Jackfield With Split Front Panel

The field of the invention generally relates to electrical jacks, and more particularly to jackfields which include a plurality of jacks in a jack housing or jack panel.

There is widespread usage of electrical jacks that have switches activated by inserting plugs through jack sleeves in the face plate of each jack. For example, one type of jack which is commonly referred to as a tri-jack has a vertically elongated face plate with three vertically aligned jack sleeves. Commonly, the top jack sleeve is used for monitoring the jack circuit, while the bottom two jack sleeves are used for interconnecting circuits such as between different tri-jacks using a patch cord with plugs on the ends. The circuits are typically digital or voice frequency and are used in such applications as, for example, telephone central offices, testing and patch panels, computer and data processing equipment, multiplex gear, and commercial and industrial patching and control applications.

Commonly, a jackfield has input and output circuits connected at the back, and the front is covered by a panel that has apertures through which the individual jack sleeves extend so that patch cord plugs can be inserted. One such jackfield is described in U.S. patent application Ser. No. 14,909, filed Feb. 13, 1987. It has significant advantage over earlier jackfields because, among other reasons, the tri-jacks have rearwardly extending pins that insert into a connector of a printed circuit board. Accordingly, the tri-jacks can easily be removed and replaced without disconnecting and reconnecting hard wiring such as wire wraps. This feature is particularly important because the tri-jacks have a higher failure rate than the other jackfield components due to their moving mechanical switches. Accordingly, the tri-jacks have to be replaced more often. Also, tri-jacks are changed in order to alter the circuit configuration of the tri-jack. However, one drawback of the above-described jackfield is that before the tri-jacks can be removed or inserted, the patch cords have to be removed so that the front panel can be taken off to expose the tri-jacks. This means that any time a tri-jack is to be removed or replaced, all of the patch cord interconnected active circuits must be disrupted.

It is an object of the invention to provide a jackfield having a plurality of jacks that can easily be removed from the front of the jackfield housing.

It is also an object of the invention to provide a jackfield having a plurality of individual jacks that can be removed from the front without disrupting patched interconnections between other jacks.

It is a further object of the invention to provide a jackfield having a front panel that is split into top and bottom independently removable sections so that the front panel can be removed without first disconnecting patch cords interconnecting jacks.

These and other objects are provided by the invention which defines an electrical jackfield comprising a plurality of electrical jacks positioned side-by-side, each of the jacks having a forward facing vertically elongated face plate having at least one horizontal jack sleeve adapted for receiving the plug of an interconnecting cable, and a housing for encasing the electrical jacks, the housing comprising first and second front panels, the first panel covering a top portion of the face plates of the jacks above the jack sleeves and the second front panel covering a bottom portion of the face plates of the jacks below the jack sleeves, the first and second front panels being independently removable wherein the first and second front panels can be removed without first unplugging plugs that are inserted in the jack sleeves. It is preferable that the jack sleeves have collar portions projecting forwardly from the face plates, and the first panel have a bottom edge with a plurality of notches for engaging the tops of the collar portions while the second panel have a top edge with a plurality of notches for engaging bottoms of the collar portions, the jacks being clamped in horizontal and vertical alignment by the first and second panels. It is also preferable that the first panel have an elongated lateral window and each of the jacks have a corresponding lamp positioned thereabove, each of the lamps having a forwardly projecting neck extending through the window of the first panel. As a result, the front panels can be removed to expose the tri-jacks for removal or insertion without disrupting interconnected circuits between other jacks.

The invention may also be practiced by an electrical jackfield comprising a plurality of electrical jacks each having a vertically elongated face bracket with at least two vertically aligned horizontal jack sleeves for receiving patch cord plugs, the jacks being positioned side-by-side with the face brackets being adjacent to each other, and a housing for encasing the electrical jacks, the housing comprising a top panel covering portions of the face brackets above the jack sleeves and a bottom front panel covering portions of the face brackets below the jack sleeves, the top and bottom panels being independently removable wherein the top and bottom front panels can be removed while leaving interconnecting patch cords inserted into jack sleeves. It is preferable that the jack sleeves on each of the jacks have collar portions extending forwardly from the face bracket, the top panel having a bottom edge with a plurality of downwardly facing semicircular notches engaging the collar portions of the top jack sleeve of each of the jacks and the bottom panel having a top edge with a plurality of upwardly facing semicircular notches engaging the collar portions of the bottom jack sleeve of each of the jacks wherein the jacks are clamped by the top and bottom panels. Accordingly, the fronts of the jacks are held in secured horizontal and vertical alignment by the clamping of the top and bottom panels onto the collar portions of the jacks. It is preferable that each of the jacks have three jack sleeves such as is commonly referred to as a tri-jack. It is also preferable that the face brackets have a built-up shoulder extending between the top jack sleeve and the bottom jack sleeve. Preferably, the shoulder is at the same level as the top and bottom panels thereby giving the appearance of a unitary front panel. Also, it is preferable that the top panel have a horizontally elonggated window and each of the jacks have a corresponding lamp positioned thereabove, each of the lamps having a forwardly projecting neck extending through the window. Also, it is preferable that the necks be rectangular and be clamped between adjacent necks and the top and bottom of the window. Further, it is preferable that the top and bottom panels mate with each other at regions laterally to the sides of the plurality of jacks, and that the top and bottom edges in these lateral regions be beveled for mating together.

The above objects and advantages will be more fully understood by reading the Description of the Preferred Embodiment with reference to the drawings wherein:

FIG. 1 is a front perspective view of a jackfield;

FIG. 2 is an exploded view of a jack module with associated guide apparatus;

FIG. 3 is a side view of a jack module mounted in the jackfield;

FIG. 4 is an exploded view of the lamp assembly;

FIG. 5 is a front sectioned view of a tri-jack;

FIG. 6 is a side sectioned view of the bus horsing;

FIG. 7 is an exploded view of a bus projection and a portion of a bus housinq slot:

FIG. 8 is a front view of a jackfield; and

FIG. 9 is a view taken along line 9--9 of FIG. 8.

Referring to the drawings wherein like characters of reference designate like parts throughout the various views, FIG. 1 shows a front perspective view of electrical jackfield assembly 10 which includes an enclosure or housing 12 and a plurality of vertically elongated modules 14 that are backwardly extending and mounted side-by-side. Housing 12 is an electromagnetic shielded casing and includes top plate 16, side plates 18, top and bottom rear plates 20 and 22 (FIG. 3), bottom plate 24 (FIG. 3), and top and bottom front plates or panels 26 and 28. Typically, jackfield assembly 10 is mounted in a standard 23-inch rack (not shown) and mounting brackets 30 are provided for this purpose. Top and bottom front panels 26 and 28, which will be described in more detail later herein, are connected to the front using screws 32 or other suitable fasteners.

Still referring to FIG. 1, a standard jackfield assembly 10 may consist of 56 side-by-side mounted modules, although other numbers could be used in various configurations. Each module 14 here has three vertically aligned plug receiving apertures 34a-c or bores, and thus the modules 14 are commonly referred to as tri-jack modules. Although the invention could be used to advantage with a variety of different types of modules 14, here bore 34a is used to monitor the module 14, bore 34b is used to patch a circuit out of module 14, and bore 34c is used to patch a circuit into module 14. Each plug receiving bore 34a-c is surrounded by a cylindrical jack sleeve 36a-c that has a collar 38. Each module 14 has a lamp assembly 40 with a lamp 42 that protrudes through an elongated lateral window 44 in the top front panel 26.

Referring to FIG. 2, an exploded view of a tri-jack module 14 with associated guide apparatus 46 is shown. Tri-jack module includes printed circuit board 48, a tri-jack assembly 50, a lamp assembly 40, a bottom guide housing 54 for tri-jack assembly 50, and a right-angle connector 56.

Printed circuit board 48 is of conventional construction such as a multi-layer epoxy glass board having a plurality of conductor leads 58 which are deposited in a predetermined pattern on both sides of printed circuit board 48. In FIG. 2, only the conductor leads 58 on one side of printed circuit board 48 are shown, and it is well known and conventional to interconnect conductor leads 58 from the opposite side at terminals such as right-angle connector 56 and at conductive eyelets 60. Here, the function of printed circuit board 48 is to interconnect wire wrap lugs or pins 62 and 64 through right-angle connector 56 to corresponding terminal pins 66 of tri-jack assembly 50. Further, as will be described in detail later herein, printed circuit board 48 interconnects conductor pads 68a-c to corresponding terminals of lamp assembly 40 and right-angle connector 56.

Still referring to FIG. 2 and also to FIG. 3 which shows a side section view of jackfield assembly 10, printed circuit board 48 has top and bottom forwardly projecting posts or necks 70 and 72, respectively, which define a notch 74 therebetween. Also, printed circuit board 48 has top and bottom rearward projections 76 and 78, respectively, which define a notch 80 therebetween. As can be seen best in FIG. 2, top rearward projection 76 on which wire wrap lugs 62 are mounted extends much further than bottom rearward projection 78 on which wire wrap lugs 64 are mounted. Conductor pads 68a-c are positioned inwardly from notch 80.

Still referring to FIG. 2, lamp assembly 40 is connected to top forwardly projecting neck 70 of printed circuit board 48. With further reference to FIG. 4, there is shown an exploded perspective view of lamp assembly 40 from the opposite side of that shown in FIG. 2. Lamp assembly 40 includes lamp housing 82, lamp housing retainer 84, conductor strips 86a and b, and a lamp 42. In fabrication, pins 88 of two conductor strips 86a and b are inserted through eyelets (not shown) in neck 70 and soldered in place so that conductor strips 86a and b are parallel and extend horizontally forward. Next, lamp housing retainer 84 or center lamp post is inserted between conductor strips 86a and b. Lamp housing retainer 84 is a molded plastic part and has two positioning pins 90 extending laterally from a flat side 92 that seats up against the neck 70 of printed circuit board 48. Retainer positioning pins 90 insert through small holes 94 in neck 70 thereby accurately locating lamp housing retainer 84 and preventing it from moving in a longitudinal or vertical direction. 0n the side opposite flat side 92 there are a series of three ramps 98a, b and c, with ramp 98c defining a retaining boss 99 with a flat top terminating at a back side wall 100. The front 102 of lamp housing retainer 84 is pointed, and is contacted on top and bottom by contact terminals 104 of conductor strips 86a and b which are spring tensioned against the top and bottom of retainer front 102.

Lamp housing 82 is a plastic molded part that includes a hollow trunk 106, upward and lower legs 108 and 110, and a face portion 112. Upper leg 108 has a downwardly facing guide channel 114 or track and lower leg has a corresponding upwardly facing guide channel 116 or track. Channels 114 and 116 face each other and are spaced so as to receive respective parallel upper and lower edges 118 and 120 of neck 70. In assembly, edges 118 and 120 are seated in respective guide channels 114 and 116, and then lamp housing 82 is pushed back onto neck 70. There is an interference fit between the inside wall 122 of hollow trunk 106 and lamp housing retainer 84. The three ramps 98a-c guide inside wall 122 away from neck 70 and also prevent lamp housing 82 from engaging or being snagged on conductor strips 86a and b. Hollow trunk 106 has a small aperture 124 which aligns with ramps 98a-c. Lamp housing 82 is pushed onto neck 70 until aperture 124 aligns with retaining boss 99 at which point edge 126 at the end of channels 114 and 116 engages a shoulder 128 of neck 70. At this position, retaining boss 99 snaps into aperture 124 due to the interference fit. The back side wall 100 of lamp housing retainer 84 engages the rear edge of aperture 124 and prevents lamp housing 84 from being slid off of neck 70. Thus, lamp housing 82 is securely attached to neck 70 and disengagement of ramp housing 82 from neck 70 is prevented. Lamp housing has a front central bore (not shown) through which lamp 42 is inserted. Each lamp has a pair of leads (not shown) which respectively insert on the top and bottom at the front 102 of lamp housing retainer 84 and are contacted by respective contact terminals 104 of conductor strips 86a and b. At the bottom of lower leg 110 is a downwardly facing guide channel 130 or track which, as will be described later herein, functions to mount tri-jack assembly 50. As will be described later herein, face portion 112 has a rectangular neck 236 which inserts through window 44 with shoulder 238 seating up against the back of top front panel 26.

Bottom guide housing 54 is similar although symmetrically different than lamp housing 82. Bottom guide housing 54 connects onto bottom forward projecting neck 72 in the same manner as lamp housing 82 connects onto neck 70. More specifically, a lamp housing retainer 84 having positioning pins 90 is seated against bottom neck 72 and bottom guide housing 54 having guide channels similar to guide channels 114 and 116 is pushed onto neck 72 and locked in place as shown in FIG. 2. Bottom guide housing 54 has an upward facing guide channel 132 or track which aligns directly under guide channel 130 of lamp housing 82.

Still referring to FIG. 2, and also to FIG. 5 which shows a front sectioned view of tri-jack assembly 50 mounted as part of tri-jack module 14, tri-jack assembly 50 has an elastic molded housing 134 which defines the left side wall 136, the roof 138, the floor 140, and the front face plate or face bracket 142. The right wall 144 is a metal shield with clips 146 that secure it to plastic molded housing 134. Roof 138 has a pair of upwardly projected guide rails 148 or runners, and floor 140 has a pair of downwardly projected guide rails 150 or runners. Rails 148 and 150 are separated into pairs so as to provide surface areas for fastening clips 146. As described in U.S. patent application Ser. No. 14,909, filed Feb. 13, 1987, which is hereby incorporated by reference, right metal wall 144, in addition to providing a shield between tri-jack assemblies 50, als provides a signal ground for plugs (not shown) that are inserted into plug-receiving apertures 34a-c. Face bracket 142 is a vertical partition that mounts jack sleeves 36a-c for plug-receiving apertures 34a-c. Between the collars 38 of jack sleeves 36a and 36c are shoulders 152 which are built up more than the ends 154 of face bracket 142.

The function and operation of jacks are well known to those skilled in the art. Although jacks can have a variety of different internal circuit connections and can be used for a number of different applications, here jacks, in conjunction with printed circuit board conductor leads 58, provide a straight through circuit between wire wrap lugs 62 and 64 for digital or voice frequency communication signals when plugs are not inserted into plug-receiving apertures 34a-c . In order to interconnect different modules 14, or patch circuits, or to monitor or test circuits, plugs are inserted into plug-receiving apertures 34a-c. By using cables connected to the plugs, a straight through circuit path can be interrupted, and the circuit re-routed to a different jack module 14. Typically, the top aperture 34a is for monitoring, the middle aperture 346 is for OUT signals and the bottom aperture 34c is for IN signals.

In assembling a tri-jack module 14, the guide rails 148 are inserted into guide channel 130 of lamp housing 82 and guide rails 150 are inserted in guide channel 132 of bottom guide housing 54. Then, the tri-jack assembly 50 is pushed in along respective guide channels 130 and 132 until terminal pins 66 engage and make electrical contact within right-angle connector 56. In order to ensure that tri-jack assembly 50 is inserted right-side-up, guide rails 148 and 150 are keyed or polarized. More specifically, as shown in FIG. 2, the back guide rail 150 has a rearward notch 156, and guide channel 132 has an upwardly extending boss 158. If tri-jack assembly were inserted up-side-down, the back guide rail 148, which does not have a corresponding notch, would bump against boss 158 thereby preventing further insertion that could bend or damage terminal pins 66 by not properly aligning with right-angle connector 56. Referring to FIG. 5, there is shown an alternate embodiment for keying or polarizing guide rails 148 and 150. More specifically, guide rails 148 on top are laterally wider than guide rails 150 on the bottom, and guide channels 130 and 132 are correspondingly grooved. Accordingly, if attempts were made to insert tri-jack assembly 50 up-side-down, guide rail 148 would not insert into guide channel 132. Thus, tri-jack assembly 50 cannot be inserted in an inverted orientation.

After each tri-jack module 14 including printed circuit board 48, right-angle connector 56, lamp assembly 40, bottom guide housing 54, and tri-jack assembly 50 are fully assembled, the module 14 is ready for insertion into housing 12. As shown in FIG. 2, guide apparatus 46 includes top wafer guide 160, bottom wafer guide 162, and bus housing 164. Also referring to FIG. 3, top and bottom wafer guides 160 and 162 are respectively mounted on top and bottom plates 16 and 24, and extend laterally across jackfield housing 12. Top and bottom wafer guides 160 and 162 have a plurality of corresponding channels or grooves 166 which face each other and are aligned to form guide slots for receiving the top and bottom edges 168 and 170 of printed circuit board 48. Grooved bus housing 164 also extends laterally and has a plurality of channels or grooves 172 which align with channels 166. As shown in FIG. 3, there is a step partition 174 which runs laterally along the back of housing 12. Bus housing 164 has a horizontal section 176 which seats on top 178 of step partition 174. A suitable fastener 180 connects horizontal section 176 to step partition 174. The channels 172 of bus housing 164 are in horizontal section 176 so they engage the under side edge 182 of the rearward projection 76 of printed circuit board 48. In summary, the combination of channels 166 and 172 define guide slots for holding modules 14 in vertical alignment, and also align the respective wire wrap lugs 62 and 64 and conductor pads 68a-c to their proper lateral position. Wire wrap lugs 62 insert through an array of small openings 177 in dielectric insulator terminal block 186 and wire wrap lugs 64 insert through an array of small openings 177 in dielectric insulator terminal block 188. Wires (not shown) are then wire wrapped to the appropriate wire wrap lugs 62 and 64 for routing the proper signals.

Still referring to FIGS. 2 and 3 and also to FIGS. 6 and 7 which respectively show side sectioned and rear perspective views of bus housing 164, vertical section 190 of bus housing 164 extends downwardly parallel to front surface of step partition 174. Vertical section 190 is a dielectric insulator and has columns of three slots 192a-c which respectively align with channels 172. Each slot 192 has a step 194, ledges 196 at the sides, and stops 198 at the rear. Busses 200a-c are inserted so that a pair of contact springs 202 protrude forwardly from each slot 192. More specifically, each bus 200, of which there is one for each of three horizontal rows of slots 192, has a plurality of projections 204 which insert through slots 192 from the rear. Each projection 204 has a horizontal portion 206 that wraps up along the sides 208 and extends forwardly from a front edge 210 of the horizontal portion 206. At the back, the sides have respective ears 212 that extend outwardly, and a pair of contact springs 202 which slant inwardly through a contact region 214 where they bow outwardly. The projection 204 is pushed into the slot 192 from the rear until the front edge 210 contacts step 194 thereby preventing further movement to the front. At this position, ears 212 spring outwardly on both sides above ledges 196 and engage stops 198 to prevent motion toward the rear. The contact springs 202 extend forwardly frcm slots 192. The busses 200a-c electrically interconnect or daisy chain each of the projections 204 along one of the respective rows of slots 192. At the end, the top bus 200a is connected to -48 volts DC, the middle bus 200b is connected to ground, and the bottom bus 200c is used for signal ground. Summarizing, each slot 192 of each column has a pair of contact springs 202 extending forwardly and the springs 202 are firmly secured so that they cannot be pushed backwardly by printed circuit board 48 or drawn forwardly by the removal of printed circuit board 48. Also, each of the contact springs 202 on the top row 192a provides -48 volts DC, each of the contact springs 202 in the middle row 192b provides ground, and each of the contact springs 202 in the bottom row 192c provides signal ground. As module 14 is pushed to its fully inserted position as shown in FIG. 3, respective conductor pads 68a-c insert between respective contact springs 202 pushing them apart and making tensioned electrical contact between busses 200a, b and c, and the respective top, middle and bottom conductor pads 68a-c. Further, it is noted that dielectric insulator 188 extends upwardly between vertical section 190 of bus housing 164 and step partitions 174 to prevent busses 200a-c from contacting step partition 174.

Referring again to FIG. 3, conductor lead 58a on the facing side of printed circuit board 48 electrically interconnects conductor pad 68a with conductor strip 86b of lamp assembly 40. Also, conductor lead 58b on the facing side of printed circuit board 48 electrically interconnects conductor pad 68b with terminal 216 of right-angle connector 56. Further, conductor lead 58c, shown as a dotted line because it is routed on the opposite side of printed circuit board 48, electrically interconnects conductor strip 86a with terminal 218 of right-angle connector 56. Although many other circuit configurations could be used, conductor pads 68a and 68b are electrically connected across conductor strips 86a and 86b of lamp assembly 40 when a plug (not shown) is inserted into the top monitor jack sleeve 36a. More specifically, when a plug is inserted into jack sleeve 36a, spring contacts (not shown) internal to tri-jack assembly 50 are urged in the vertical direction thereby electrically interconnecting terminals 216 and 218 of rightangle connector 56. In this state, conductor pad 68b is electrically interconnected with conductor strip 86a. As a result, when a plug is inserted into the monitor jack sleeve 36a, -48 volts DC from bus 200a is connected to one side of lamp 42 via conductor pad 68a and conductor lead 58a, and ground from bus 200b is connected to the opposite side of lamp 42 via conductor pad 68b, conductor lead 58b, an internal circuit of tri-jack assembly 50, and conductor lead 58c. Accordingly, lamp 42 is lit when a plug is inserted into the monitor jack sleeve 36a.

Referring to FIGS. 8 and 9, front and side views of front plates or panels 26 and 28 are shown. Bottom front panel 28 extends laterally below the bottom of jack sleeves 36c and has a scalloped top edge 220 defining a series of semicircular notches 222 into which corresponding collars 38 of jack sleeves 36c fit. Similarly, top panel 26 extends laterally above the top jack sleeves 36a and has a scalloped bottom edge 224 defining a series of semicircular notches 226 into which corresponding collars 38 of jack sleeves 36a fit. Bottom panel 28 further has upwardly projecting arms 228 at the sides and preferably at the middle that extend upwardly and mate with top panel 26. More specifically, as shown in FIG. 9, the bottom edge 227a of top panel 26 and the top edge 227b of bottom panel 28 at the projecting arms 228 are beveled so that they interlock thereby eliminating any gap therebetween that would visually emphasize the fact that the top panel 26 and bottom panel 28 are two separate parts. Further, the shoulder 152 between jack sleeves 36 a and jack sleeves 36c are built up to the level of top and bottom panels 26 and 28 making the front of housing 12 flat so as to provide the conventional appearance of having one front panel that covers the entire front.

Still referring to FIGS. 8 and 9, the front panel is split into top panel 26 and bottom panel 28 so that tri-jack assemblies 50 and/or tri-jack modules 14 may be removed or inserted from the front without disrupting service to any other active channels in the jackfield 10. More specifically, the front panel consisting of top panel 26 and bottom panel 28 may be removed without first unplugging plugs (not shown) that have interconnecting cables between different modules 14. Stated differently, even though two modules 14 are interconnected by a patch cable at the front, top and bottom panels 26 and 28 can be independently removed without interrupting the interconnection. Once the top and bottom front panels 26 and 28 are removed, tri-jack assemblies 50 and/or tri-jack modules 14 may be removed and replaced from the front, still without interrupting interconnected jack modules 14, unless, of course, the particular module 14 is between the interconnected modules 14 and the cable is relatively taut thereacross. Another important feature of top and bottom panels 26 and 28 is that their respective semicircular notches 222 and 226 clamp each module 14 from the top and bottom locking it securely in place. In particular, notches 227 and 226 engage sleeves 36a and 36c of each tri-jack assembly 50 preventing it from moving or wobbling which may be especially important if some module slots are not filled with modules 14. In other words, each module 14 is rigidly affixed in vertical and horizontal alignment by the combination of notches 222 and 226, and channels 166 and 172.

Referring again to FIG. 3, tri-jack assemblies 50 are removed by pulling them forwardly such that terminal pins 66 slidably disengage from right-angle connector 56 and respective guide rails 148 and 150 or runners slide forwardly within guide channels 130 and 132. Front support plate 232 extends laterally across the front of jackfield assembly 10 and engages respective notches 234 of bottom guide housings 54 thereby preventing the printed circuit board 48 and the rest of the module 14 from moving forwardly by the force put on right-angle connector 56 by the removal of a tri-jack assembly 50.

If, instead of removing just tri-jack assembly 50, the intended operation is to remove the entire tri-jack module 14 for service or reconfiguration of electrical jackfield assembly 10, two additional steps are required. First, the wire wraps are removed from wire wrap lugs 62 and 64. Second, front support or retaining plate 232 is removed by removing screws 233. Then, the module 14 is free to be pulled forwardly and removed from housing 12. Wire wrap lugs 62 and 64 slide through their respective openings 177 in top and bottom terminal block sections 186 and 188, and conductor pads 68a-c slide out of engagement with the respective contact springs 202. For inserting a module 14 in housing 12, the process is reversed. Specifically, top and bottom edges 168 and 170 of printed circuit board 48 are correspondingly inserted into channels 166 of top and bottom nylon wafer guides 160 and 162, and the module 14 is pushed longitudinally towards the rear. The under edge 182 of rearward projection 76 of printed circuit board 48 engages a corresponding channel 172 in horizontal section 176 of bus housing 164 at a position further to the rear. In the installed position, wire wrap lugs or pins 62 insert through openings 177 in the array of top terminal block section 186 and wire wrap lugs or pins 64 insert through openings 177 in the array of bottom terminal block section 188. Also, conductor pads 68a-c automatically align with and engage corresponding contact springs 202 of respective busses 200a-c. Accordingly, -48 volts DC, ground, and signal ground are disengageably provided to the rear of module 14 such that module 14 can be longitudinally inserted and removed from the front of housing 12. Wire wrap lugs 62 and 64 are wire wrapped as described earlier herein. Next, after all of the desired modules 14 are inserted, front support plate 232 is affixed in place using screws 233. Then, the bottom and top front plates 28 and 26 are positioned in place and screws 32 are used to secure them. The neck 236 of the face portion 112 of each lamp housing 82 protrudes through window 44 and the back of top front plate 26 seats against shoulder 238 of the face portion 112 (FIG. 4).

Referring again to FIG. 2, metal plate shields 240 are slid longitudinally in from the front between the slots for modules 14 during initial assembly. Shields 240 function to suppress crosstalk between adjacent modules 14. Thin shield slots 242 are cut in between and parallel to channels 166 in guide wafers 160 and 162. Top and bottom edges 244 and 246 of shields 240 slidably engage shield slots 242. Further, shields 240 each have an upper rear projection 248 wit an under edge 250 that slidably engages a guide slot 252 positioned parallel and in between channels 172 of bus housing 164. The under edge 250 of each shield 240 has a notch 254 which engages a flexible hook 256 extending from the rear of bus housing 164. More specifically, with reference to FIG. 6, the bottom edge 250 of shield 240 rides along ramp 258 during initial assembly thereby depressing hook 256. When notch 254 arrives at hook 256, hook 256 springs upward into notch 254 and thereby prevents removal of shield 240 to the front. Accordingly, shields 240 stay in place in housing 12 even though modules 14 may be removed for repair or replacement with other types of modules. If shields 240 could be pulled forwardly, a module 14 could be replaced and the shield 240 inadvertently left out.

This concludes the description of the preferred embodiment. A reading of it by those skilled in the art will bring to mind many modifications and alterations without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only by the appended claims.