Abstract:
A spring clamp assembly for an electrical terminal block includes a termination spring, a trigger and a return spring. The trigger is biased by the return spring into an opening of the termination spring to impede a clamping movement of the termination spring. A wire inserted into the terminal block trips the trigger so that it clears the termination spring allowing it clamp the exposed end of the wire against a metal terminal contact. Thus, the wire is clamped in place simply by the simple and necessary action of inserting the wire into the terminal block. The wire is removed and the assembly is reset by manually moving the termination spring to its original position, removing the wire and allowing the return spring to reset the trigger.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not applicable. 
   STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to electrical termination blocks and clamps for clamping wires to the terminal contact(s). 
   Industrial electrical components, such as controls, switches, timers, relays and other components for machine monitoring, control and operator interfacing, typically have terminal blocks with one or more electrical contacts to couple power and/or interconnect wires. Complex wiring applications, such as factory automation, process and motion control, data acquisition, electrical utility, telecommunications, and HVAC applications, typically use a series of modular terminal blocks to couple the wire leads. These terminal blocks are often mounted on a common metal rail known as a “DIN rail”. 
   Conventional DIN mounted modular terminal blocks have a thin, non-conductive body that houses an electrical contact and a wire clamping mechanism. Conventional terminal blocks of screw, spring or insulation displacement types are commercially available from Rockwell Automation of Milwaukee, Wis. as the Allen-Bradley “J”, “K” and “L” line of terminal blocks. 
   The terminal blocks are common in the “feed through” form in which two or more wires are clamped to a metal contact bar inside the terminal block to simply make an electrical connection between the wires. Other terminal blocks have disconnect mechanisms, fuses, thermocouples, diodes, surge protectors and other such components interposed between separate contacts inside the housing for interrupting or otherwise affecting the current path between the wires. 
   The housings of conventional terminal blocks usually have flexible rail clips that mechanically mount it to the rail. The wire(s) are inserted into the housing and clamped to the contact(s) by a screw or spring inside the housing. The clamp is accessible from outside the housing, but to comply with IP2X “finger-safe” standards, the access opening must be small enough so that a probe approximately the size of a finger cannot make contact with energized parts of the terminal block, namely the contact. Thus, it is conventional to have small funneled openings just large enough to accommodate individual insulated wires. Also, access to the clamping mechanisms is either limited or they are made to be operated by non-conductive parts. 
   Given the typically large number of wires that must be connected in large industrial applications, it is desirable to make the termination of the wire to the contact as simple and quick as possible. However, the generally enclosed housing of conventional finger-safe terminal blocks can make it difficult to clamp the wire to the terminal contact. 
   One simple and effective method for terminating the wire to the contact is a “push in” connection in which the exposed end of the wire is clamped to the contact simply by the user inserting the wire into an opening in the terminal block. Existing push in clamp mechanisms typically include a leaf spring that is biased against the contact such that when a wire is inserted therebetween the wire displaces the leaf spring, which in turn provides a biasing force that clamps the wire against the contact. While simple, such systems are only effective for solid wires that have the structural rigidity to displace the leaf spring. Stranded wire lacks sufficient rigidity and thus such systems are not suitable for stranded wire. Another problem with such systems is that it is often difficult to determine whether the wire is securely clamped in place. If the spring fails to clamp the wire adequately, the wire can be dislodged and disrupt the circuit. 
   Accordingly, an improved wire clamp is desired. 
   SUMMARY OF THE INVENTION 
   The present invention provides a spring clamp assembly for a wire terminal that addresses the above problems. The spring clamp assembly of the present invention can be used with solid and stranded wire, and can provide feedback to the user that the wire has been successfully clamped to the terminal contact. Moreover, the spring clamp assembly of the present invention can be used with top, bottom and side wire entry terminal blocks. 
   In one aspect the present invention provides a spring clamp assembly for securing a wire to a terminal contact. The spring clamp assembly includes a termination member, a trigger and a return member. The termination member provides the wire clamping force and has an opening receiving the wire. The termination member is movable between first and second positions. The first position locates the opening to receive the wire, and the second position biases the wire received in the opening against the contact. The trigger engages the termination member and is movable from an initial position to effect movement of the termination member from the first position to the second position. The return member biases the trigger toward the initial position. 
   The most preferred form of the spring clamp assembly is arranged to allow the trigger to be tripped by the wire. Thus, by simply inserting the wire into an opening in the terminal block sufficient to contact the trigger, the trigger will release the termination member so that it can clamp the wire against the terminal contact. In this way, no extraneous steps need be undertaken to couple the wire to the terminal contact. 
   In other forms, the termination member is a leaf spring and movement from the first position to the second position is effected by deflection of a portion of the leaf spring. The return member is a coil spring disposed in to abut a part of the trigger that does not engage the termination spring. The trigger defines a space to receive the end of the wire and has an open side allowing for surface contact with the terminal contact when clamped. The return spring moves essentially along a wire insertion axis and portion of the termination spring moves by deflecting along a path intersecting that axis. When in its initial position the trigger interferes with movement of the termination spring from the first position to the second position preferably by engaging the opening of the termination spring. 
   In another aspect the invention provides a spring clamp assembly for securing a wire to a terminal contact having a termination member, trigger and return member. The termination member is deflectable between a position in which its opening is located to receive the wire and a position in which the wire is biased against the terminal contact. The trigger initially engages the termination member to interfere with deflection of the termination member from the first position to the second position. The trigger is tripped by contact with the wire to move out of engagement with the termination member and permit deflection of the termination member from the first position to second position. 
   In still another aspect the invention provides a method of connecting a wire to a terminal contact using a spring clamp assembly. The method includes inserting a wire into the terminal block to trip a trigger against the bias of a return spring, which releases a termination spring to clamp the wire against the terminal contact. Preferably, the wire is inserted into the terminal block until an audible “click” sounds, which notifies the user that proper coupling has been achieved. 
   These and other advantages of the invention will be apparent from the detailed description and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front sectional view of a terminal block having spring clamp assemblies according to the present invention; 
       FIG. 2  is an enlarged partial sectional view thereof showing one of the spring clamp assemblies in its open, ready-to-wire position; and 
       FIG. 3  is view similar to  FIG. 2  showing one spring clamp assembly clamping a wire to a terminal contact. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates spring clamp assemblies  10  and  11  for a wire terminal block  12  used to couple wires together or to the electrical contacts of an electrical component. The preferred version of the spring clamp assemblies  10  and  11  disclosed herein each include a termination spring  14 , a trigger  16  and a return spring  18 . The termination spring  14  is preferably an elongated spring member that is bent to provide a pre-load spring force for clamping the wire, as detailed below. The termination spring  14  can be a leaf type spring made of metal, plastic or other suitable material. The return spring  18  can also be of any suitable type or material, and in one preferred form is a metal coil spring. 
   As shown, the spring clamp assemblies  10  and  11  can be used to couple two or more wires to a terminal contact  20  in the terminal block  12 . The contact  20  is a metallic piece that can take the form of an elongated bus or current bar. In the embodiment shown, the contact bar  20  has a U-configuration so that its upwardly extending legs interplay with each spring clamp assembly  10  and  11 . Using the spring clamp assemblies  10  and  11  to clamp a wire conductor to each vertical leg by the contact bar  20  will electrically couple the two wires together. 
   The terminal block  12  is shown as a modular feed-through type finger-safe terminal block with top wire entry. The terminal block  12  has a non-electrically conductive housing with a wide, thin profile and a hollow interior and two mounting tabs  22  at lower corners that have a standard configuration designed to mate with a standard DIN rail (not shown) and mechanically connect the terminal block to the DIN rail. It should be noted that the spring clamp assembly of the present invention could be used with any other suitable terminal block configuration with top, bottom or side wire entry ports, and therefore the disclosed embodiment is not limiting in this regard. 
   The terminal block  12  has internal ribbing and wall structure that support and fix the location of the spring clamp assemblies  10  and  11  and the contact bar  20  in relation to two cylindrical openings  24  leading from the top side of the terminal block  12 . Specifically, as shown in  FIG. 2 , each termination spring  14  forms a bend that loops about a dumbbell-shaped wall  26  and the return spring  18  and the trigger  16  are disposed in a pocket of an L-shaped wall  28  so as to be aligned generally with an axis of insertion  29  of the wire through the associated opening  24  in the terminal block  12 . 
   Since both spring clamp assemblies  10  and  11  are identical, for simplicity their construction and operation will be discussed below and illustrated in  FIGS. 2 and 3  with reference to only assembly  10 . When assembled, the return spring  18  is captured between the horizontal ledge of wall  28  and the bottom wall of the trigger  16 . The trigger  16  rests on the return spring  18  so that its open cavity or pocket  30  is generally aligned with the opening  24  in position to receive the wire. The trigger  16  and the return spring  18  thus are movable along the wire insertion axis  29  and are disposed alongside the vertical leg of the contact bar  20 . The vertical leg of the contact bar  20  extends alongside a leg of the termination spring  14  that contacts the terminal block wall  26 . The contact bar  20  is generally stationary and its vertical leg fits through an opening  40  in a lateral leg of the termination spring  14 . The opening  40  is generally disposed about the wire insertion axis  29  in registration with the opening  24 . The opening  40  serves to accommodate insertion of the wire into the vicinity of the spring clamp assembly  10  and also provides a location for engaging the wire to apply the clamping force. Thus, the opening  40  can be a hole as shown and described herein or it could by a notch, recess, hook or other structure that both allows space for the wire to pass along the insertion axis  29  and provides a surface for engaging the wire. 
   The termination spring  14  moves, by way of flexure or deflection of the lateral leg, from a first position when the spring clamp assembly is in a ready-to-wire state (shown in  FIG. 2 ) to a second position in which it is in a wire clamping state (shown in  FIG. 3 ). In the ready-to-wire state of  FIG. 2 , the termination spring  14  is in its first position such that upper part of the trigger  16  extends into the opening  40  under the force of the return spring  18 . In this state, the trigger  16  interferes with the movement, particularly flexure or deflection, of the termination spring  14  to its second position. Thus, the opening  40  is ready to receive the wire. As shown in  FIG. 2 , a wire  50  that has its insulation stripped away at one end to expose the conductor is inserted into the opening  24  of the terminal block  12 . The wire  50  can be inserted far enough so that the bare end passes through the opening  40  of the termination spring  14  and into the cavity  30  of the trigger  16 . When the tip of the wire  50  contacts the bottom of the trigger  16  further insertion will drive the trigger  16  against the return spring  18  so that it moves in the axial direction. Minimal insertion force is required to move the trigger  16  since it is moving the trigger  16  only a short axial distance and the return spring  18  is a relatively low force spring. In any event, the insertion force is generally less than that required to displace the leaf spring in conventional push-in type spring clamp mechanisms. As such, the spring clamp assembly of the present invention is suitable for use with both solid wires and stranded wires. When the trigger  16  moves far enough, its upper end will pass out of the opening  40  and disengage the termination spring  14 . When the trigger  16  is tripped, the spring force of the termination spring  14  will cause it to move to its second position shown in  FIG. 3 . The trigger  16  is open at one side  52  so that the exposed conductor of the wire  50  is clamped against the vertical leg of the contact bar  20  by the clamping force of the termination spring  14 , particularly the abutment of the inner periphery of the opening  40  with the wire  50 . When the termination spring  14  clamps the wire  50  against the vertical leg of the contact bar  20 , an audible “click” can be heard by the user. This provides feedback that the wire  50  was inserted far enough into the terminal block  12  to trip the trigger  16  and that the wire has been successfully clamped to contact bar  20 . The spring force of the termination spring  14  maintains a clamping force sufficient to keep the wire conductor in contact with the contact bar  20  absent a significant pulling force on the wire. 
   To disconnect the wire from the contact bar  20 , the termination spring  14  is simply moved back manually to its initial position (as in  FIG. 2 ). This can be accomplished in the enclosed terminal block  12  by fitting the tip of a tool, such as a screwdriver, into an opening (not shown) in the terminal block  12  and forcing the termination spring  14  against its spring force until the return spring  18  drives the trigger  16  back up into the opening  40  in the termination spring  14 . The spring clamp assembly  10  is thus reset to the ready-to-wire state of  FIG. 2 . 
   The present invention thus provides a simple and easy to operate spring clamp assembly for a wire terminal block. The spring clamp assembly of the present invention can be used with solid and stranded wire, and can provide feedback to the user that the wire has been successfully clamped to the terminal contact. Moreover, the spring clamp assembly of the present invention can be used with top, bottom and side wire entry terminal blocks 
   The invention also provides a method of connecting a wire to a terminal contact using a spring clamp assembly. The method includes inserting a wire into the terminal block to trip a trigger against the bias of a return spring, which causes a termination spring to release and clamp the wire against the terminal contact. Preferably, the wire is inserted into the terminal block until an audible “click” sounds, which notifies the user that proper coupling has been achieved. 
   A preferred embodiment of the invention has been described above. However, modifications and variations to the preferred embodiment will be apparent to those skilled in the art, which will be within the spirit and scope of the invention. Therefore, the invention should not be limited to just the described embodiment. To ascertain the full scope of the invention, the following claims should be referenced.