WO2014133482A1

WO2014133482A1 - Busbar clamp with a cup-shaped member

Info

Publication number: WO2014133482A1
Application number: PCT/US2013/027770
Authority: WO
Inventors: Richard M. Trussler
Original assignee: Schneider Electric USA, Inc.
Priority date: 2013-02-26
Filing date: 2013-02-26
Publication date: 2014-09-04

Abstract

To electrically couple a pair of busbars together, a busbar clamp is positioned between the busbars and exposed portions of each busbar are positioned between first and second clamp halves of the busbar clamp. The first clamp half includes a flange portion integral with a cup portion. The flange portion forms a first clamping surface of the busbar clamp. The second clamp half forms a second clamping surface of the busbar clamp. A saddle is positioned within the cup portion such that the saddle partially protrudes through an aperture in a base of the cup portion. A biasing member is positioned within the cup portion and between the saddle and the cup portion to bias the saddle away from the cup portion. A bolttype fastener is threadably engaged with a threaded bore of the second clamp half to keep the busbar clamp in an assembled configuration.

Description

BUSBAR CLAMP WITH A CUP-SHAPED MEMBER

FIELD OF THE INVENTION

[0001] The present invention relates generally to clamps and, more particularly, to a busbar clamp with a cup-shaped member.

BACKGROUND OF THE INVENTION

[0002] A busbar system typically includes two or more busbars and one or more busbar clamps for connecting two busbars together. Each busbar clamp is used to physically and electrically connect two busbars together. Typically, busbar clamps are tightened using a torque wrench to apply a desired predetermined amount of clamping force (e.g., not too much and not too little clamping force). Torque wrenches require additional space around the busbar clamp to use as compared to a standard non-torque wrench. Further, torque wrenches are more expensive than non-torque wrenches.

[0003] Thus, a need exists for an improved apparatus and system without requiring a torque wrench for installation. The present disclosure is directed to satisfying one or more of these needs and solving other problems.

SUMMARY OF THE INVENTION

[0004] The present disclosure is directed to providing a busbar clamp that can be tightened with a standard wrench (e.g., non-torque wrench) to electrically and physically connect a pair of busbars with a guaranteed minimum amount of contact pressure. A pair of busbars can be electrically and physically connected by positioning a busbar clamp between the busbars. Exposed portions of each busbar are positioned between first and second clamp halves of the busbar clamp while a fastener (e.g., a bolt) of the busbar clamp is in a loosened position. The fastener is then tightened from the loosened positioned to a maximum tightened position by rotating the fastener using the standard wrench (e.g., a non-torque wrench). Once the fastener is tightened, a biasing member positioned within a cup-shaped portion of the first clamp half causes the first and the second clamp halves to provide the guaranteed minimum amount of contact pressure on the busbars. The first clamp half includes a flange portion integral with the cup-shaped portion. The flange portion forms a first clamping surface of the busbar clamp. The second clamp half forms a second clamping surface of the busbar clamp. A saddle is positioned within the cup portion such that the saddle partially protrudes through an aperture in a base of the cup portion. The biasing member is positioned between the saddle and the cup portion to bias the saddle away from the cup portion, which is what causes the busbar clamp to provide the guaranteed minimum amount of clamping force. The fastener is threadably engaged with a threaded bore of the second clamp half such that when the fastener is tightened to the maximum tightened position, a bottom surface of the saddle abuts the second clamp half, which prevents further tightening of the fastener (e.g., the fastener is tightened to its maximum tightened position).

[0005] The foregoing and additional aspects and implementations of the present disclosure will be apparent to those of ordinary skill in the art in view of the detailed description of various implementations and/or aspects, which is made with reference to the drawings, a brief description of which is provided next.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings.

[0007] FIGS. 1A and IB are a perspective views of a busbar clamp according to some implementations of the present disclosure;

[0008] FIGS. 2 A and 2B are exploded perspective views of the busbar clamp of

FIGS. 1A and IB;

[0009] FIGS. 3A and 3B are cross-sectional views of the busbar clamp of FIGS. 1A and IB; and

[0010] FIGS. 4A and 4B are perspective views of the busbar clamp of FIGS. 1A and IB positioned within a housing.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0011] Although the present disclosure will be described in connection with certain aspects and/or implementations, it will be understood that the present disclosure is not limited to those particular aspects and/or implementations. On the contrary, the present disclosure is intended to cover all alternatives, modifications, and equivalent arrangements and/or implementations as may be included within the spirit and scope of the present disclosure as defined by the appended claims.

[0012] Words of degree, such as "about", "substantially", and the like are used herein in the sense of "at, or nearly at, when given the manufacturing, design, and material tolerances inherent in the stated circumstances" and are used to prevent the unscrupulous infringer from unfairly taking advantage of the invention disclosure where exact or absolute figures and operational or structural relationships are stated as an aid to understanding the invention.

[0013] Referring generally to FIGS. 1A to 2B, a busbar clamp 10 is shown for electrically coupling a pair of busbars 5a,b. While the busbars 5a,b are shown as round busbar conductors (e.g., busbars having a circular cross-section), the busbars 5a,b can have a variety of shapes and sizes (e.g., rectangular cross-section, square cross-section, etc.). The busbar clamp 10 includes a first clamp half 20, a second clamp half 40, a saddle 60, a fastener 80, biasing member(s) 100 (FIGS. 2A and 2B), and optionally a housing 110 (FIGS. 4A and 4B).

[0014] As best shown in FIGS. 2A and 2B, the first clamp half 20 has a flange portion 22 and a cup portion 24. The cup portion 24 has a cup-shape including a rim 25 and a base 26. By "cup-shape" it is generally meant that cup portion 24 is generally shaped like a typical drinking cup (with modifications as described herein) having a generally cylindrical body that terminates with an open rim on one end and a closed base on the other end. The term "portion" in flange portion 22 and cup portion 24 refers to the fact that the flange and the cup are portions of an assembly, namely the busbar clamp 10. The rim 25 is shown as being generally circular but can alternatively have any shape (e.g., square, oval, triangular, etc.). The base 26 of the cup portion 24 is shown as being substantially flat but alternatively can be non-flat (e.g., curved, angled, etc.). The base 26 includes an aperture 27 (best shown in FIG. 2B) such that respective portions of the saddle 60 and the fastener 80 can pass therethrough as described in further detail herein and as shown in FIGS. 3A and 3B.

[0015] The flange portion 22 of the first clamp half 20 is integral with the rim 25 of the cup portion 24. That is the flange portion 22 and the cup portion 24 are integrally formed as a single component/part. In such implementations, both the flange portion 22 and the cup portion 24 of the first clamp half 20 are made of the same electrically conductive material, such as, for example, copper, aluminum, a combination thereof, etc. [0016] Alternatively, the flange portion 22 and the cup portion 24 can be separate components/parts that are attached together, such as, for example, by welding, gluing, press fitting (e.g., the cup portion 24 can be press fit into a recess of the flange portion 22), etc. In such alternative implementations, both the flange portion 22 and the cup portion 24 of the first clamp half 20 can be made of the same electrically conductive material or different materials. For example, the flange portion 22 can be made of copper and the cup portion 24 can be made of steel. For another example, the flange portion 22 can be made of copper and the cup portion 24 can be made of plastic.

[0017] The flange portion 22 of the first clamp half 20 has an upper major surface 22a (FIG. 2A) opposing a bottom major surface 22b (FIG. 2B). At least a portion of the bottom major surface 22b of the flange portion 22 is a first clamping surface of the busbar clamp 10. That is, at least a portion of the bottom major surface 22b of the flange portion 22 acts as the first clamping surface when the busbar clamp 10 is used to couple the busbars 5a,b. By "first clamping surface" it is meant to include the portion of the bottom major surface 22b that physically contacts the busbars 5a,b when the busbar clamp 10 is used to mechanically clamp and electrically couple the busbars 5a,b together. The busbar clamp 10 can mechanically couple any part of the busbars 5a,b together, such as an exposed end of a busbar or a surface portion of a busbar.

[0018] The second clamp half 40 has an upper major surface 40a (FIG. 2A) opposing a bottom major surface 40b (FIG. 2B). At least a portion of the upper major surface 40a of the second clamp half 40 is a second clamping surface of the busbar clamp 10. That is, at least a portion of the upper major surface 40a of the second clamp half 40 acts as the second clamping surface when the busbar clamp 10 is used to couple the busbars 5a,b. By "second clamping surface" it is meant to include the portion of the upper major surface 40a that physically contacts the busbars 5a,b when the busbar clamp 10 is used to couple the busbars 5a,b. As shown in FIGS. 1A and IB, the first clamping surface of the busbar clamp 10 opposes the second clamping surface of the busbar clamp 10 when the busbar clamp 10 is in the assembled configuration.

[0019] The second clamp half 40 further includes a threaded bore 42 (FIGS. 2A and 2B) for threadingly coupling with the fastener 80 to maintain the busbar clamp 10 in an assembled configuration (FIGS. 1A, IB, 3A, 3B). As described in further detail below, the busbar clamp 10 can be converted and/or switched between a loosened assembled configuration (FIG. 3A) and a fully tightened assembled configuration (FIG. 3B) by rotating the fastener 80.

[0020] As best shown in FIGS. 2A and 2B, the saddle 60 has a generally cylindrical throughbore 62 and a flange 64. The saddle 60 can be made of a variety of materials, such as, for example, copper, aluminum, steel, plastic, etc. In the assembled configuration of the busbar clamp 10 (FIGS. 1A, IB, 3A, and 3B), the saddle 60 is positioned substantially within the cup portion 24 of the first clamp half 20 such that a bottom surface 65 (FIG. 2B) of the saddle 60 extends through the aperture 27 (FIG. 2B) in the base 26 of the cup portion 24, which is best shown in FIGS. 3A and 3B. The aperture 27 provides access for the saddle 60 to abut and/or contact the second clamp half 40. Specifically, in the installed (e.g., the busbar clamp 10 is attached between two busbars) and fully tightened assembled configuration of the busbar clamp 10 (best shown in FIG. 3B), the bottom surface 65 (FIG. 2B) of the saddle 60 contacts the upper major surface 40a (FIG. 2A) of the second clamp half 40 about the threaded bore 42.

[0021] As shown in the figures, the biasing members 100 correspond to a multitude of disk springs. In the assembled configuration of the busbar clamp 10 (FIGS. 1A, IB, 3 A, 3B), the biasing members 100 are positioned about the generally cylindrical throughbore 62 of the saddle 60. The disk springs can be, for example, Belleville washers, coned-disc springs, conical spring washers, Belleville spring, cupped spring washer, etc. Alternatively to the biasing members 100 corresponding to a multitude of disk springs, the biasing members 100 can be one or more coil springs (not shown). The biasing members 100 are positioned within the cup portion 24 of the first clamp half 20. In particular, the biasing members 100 are positioned between the flange 64 of the saddle 60 and the base 26 of the cup portion 24. As such, the biasing members 100 bias the flange 64 and the base 26 away from one another when the busbar clamp 10 is in the fully tightened assembled configuration, which is shown in FIG. 3B. By "fully tightened assembled configuration" it is meant to include the configuration of the busbar clamp 10 when the fastener 80 is tightened to a maximum tightened position by screwing down the fastener 80 such that the bottom surface 65 of the saddle 60 contacts the upper major surface 40a (FIG. 2A) of the second clamp half 40 about the threaded bore 42 and cannot be tightened further, which is shown in FIG. 3B.

[0022] The fastener 80 includes a head 82 and a shaft 84. The shaft 84 has a first end attached to the head 82 and a second opposing end spaced from the head 82. Adjacent to the second end of the shaft 84, the shaft 84 includes a threaded section 86 and a notch 88. The threaded section 86 is configured to threadingly engage with the threaded bore 42 (FIGS. 2 A and 2B) of the second clamp half 40. In particular, when the busbar clamp 10 is in the assembled configuration (FIGS. 1A, IB, 3A, and 3B), the fastener 80 is positioned through the throughbore 62 of the saddle 60 and can be tightened (e.g., screwed in, rotated clockwise, etc.) and/or loosened (e.g., unscrewed, rotated counterclockwise, etc.) by rotating the head 82 of the fastener 80 using a tool (e.g., a wrench, a screw driver, etc.) such that the threaded section 86 of the shaft 84 threadingly engages or disengages the threaded bore 42 of the second clamp half 40. Specifically, the threaded section 86 threadingly engages the threaded bore 42 when a tool is used to rotate the fastener 80 in a first direction (e.g., clockwise), thereby tightening the fastener 80. Similarly, the threaded section 86 threadingly disengages the threaded bore 42 when the tool is used to rotate the fastener 80 in a second direction opposite the first direction (e.g., counterclockwise), thereby loosening the fastener 80.

[0023] In some implementations of the present disclosure, the fastener 80 is rotatable between a loosened positioned (FIG. 3A) and the maximum tightened position (FIG. 3B) by no more than a single turn of the fastener 80. By "loosened position" it is meant that the fastener 80 is threadingly engaged with the threaded bore 42 but not tightened to the maximum tightened position such that the busbars 5a,b can be inserted and/or removed from the space between the first and the second clamp halves 20, 40. That is, the fastener 80 can be rotated a single turn or less (e.g., 360 degrees or less) and place the busbar clamp 10 into its maximum tightened configuration (FIG. 3B). As such, the busbar clamp 10 can be readily installed by placing the busbars 5a,b between the first and the second clamp halves 20, 40 and then rotating the fastener 80 no more than a single turn (e.g., 360 degrees or less) to fully tightened the busbar clamp 10, thereby electrically coupling the busbars 5a,b together.

[0024] Further, when the fastener 80 is tightened to the maximum tightened position (FIG. 3B), the first and the second clamping surfaces of the busbar clamp 10 apply a guaranteed minimum amount of contact pressure on the busbars 5a,b by virtue of the biasing members 100. In some implementations of the present disclosure by "guaranteed minimum amount" it is meant, for example, that the busbar clamp 10 exerts a minimum amount of contact force on the busbars 5a,b to prevent the busbars 5a,b from being removed (e.g., pulled away from) from the busbar clamp 10 in the assembled and fully tightened position (e.g., FIGS. 1A, IB, and 3B) by a hand of an average human. The guaranteed minimum amount of contact pressure is a function of spring constant(s) of the biasing member(s) 100. For example, when the biasing members 100 include a plurality of disk springs, the guaranteed minimum amount of contact pressure is based on a combined spring constant of the plurality of disk springs. The number and/or type of biasing members selected for use in the busbar clamp 10 can depend on the size of the busbars 5a,b and the load designed to be distributed therethrough. For example, in some implementations, the combined spring constant of the plurality of disk springs is between about fifty kN/mm and about seventy-five kN/mm.

[0025] The fastener 80 is designed to be tightened to the maximum tightened position using a non-torque wrench. For example, a standard wrench like an Allen wrench or even a screw driver (e.g., flat-head screw driver or Phillips screw driver) can be used to tighten the fastener 80 to its maximum tightened position. As such, the relatively expensive and relatively physically larger torque wrench is unnecessary and unneeded to tighten the fastener 80. Thus, the fastener 80 can be tightened and loosened in relatively smaller areas. Further, the housing 110 (FIGS. 4 A and 4B) of the busbar clamp 10 can include a relatively smaller tool aperture 122 for providing access to the head 82 of the fastener 80.

[0026] When the fastener 80 is tightened to the maximum tightened position, many forces are exerted throughout the busbar clamp 10 by the biasing members 100 that aid in coupling the busbars 5a,b with the guaranteed minimum amount of contact force. Specifically, the biasing members 100 are configured to exert a first force in a first direction (e.g., downward relative to the orientation shown in FIGS. 2A and 2B) on the base 26 of the cup portion 24 of the first clamp half 20. Exertion of such a first force causes the flange portion 22 of the first clamp half 20 to exert a second force in the first direction (e.g., downward) on the busbars 5a,b.

[0027] Similarly, the biasing members 100 are configured to exert a third force in a second direction opposite the first direction (e.g., upward relative to the orientation shown in FIGS. 2 A and 2B) on the flange 64 of the saddle 60. Exertion of such a third force causes (i) the saddle 60 to exert a fourth force in the second direction (e.g., upward) on the head 82 of the fastener 80, (ii) the fastener 80 to exert a fifth force in the second direction (e.g., upward) on the threaded bore 42 of the second clamp half 40, and (iii) the second clamp half 40 to exert a sixth force in the second direction (e.g., upward) on the busbars 5a,b. In some implementations of the present disclosure, the first, the second, the third, the fourth, the fifth, and the sixth forces are substantially equal. [0028] As best shown in FIGS. 2A and 2B, the notch 88 of the shaft 84 of the fastener 80 can at least partially receive a rotation limiter 89 therein, such as, for example, an e-clip, a pin, etc. The rotation limiter 89 can be coupled to the shaft 84 by way of the notch 88 to aid in preventing the fastener 80 from being completely unthreaded from the threaded bore 42 of the second clamp half 40. As the fastener 80 is rotated towards its loosened position (FIG. 3A) from its maximum tightened position (FIG. 3B), the rotation limiter 89 is moved (e.g., translated) closer to the bottom major surface 40b (FIG. 2B) of the second clamp half 40 and at some point, the rotation limiter 89 abuts the bottom major surface 40b (shown in FIG. 3A), thereby preventing further unscrewing of the fastener 80 and maintaining the busbar clamp 10 in an assembled, but loosened configuration (FIG. 3 A).

[0029] Referring to FIGS. 4A and 4B, the assembled configuration of busbar clamp 10 of FIGS. 1A and IB is shown inside of the housing 110. The housing includes a body 115 and a lid 120. The body 115 of the housing 110 has a pair of busbar apertures 116a,b for providing access therein such that the busbars 5a,b can be positioned between the first and the second clamp halves 20, 40. The lid 120 of the housing 110 has the tool aperture 122 adjacent to the head 82 of the fastener 80 such that the housing 110 is configured to provide access to the fastener 80 without having to remove the lid 120 from the body 115. The lid 120 can be fixedly attached to the body 115 (e.g., sonically welded thereto, glued, etc.) or removably attached to the body 115 (e.g., press fitted, etc.). The housing 110 can be made of one or more materials, such as, for example, any electrically insulating material (e.g., plastic).

[0030] According to some implementations of the present disclosure, the base 26 (FIG. 2B) of the cup portion 24 of the first clamp half 20 is substantially flat and is spaced from the bottom major surface 22b leaving a predetermined distance between the bottom major surface 22b (FIG. 2B) including the first clamping surface and the upper major surface 40a (FIG. 2A) including the second clamping surface when the busbar clamp 10 is in the assembled configuration (FIGS. 1A and IB). That is, the base 26 being spaced from the bottom major surface 22b ensures that the upper major surface 40a will always be spaced from the bottom major surface 22b by the predetermined distance when the busbar clamp 10 is in the assembled configuration (FIGS. 1A and IB). That predetermined distance can be varied (e.g., increased or decreased) against a force of the biasing members' tension in the cup portion 24 of the first clamp half 20. Further, the varied predetermined distance is slightly less than an average thickness of the busbars 5a,b to be clamped. By "slightly less" it is meant to include any amount, even on the atomic scale (e.g., one nanometer less, one micrometer less, one millimeter less, etc.). As those skilled in the art will appreciate, a small amount of deformation will occur between the clamping and busbar surfaces when a clamping force is applied, and this clamping action will cause the predetermined distance to be slightly less than the average thickness of the busbars 5a,b.

[0031] While particular aspects, implementations, and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the present disclosure as defined in the appended claims.

Claims

What is claimed is:

1. A busbar clamp for electrically coupling a pair of busbars, comprising:

a first clamp half including a flange portion and a cup portion, the cup portion having a rim and a base, the flange portion being integral with the rim, the flange portion having an upper major surface opposing a bottom major surface, the bottom major surface of the flange portion being a first clamping surface of the busbar clamp;

a second clamp half having an upper major surface opposing a bottom major surface, the upper major surface of the second clamp half being a second clamping surface of the busbar clamp opposing the first clamping surface of the busbar clamp;

a saddle positioned substantially within the cup portion of the first clamp half and partially extending through an aperture in the base of the cup portion, the saddle having a generally cylindrical throughbore and a flange; a biasing member positioned within the cup portion of the first clamp half and between the flange of the saddle and the base of the cup portion so as to bias the flange and the base away from one another; and

a fastener including a head and a shaft, the shaft extending from the head of the fastener, through the throughbore of the saddle, and being configured to threadably engage a threaded bore of the second clamp half.

2. The busbar clamp of claim 1, wherein the fastener is configured to threadably engage the threaded bore of the second clamp half and be tightened to a maximum tightened position such that a bottom surface of the saddle abuts the upper major surface of the second clamp half.

3. The busbar clamp of claim 2, wherein the fastener is rotatable between a loosened positioned and the maximum tightened position, and wherein the fastener is configured to be rotated from the loosened positioned to the maximum tightened position by no more than a single turn of the fastener.

4. The busbar clamp of claim 2, wherein in response to the fastener being tightened to the maximum tightened position, the first and the second clamping surfaces of the busbar clamp are configured apply a guaranteed minimum amount of contact pressure on the pair of busbars by virtue of the biasing member.

5. The busbar clamp of claim 4, wherein the fastener is configured to be tightened to the maximum tightened position using a non-torque wrench.

6. The busbar clamp of claim 4, wherein the biasing member is positioned about the generally cylindrical throughbore of the saddle.

7. The busbar clamp of claim 4, wherein the biasing member is configured to exert a first force in a first direction on the base of the cup portion which causes the flange portion of the first clamp half to exert a second force in the first direction on the pair of busbars.

8. The busbar clamp of claim 7, wherein the biasing member is configured to exert a third force in a second direction opposite the first direction on the flange of the saddle which causes (i) the saddle to exert a fourth force in the second direction on the head of the fastener, (ii) the fastener to exert a fifth force in the second direction on the threaded bore of the second clamp half, and (iii) the second clamp half to exert a sixth force in the second direction on the pair of busbars.

9. The busbar clamp of claim 8, wherein the first, the second, the third, the fourth, the fifth, and the sixth forces are substantially equal.

10. The busbar clamp of claim 1, further comprising a rotation limiter coupled to the shaft of the fastener, the rotation limiter being configured to prevent the fastener from being completely unthreaded from the threaded bore of the second clamp half.

11. The busbar clamp of claim 10, wherein the rotation limiter is an e-clip.

12. The busbar clamp of claim 1, further comprising a housing having a body and a lid, the first and the second clamp halves being positioned within the body of the housing, the body of the housing including a pair of apertures configured to receive the pair of busbars therein, the lid of the housing including an aperture adjacent to the head of the fastener such that the housing is configured to provide access to the fastener without having to remove the lid from the body.

13. The busbar clamp of claim 12, wherein the housing is made of an electrically insulating material.

14. The busbar clamp of claim 1, wherein the first clamp half and the second clamp half are made of copper.

15. The busbar clamp of claim 14, wherein the saddle is made of steel.

16. The busbar clamp of claim 1, wherein the first and the second clamp halves are configured to receive the pair of busbars therebetween.

17. A busbar system, comprising :

a first busbar having a first exposed portion;

a second busbar having a second exposed portion;

a busbar clamp positioned between the first and the second busbars and being configured to operatively couple the first exposed portion of the first busbar to the second exposed portion of the second busbar, the busbar clamp including: a first clamp half including a flange portion and a cup portion, the flange portion forming a first clamping surface of the busbar clamp;

a second clamp half forming a second clamping surface of the busbar clamp; a saddle positioned substantially within the cup portion and partially protruding through an aperture in a base of the cup portion;

a biasing member positioned within the cup portion and between the saddle and the cup portion to bias the saddle away from the cup portion; and a fastener threadably engaged with a threaded bore of the second clamp half thereby maintaining the busbar clamp in an assembled configuration.

18. The busbar system of claim 17, wherein the flange portion of the first clamp half is made of a first material and the cup portion of the first clamp half is made of a second material different than the first material.

19. The busbar system of claim 18, wherein the first material is copper and the second material is steel.

20. A busbar clamp with guaranteed contact pressure, comprising:

a cup-shaped clamp half having a first clamping surface, the cup-shaped clamp half having a cup portion with a substantially flat bottom side and a flange portion, the flange portion containing the first clamping surface of the cup-shaped clamp half;

a second substantially planar clamp half having a second clamping surface;

a saddle positioned within the cup portion and being configured to confine a spring within the cup portion; and

a bolt passing through the cup portion and into threaded engagement with the second substantially planar clamp half,

whereby the substantially flat bottom side of the cup portion is spaced from the first clamping surface leaving a predetermined distance between the first and the second clamping surfaces, which predetermined distance can be varied against a force of the spring's tension in the cup portion, the predetermined distance between slightly less than an average thickness of the busbars to be clamped.