AU2018319223B2

AU2018319223B2 - Electrical conduit

Info

Publication number: AU2018319223B2
Application number: AU2018319223A
Authority: AU
Inventors: Jason Cong
Original assignee: Icon Plastics Pty Ltd
Current assignee: Icon Plastics Pty Ltd
Priority date: 2017-08-23
Filing date: 2018-08-23
Publication date: 2023-09-07
Anticipated expiration: 2038-08-23
Also published as: WO2019036745A1; AU2018319223A1

Abstract

An electrical conduit (10) comprises a wall (40) of flexible thermoplastic material and a wound reinforcement (30) forming full turns (31,32) of crush-resistant material partially or wholly embedded in the wall. The wound reinforcement (30) resists radial compression forces of at least 500N with a maximum deflection of lateral tube diameter of less than 25 per cent in operative temperatures in the range of -25°C to +80°C. The wall forms a tube (12) that is a substantially hollow cylinder. The tube (12) is flexible and adapted to bend in the operating temperature range to the extent that the longitudinal axes (26,28) of the respective ends (22,24) of the tube are capable of orienting to angles up to 180° relative to each other whilst maintaining the integrity of the hollow cylinder.

Description

ELECTRICAL CONDUIT

FIELD OF INVENTION

This invention relates to an electrical conduit. More particularly, this invention relates to an electrical conduit, particularly used as joining electrical conduit.

BACKGROUND ART

The following references to and descriptions of prior proposals or products are not intended to be, and are not to be construed as, statements or admissions of common general knowledge in the art. In particular, the following prior art discussion should not be assumed to relate to what is commonly or well known by the person skilled in the art, but to assist in the inventive process undertaken by the inventors and in the understanding of the invention.

Electrical conduits are generally designed to protect cables in a range of different installation types, including submerged, subterranean, above ground, installations, as well as internal ceiling and wall domestic, industrial and commercial applications. Electrical conduits are traditionally provided in a range of internal diameters between 50-225 mm. According to Australian and New Zealand Standards (2053), conduits and fittings are classified into five categories: very light, light, medium, heavy and very heavy duty. For this purpose, joins for electrical conduit for medium and heavy duty applications are necessarily made from rigid extruded tubing that is subsequently heated and bent to provide a variety of fixed angled joints, and separately heated and belled to receive the ends of rigid conduit to be joined thereto. The applications of such conduits include; electrical, telecommunications, civil infrastructure,

construction, solar energy and mining sector applications.

The process of bending rigid conduit and belling at both ends is expensive and time consuming. Moreover, use of such joins in the installation of electrical conduit requires careful calculations, accurate cutting to length, and insertion, with little flexibility for miscalculations. Flexible corrugated conduit is available for light duty applications whereby the maximum internal diameter of such components is normally 50 mm. Corrugated conduit does not meet the standard requirements for medium and heavy-duty classes of conduit, in terms of crush - resistance. Therefore, the only option heretofore has been to use rigid joining conduit. Moreover, corrugated conduit may be less easy to use in some applications because of the annular internal grooving that increases the difficulty of feeding a conduit therethrough.

An object of the present invention is to ameliorate the aforementioned disadvantages of the prior art or to at least provide a useful alternative thereto. STATEMENT OF INVENTION

The invention according to one or more aspects is as defined in the independent claims. Some optional and/or preferred features of the invention are defined in the dependent claims.

Accordingly, in one aspect of the invention there is provided:

an electrical conduit comprising:

a wall of flexible thermoplastic material; and

a wound reinforcement forming full turns of crush - resistant material partially or wholly embedded in the wall,

wherein:

the wound reinforcement resists radial compression forces of at least 500N with a maximum deflection of lateral tube diameter of less than 25 per cent in operative temperatures in the range of -25°C to +80°C;

the wall forms a tube that is a substantially hollow cylinder; and

the tube is flexible and adapted to bend in the operating temperature range to the extent that the longitudinal axes of the respective ends of the tube are capable of orienting to angles up to 180° relative to each other whilst maintaining the integrity of the hollow cylinder.

In another aspect of the invention there is provided:

an electrical conduit, characterised in that/wherein the electrical conduit comprises: a wall of flexible thermoplastic material forming a tube with longitudinal axes, including a first longitudinal axis at a first end, an intermediate longitudinal axis intermediate the length of the tube, and a second longitudinal axis at a second end; a tube reinforcement formed by being wound in full turns about the longitudinal axes; and

the reinforcement being made of crush - resistant material partially or wholly embedded in the wall,

further characterised in that:

the reinforcement resists radial compression forces of at least 500N with a maximum deflection of lateral tube diameter of less than 25 per cent in operating temperatures in the range of -25°C to +80°C;

the tube is in the shape of a substantially hollow cylinder; and the tube is flexible and adapted to bend in the operating temperature range to the extent that the longitudinal axes of the respective ends of the tube are capable of orienting to angles up to 180° relative to each other whilst maintaining the integrity of the electrical conduit.

In yet another aspect, the invention provides:

A method of manufacture of an electrical conduit as described above, the steps of the method including:

providing an extrusion comprising a length having a central reinforcement of the crush - resistant material set in flexible thermoplastic material and at least a first lateral flange of the flexible thermoplastic material extending to one side of the central reinforcement;

applying heat to the continuous lengths of the extrusion to render it in a semi- molten form in which the first lateral flange is meldable with an adjacent length of the extrusion;

feeding the semi-molten extrusion onto a forming tool such that the central reinforcement forms a full wind about the fonning tool and the flange overlays or superimposes over either an adjacent length of the central reinforcement or an adjacent length of a second flange extending to the other side of the central reinforcement; forming a cylindrical tube with a wall which includes a length of the central reinforcement spirally wound and inset in the wall of the tube; and cooling the cylindrical tube and removing the tube from the forming tool.

In still another aspect, the invention provides:

A method of manufacture of an electrical conduit optionally as described above, the steps of the method including:

providing an extrusion comprising a length having, in section, a central reinforcement reinforced with a co-extrusion of the crush - resistant material set in flexible thermoplastic material, and at least a first lateral flange of the flexible thermoplastic material extending to one side of the central reinforcement zone in a first flange zone;

winding the extruded length with full, multiple turns to form a hollow, substantially cylindrical, tube having longitudinal axes, including:

a first longitudinal axis at a first end;

an intermediate longitudinal axis intermediate the length of the tube; and a second longitudinal axis at a second end, applying heat to the lengths of crush - resistant material and flexible thermoplastic material of the extrusion to render it in a semi-molten form in which the first lateral flange is meldable with an adjacent length comprising the next full turn of the extrusion;

feeding the semi-molten extrusion onto a forming tool such that the central reinforcement is wound in a full turn about the forming tool and the first lateral flange melds with either an adjacent length of the central reinforcement or an adjacent length of a second flange extending to the other side of the central reinforcement in a second flange zone, to form a substantially cylindrical tube with a wall which includes a length of the central reinforcement spirally wound and inset in the wall of the tube; and

cooling the cylindrical tube and removing the tube from the forming tool.

ELECTRICAL CONDUIT

The electrical conduit is preferably adapted to protect cables in a range of

installations, including above- ground and buried installations. The electrical conduit may be capable of being bent to a varying degree of angles around the structures, such as trees, posts, wall and ceiling corners, other building features and the like.

SPIRAL REINFORCEMENT

The reinforcement is preferably adapted to impart strength and compression resistance to the tube. The reinforcement may be in the form of a length of cord, ribbon, strap, bead or rib. The reinforcement may be wound about the longitudinal axes in a spiral pattern or shape. The reinforcement may be shaped to be greater in a radial direction rather than a direction parallel to the longitudinal axis of the tube. Preferably, the reinforcement is substantially round in section at rest or when not stressed. Preferably, the reinforcement is in the form of a length of cord or bead.

Alternatively, the reinforcement may comprise a substantially flat ribbon.

The reinforcement may form a spiral extending through the tube wall. This may enable a continuous length of extruded material to be used to form the tube, rather than by joining discreet adjacent coaxial rings. However, the tube wall may be formed by feeding discrete lengths of substantially cylindrically shaped extrusion on to a forming tool whereby the wall is formed using discrete annular sections to provide each segment of the tube.

The reinforcement may be formed from a variety of substantially rigid materials, including metals and rigid polymers, such as polyvinyl chloride (PVC), high density polyethylene (HDPE) or rigid poly propylene. The reinforcement may be in the form of wire. Preferably, the reinforcement comprises a length of thermo-plastic material adapted to wind in a spiral formation or shape. [

Accordingly, when wound, the reinforcement material and the sectional shape of the reinforcement should have combined properties of sufficient rigidity to withstand radial compressive forces that may be expected by the relevant application and sufficient flexibility to permit a length of the tube to be bent to a varying degree of angles around the structures.

FLEXIBLE THERMOPLASTIC MATERIAL

The wall may be formed using a continuous length of material. The continuous length of material may be fed on to the forming tool as a length of extruded semi molten or plasticised ribbon. Various suitable polymeric materials may be used for the flexible wall, including thermoplastic elastomers (TPEs), polyvinyl chloride (PVC) or low density polyethylene (LDPE).

HEATING DEVICE

The extrusion of the reinforcement and the flexible thermoplastic material may be fed from a reel. The extrusion may be passed through a heating unit adapted to continuously render a portion of the extrusion semi-molten. The extrusion may be delivered in a sufficiently plasticised state such that the first flange of a newly extruded section of extrusion melds with adjacent extruded material that has been previously wound on to the forming tool. The temperature settings, and the dimensions, such as length, of the heating device, are dependent on the nature of the material, including physical properties such as hardness, melt temperature, thickness and the like.

FORMING TOOL

The forming tool may be static and the extrusion may be wound around the forming tool. However, preferably the extrusion is fed continuously from the heating device until the tube is completed. Belling at one or both ends of the tube may be achieved by providing the forming tool with flared ends. The flared ends may form a substantially truncated conical shape.

The forming tool may be formed from a set of axially aligned rods, a solid tube, or a perforated tube. Preferably, the forming tool comprises mainly metal, and preferably stainless steel or aluminium or composite corrosion resistant materials or alloys.

COOLING DEVICE

The cooling device may use gas, such as air, or liquid, such as water, to cool. Cooling may be achieved by air cooling, including air blowers or passive air cooling using ambient air. Preferably, the cooling device is in the form of a water bath. The formed tube may be dipped in the water bath. The formed tube, still wrapped around the forming tool, may be dipped into the water bath to cool the formed tube.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be better understood from the following non-limiting description of preferred embodiments, in which:

Figure 1 is a schematic illustration of a compression test of a section of electrical conduit made according to a first embodiment of the invention;

Figure 2 is a perspective view of an electrical conduit made according to a second embodiment of the invention shown in a in a controlled compression test device;

Figure 3 is a perspective view of an electrical conduit made according to the first embodiment;

Figure 4 is a perspective view of the electrical conduit made according to the first embodiment showing a reinforcing portion and a flexible wall component;

Figure 5(a) is a schematic cross-sectional representation of a reinforcing portion of a wall of an electrical conduit of the type shown in Fig. 2 created for the purpose of computer modelling to run simulations;

Figure 5(b) is a schematic cross-sectional representation of a portion of the wall of the electrical conduit of the computer model shown in Fig. 5(a);

Figure 5(c) is an isometric view of the electrical conduit of the computer model of Fig. 5(a) showing a "heat" map simulation of the compression forces that would likely be sustained by the conduit in a compression test;

Figure 6(a) is a schematic cross-sectional representation of a reinforcing portion of a wall of the electrical conduit of the first embodiment;

Figure 6(b) is an isometric view of the electrical conduit of the first

embodiment;

Figure 6(c) is a cross-sectional representation of the electrical conduit of the first embodiment through a plane parallel to the longitudinal axis of the conduit;

Figure 6(d) is an isometric view of the electrical conduit of the first

embodiment showing a "heat" map of the compression forces sustained by the conduit in the compression test shown in Fig. 1;

Figure 7 is a schematic cross-sectional representation of a portion of the wall of the electrical conduit of the first embodiment showing the rigid reinforcing member encased in a flexible material of the conduit wall; and

Figure 8 is a perspective view of an electrical conduit manufacturing apparatus according to a method of manufacture aspect of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention will now be described with particular reference to the accompanying drawings. However, it is to be understood that the features illustrated in and described with reference to the drawings are not to be construed as limiting on the scope of the invention.

An electrical conduit 10 comprises a tube 12 formed by a substantially cylindrical case 40 of flexible thermoplastic material and a wound reinforcement 30 forming full turns 31,32 of crush - resistant material partially or wholly embedded in the wall. The wound reinforcement 30 resists radial compression forces of at least 500N with a maximum deflection of lateral tube diameter of less than 25 per cent in operative temperatures in the range of -25°C to +80°C. The wall forms a tube 12 that is a substantially hollow cylinder. The tube 12 is flexible and adapted to bend in the operating temperature range to the extent that the longitudinal axes 26,28 of the respective ends 22,24 of the tube are capable of orienting to angles up to 180° relative to each other whilst maintaining the integrity of the hollow cylinder.

Referring to Figs. 1, 3, 4. 6(a) - (d), 7 and 8, there is shown an electrical conduit 10 made according to a first embodiment of the invention.

The conduit is formed as a substantially cylindrical tube 12 having a continuous wall 20. The wall 20 comprises a cord 30 fully or partially embedded in the substantially cylindrical case 40.

The cord 30 is in the form of an extruded bead shaped as a spiral. The cord 30 is made of substantially rigid material. The cord 30 is adapted, when in the spiral formation, to resist radial compression of the wall 20.

The case 40, exemplified in Fig. 4, forms a webbing 42 between adjacent turns, ribs or passes of the spirally wound cord 30. The webbing may be relatively thin-walled in these regions. The case 40 material may encase the cord 30 between the webbing 42.

The tube 12 may have expanded ends 22,24 formed by belling. This enables the tube 10 to engage, as a partial sleeve, with an end of standard electrical conduit in male- female relationship. The standard electrical conduit will have an outer diameter that is marginally smaller than the internal diameter of the tube ends 22,24. Extending between the ends 22,24, the tube 12 has a main body 13. The main body 13 has an internal diameter similar to that of a standard electrical conduit to which it is to be engaged in the particular application. For most applications, there may be a standard electrical conduit. Advantageously, the electrical conduit of the present invention may be sized and shaped to engage the relevant standard electrical conduit.

The case 40 material may be flexible so that the tube 12 may be bent to collapse the webbing 42 in the region on an inside 14 of a bend (see Fig. 1) and to stretch or attain full extension of the webbing 42 on an outside 16 of the bend. The flexibility of the webbing 42 may be to the extent that the conduit 10 can be bent from a substantially linear formation as shown in Fig. 4, to a bent formation as shown in Fig. 3 in which respective longitudinal axes 26,28 of the tube ends 22,24 can assume angles of between 0 - 180° relative to each other, the maximum extent of the angle depending inter alia on the length of the tube 12.

The cord 30 is substantially round in cross-section, as shown in Figs. 5(a) and (b). Adjacent passes 31,32 of the cords 30 may be joined by a thin web of material forming the webbing 42.

Preferably, the inner surface 46 of the tube 12 is relatively smooth, so that the webbing 42 and/or flexible material 44, combined or severally, provide a smooth inner surface 46 presentation. The smooth inner surface 46 may serve to mitigate against snagging or other obstruction of wiring and cables as they are fed into a tube 12 on installation.

In Figs. 1 and 6(a) - (d), a compression test in accordance with AS/NZS 2053.1 :2001 is depicted. The test is for conduits and fittings for electrical installations and particularly for flexible plain conduits and fittings of insulating material. The mechanical properties test includes a 9.6 pull-out to test the strength of joints involving 160N of pulling force applied for 5 minutes. The flexible conduit tube 12 of this embodiment exhibited substantial resistance to compression and impact, whilst remaining flexible to perform as bend joints.

In Figs, la and lb, an arrangement for a compression test involves a sample tube 12 that is positioned on a flat steel support 50. A steel intermediate piece in the form of a block 52 is centrally positioned over the tube 12 sample. A uniformly increasing compression force F, reaching a compression force measured in Newtons to a tolerance of +/- 4% is applied according to the tube's 12 required rating (medium = 750N as for conduit 10 or heavy = 1250N as for conduit 110). The compression force is the force necessary to effect measurable compression on tube 12 and is applied through the intermediate steel block 52 to the tube as indicated by localised

compression forces Rl tninsmitted centrally through the steel block 52. After the force has been applied for 60 +/- 2 sees., the outside diameter of the sample tube 12 is measured (whilst maintaining the force F in place) where flattening has occurred. The difference between an initial outside diameter and the diameter of the flattened sample 10 should not exceed 25% of the initial outside diameter measured before the test.

The force and the intermediate piece 52 may then be removed and, 60 +/- 2 sees, after removal, the outside diameter of the sample tube 10 where it has flattened can again be measured. Preferably, the difference between the initial diameter and the diameter of the flattened sample 10 should not exceed 10% of the outside diameter as measured before the force was applied.

In the embodiment shown, the sample 10 had an outside diameter of 74mm, an internal diameter of 65mm and a wall thickness of 5.0mm as depicted in Fig. 6(a). The cord 30 is provided as a rigid spiral made of PVC and is 4.5mm x 4mm. In section, the cord 30 is oval shaped with a flight pitch of the section 31 of the cord 30 relative to an adjacent turn or flight 32 of 9mm and a spacing of 4.5mm. When applying a 750N of force in the centre of the conduit sample 10, an 8mm increase on the diameter was recorded.

Referring to Figs. 2 and 5(a)-(c), there is shown a second embodiment in the form of an electrical conduit 110 with similar features to the first embodiment and given similar reference numbers (plus 100). As shown in Fig. 2, the intermediate piece 52 may for the direct force applicator of a press 53. The tube 12 may have a first longitudinal axis 126, second longitudinal axis 128, and an intermediate longitudinal axis 127. The longitudinal axes 126,127,128 are not coaxial when the tube 12 is bent.

The adjacent cords 131,132 can be bridged by a thin webbing 142. The adjacent passes of cord 131,132 are preferably embedded in a casing of the flexible material 134. The casing 134 may envelope the cords 130 whereby to provide a smooth inner surface 146. In another variant, the outer surface 148 may retain the corrugated profile to facilitate the flexibility of the tube 12 by allowing spiral portions of adjacent cords 131,132 to bend into the interstitial spaces or gullies 133 extending between adjacent turns or passes of the cords 131,132.

In Fig. 5(c) in particular, a computer model of an electrical conduit 110 having an outer diameter of 77mm, an internal diameter of 65mm and a wall thickness of 6mm is shown. The rigid PVC spiral 130 is modelled to be about 5mm round in a pitch of 9mm. When applying a 1250N force in the centre of the conduit 110 sample, as shown in Fig. 2, a 7mm increase in the diameter can be calculated, whereby the second embodiment and the corresponding computer model exemplified are considered capable of passing the heavy duty compression test.

A section of two adjacent cord turns 131,132 embedded in flexible material is shown in Fig. 5(b). The cords 130 are wholly embedded in the flexible material 134 . The flexible material 143 includes a webbing zone 142 and an encasement zone 147 immediately surrounding each of the cords 130. The inner surface 146 is generally smooth and free from gullies in the webbing zone 142. The outer surface 148 is generally smooth and free from gullies in the webbing zone 142.

In Fig. 7, a single turn or pass of the cord 30 is represented and shown as embedded in flexible material, the resultant bead having an overall oval shape in cross-section. As the the flexible material 40 of the bead melds with an adjacent, like turn of the bead of material from the same length of bead, the overall wall 40 formed from a plurality of turns of the bead comprises nodes corresponding to the embedded zones immediately surrounding the cord 30, and gullies or toughs corresponding to the webbing zones extending between the cords 30.

With reference to Fig. 8, in a method aspect, there may be provided a method of manufacture of an electrical conduit 10. The steps of the method include providing an extrusion 72 comprising a length having a central reinforcement 30 of the crush - resistant material set in flexible thermoplastic material 40. At least a first lateral flange 74 of the flexible thermoplastic material extends to one side of the central

reinforcement 30.

Heat is applied to the continuous lengths of the extrusion 72 to render it in a semi- molten form in which the first lateral flange 74 is meldable with an adjacent length of the extrusion 72 spirally wound around the former 60. The semi-molten extrusion 72 is fed onto the forming tool 60 such that the central reinforcement 30 forms a full wind about the forming tool and the flange 74 overlays or superimposes over either an adjacent length of the central reinforcement 30 or an adjacent length of a second flange 76 extending to the other side of the central reinforcement. A cylindrical tube 12 is formed that has a wall 40 which includes a length of the central reinforcement 30 spirally wound and inset in the wall 40 of the tube 10. The cylindrical tube 10 is then cooled and removed from the forming tool 60.

,A method of manufacture of the tube 10 is shown in Fig. 8 using a hot melt former 60. The device 60 includes a rotating former comprising a first section that is cylindrical in shape and has a narrow outer diameter section 62. The outer diameter section 62 is adapted to form the cylindrical body 12 of the tube 10. The first section 62 is continuous with a second partially conical section 64 that is adapted to form the end bell portion of the tube 10 such that it can engage as a sleeve with standard sized traditional electrical conduit sections.

The cord 30 is extruded from a hot melt extruder 70 as a meldable ribbon 72 that is wound on to the rotating former device 60 under reasonable tension to ensure a consistent application. The ribbon 72 comprises a central cord 30 that is substantially rigid (at room temperature) and a first flange 74 of flexible plastic material of a first side. The ribbon 72 may include a second flange 76 of flexible material on a second and opposed side to the first. The flanges 74,76 may be continuously formed across the central cord 30 in cross-section.

A hot glue nozzle 80 dispenses molten PVC into the interstitial spaces between the cord flights 31,32 to complete the wall 40. Once the wall 40 is formed, the former 60 and the mounted and formed tube 10 are submerged into a cooling tank 90 and cured.

DEFINITIONS

In this specification, maintenance of the integrity of the electrical conduit means that the conduit is not deformed beyond its elastic and recoverable limits. Integrity of the conduit would be broken or the integrity not maintained by the component parts of the conduit tearing, rupturing, separating, or otherwise breaking, so that the original form of the conduit is not elastically restorable.

For sake of clarity, in the specification, unless the context clearly indicates otherwise, the term "wind" means to wrap around, including in a spiral pattern, and the word "wound" is the past tense of "wind".

The term "longitudinal axes" of the tube includes the longitudinal axis at any point along the length of the tube and corresponds to the longitudinal axis at or associated with the intermediate, first or second end.

The term "radial direction", in the specification, is a radially outward direction from the longitudinal axes of the tube.

Throughout the specification and claims the word "comprise" and its derivatives are intended to have an inclusive rather than exclusive meaning unless the contrary is expressly stated or the context requires otherwise. That is, the word "comprise" and its derivatives will be taken to indicate the inclusion of not only the listed components, steps or features that it directly references, but also other components, steps or features not specifically listed, unless the contrary is expressly stated or the context requires otherwise.

In the present specification, terms such as "apparatus", "means", "device" and

"member" may refer to singular or plural items and are terms intended to refer to a set of properties, functions or characteristics performed by one or more items or components having one or more parts. It is envisaged that where an "apparatus", "means", "device" or "member" or similar term is described as being a unitary object, then a functionally equivalent object having multiple components is considered to fall within the scope of the term, and similarly, where an "apparatus", "assembly", "means", "device" or "member" is described as having multiple components, a functionally equivalent but unitary object is also considered to fall within the scope of the term, unless the contrary is expressly stated or the context requires otherwise.

Orientational terms used in the specification and claims such as vertical, horizontal, lop, bottom, upper and lower are to be interpreted as relational and are based on the premise that the component, item, article, apparatus, device or instrument will usually be considered in a particular orientation, typically with the tube 10,110 lying in a horizontal orientation.

It will be appreciated by those skilled in the art that many modifications and variations may be made to the methods of the invention described herein without departing from the spirit and scope of the invention.

Claims

The claims:

1. An electrical conduit, characterised in that/wherein the electrical conduit

comprises:

a wall of flexible thermoplastic material forming a tube with longitudinal axes, including a first longitudinal axis at a first end, an intermediate longitudinal axis intermediate the length of the tube, and a second longitudinal axis at a second end;

a tube reinforcement formed by being wound in full turns about the

longitudinal axes; and

further characterised in that:

the tube is in the shape of a substantially hollow cylinder; and

the tube is flexible and adapted to bend in the operating temperature range to the extent that the longitudinal axes of the respective ends of the tube are capable of orienting to angles up to 180° relative to each other whilst maintaining the integrity of the electrical conduit.

2. An electrical conduit as claimed in claim 1, characterised in that/wherein the electrical conduit is capable of being bent to a varying degree of angles around structures, including trees, posts, wall and ceiling corners, and other building features.

3. An electrical conduit as claimed in claim 1 or 2, characterised in that/wherein the reinforcement is in the form of a length of cord, ribbon, strap, bead or rib.

4. An electrical conduit as claimed in any one of the previous claims,

characterised in that/wherein the reinforcement is wound about the longitudinal axes in a spiral pattern or shape.

5. An electrical conduit as claimed in any one of Claims 2 - 4, characterised in that/wherein the reinforcement in transverse section is shaped to be greater in a radial direction rather than a direction parallel to the longitudinal axes of the tube, whereby the reinforcement has combined properties of sufficient rigidity to withstand radial compressive forces and sufficient flexibility to permit a length of the tube to be bent around the structures.

6. An electrical conduit as claimed in Claim 4 or 5, characterised in that/wherein the reinforcement spiral extends through the tube wall to enable a continuous length of extruded material to be used to form the tube.

7. A method of manufacture of an electrical conduit optionally as described above, the steps of the method including:

a first longitudinal axis at a first end;

an intermediate longitudinal axis intermediate the length of the tube; and a second longitudinal axis at a second end,

applying heat to the lengths of crush - resistant material and flexible

thermoplastic material of the extrusion to render it in a semi-molten form in which the first lateral flange is meldable with an adjacent length comprising the next full turn of the extrusion;

feeding the semi-molten extrusion onto a forming tool such that the central reinforcement is wound in a full turn about the forming tool and the first lateral flange melds with either an adjacent length of the central reinforcement or an adjacent length of a second flange extending to the other side of the central reinforcement in a second flange zone, to form a substantially cylindrical tube with a wall which includes a length of the central reinforcement spirally wound and inset in the wall of the tube; and cooling the cylindrical tube and removing the tube from the forming tool.

8. A method of manufacture of an electrical conduit as claimed in Claim 7, characterised in that/wherein a continuous length of extruded material is fed on to a forming tool as a length of extruded semi molten or plasticised ribbon.

9. A method of manufacture of an electrical conduit as claimed in Claim 7 or 8, characterised in that/wherein the flexible thermoplastic material is fed from a reel.

10. A method of manufacture of an electrical conduit as claimed in Claim 8 or 9, characterised in that/wherein the extrusion is passed through a heating unit adapted to continuously render a portion of the extrusion semi-molten.

11. A method of manufacture of an electrical conduit as claimed in any one of claims 7 - 10, characterised in that/wherein the extrusion is delivered in a sufficiently plasticised state such that the first flange of a newly extruded section of extrusion melds with adjacent extruded material that has been previously wound on to the forming tool.

12. A method of manufacture of an electrical conduit as claimed in any one of Claims 8 - 11, characterised in that/wherein the forming tool rotates and the extrusion is wound around the forming tool and the extrusion is fed continuously from the heating device until the tube is completed.

13. A method of manufacture of an electrical conduit as claimed in any one of Claims 8 - 12, characterised in that/wherein the belling at one or both ends of the tube is achieved by providing the forming tool with flared ends.

14. A method of manufacture of an electrical conduit as claimed in any one of Claims 8 - 13, characterised in that/wherein the forming tool is formed from a perforated tube.

A method of manufacture of an electrical conduit as claimed in any one Claims 8 - 14, characterised in that/wherein the cooling device is in the form of a water bath and the formed tube, still wrapped around the forming tool, is dipped into the water bath to cool the formed tube.