GB2173359A - Electric coupler - Google Patents

Abstract

An electric coupler (1) for use in mines and quarries comprises a housing (14) with a metal head (2) at one end, at least two tubes (3) of electrically insulating material secured in the head, and an electric contact (4) positioned within each tube. An electric cable (6) passes through an opening at the other end of the housing and each conductor (5) of the cable is electrically connected to one of the contacts. Clamping means (10) positioned within the housing and electrically connected to the head, clamps the wire armouring (9) of the cable, voids (17) within the housing being filled with a hard-setting resinous insulating compound inserted through an aperture (18) in the housing after the coupler has been assembled, and which hardens to form a weatherproof coupler. The housing is formed from a material, such as pulpboard, cardboard, paper/plastics laminate or metal foil, which, when the insulating compound has hardened, contributes negligible mechanical support to the coupler. <IMAGE>

Description

SPECIFICATION Electric coupler This invention relates to an electric coupler, especially, though not exclusively, an electric coupler for use in mines and quarries.

In a known arrangement, an electric coupler comprises a metal housing; an insulator at one end of the housing within which electric contacts are secured; an opening at the other end of the housing through which the insulated conductors of an electric cable pass, the conductors being attached to the contacts; and a gland for clamping the wire armouring of the cable to the outer surface of the housing; the voids within the coupler being filled with a resin or compound passed through an aperture in the housing after the coupler has been assembled, and which hardens to form a weatherproof coupler.

This known arrangement has the disadvantages that the metal housing makes the coupler heavy and expensive to produce; no screening is normally provided between the contacts; and that a different size of gland has to be used for each size of cable.

It is the object of this invention to overcome these disadvantages.

According to the present invention an electric coupler comprising a housing; a metal head at one end of the housing; at least two tubes of electrically insulating material secured in the head; an electric contact positioned within each tube; an opening at the other end of the housing through which an electric cable passes, each conductor of the cable being electrically connected to one of the contacts; and clamping means positioned within the housing, and electrically connected to the head, for clamping the wire armouring of the cable; the voids within the housing being filled with a hard-setting resinous insulating compound inserted through an aperture in the housing after the coupler has been assembled, and which hardens to form a weatherproof coupler; the said housing being formed from a material which, once the insulating compound has hardened, contributes negligible mechanical strength to the coupler.

Preferably, the housing is formed from pulpboard or cardboard, although this does not exclude any other suitable material such as paper/plastics laminate or thin metal foil.

Preferably the conductors are crimped to the contacts. An insulating sleeve preferably surrounds each crimped joint. Preferably the sleeve is of heat shrinkable plastics. Alternatively the sleeve may be formed from a wound tape of insulating material.

By using a metal head, portions of the head can be designed to extend between the contacts, thereby screening the contacts from one another. The metal head is preferably in one piece. Alternatively the head may be in two parts, a front part forming a face for the coupler, and a rear part forming screening fins between the contacts; the insulating tubes may then have flanges which are gripped between the two parts.

Preferably the wire armour clamping means is mounted on to at least one metal support pillar attached to the metal head. If each conductor has a surrounding screen of wire or metal tape, preferably the clamping means has a fastening screw or screws by which each conductor screen can be mechanically and electrically connected to. the clamping means.

The clamping means preferably comprises at least two metal rings through which the cable conductors pass, the rings being fastened together by nuts which are screwed on to threaded portions on the support pillar(s) with the wire armouring clamped between the rings.

Preferably there are three support pillars attached to the metal head. Preferably the support pillars are screw threaded to the head.

Where the head is in two parts, preferably a threaded portion of at least one support pillar extends through an aperture in the rear part and is screw threaded to the front part and a shoulder on that pillar bears on the other part thereby securing the parts together.

Alternatively, the wire armour clamping means is mounted on metallic screening fins which extend from the metal head to form interphase barriers both between the contacts and between the conductors. In this case, the wire armour clamping means may comprise at least two metal rings through the centres of which the conductors pass, and which are drawn together axially to grip the wires between them. For example, two separate rings may be secured by nuts which are screwed into threaded spigots or studs which extend from the screening fins; or one ring may be formed integrally with the screening fins and at least one separate ring be fastened to it by screws.

The insulating tubes are preferably of a thermoset polyester dough moulded material. If the metal head is in one piece, they are preferably bonded to the metal head by a suitable adhesive.

Preferably a preformed metal (e.g. brass) mesh or other foramenous earth screen is positioned around the contacts and conductors and embedded in the insulating compound, the screen preferably being mechanically and electrically connected by clamping rings to the head and the wire armouring clamping means.

The housing is preferably clamped to the head, but could be secured with adhesive, or possibly forcefitted in some cases. At the cable entry end, the housing is preferably tapered (or stepped) to reduce the diameter of the housing. The housing may be secured and sealed to the cable by clamping the housing to the cable around which sealing tape has been wound. Alternatively a stepped or tapered housing may be accurately cut to form an opening having substantially the same diameter as the outer diameter of the cable, thereby forming a tight fit with the cable.

The insulating compound is preferably based on an epoxy resin, a polyurethane or an acrylic casting resin.

This invention has the advantage that it is much lighter than conventional metal-clad couplers, and less expensive to produce. The wire armouring clamping means can be used for cables having a diameter within a predetermined relatively wide range. The metal head can provide a screen between the contacts, and the coupler can therefore be fully screened so that phase-to-phase faults are practically eliminated.

The invention is further described, by way of example, with reference to the accompanying drawing which is a longitudinal cross-section of an electric coupler in accordance with the invention.

The coupler (1), comprises a single part metal head (2) having three insulating tubes (3) secured within it.;he tubes (3) are of a thermoset dough-moulded polyester insulating material and are secured in the head by an epoxy adhesive.

Each tube (3) forms an insulator for a contact (4) on the end of a respective screened conductor (5) of a three core wire armoured cable (6). The contact (4) is made of copper and is crimped on to its exposed conductor (5) and held within the corresponding tube (3) by a contact securing ring (7) screwed on to the contact. An insulating sleeve (8), formed from a heat shrinkable plastics material, surrounds each crimped joint to keep the interstices of the stranded conductor free from the insulating compound with which the coupler wiil in due course be filled.

The cable armouring (9) is connected to a clamp (10) which is mounted on metal support pillars (11) which are screwed into and extend.from the metal head (2). The clamp (10) comprises three metal rings (12) through which the cable conductors pass, the rings being fastened together by nuts (13) which are screwed on to the support pillars (11), with the armouring clamped between the rings.

In this particular example, the cable (6) comprises three screened conductors (5) The conductor screens (14) are mechanically and electrically connected to the clamp (10) by a fastening screw (15).

A brass screening mesh (16) is positioned around the contacts and conductors to form an outer screen, the mesh being mechanically and electrically connected by clamping rings (17,18) to the head (2) and the clamp (10).

The housing (19) is a seamless sleeve formed from cellulosic pulpboard. The housing (19) is clamped to the metal head and to the outside of the cable (6) by clamping rings (17) and (20) respectively.

To provide a tight fit between the housing (19) and the cable (6), a sealing tape (23) may if necessary be wrapped around the cable before the housing is clamped down.

The void space (21) within the housing (19) is filled with an polyurethane casting resin which was poured through an aperture (22) in the housing after the coupler had been assembled and which, once hardened, gives all necessary mechanical strength, even if the pulpboard housing is eventually worn away.

Claims (7)

1. An electric coupler for use in mines and quarries comprising a housing; a metal head at one end of the housing; at least two tubes of electrically insulating material secured in the head; an electric contact positioned within each tube; an opening at the other end of the housing through which an electric cable passes, each conductor of the cable being electrically connected to one of the contacts; and clamping means positioned within the housing, and electrically connected to the head, for clamping the wire armouring of the cable; the voids within the housing being filled with a hard-setting resinous insulating compound inserted through an aperture in the housing after the coupler has been assembled, and which hardens to form a weatherproof coupler; the said housing being formed from a material which, once the insulating compound has hardened, contributes negligible mechanical strength to the coupler.

2. An electric coupler as claimed Claim 1 wherein the housing is formed from pulpboard.

3. An electric coupler as claimed in Claim 1 wherein the housing is cardboard.

4. An electric coupler as claimed in Claim 1 wherein the housing is of a paper/plastics laminate or metal foil.

5 An electric coupler as claimed in any one of the preceeding Claims, wherein the housing is clamped to the head.

6. An electric coupler as claimed in any one of the preceeding Claims, wherein at the cable entry end, the housing is tapered or stepped to reduce the diameter of the housing.

7. An electric coupler substantially as hereinbefore described with reference'to and as shown in Figure 1.