGS.  1 A and  1 B), for example, are designed for limited movement under the influence of a compression spring such as spring  924  (FIG. 9) upon the occurrence of a voltage surge or sneak current event. However, some sudden movements of sleeves  912  may be of sufficient magnitude to breach contact of the terminals  110  with the sleeves  912 . 
     Terminal movement responsiveness may be enhanced by substituting the compression springs  924  with heavier duty springs with higher spring force. However, the force associated with such springs may damage other components of protection unit  900 . Rather than using more forceful springs, the present invention proposes increasing the flexibility of the tip and ring terminals  504 ,  506 . 
     Tip and ring terminals  504 ,  506  are preferably formed from copper alloy approximately 0.016 inch in thickness. As illustrated in FIG. 14, each terminal  504 ,  506  is preferably comprised of three portions. The first portion  504   a ,  506   a  is disposed between diodes  510  and  512  (FIG.  6 ). The second portion  504   b ,  506   b  is generally paddle-shaped and contacts the end of the compression spring  924  and the sleeve  912  as shown in FIG. 9. A comparatively narrow third portion  504   c ,  506   c  connects the first and second portions. 
     When the width W 3  of the terminal third portion  504   c ,  506   c  is about 50% or less of the width W 2  of the second portion  504   b ,  506   b , increases in terminal flexibility are realized versus terminals configured according to terminals  110  of voltage unit  100 . Moreover, the considerable flexibility imparted to terminals  504 ,  506  by third portions  504   c ,  506   c  reduces potential stresses from harming the integrity of the diode stack assemblies. 
     According to a presently preferred embodiment, for example, the width W 2  of second portion  504   b ,  506   b  is preferably about 0.14 inches and the width W 3  of the third portion  504   c ,  506   c  is approximately 0.04 inches. W 3  is thus approximately 29% of W 2 . In contrast, the width of the corresponding notched portion of terminals  110  of voltage unit  100  is approximately two-thirds of the width of the paddle-shaped contact portion. Such a reduction in the terminal width of terminals  504 ,  506 , however, has been found to afford sufficient strength to withstand the rigors normally encountered in the operation of a telecommunications protection unit yet provide terminal flexibility sufficient to respond to sudden movements of sleeve  912  (FIG.  9 ).