GB2367957A

GB2367957A - An electrical earth clamp

Info

Publication number: GB2367957A
Application number: GB0024598A
Authority: GB
Inventors: Richard Stephen Cur Litchfield
Original assignee: KOMPRESS HOLDINGS Ltd
Current assignee: KOMPRESS HOLDINGS Ltd
Priority date: 2000-10-07
Filing date: 2000-10-07
Publication date: 2002-04-17
Also published as: GB0124060D0; GB2367960B; GB2367960A; GB0024598D0

Abstract

An electrical earth clamp 10 includes a rigid body 11 supporting a clamping surface 12. A shear headed, electrically conductive screw 16 goes through an aperture 13 in the body 11. As the screw is tightened an article 30 such as a radiator is clamped between the screw and the surface. The screw has a conical tip 22 to pierce any coating (eg paint or rust) on the article and to make electrical contact. As the screw is tightened further, the head 14 shears off, leaving a threaded stud 16A. A nut 21 screws onto this stud to secure an earth terminal 18 to the clamp.

Description

AN ELECTRICAL EARTH CLAMP

The invention relates to an electrical earth clamp for earthing electrically conducting articles and in particular for earthing eg. heating radiators, sinks, baths, metal cladding, working surfaces of metal, trunking, ducting and plumbing components.

There is a requirement to earth such articles to reduce the risk of serious accidents in the event of such an article becoming charged or electrically live. This can occur as a result eg. of wiring faults, DIY errors and lightning strikes.

GB 2195837 discloses an electrical earth connector for earthing a radiator.

The connector includes a solid, metallic body and a clamp screw threadedly engaged in an aperture intersecting a slot provided in the body. A laminar part of a radiator or another electrically conducting article may be clamped in the slot by tightening the clamp screw. The connector also includes a connecting screw threadedly engaged in the body for connecting an earth wire to the body.

The clamp screw and the connecting screw are located on opposite sides of the body so that a user must have access to both sides of the body when fitting the connector to an article. When it is used on a radiator, the connector is typically positioned on a flange extending along a bottom edge of the radiator. This location allows access to both of the screws but also means that one side of the body of the connector, including one of the screws, is visible from the front of the radiator. This is unsightly and also means that the connector is visible eg. to children who may tamper with it.

According to a first aspect of the invention there is provided an electrical earth clamp according to Claim 1.

The provision of a shear headed screw means that the connector only requires a single aperture on one side of the body. A user therefore only requires access to one side of the clamp when fitting it to an electrically conducting article. This means that it is possible to secure the connector on a fin, for example, provided on the back of a radiator, in order to hide the connector from view.

Also, if the connector is fitted to a flange on the bottom edge of a radiator, the connector may be arranged so that the shear headed screw is located on the back of the radiator. This hides the shear headed screw and consequently provides a more aesthetically pleasing arrangement than that of the prior art connector.

The shear headed screw additionally reduces the number of components of the clamp, compared with the prior art connectors. Since the earth clamps are typically packed into bags either by count-weighing or by"outworkers" working manually, a reduction in the number of components is especially advantageous.

The shear headed screw also advantageously provides essentially permanent, tamper-proof attachment of the clamp to the electrically conducting article since it is relatively difficult to unscrew the screw after shearing of the shear head.

In preferred embodiments of the invention the body of the clamp is electrically conducting. This provides an earthing path between the

clamping surface and the screw via the body ; although it is possible to construct embodiments of the invention in which the body is non conducting or insulated, in which case the earthing path is via the screw.

Preferably the screw has a projection, especially a conical tip, for deforming the electrically conducting article to improve electrical contact between the screw and the article.

The provision of eg. a conical point on the screw tip causes a clean electrical connection between the screw and an article because the tip pierces or removes any coating (eg. of paint or oxides) on the surface of the electrically conducting article.

Use of a conical tip also advantageously limits movement of the earth clamp relative to the surface of the conducting article during tightening of the screw.

Conveniently the protruding stud is threaded to receive a member, having a portion including a complementary thread, for securing the earth terminal to the stud. This advantageously permits securing of an earth terminal having an eye or a spade connector to the stud by means of a nut and a shakeproof washer.

The body may include a recess formed in the clamping surface opposite the through-going aperture.

Conveniently the clamping surface is integral with the body. More specifically the clamping surface and the through-going aperture are respectively formed in juxtaposed limbs of a U-section channel member

defining the body. These features advantageously permit manufacture of a large number of the bodies from eg. a length of U-section metal bar. However in other embodiments of the invention the clamping surface need not be integral with the body. Thus for example the surface may be part of a further member that is secured to the body eg. by means of a moveable ball and socket joint or any of a number of other arrangements.

Also the body need not be a U-section channel member. It is sufficient merely that the tightening of the screw is reacted by the clamping surface to define the clamping function.

Optionally the clamp may include a locknut threadedly engaged with the screw for locking the screw relative to the body after tightening of the screw. This feature further reduces the risk of loosening of the clamp after installation.

According to a second aspect of the invention there is provided a kit of parts as defined in Claim 10 and claims dependent therefrom.

There follows a description of a preferred embodiment of the invention, by way of non-limiting example, with reference to the accompanying drawings in which: Figures la and lb are cross-sectional views of an earth clamp according to the invention.

Referring to the drawings there is shown an electrical earth clamp 10 comprising a body 11 in the form of an elongate, U-section channel member that in the preferred embodiment is formed of eg. solid brass or another

electrically conducting material. Non-ferrous, conducting metals are preferred in order to minimise the risk of changes in resistivity of the material of the body 10 as a result of corrosion in use.

In other embodiments of the invention the body 11 may be manufactured from an insulated material; or a non-conducting material.

Body 11 supports a clamping surface 12 defined by an inner wall of one of the limbs of the U-section.

Body 11 also supports a threaded, through-going aperture 13 that extends between a location juxtaposed to the clamping surface and an outer surface of the body 11.

In practice aperture 13 extends through the opposite limb of the U shaped cross section, to that supporting the clamping surface 12.

A shear headed, electrically conducting screw 16 that in the embodiment shown has a conventional hex head 14 is threadedly engaged in aperture 13, by virtue of screw 16 having an external thread that is complementary to the thread of aperture 13.

As is evident from the drawing figures, tightening of the screw 16 (by a conventional means such as engagement of hex head 14 by a spanner or pliers) causes the end of screw 16 remote from head 14 to protrude from aperture 13 into a slot 17 defined by the limbs of the U-section of body 11.

Such tightening may be employed to clamp an article such as radiator cooling fin 30 relative to clamping surface 12, whereby earth clamp 10 is

secured to the article 30.

Since the screw is electrically conducting, engagement of the screw with the article during such tightening provides an electrically conducting path between the article 30 and the screw 16.

Since screw 16 is shear headed, further tightening of screw 16 after clamping of the article 30 in the slot 17 causes the head 14 of the screw to shear therefrom.

As shown in the drawings the shear head forming part of screw 16 is defined by a tapered shank extending between hex head 14 and the threaded portion of screw 16, but other forms of shear head (such as a machined groove or cross drillings) that are well known in the art may alternatively be employed.

The part 16a (Figure I b) of screw 16 remaining after such shearing defines a stud protruding from a surface of the body 11.

Stud 16a is sufficiently long as to permit securing to the stud 16a of an earth terminal 18 having an aperture therein, eg. by means of a conventional nut 21 that may be screwed onto the protruding part of stud 16a. Terminal 18 may be eg. a"ring"or eye-type; or a spade-type terminal.

Earth terminal 18 has conductingly secured thereto an earth wire 19, that may be connected to a suitable ground at a location remote from clamp 10.

If necessary a shakeproof washer (not visible in the drawing figures) may be employed in a conventional manner to assist in securing terminal 18.

Preferably the body 11 of clamp 10 is electrically conducting, whereby earthing paths from the article 30 to the terminal 18 exist via both the conducting screw 16 and the body 11.

As shown screw 16 has at its end remote from head 14 a conical tip 22 whose function is to scrape the article 30 or under some circumstances (eg. when attaching the clamp 10 to an article 30 other than a pipe) deform it to a limited extent, for the purpose of improving electrical contact between the screw 16 and the article 30.

Such action may take the form of eg. piercing of a coating (such as paint or a layer of oxide) that overlies the surface of article 30 adjacent screw 16; indenting or bending article 30; or scraping of a coating from article 30.

To this end in other embodiments of the invention the free end of screw 16 may include other forms of projection, or plural projections.

As noted, the protruding portion of screw 16 defining stud 16a after shearing of head 14 is threaded. However, in other embodiments of the invention alternative means of securing earth terminal 18 to stud 16a may be employed.

Such means include but are not limited to the provision of an annular groove in stud 16a, at a location spaced from body 11 after tightening of screw 16.

Such a groove could receive and retain eg. a circlip or other resiliently deformable fastener whose function is to retain an eye-type terminal 18 trapped between the circlip and the body 11. However this embodiment is not presently preferred because of difficulties in assuring firm contact

between the earth terminal and the stud 16a following attachment of the circlip. As shown in the drawings, clamping surface 12 includes a recess 23 located opposite aperture 13.

In the embodiment shown optional recess 23 is of complementary profile to the conical tip 22 of screw 16. Recess 23 assists in permitting deformation of clamped article 30, on tightening of screw 16.

In addition the conical tip 22 of screw 16 reduces the tendency of clamp 10 to skid relative to article 30 during initial tightening of clamp 10.

Other arrangements of earth clamp are possible, within the scope of the invention, in which eg. the clamping surface 12 is moveable relative to the remainder of body 11. This may be achieved eg. by virtue of clamping surface 12 being defined by a member that is separate from body 11 but is secured thereto by virtue of eg. a ball and socket joint in the manner of the clamping pad of a G-cramp.

Also of course if desired the direction of through-going aperture 13 may differ from that shown in the drawings.

Typically the length of the body 11 in the direction perpendicular to the plane of Figures la and 1 b is approximately 1 cm.

Optionally the clamp assembly of the invention may include eg. a locknut 27 threadedly received on the protruding portion 16a, for the purpose of locking the screw 16 in position after tightening.

The invention also resides in a kit of parts comprising an electrical earth clamp 10 as defined herein ; an earth terminal 18 that is securable to the protruding stud of the earth clamp 10 after clamping thereof to an article 30; and a fastener such as nut 21 for securing the earth terminal to the protruding stud. An optional locknut 27 may also be provided.

The kit may optionally include a plurality of such components; and optionally a tool (such as a spanner) for tightening the screw and subsequently shearing the head therefrom.

The tool is not visible in the drawings, but may be eg. a pressed steel spanner having formed therein an hexagonal aperture of the appropriate size.

In use of the clamp 10 an electrician would initially secure a body 11 to an article 30 requiring earthing, by screwing the screw 16 into aperture 13 until: 1. The screw 13 deforms, penetrates or otherwise firmly contacts the conducting material of article 30 to form an electrical path from article 30 via screw 16; and 2. Article 30 is firmly clamped against clamping surface 12.

The electrician may of course achieve this result through use of a tool included in a kit of parts as defined herein.

Further rotation of the head 14 of screw 16 causes shearing of head 14,

leaving a threaded stud 16a protruding from the outer surface of clamp 10. The electrician may then simply secure an earth terminal 18 to stud 16a, by screwing a nut 21 onto stud 16a (and if necessary adding a shakeproof washer).

If present a locknut 26 may at an appropriate time be tightened further to prevent unintended unscrewing of screw 16.

Claims

1. An electrical earth clamp comprising : a body supporting a clamping surface and a limb that is spaced from the surface and has formed therein a threaded, through-going aperture extending between a location juxtaposed to the clamping surface and an outer surface of the body; and a shear headed, electrically conducting screw; wherein the screw is threadedly receivable in the aperture, tightening of the screw allowing clamping of an article between the screw and the clamping surface engagement of the screw with the article providing an electrically conducting path between the article and the screw; and further tightening of the screw causing the head to shear from the screw the remaining part of the screw being sufficiently long as to provide a stud, protruding from a surface of the body, for securing to the stud an earth terminal in electrically conducting contact therewith.

2. An electrical earth clamp according to Claim 1 wherein the body is electrically conducting.

3. An electrical earth clamp according to Claim 1 or Claim 2 wherein the screw has a projection for deforming the article to improve electrical contact between the screw and the article.

4. An electrical earth clamp according to any preceding claim wherein the protruding stud is threaded to receive a member, having a portion including a complementary thread, for securing the earth terminal to the stud.

5. An electrical earth clamp according to any preceding claim wherein the clamping surface includes a recess formed in the clamping surface opposite the through-going aperture.

6. An electrical earth clamp according to any preceding claim wherein the clamping surface is integral with the body.

7. An electrical earth clamp according to Claim 6 wherein the clamping surface and the through-going aperture are respectively formed in juxtaposed limbs of a U-section channel member defining the body.

8. An electrical earth clamp according to any preceding claim wherein the longitudinal axis of the through-going aperture extends generally perpendicular to the clamping surface.

9. An electrical earth clamp according to any preceding claim including a locknut threadedly engaged with the screw for locking the screw relative to the body after tightening of the screw.

10. A kit of parts comprising: an electrical earth clamp according to any preceding claim; an earth terminal that is securable to the protruding stud; and a fastener for securing the earth terminal to the protruding stud.

11. A kit according to Claim 10 wherein the protruding stud is threaded and the fastener is a nut having a thread that is complementary to the thread of the stud.

12. A kit according to Claim 10 or Claim 11 including a tool for

tightening the screw and subsequently shearing the head therefrom.

13. A kit according to any of Claims 10 to 12 including a plurality of the earth clamps, a corresponding plurality of the earth terminals and a corresponding plurality of the fasteners.

14. An electrical earth clamp generally as herein described with reference to and/or as illustrated in the accompanying drawings.

15. A kit of parts generally as herein described.