EP0106535A2

EP0106535A2 - Electrical track

Info

Publication number: EP0106535A2
Application number: EP83305363A
Authority: EP
Inventors: Norman Edward Bruce Reynolds; Leslie King
Original assignee: MK Electric Ltd
Current assignee: Novar ED&S Ltd
Priority date: 1982-09-14
Filing date: 1983-09-13
Publication date: 1984-04-25
Also published as: IN164501B; EP0106535A3; DE3379822D1; EP0106535B1

Abstract

An electrical distribution track has an elongate duct containing exposed conductors which may be mounted on or in a wall. The duct has an opening which may receive an electrical accessory to make contact with the conductors at any point and is provided with cover means which cover the whole of the opening and surrounding parts of the duct. The cover means may be snap fitted to supporting brackets or to the duct itself. When assembled the whole of the duct is protected from damage or penetration of unwanted materials by the cover means.

Description

This invention relates to an electrical distribution track in which electrical conductors are enclosed in a duct having an aperture allowing access to the conductors for electrical connection to a switch or the like mounted on the track. It is especially but not exclusively applicable to domestic mains distribution systems in which a plurality of switches or other accessories are to be connected to the conductors at different locations.
It is desirable to provide a distribution system comprising such a track in which an accessory may be connected to the conductors at any desired point along the track and which is cheap to manufacture, easy to install and capable of accommodating a variety of types of accessory.
It is preferred that the track shall be able to receive accessories which are of a design compatible with electrical equipment which is already in use, such as the British Standard 13-amp distribution system.
According to one aspect of the invention there is provided an.electrical distribution track comprising a longitudinal hollow duct adapted to be mounted on a support surface or in a channel embedded in a support surface, the duct containing exposed electrical conductors extending therealong, the duct comprising a base and a pair of longitudinally extending side walls having a continuous longitudinal opening therebetween to allow insertion into the duct of an electrical accessory at any point along the duct, the side walls comprising outwardly facing edges capable of engaging flanges on opposite sides of an accessory positioned in the duct or of a mounting device capable of holding an accessory in the duct, means for clamping an accessory or mounting device to the duct with said flanges abutting said edges, and cover means adapted to be attached to the duct such that the parts of the opening not occupied by the accessory, the edges of the walls of the duct and the flanges of an accessory or mounting means therefor abutting said edges are covered by the cover means, the cover means extending to the support surface outside the duct or the duct having outer walls extending from the support surface to the cover means so that the parts of the duct which are exposed when the duct is mounted on a support surface or in a channel thereon are enclosed by the cover means or by the cover means and the outer walls.
The accessory may be a switch socket or other device such as a circuit-breaker.
The duct may generally be attached directly to the surface of a wall or like supporting structure to which the track is attached or it may be positioned in a channel inserted in a groove in the wall. In both cases the covering means for the duct may have sides abutting the wall on which the track is mounted. Alternatively, especially when the duct is mounted on the surface of a wall, the duct may have upstanding outer side walls covering the duct side walls which come into contact with the accessory and the outer side walls abut the covering means. In both cases the duct itself is completely enclosed and protected against damage and entry of unwanted material such as water which might come into contact with the conductors.
The covering means may be attached to the duct by means of brackets secured to the duct at intervals or it may be attached to the duct itself, for example by means of beads and grooves forming a snap fit. The covering means may comprise a single cover member extending over the opening and duct side walls and abutting either the wall on which the track is mounted or outer side walls of the duct; alternatively it may comprise a central cover extending over the opening and separate side covers, which may engage the central cover by means of flanges fitting into grooves. The use of beads and grooves for fitting the covering means in place may render the use of screws unnecessary.
The accessory may itself have flanges engaging the edges of the duct walls or it may be mounted on a plate which engages the duct walls. The use of a plate allows many types of standard accessory,which are not provided with flanges, to be mounted on the track.
The accessory, or plate carrying the accessory, may be clamped against the edges of the duct wall by screws or it may be held in place on the duct by the covering means itself.
The conductors may be mounted on the rear wall of the duct opposite the opening and the rear wall of the accessory may comprise terminals, for example sprung fork terminals, to make electrical contact with the conductors when the accessory is mounted in the duct.
Track arrangements according to embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 shows an accessory mounted on a track with the track cover and accessory cover removed,
Figure 2 is a cross-section of the accessory and track of Figure 1 with the accessory cover in place,
Figure 3 is a view similar to Figure 1 but with two adjacent accessories mounted on the track and the track cover and accessory covers in place,
Figure 4 is a section similar to Figure 2 but with the track supported in a different manner,
Figure 5 shows a track portion with no accessory or cover,
Figure 6 is a section of part of the track of Figure 5,
Figures 7 and 8 are sections of part of a track according to other embodiments,
Figure 9 is a section of a track cover,
Figures 10 and 11 are sections of cleats for holding bus-bars in the track,
Figures 12 and 13 are a face view and a cross-section of a track cover connecting unit.
Figure 14 is a perspective view of a track having covers and an accessory mounted thereon according to another embodiment of the invention,
Figure 15 is a section of part of the track of Figure 14 on a larger scale,
Figure 16 is a section similar to Figure 15 of part of a track according to another embodiment,
Figure 17 is a schematic section showing an accessory mounted on the track of Figure 16,
Figure 18 is a section similar to Figure 17 showing another method of mounting an accessory,
Figure 19 shows a mounting plate used in the embodiment of Figure 18,
Figure 20 is a view of a joint cover used in the embodiment of Figure 14,
Figures 21 and 22 are sections of the joint cover of Figure 20,
Figure 23 shows a corner piece for use with the track of Figure 14,
Figure 24 is a side view of the corner piece of Figure 23, and
Figure 25 shows another corner piece.

As shown in Figures 1 and 2 a power supply track comprises a longitudinal channel-shaped duct 1 of uniform cross-section formed of electrically insulating plastics material. It may be made by extrusion. Duct 1 comprises a flat base 2 provided with upstanding portions forming grooves 3a, 3b and 3c containing respective longitudinal conductors in the form of copper bus- bars 4a, 4b and 4c. The bus-bars 4 are narrower than the grooves 3 and are.held in the grooves by cleats 5, only one of which is shown in Figure 2, distributed at intervals along the grooves. The cleats 5 are of resilient plastics material, are generally U-shaped and dimensioned to surround and engage the bus-bar and fit tightly in the grooves 3 so that the bus-bar is held securely in place. The open end of the U-shaped cleat is turned inwardly to partially enclose the corresponding edge of the bus-bar and so grip the bus-bar firmly. The outer surfaces of the cleats engaging the walls of the grooves have serrations extending parallel to the bus-bar to provide a secure frictional engagement with the grooves.
The bus-bars are easily mounted in the grooves by snap- fitting the cleats on the bars and then pushing the bus-bars into the grooves.
The side walls 6 of duct 1 are provided at their edges with continuous longitudinal grooves 7 to receive thread-forming screws 8 for clamping switch 9 to the duct. As shown in Figure 2 the main body of the switch is positioned inside the duct and the upper and lower sides of the switch have flanges 9a which abut the edges of wall 6 and are clamped thereto by screws 8. Screws. 8 are of a size such that their threads bite the interior surfaces of grooves 7. Switch socket 9 may thus be mounted in the duct 1 at any arbitrary position along the length of the duct, no holes being needed to receive the screws 8.
The rear surface of the switch socket 9 is provided with three fork terminals 10, of which only one is shown in Figure 2, to make contact with the respective bus-bars. Terminals 10 are dimensioned to enter the grooves 3 and bracket the bus-bars, the prongs of the forks being inwardly sprung so that they clamp the bus-bars between the prongs to establish a reliable electrical contact between terminal and bus-bar. The switch socket is designed to receive a conventional 13-amp plug. The terminals 10 connect the sockets receiving the plug pins to the respective bus-bars by means of a conventional wiring arrangement in the switch. In the drawings three bus-bars are shown in respective grooves but a greater number of bus-bars and grooves may be provided if required.
As shown in Figure 2 the duct 1 is contained in a longitudinal channel member 11 which is embedded in a wall 12 which provides a support surface for the track. Channel member 11 may be formed by extrusion and composed of plastics material or of a metal such as aluminium; it need not be electrically insulating. Duct 1 is provided with cover securing brackets 13 which are positioned on each side of the switch and at intervals along the track. The securing brackets are provided with holes through which thread-forming screws 14 pass, the screw heads abutting the brackets around the holes. The edges of the walls of channel member 11 are provided with longitudinal grooves 15 opposite screws 14 so that when brackets 13 are mounted in place the threads of screws 14 bite the internal walls of grooves 15 to hold the bracket in place. The brackets are also provided with holes through which screws 18 may pass to clamp the bracket to the duct 1.
When the track is assembled duct 1 containing the bus-bars is placed in the channel member 11, brackets 13 are placed at positions spaced along the duct and screws 14 and 18 are passed through their respective holes and tightened to clamp the duct and channel member to the brackets, thus holding these members in place. At locations where an accessory is provided, the accessory is inserted in duct 1 as shown in Figures 1 and 2 so that its terminals engage the bus-bars and is secured to the duct 1 by screws 8. Brackets 13, which are shaped so that their sides overlay the side edges of the accessory, are then mounted as described above in the positions shown in Figure 1 to help secure the switch in place.
As shown in Figure 2, the brackets 13 are provided with an upstanding bead 19 at both ends to support a cover for the switch,shown in Figures 2 and 3. The cover comprises a plate 20 of plastics material covering the periphery of the accessory having a rectangular aperture 21 exposing the central part of the accessory. The edges of the cover have flanges 22 dimensioned to extend to and abut the wall so that the whole assembly is enclosed by the cover apart from the part of the switch to which access is required. The interior of the cover is provided with part-circular slots 23 to receive the beads 19 of the cover support bracket. The area of contact of the inside walls of the slots 23 and the bead exterior extends over an angle exceeding 180^o and the plastics material of the beads is slightly resilient so that when the cover is applied to the brackets 13 the beads snap into the slots to hold the cover in place.
The cover may be of plastics material or of other material such as aluminium.
The parts of the track not occupied by switches or other accessories are covered with track cover plates 24, shown in Figure 3, of identical construction to plate 20 but having no aperture 21. Plates 24 are applied to the brackets 13, spaced along the track, in the same manner as plate 20 so that the track assembly is completely enclosed. Plates 24 may be cut to any required length from an extruded body having the required cross-section and this operation is easily performed on site when the track is installed. Alternatively, the track cover may be supplied in different standard lengths which are selected on site to fit the track being installed.
Figure 4 shows an alternative arrangement which is similar to that of Figures 1 and 2. The duct 1, bus-bars 4, switch 9 and brackets 13 are identical to those of Figures 1 and 2 but instead of being mounted in a channel within the wall the duct 1 is mounted directly on the surface of the wall 12, for example by screws (not shown) passing through the base of the duct engaging plugs inserted in the wall. In this arrangement the brackets are not screwed to any channel member but are held in place by the moulding secured to the wall. The switch cover and track cover are of similar construction to those of Figures 1 and 2 but have flanges 22 which are wider to extend to the wall.
The bus-bars 4 are connected to leads to supply them with electric current and a connector for this purpose is shown in Figures 5 and 6. The connector 25 is made of metal and comprises a pair of walls 26 dimensioned to clamp tightly the side walls of the bus-bar 4 and an aperture 27 into which the exposed end 28 of a current-carrying cable is inserted and clamped by at least one screw 29. The walls 26 are of such a thickness that they may fit into the grooves 3 and are retained on the bus-bars by friction. The upper part of the connector through which the screw passes is provided with a slot 50 so that when screw 29 is tightened the upper part expands, transmitting to walls 26 through hinge point 51 an additional clamping force on the bus-bar 4. The cables themselves may enter the track through the open end of the duct 1 or they may pass through a hole (not shown) in the duct. In the embodiment of Figures 1 and 2 they may pass through a hole in channel 11 also.
The connectors 25 may also be used to join lengths of bus-bar end-to-end so that a bus-bar of any required length may be made up from standard lengths. Adjacent bars may be joined by clamping the ends of the bars in the same lug in the manner shown in Figures 5 and 6.
Figure 7 shows another type of channel member 11 for use when the duct is mounted within a wall, as shown in Figure 1. In this case each inner wall of the channel defining the groove 15 has an extension 30 extending towards the bottom of the channel member and defining a groove 31 opposite the bottom of groove 15.
This type of channel member may be used in the manner shown in Figure 1, in which a relatively short screw engages the groove 15 to secure the support bracket to the channel member. However it may also be used with a longer screw which has a cutting point capable of penetrating the channel member material at the bottom of groove 15 so that the screw may pass through this material and extend into the groove 31. A suitable screw for this purpose has a pyramid point of about 30° included angle. The use of a longer screw in this way allows the channel member to be embedded in a wall to a variable depth. When it is embedded with the open ends of grooves 15 substantially flush with the wall surface, as shown in Figure 1, or when the groove ends extend above the wall surface, a long screw securing the bracket to the channel member may pass through the bottom of groove 15 and extend into groove 31. Wall 30 prevents the screw end coming into contact with any cables, for example current-carrying cables leading from accessory 9, which are situated inside the channel member 11, so that these cables will not be damaged when the screw is inserted. However when the channel member is embedded deeply in the wall so that the open ends of grooves 15 are themselves embedded in the wall by a significant distance the screw is long enough to extend into groove 15 to secure the bracket.
The channel member may be formed of polyvinyl chloride which is penetrated relatively easily by the point of a screw.
Figure 8 shows another type of duct for the bus-bars which is suitable for mounting on the surface of a wall, as shown in Figure 4. In this arrangement the duct 1 has side walls 6 and grooves 7 for receiving screws as in the embodiment of Figure 1 but the base 2 of the duct extends outwardly beyond the walls 6 and is provided with upstanding outer walls 32 of which the inturned ends 33 carry outwardly extending flanges 34. Brackets for supporting the cover may be mounted on this duct by screws entering grooves 7, as in the arrangement of Figure 4. However the cover itself is dimensioned as shown in Figure 9 with side walls 35 of lesser depth having interior shoulders 36 to accommodate flanges 34 when the cover is mounted on the brackets. When the cover is mounted on the brackets with the beads of the brackets within the slots 23 the walls 32 and 35 together form an outer wall for the track.
Figure 8 also shows an alternative design for the grooves to contain the bus-bars. In this embodiment the interior wall of groove 3 has serrations extending in the longitudinal direction of the track to form internal abutments 37 to retain the cleats holding the bus-bars. Two types of cleat which may be used in these grooves are shown in Figures 10 and 11 respectively. In both cases the outer walls of the cleats have outstanding flanges 38 to engage abutments 37 to hold the cleats in place in the grooves. However the rearward surfaces 39 of the flanges are inclined so that the cleats may be easily inserted into the grooves by pressing.
The interior slots 40 of the cleat of Figure 10, intended to contain the bus-bar, is of uniform width so that the bus-bar may have a width nearly equal to the overall length of the cleat. The cleat of Figure 11 has a shorter internal slot 40 terminated by constriction 41 to receive a bus-bar of lesser width.
Figures 12 and 13 show a bracket unit for supporting the cover when two adjacent lengths of the cover are joined end-to-end. This unit comprises two members 42 which are of the same profile as brackets 13 shown in Figures 1 and 4 and are mounted on the duct and support the cover in the same way, screws passing through holes 43 to enter the grooves of the duct and beads 19 entering the slots 23 of the cover. Members 42 are joined together by a connecting cover portion 44 which has the same overall cross-section as the cover plates 24. When this bracket unit is mounted on the duct the opposed ends of adjacent cover lengths may be mounted on the respective members 42 with their end edges abutting the portion 44 so that the latter forms a continuous outer surface with the adjacent covers.
The connecting bracket unit shown in Figures 12 and 13 is intended for use with a surface-mounted track of the kind shown in Figure 4 but a similar unit may be used with a flush-mounted track as shown in Figure 1, the flanges 22 then being shorter to match those of the cover in Figure 1.
The track shown in Figure 14 comprises a longitudinal channel-shaped duct 1 of uniform cross-section formed of electrically insulating plastics material such as polyvinyl chloride. It may be made by extrusion. Duct 1 comprises a flat base 2 provided with upstanding portions forming grooves 3a, 3b and 3c containing respective longitudinal copper conductors in the form of bus- bars 4a, 4b and 4c. The bus-bars 4 are narrower than the grooves 3 and are held in the grooves by cleats, not shown in Figure 14, distributed at intervals along the grooves.
Duct 1 has upstanding side walls 6 provided at their edges with continuous longitudinal grooves 7 defined by longer outer walls 8 and shorter inner walls 109. The grooves 7 have a portion 110 (Figure 15) of increased width extending along the groove.
The track also comprises a longitudinal cover for closing the duct. The cover comprises a flat front 111 provided with a flange at opposite longitudinal edges. The flanges at opposite edges are identical and as best seen in Figure 15 each flange extends sideways from front 111 and is provided with an outwardly facing groove 112 formed by wall 113 having a lip 114 extending into the groove.
The flange also has an inwardly facing groove positioned to receive wall 109 of the duct when the cover is applied to the duct. One wall defining groove 115 has an inwardly projecting bead 116 which is bifurcated and has bulges 117 dimensioned to fit into portion 110 of the groove 7. When the cover is applied to the duct the bead is pushed into groove 7 and the bead can expand to occupy portion 110 so that the cover is snap fitted to the duct and a significant force has to be applied to remove it. Wall 8 of the duct is shaped as shown to engage part 118 of the flange and a wedge-shaped gap 119 is provided between these members. When the cover is to be removed a screwdriver blade or like device may be inserted in this gap to lever the duct and cover apart.
The flange is also provided with an outwardly facing groove 120 opposite the bead intended to receive screws 121, of which one is shown in Figure 14. The screws are intended to penetrate the bead inside groove 7 and push bulges 117 apart to secure the cover on the duct. Holes in the bottom of groove 120 may be provided to receive the screws, or alternatively the screws may be capable of penetrating the plastics material of the cover. A suitable screw for this purpose has a pointed pyramidal end for cutting into the plastics material as it is inserted.
The duct 1 is also provided with a pair of upstanding outer walls 122 which may be perpendicular to the base 2, as shown in Figure 15, or be inclined at an angle thereto. The edges of walls 122 are provided with bifurcated beads 123 similar to beads 116 and a shoulder 124. Outer walls 122, together with grooves 112, are intended to hold in place edge covers 125 which may be plastics material or may be of metal such as aluminium. One side of the edge cover has a flange 126 having a widened edge to snap fit in groove 112 behind lip 114. The other side of the edge cover has a groove 127 of part-circular cross-section to snap over bifurcated bead 123. A small gap between shoulder 124 and the edge of side cover 125 is provided to receive a screwdriver blade or other tool to allow the side cover to be removed by leverage.
The track of this embodiment is intended to be mounted with the rear surface of base 2 in contact with a wall and grooves 128 (not shown in Figure 14) are provided on the base to facilitate location of screws (not shown) to pass through the base and secure it to the wall in known manner. Such a groove may be provided between both pairs of walls 6 and 122. Grooves 128 may have holes at intervals to receive the screws, alternatively screws capable of penetrating the plastics material of base 2 may be used.
The outermost of the walls defining grooves 3a and 3c are provided with flanges 129 extending at an angle towards walls 6 to receive an edge of strips 130, the opposite edges of the strips being received in grooves 131 on walls 6. The grooves are dimensioned so that the strips may be snapped into place and isolate the spaces 132 in the duct from the remainder of the duct. Spaces 132 may be used to accommodate telephone wires or other services which run along the duct and are not associated with the circuits formed by bus-bars 4.
Figure 15 shows one cleat of the type shown in Figure 10 holding a bus-bar 4 in place. Cleats are provided at intervals along each bus-bar.
The arrangement shown in Figure 16 is similar to that of Figures 14 and 15 but is intended for flush mounting in a groove in a wall instead of surface mounting. The cover 111 and side covers 125 are identical to those of Figures 14 and 15 and fit on to the duct in the same way. However instead of having outer walls 122 the side walls 6 of the duct in this embodiment have outstanding flanges 141 provided with bifurcated beads 142 of the same kind as beads 123 to engage groove 127 of the side cover. When the duct is mounted in the wall flange 141 will be substantially flush with the wall surface and the duct is surrounded by channel 11 of plastics material of the type shown in Figure 7 which is embedded in the groove in the wall. The channel has outstanding flanges 144 to secure the channel in the material of the wall.
Flange 141 has a groove 149 which is aligned with groove 15 when the duct is fitted in the channel as shown in Figure 16. The duct is secured to the channel by screws 150 inserted at intervals along the groove 149: holes for this purpose may be provided in the bottom of groove 149 but it is preferred to use screws 150 capable of penetrating the plastics material of the duct and channel so that no preformed holes are required.
The remainder of the assembly is identical to that of Figures 14 and 15.
Figure 14 shows a 13-amp plug socket 151 mounted in the track. This socket is of standard internal construction but is connected to the bus-bars 4 by forked connectors, extending behind the socket to engage a respective bus-bar in the same manner as indicated in Figures 2 and 4.
The manner in which the socket is mounted in the track is shown in Figures 14 and 17. The socket itself has a front surface 152 which, when mounted on the track, projects slightly above the surface of cover 111. The socket may be mounted between two lengths of cover 111 in the longitudinal direction, as shown in Figure 14. Its longitudinal side surfaces 153 are aligned with corresponding side surfaces of cover 111 and engage side covers 125 when the track is assembled, the side covers extending beside both the cover 111 and the socket. Side surfaces 153 have flanges 154 which abut the edges of walls 6.
The sides of the socket transverse to the track are provided with outstanding flanges 155 which, when the track is assembled, extend behind and engage the inside surface of cover 111. The socket is thus clamped in place on the track by the cover 111 engaging flanges 155.
Figure 17 shows only one (the upper) longitudinal side of the socket; the lower side is engaged with the track in the same way. The socket may be mounted in the same way in the surface and flush tracks shown in Figures 14 and ₁6.
Other electrical accessories, such as switches and circuit-breakers, may be similarly mounted in the track provided that they have similar flanges 155.
A method of mounting a standard accessory, which need not be manufactured with flanges as in the above-described embodiments,is illustrated by Figures 18 and 19 with reference to the embodiment of Figure 14; a similar method may be used with the other types of track shown in the drawings. The front plate 156 of the accessory is mounted in front of the track covers, to overlap the edges of the adjacent covers 111 and side covers 125. It is held in place by screws 157 passing through holes 158 in a rectangular mounting plate 159 which has a generally square central aperture 160 to accommodate the working parts of the accessory on the rear surface of plate 156. The edges of the plate are provided with holes 161 positioned so that when the plate is positioned on the track as shown in Figure 18 the holes are aligned with the groove in wall 6 and the mounting plate may be secured to the track by screws 162 passing through holes 161 and engaging the inner surfaces of the grooves.
On assembly of the track the mounting plate may first be attached in this way, followed by mounting of the cover 111 and side covers 125 and mounting of the accessory 156 using screws 157. The mounting plate may have flanges at its edges to increase its rigidity.
This method of mounting may be used for any standard accessory of appropriate dimensions which has holes to receive screws 157 at the required locations.
When the track shown in Figure 14 is installed in a building the duct 1 is first attached to the surface of a wall or like supporting structure by screws applied to grooves 128 (Figures 14 and 15) or mounted in a groove in the wall with flange 41 flush with the wall surface (Figure 16). The bus-bars are then mounted in their grooves using cleats spaced at intervals (if they are not mounted in the duct already) and if desired any telephone cables or the like which are required may be passed through spaces 132 which are then closed by application of members 130. Electrical accessories such as plug 151 may then be positioned at any desired point along the duct with their fork terminals in contact with the bus-bars. As shown in.Figure 14 the three bus-bars are positioned unsymmetrically with respect to the longitudinal axis of the duct to avoid any risk of an accessory being mounted upside-down. Any accessories requiring use of a mounting plate 159 are similarly mounted at any desired position. The main cover 111 and side covers 125, may then be applied as shown in Figure 14 to close the duct: the covers are easily cut to the appropriate length on site.
It will be appreciated that this method of assembly is quick and easy, especially when no screws are required for assembling the duct and covers. No separate crosspieces are needed to support the duct covers or accessories. The assembly is easily dismantled using the reverse procedure. The track is highly suitable for installation at floor level around a room but it may equally be installed in the middle of a wall, running horizontally or vertically.
When the track is installed the duct and covers may be supplied in standard lengths and it may be necessary to join adjacent pieces of duct and cover end-to-end, in which case the joint should be protected especially to prevent entry of water or other unwanted matter from the outside. Such protection may be provided by a joint cover 171 shown in Figure 14 and in Figures 20-22.
Figure 20 shows the outside surface of the joint cover as seen in Figure 14 but without the intervening cover parts, Figure 22 is a section through the joint cover and Figure 21 is a view of the joint cover seen from the side. The joint cover comprises a strip of plastics material forming side walls 173 which fit over the walls 122 of the duct and central portion 172 extending between the walls 122 of the duct and shaped so that the outer surface of the cover joint is substantially flush with the outer surfaces of the main cover 111 and side covers 125.
The inner surface of the joint cover is provided with projections 174 to enter grooves 7 of walls 6 and the adjacent parts of the inner surface are shaped to abut the edges of walls 8 and 9 around the grooves. Grooves 175 are provided to engage the bead 123. The joint cover has flanges 177 to extend sideways to fit underneath the ends of the adjacent covers so that the latter hold the joint covers in place and prevent access to the interior.
Figure 14 also shows an end plate 180 which is of similar construction to joint cover 171 except that it also comprises a wall closing off the open end of the track.
Similar joint covers and end plates may be provided for the flush-mounted track of Figure 16 but in this case side walls 173 will not be required.
Figures 23 and 24 show a corner-piece which may be used when the surface-mounted power track of Figure 14, mounted on a wall, is to continue around a convex right- angle corner. Surfaces 181 of the corner-piece engage the wall and surfaces 182, 183 provide a continuation of the outer surfaces of the covers 111 and 125 around the corner. Surfaces 182 are substantially flush with the outer surfaces of the covers 111, 125 of an adjacent length of track and projections shown generally at 184 engage the adjacent track behind the covers to join the track to the corner-pieces. The interior surfaces behind surfaces 182 are of similar profile to the inner surface of covers 111 and 125 to engage the end portions of adjacent ducts 1 and clip the corner-piece to the track.
Figure 25 shows a corner-piece for a concave right-angled corner. Surfaces 185 will engage the walls of the room and surfaces 186 will be flush with corresponding surfaces of the covers of the adjacent track lengths. Projections 187 extend behind the adjacent covers, as in the corner-piece of Figure 23.
With both these types of corner-piece the adjacent duct 1 will extend up to the corner itself, the bus-bars of the adjacent ducts being joined by suitable connectors at the corner, and the ends of the ducts at the corner are covered by the corner-piece.
The embodiments shown in the drawings have been described in relation to the mounting of a 13-amp switch on the track but it will be understood that a wide variety of circuit accessories, including circuit-breakers, may be mounted on the track and connected to the bus-bars, in the same manner. When the accessory is a socket of the type shown current is supplied from the bus-bars to the point of use through a plug inserted in the socket. With other types of accessory the accessory itself may be provided with cables running to the point of use and these cables may extend from the front of the accessory, which is exposed when mounted on the track. Alternatively cables may extend from the back or a side of the accessory which are enclosed in the assembled track and holes in the duct, and channel when used, are then required to allow passage of the cables. These holes may be provided by knock-out portions formed in known manner in the duct and channel.
The duct, bus-bars, track cover and channel may all be supplied in a variety of standard lengths or may be cut to any required length on site so that the length of the track is easily adapted to any given requirement, for example installation in a room of a house where the length of a wall is non-standard.
Once the duct and its bus-bars are installed the switch sockets or other accessories may be mounted on the track at any arbitrary point so that they may be positioned to suit the requirements of an individual customer. The track cover may then be cut to length using a tenon saw or the like and mounted in place on the brackets.
Alternatively the various components may be assembled in a workshop, for example to a previously determined arrangement thus saving assembly time on site.
Any number of accessories may be mounted on the same track, either side-by-side or spaced along the track, and spaces between the accessories are occupied by the track cover so that the track is completely enclosed. The snap-on track cover is held firmly by beads in grooves so that it will not be removed accidentally and there is little risk of unauthorized removal, for example by a child.
The bus-bars may be designed to carry any required current, for example up to 60 or 100 amps. As shown in the drawings, the distance between bus- bars 4a and 4b may differ from that between 4b and 4c. This unsymmetrical arrangement avoids any risk of a switch or other accessory being mounted on the track upside-down.
The embodiments described above use three bus-bars, intended for use as live,neutral and earth in a domestic power supply but substantially the same arrangement may be used with a different number of bus-bars for example in a polyphase system.
The dimensions of the track may be such that switches and other accessories mounted on it may be of standard types and sizes which are already established in the art. The track will then be compatible with existing equipment.

Claims

1. An electrical distribution track comprising a longitudinal hollow duct adapted to be mounted on a support surface or in a channel embedded in a support surface, the duct containing exposed electrical conductors extending therealong,

the duct comprising a base and a pair of longitudinally extending side walls having a continuous longitudinal opening therebetween to allow insertion into the duct of an electrical accessory at any point along the duct,

the side walls comprising outwardly facing edges capable of engaging flanges on opposite sides of an accessory positioned in the duct or of a mounting device capable of holding an accessory in the duct,

means for clamping an accessory or mounting device to the duct with said flanges abutting said edges,

and cover means adapted to be attached to the duct such that the parts of the opening not occupied by the accessory, the edges of the walls of the duct and the flanges of an accessory or mounting means therefor abutting said edges are covered by the cover means,

the cover means extending to the support surface outside the duct or the duct having outer walls extending from the support surface to the cover means so that the parts of the duct which are exposed when the duct is mounted on a support surface or in a channel thereon are enclosed by the cover means or by the cover means and the outer walls.

2. A track according to claim 1, in which the edges of the walls of the duct are provided with continuous longitudinal grooves to receive screws for clamping said flanges to the edges.

3. A track according to claims 1 or 2, provided with transverse brackets engaging the edges of the walls of the duct, the brackets being adapted to support the cover means.

4. A track according to claim 3, in which the brackets are screwed to the edges of the walls of the duct.

5. A track according to claim 3 or 4, in which the cover means and the brackets are provided with respective grooves and upstanding beads such that the beads may be snap fitted into the grooves to hold the cover means in place on the brackets.

6. A track according to claim 3, 4 or 5 in which the brackets are dimensioned to engage a transverse edge of an accessory or mounting device therefor to clamp the accessory or mounting device to the duct.

7. A track according to any one of claims 3 to 6 including a longitudinal channel member to be mounted in a groove in a support surface for the track to contain the duct channel member comprising side walls having edges provided with grooves for receiving screws, the brackets being screwed to the edges of the channel side walls to retain the duct in the channel member.

8. A track according to claim 7, in which the edges of the channel member are provided with inner walls, said grooves being defined by the inner walls and the side walls of the channel member, the inner walls and the side walls of the channel member are connected by a body of material which a screw may penetrate, and the inner walls extend from said body to define further grooves on the side of said body remote from the edges of the side walls of the channel member.

9. A track according to any preceding claim, in which the cover means comprises an integral body extending over the opening and the side wall edges of the duct and engaging the support surface on or in which the track is mounted.

10. A track according to any one of claims 1 to 8, in which the duct is provided with a pair of upstanding outer walls and the cover means comprises an integral body extending over the opening and the side wall edges of the duct and engaging the edges of the outer walls of the duct.

11. A track according to claim 1, in which the cover means comprises a centre cover extending over the opening and the edges of the side walls of the duct and the centre cover and the edges of the side walls are provided with respective grooves and beads such that the beads may snap fit into the grooves to secure the centre cover to the side walls.

12. A track according to claim 11, in which the beads are bifurcated and capable of expanding inside the grooves.

13. A track according to claim 11 or 12, inwhich the centre cover is provided with grooves in its surface opposite the-beads to receive screws to penetrate the centre cover and extend through the beads within the grooves of the side wall edges.

14. A track according to any one of claims 11 to 13, in which the cover means comprises side covers covering the track on respective sides of the centre cover having surfaces substantially flush with the surface of the centre cover.

15. A track according to claim 14, in which the side covers comprise flanges engaging inside a corresponding groove formed in the centre cover.

16. A track according to claim 14 or 15, in which the side covers and theduct have respective grooves and beads and the beads snap fit into the respective grooves to secure the side covers to the duct.

17. A track according to claim 16, in which the duct has outer walls extending from the support surface and the side covers and the edges of the outer walls have engaging grooves and beads.

18. A track according to claim 16, comprising a longitudinal channel member to be mounted in a groove in a support surface for the track to contain the duct,the channel member comprising side walls having edges provided with grooves for receiving screws, the walls of the duct having outwardly extending flanges screwed to the edges of the channel member walls and the flanges being connected to the side covers by engaging grooves and beads.

19. A track according to any preceding claim, in which the exposed conductors are mounted in parallel channels on the base of the duct.

20. A track according to claim 19, in which the conductors are metal strips held in their channels by cleats gripping the strips and engaging the interior surfaces of the channels.

21. A track according to claim 20, in which the channels containing the conductors are provided with interior abutments to retain the cleats in the channels.

22. A track according to claim 19, 20 or 21 in which the conductors are three in number and the transverse distances between the middle conductor and the outer conductors are unequal.

23. A track according to any preceding claim, in which the interior of the duct is provided with at least one chamber extending longitudinally along the duct and isolated from the remainder of the duct interior by a removable strip.

24. A track according to any preceding claim, in which adjacent lengths of said cover means attached to the duct are joined together at their ends by connectors covering the opening and the edges of the walls of the duct and extending to the wall of the support surface, at least the parts of the connectors covering the opening and the edges of the walls of the duct having an outer surface substantially flush with that of the cover means.

25. An assembly comprising a track according to any one of the preceding claims and an electrical accessory,in which the accessory is mounted in the opening of the duct and has a pair of outstanding flanges abutting the edges of the walls of the duct.

26. An assembly comprising a track according to any one of claims 1 to 24 and an electrical accessory, in which the accessory is secured to a mounting plate and is mounted in the opening of the duct with the mounting plate abutting the edges of the walls of the duct.

27. An assembly according to claim 25 or 26, in which the flange of the accessory or the mounting plate is clamped to the edges of the walls of the duct by screws.

28. An assembly according to claim 25 or 26, in which the accessory or the mounting plate is clamped in position by the cover means.

29. An assembly according to any one of claims 25 to 28, in which the accessory is provided with sprung forked terminals to make electrical contact with the conductors when the accessory is mounted in the track.