Terminal Blocks for One-Side Wire Entry and Screw Access

The present application relates to novel electrical terminal blocks, especially those having screw fasteners for wires, in which the screws are accessible for operation at the wire-entry side of the structure.

The present invention is discussed here and it is described below in relation to a terminal block for making connections to the terminals of a printed-circuit board ("P-C board") but, as will be readily understood, such terminal blocks may be used for other purposes in which a second set of wires (for example) replaces the P-C board.

Terminal connections to a printed circuit board may extend along one margin, or there may be multiple rows of connections along sides of the P-C board. Each connection should be highly dependable, and it should be reversible for releasing a wire that has once been secured to a P-C board terminal, so that another wire can be connected to that terminal of the P-C board. Moreover, the connection apparatus is to accommodate insertion of the wires at the same side where wire fasteners are to be accessible for operation by a screw-driver or other equivalent tool, e.g., an Allen wrench.

Many terminal blocks are known having wire securing devices operable to fasten or release an inserted wire at the wire entry side of the terminal block. Such terminal blocks may be compared--or contrasted--with the present novel terminal blocks. Known terminal blocks of the type required may be more expensive, bulky, complicated, etc. than those here involved, or they depend on a kind of wire fastener that does not instill a feeling in the user that the connections are highly stable and dependable, or are based on deformable nonreusable clamping members, or that, in operating the wire fasteners, undue stress may be developed at P-C board connections as the wire fasteners are being operated.

The exemplary terminal block described in detail below represents the presently preferred embodiment of the invention. Each wire fastener of that terminal block includes a screwoperated hollow clamp having one wall or jaw that shifts and clamps an inserted wire against one side of a contact member while the screw bears oppositely against the contact member. The wire and the screw both enter one end of the hollow in the clamping member, promoting operating access and wire entry at the same side of the terminal block. There is no tendency of the screw to become deflected due to the force it develops against the contact member because the screw is guided in the clamp in a manner that provides a deflection-nullifying reaction force. The contact member tends to stay in place as the screw fastener is being operated.

The nature of the invention including the foregoing and other aspects, some mentioned hereinafter, will be appreciated from the following detailed description of an illustrative embodiment which is shown in the accompanyign drawings.

In the drawings:

FIG. 1 is a fragmentary elevation of a novel terminal block, including part of a printed-circuit board shown in phantom;

FIG. 2 is a cross-section of the terminal block and the printed-circuit board as seen at the plane 2--2 of FIG. 1;

FIG. 3 is a fragmentary top plan view of the apparatus of FIG. 2; and

FIG. 4 is a cross-section of the clamp at the plane 4--4 in FIG. 2.

The terminal block includes a row of regularly spaced connecting devices only one of which is shown in FIGS. 2 and 3. (A fragment of a second connecting device appears in FIG. 1). Mount or enclosure 10 of electrical insulation provides an internal cavity 10a and a wire-entry passage 10b extending to an external opening 10c. A screw access opening 10d is also provided; both openings 10c and 10d are near each other, at the same side of mount 10.

Contact member 12 disposed largely in cavity 10a, has an external terminal 12a, a contact portion 12b and a tail 12c. At the bottom of enclosure 10, contact member 12 extends through an opening in the enclosure so that the contact member cannot move straight down or straight up, and so that contact member 12 cannot pivot clockwise about the point, near terminal 12a, where the contact member emerges from the enclosure. Counterclockwise pivoting is blocked by engagement of tail 12c with the enclosure.

Clamping member 14 (briefly "clamp") is a four-walled structure as of steel, including essentially parallel side walls 14a and spaced-apart end walls, i.e., jaw 14c and rear or bearing wall 14d. The end walls of the clamp diverge upward, in the direction of the common wire-entry and fastener-access side of the terminal block. Tangs 14e are staked in openings in one of the clamp's side walls, so that clamping member 14 is rigid and hollow. Screw threads 14f are swaged in opposite side walls 14a, close to bearing wall 14d.

Screw 16 has a head 16a, a conical end 16b remote from head 16a and, along its length, screw 16 is threaded and operable in screw threads 14f of the clamp. Screw threads 14f are close to rear wall 14d so that, in use, the threaded length of the screw bears against wall 14d. In a slight modification, screw threads 14f as shown in FIG. 4 would extend continuously from one side wall 14a to the other, across rear wall 14d. Side walls 14a and rear wall 14d guide the clamp along the screw and provide the required screw threads.

Mount 10 comprises two molded parts at opposite sides of the screw 16 and provides shoulders 10e and 10f. Head 16a bears against shoulder 10e of the mount when the screw is turned in the tightening direction, in which it draws clamping member 14 upward. Accordingly, shoulder 10e resists inward thrust of a screw driver against the screw. A wire is inserted via opening 10c, and along passage 10b to the space between contact portion 12b of member 12 and jaw 14c of the clamp member. The inserted wire and contact portion 12b and jaw or wall 14c are parallel to each other and they extend at a small acute angle to the screw axis. This angle, about 30.degree. in this example, is shown to scale in FIG. 2, which is otherwise enlarged. As the screw is tightened, wall 14c shifts upward and to the right, parallel to the screw's axis. One component of this motion is toward contact portion 12b and one component of motion is along the contact portion. As soon as jaw 14c presses a wire against contact portion 12b, the conical end 16b of the screw presses with equal force against the opposite side of contact portion 12b. In turn, the force of screw end 16b against contact portion 12b is balanced by the reaction of the screw mainly against wall 14d of the clamp. The clamping force developed by wall or jaw 14c and contact portion 12b is thus balanced by a reaction force of the screw against the contact portion; and this, in turn, is balanced by the bearing force that wall 14d provides for the screw. The wire-clamping stresses are thus contained within the four-wall metal clamping member 14. Smaller balanced forces develop along screw 16 between shoulder 10e and clamp 14.

Cavity 10 as seen in FIG. 2 has two opposite parallel surfaces 10g and 10h between which clamping member 14 is moved by screw 16. The wire clamping jaw is shown at nearly opposite extreme positions 14c and 14c'. In all positions of member 14, an ordinary wire inserted at opening 10c can only be admitted between contact member 12 and jaw 14c; it is blocked against entry behind jaw 14c (to the left of jaw 14c, 14c' in FIG. 2).

Screw 16 is captive in the insulation of enclosure 10. Shoulders 10f prevent removal of screw 16. Shoulders 10f also react against screw 16 when the screw is being unscrewed to release a wire. As the screw is being unscrewed, it bears against shoulders 10f and drives clamping member 14 downward, serving in a positive manner to release the clamping grip of a wire by parts 12b and 14c.

Downward shift of member 12 is blocked by engagement of contact member 12 (as shown) with the insulating mount; and upward shift of member 12 during tightening of the wire fastener is also blocked, in the manner described above. Consequently, the soldered (or other) joint of member 12 to an external circuit device is essentially isolated from stress and displacement. Obviously, positioning of contact member 12 in enclosure 10 could be modified for making it still more secure, if desired.

In an example, contact member 12 is a hard metal such as beryllium copper to resist deformation when screw 16 is being tightened. In this example, contact member 12 is 0.090 inch wide and 0.032 inch thick. Its end portion 12a is 0.040 inch wide where it passes through an opening in the P-C board PC. As usual, a metal foil or bonded film surrounds the opening in the P-C board where it is penetrated by each terminal 12a, and the joint is soldered at that point. That joint is not stressed in any significant degree as the connection device is tightened or loosened. A wire can be tightened in place, and another wire may be substituted if desired by loosening and re-tightening the wire fastener.

The wire-entry opening 10c and the nearby screw access opening 10d are at the same side of mount 10. Between those openings and on mount 10, there is a labeling strip 18.

It is evident that changes may be introduced in the described construction by those skilled in the art. For example, the wire enters the terminal block (as described above) along an angled path relative to the screw's axis, but cavity 10c may be rearranged to accommodate entry of a wire parallel to the screw's axis, such that a bend would form in the wire between the portion entering the terminal block and the wire's end portion that is gripped by parts 12b and 14c. Other modifications will be obvious. Consequently, the invention should be construed broadly in accordance with its true spirit and scope.