GB2117438A - Cable clamp - Google Patents

Abstract

A trefoil clamp comprises a U-bolt 5 of non-magnetic material and a keeper strap 14 extending across the bite of the U-bolt 5 and provided with end portions 16 outboard of the U-bolt arms to extending perpendicularly of the keeper in contact with parallel end portions 13 of such arms. The clamp provides an assembly which can clamp three electric cables therein with sufficient rigidity to resist the stresses occasioned by electromagnetic repulsive movement between the cables. <IMAGE>

Description

SPECIFICATION Trefoil cable clamp This invention relates to trefoil cable clamps, that is to say clamps intended to surround three electric cables to hold them as a unit in trefoil formation.

Under fault conditions with high currents flowing in the cables the electromagnetic repulsion tending to cause the cables to move away from each other creates high stresses in the clamp and difficulty has been experienced in designing a clamp which is able to counteract those stresses and at the same time is relatively inexpensive and convenient in use.

Those difficulties are enhanced because the clamps cannot be made entirely of steel (because of the need to avoid completely encircling the cables with magnetic material) and because the clamp should preferably be capable of holding the cables firmly together notwithstanding the considerable variation from their nominal diameters that such cables are likely to exhibit.

An object of the present invention is to provide a clamp which more nearly meets the above indicated desiderata than do prior art clamps.

The invention consists in a trefoil cable clamp, comprising a non-magnetic U-bolt and a keeper spanning the bite of the U-bolt and pierced by two clearance holes through which the limbs of the U-bolt respectively extend, characterised in that said keeper has end portions projecting perpendicularly from the remainder of the keeper adapted to lie flatly against the respective arms of the U-bolt.

Thus the keeper ends reinforce the bolt arms against shearing forces produced in the bolt where it penetrates the keeper as a result of applied forces from the cable tending to separate the arms of the U-bolt.

By way of example, a preferred embodiment of the above-described invention is described in more detail hereinafter with reference to the accompanying drawings.

Figure 1 is a front elevation of a trefoil clamp according to the invention with a portion of its keeper cut away.

Figure 2 is a sectional view taken on any one of the lines 2-2 of Figure 1.

Figure 3 is a sectional view taken on either of the lines 3-3 of Figure 1.

Figure 4 is a side elevation of the clamp of Figure 1.

In the illustrated embodiment of the invention a U-bolt 5 is manufactured from a stainless steel rod which is initially straight and has roll-formed or otherwise threaded end-portions 6.

The U-bolt 5 preferably backs up a U-shaped liner strap 7 which, when the clamp is in use, makes contact with the cables 8, thereby reducing the pressure on the cables 8 by spreading the load from the U-bolt 5 over a bigger area.

That liner strap 7 may be an extruded aluminium alloy strap having two locating ribs 9 on what becomes its outer face in the finished article and between which the U-bolt rod is a neat fit. In manufacture the liner strap is cut to length and the stainless steel rod is laid between the locating ribs with its threaded end-portions projecting beyond the ends of the strap. The assembly is then press-formed into the required U-shape and, for preference, at least parts 10 of the ribs 9 are crimped over so as to grip the U-bolt 5 tightly. In the finished article the U-bolt has a rounded centre portion 11 flanked by straight, diverging, arm portions 12 with an included angle of approximately 60% terminating in endportions 13 which are substantially parallel to each other and which are partly threaded at 6 as aforesaid.

A keeper 14, which may be a mild steel strap extends across the bite of the U-bolt 5. The keeper constitutes the base of a triangle of which the rounded centre portion 10 of the U-bolt 5 constitutes the apex. The parallel end-portions 13 of the U-bolt 5 extend through clearance holes 15 in the keeper 14.

In accordance with the invention, end portions 16 of the keeper 14 outboard of the U-bolt arms are extended perpendicularly of the remainder of the keeper in contact with the parallel end-portions 13 of those arms.

For preference, the clearance holes 15 are elongated holes and after the keeper strap has been shaped an end-portion of each hole 15 extends into a bent up end-portion 16 of the strap. This enables the ends of the U-bolt to make firm contact with the end-portions 16 of the keeper 14 withough the need for extreme precision in the manufacturing process.

In use, those portions of the U-bolt arms extending beyond the keeper are furnished with nuts 17 (and preferably washer 18) to enable the clamp to be secured to a suitable support structure and to draw the U-bolt towards the keeper to make firm engagement between the cables on the one hand and the U-bolt liner strap and keeper on the other hand.

Claims (6)

1. Atrefoil cable clamp comprising a nonmagnetic U-bolt and a keeper spanning the bite of the U-bolt and pierced by two clearance holes through which the limbs of the U-bolt respectively extend, characterised in that said keeper has end portions projecting perpendicularly from the remainder of the keeper adapted to lie flatly against the respective arms of the U-bolt.

2. A clamp according to claim 1 wherein said U-bolt comprises a rod having threaded end portions and a liner strap adapted to be interposed between the U-bolt and the cables to be clamped.

3. A clamp according to claim 2 wherein said liner strap is affixed to said U-bolt.

4. A clamp according to claim 3 wherein said liner strap includes two locating ribs projecting from and extending along its outer face between which said U-bolt lies; at least a portion of said ribs being crimped over so as to grip the U-bolt.

5. A clamp according to any one of the preceding claims wherein said clearance holes are elongated and extend into the remainder of the U-bolt at one end into the corresponding end portion of the keeper at the other end.

6. A trefoil cable clamp substantially as de scribed herein with reference to the accompanying drawings.