GB2243028A

GB2243028A - Bonding device for lead sheathed cables.

Info

Publication number: GB2243028A
Application number: GB9007305A
Authority: GB
Inventors: Barry James Harrison
Original assignee: Manweb PLC
Current assignee: Manweb PLC
Priority date: 1990-03-31
Filing date: 1990-03-31
Publication date: 1991-10-16
Also published as: MY104642A; EP0450838A1; ZA912300B; GB9007305D0

Description

DESCRIPTION BONDING DEVICE FOR LEAD SHEATHED CABLES

The present invention relates to a bonding device for connections to lead sheathed cables.

Situations often arise when it is required to connect conductive earthing bonds to the exterior lead sheathing of electric cable of the type which is normally buried underground. Lead sheathing continues to be a favoured material for such sheathing because of its inherent chemical and mechanical stability when buried in the ground. The earthing bonds usually comprise one or more strips of copper braiding or conductor and the traditional method for attaching these to the cable sheathing involves fairly skilful and very time-consuming plumbing techniques. Layers of solder are built up on the sheathing with the ends of the bonding conductor strip(s) enveloped therewithin.

The traditional technique has the associated problems of (a) being timeconsuming to achieve, (b) having a substantial skill requirement on the part of the fitter, (c) requiring substantial quantities of materials, such as plumbing metal, (d) inevitably requires substantial heating of the cable sheathing which can risk damage to the cable insulation and (e) potential unreliability of the joint depending on the particular plumbingskills of the fitter.

It is an object of the present invention to provide an alternative means of connecting earthing bonds to lead sheathed cables which avoids or at least substantially reduces the aforelisted problems associated with the traditional technique.

According to the present invention, there is provided a bonding device for connecting earthing bonds to lead sheathed cables, comprising a metal plate to which may be fixed at least one earth bonding lead, the metal plate having one or more grooves or recesses in one side surface which each carry charges of solder and flux.

In use., the metal plate is laid over a lead sheathed cable so that said one side surface faces the outer periphery of the cable. Heat is then applied to the other side surface of the plate so that the solder in the recess/groove(s) flows between the plate and the cable periphery and forms a joint therebetween when subsequently allowed to cool.

Preferably, the plate is of copper. Advantageously, one end of the earth bonding lead, preferably a strip of copper braiding, is mounted within a further recess in said one side surface of the metal plate. The latter recess preferably terminates at one edge of the metal plate.

Advantageously, the width of the metal plate is such that when it is laid around a typical cable, it extends approximately half way around the cable, i.e., the width of the plate is roughly 50% of the circumference of a typical cable with which it is to be used. However, this is by no means critical and any given bonding device may be used with a wide range of cable sizes.

The invention is described further hereinafter, by way of example, with reference to the accompanying drawings, in which:

Fig.1 is a transverse cross-section (on the line I-1 in Fig.2) through one embodiment of a bonding device in accordance with the present invention; Fig.2 is a perspective view of the bonding device of Fig.1 prior to bonding about the cable; Fig.3 is a side elevation showing the bonding device attached to a cable; and Fig.4 is a cross-section on the line IV-IV in Fig.3.

With reference to the drawings, a bonding device 10 comprises a copper plate 12 of generally rectangular peripheral configuration. The plate 12 is of relatively thin grade copper that can be readily bent around the cable but has sufficient rigidity and strength to provide a strong coupling when fitted as a described hereinafter. The actual thickness and area of the plate will depend to a large extent on the current carrying requirements. The plate 12 is formed, for example by stamping, with a central, blind recess 14 of sufficient depth and width to receive an end portion 16a of a copper braiding strip 16 which is to form the earth bond. The plate 12 is also formed with a plurality (four in this embodiment) of narrow, elongate recesses or grooves 18a,18b,18c,18d, which preferably extend in directions parallel to the recess 16. The plate 12 is also formed with a peripheral lip or flange 20 and, in some cases, a plurality of through- holes 22.

The recesses 18 are each provided with a mass of suitable solder and flux (normally a Pb/Sn solder) as indicated at 24 in Fig.l. The copper braiding strip 16 is fixed to the recess 14 by any suitable means, e.g. welding, brazing, or any type of convenient mechanical fixture, so that its main portion 16b extends therefrom. The strip 16 may be pre-fixed to the recess 14 or may be supplied loose and fixed on site.

In use, the plate 10 is simply laid along the lead sheath of the cable 26, bent around the cable so as to assume the same curvature and secured such that the lip 20 bites into the lead sheath to form an edge 1 1 j i 1 1 1 1 -5seal. Alternatively, it may be preformed to suit the cable curvature. The orientation of the plate 10 is such that the recess 14. and hence the copper braiding strip, lies generally parallel to the longitudinal axis of the cable. The outside surface of the plate 10 is then heated, for example by a gas torch, so as to melt the solder in the recesses 18. The molten solder flows between the underside of the plate 10 and the lead sheathing so as to form a joint therebetween when allowed to cool. The peripheral lip 20 bites into the lead sheathing and prevents the solder from passing beyond the edges of the plate 10. The holes 22 allow air to escape and thereby facilitate flow of the solder beneath the plate. The holes may also be used for feeding in an additional charge of solder (for example when only a poor fit to the cable can be achieved) and as witness holes to determine when the internal solder has run. Preferably, the surface of the lead sheathing is cleaned beforehand such as to improve its solderability.

The recesses 18 need not run in the direction illustrated, but could lie in any convenient direction, not necessarily parallel to one another. In principle, the plate need not be of copper, although copper would be preferred in practice. The overall shape need not be rectangular but could be any 1 -6convenient shape. More than one braiding strip 16 could be attached to one plate 10, either in the same recess 14 or in a plurality of such recesses (not shown). The means of providing the electrical connection.to the plate need not be braiding but could include other mechanical coupling means such as an upstanding lug or stud fixed to the plate.

A bonding device as described above has the following advantages over the current plumbing techniques:- a) Reduced installation time, saying perhaps fifteen minutes per connection in a typical case.

(b) Improved reliability of the connection.

(c) Traditional plumbing skills are not required so that it can be installed by an unskilled fitter.

(d) The amount of plumbing materials used can be reduced.

(e) There can be a reduced heat input to the cable, thereby reducing the risk of damage to the cable insulation.

1 i 1 1 1;

Claims

1. A bonding device for connecting earthing bonds to lead sheathed cables, comprising a metal plate to which may be fixed at least one earth bonding lead, the metal plate having one or more grooves or recesses in one side surface which each carry charges of solder and flux.

2. A bonding device as claimed in claim 1 wherein one end of the earth bonding lead is mounted within a further recess in said one side surface of the metal plate.

3. A bonding device as claimed in claim 2 wherein said further recess terminates at one edge of the metal plate.

4. A bonding device as claimed in claim 1, 2 or 3 wherein the metal plate is of copper.

5. A bonding device as claimed in any of claims 1 to 4, wherein said earth bonding lead is made of copper braiding.

6. A bonding device as claimed in any of claims 1 to 5 wherein the width of the metal plate is selected such that when it is laid around a cable, it extends approximately half way around the cable. i.e., the width of the plate is roughly 50% of the circumference of a typical cable with which it is to be used.

7. A bonding device as.claimed in any of claims 1 to 6 in which the earth bonding lead is attached rigidly to the metal plate.

8. A bonding device as claimed in claim 7 in which the earth bonding lead is attached rigidly to the metal plate by welding or brazing.

9. A bonding device as claimed in any of claims 1 to 8 in which the metal plate has a peripheral lip or flange adapted to bite into the lead sheathed cable for forming an edge seal around the plate.

10. A bonding device as claimed in any of claims 1 to 9 in which the metal plate is preformed into a part cylindrical shape.

11. A bonding device as claimed in any of claims 1 to 9 in which the metal plate is generally flat for bending around a lead sheathed cable in use.

12. A bonding device as claimed in any of claims 1 to 11 having a plurality of holes therein for the escape of air during fitting.

13. A bonding device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Published 1991 2t The Patent Office. Concepi House. Cardiff Road. Newport. Gwent NP9 1RH- Further copies max. be obtained from Sales Branch. Unit 6. Nine Mile Point. Cii7nfelinfa,.'-.. zoss Keys. Newport. NPI 7HZ. Printed bv.Multiplex techniques ltd. St Mary Cray. Kent- 1