GB2286925A

GB2286925A - An electrical switching system

Info

Publication number: GB2286925A
Application number: GB9503791A
Authority: GB
Inventors: Graham Bickford
Original assignee: Caradon MK Electric Ltd
Current assignee: Caradon MK Electric Ltd
Priority date: 1994-02-25
Filing date: 1995-02-24
Publication date: 1995-08-30
Also published as: GB9403621D0; GB9503791D0

Abstract

An electrical switching system for use in a control and connection system includes several linear conductors (3, 4), enclosed in a casing (2). The casing has one or more socket apertures. One of the conductors is interrupted in the socket and at the point of interruption the conductor has a contact (13, 14), either side of the interruption. A switch means (10) is provided to electrically connect the contacts. A switch operating means (50) can be inserted into the socket aperture. <IMAGE>

Description

An Electrical Switching System The present invention relates to an electrical switching system for use in a linear electrical control and connection system such as that described in co-pending application publication number GB 2 275 835.

The problem of providing a switch in an electrical circuit for the purpose of control is well known. The normal practice is to construct a switch and then connect the switch to the conductors of the electrical circuit. Such a switch is a self contained module, containing terminals, contacts, and means for interrupting the electrical connection between at least two of the terminals. Costs are incurred both in the manufacture of the components of the switch and in its subsequent assembly, and also in the installation of the switch into the electrical circuit it is to control.

For example, in a busbar trunking system such as the electrical control and connection system referred to in co-pending application publIcatIon number GB 2 275 835 a large number of switches are required to be fitted during manufacture, as such a design would probably require a switch to be incorporated into every socket outlet. The purpose of the switches is to break the electrical continuity of the conductor they are incorporated into, so that the conductor is segmented, and then each of the segments may be controlled by a control device connected to that segment independently of other segments. When the system is installed in a typical installation, long lengths of busbar trunking will have many electric light fittings controlled by one control device. Hence since the switch is only operated when it is required to segment a length of busbar, only a very few of these switches will ever be operated to break the electrical continuity of the conductor they are fitted into.

It is an object of an embodiment of this invention to provide for a simplified switch design for the conductors of an electrical circuit which eliminates the costs of installation of the switch into the electrical circuit.

An electrical switching system according to the present invention comprises a plurality of linear conductors enclosed in a casing, the casing having one or more sockets along its length, at least one conductor interrupted in the socket, the interrupted conductor having a pair of contacts at the point of interruption, and a switch means to electrically connect the contacts.

is is a further advantage to attach the contacts directly to the ends of the conductors since this reduces the number of inter-connections. Each inter connection is a potentla w of hIgh resistance which on a long length cf conductor with many such Interruptions would s:Je an unacceptable voltage drop along the conductor. Further each inter-connection requires an assembly operation which inevitably adds cost to the finished product.

It is also ncwn or sites to be provided with permanent operating means, commonly â rocker or a toggle or a lever. Occasionally the operating means is removable as in the MK (Registered Trade Mark) Secret Key Switch so that it is not possible to operate the switch without the operating means. A disadvantage of using a switch such as the Secret Key Switch is that when the operating means has been removed from the switch it is not possible to ascertain by visual inspection the state of the switch. A further design is where the operating means is retained in the switch when it is in the on position, and when the operating means is removed the switch must be left in the off position, an example of this being the MK (Registered Trade Mark) Energy Saving Switch intended for use in hotel bedrooms.

However in all these designs it is more expensive to provide the removable operating means than the common rocker operating means. The cost of such known switches would make a system using a very large number of switches uneconomic.

Embodiments of the present invention include a contact member movable to make an electrical connection between the pair of contacts, where the movable contact member is biased to make the electrical connection and a switch operating means is provided which is insertable into tne socket to operate the movable contact member to break the electrical connection.

The benefit cf the arrangement where the contact member ;s biased is tat at each of the sockets there is normally electrical connectIon across the point of interruption cf the conductor, and =is is the condition required at the majority of the sockets in a typical installation. In the instances where it is required to operate the switch means to break the electrical ccntinuity at the point of interruption, this may be done by the addition of a switch operating means at a particular socket. Hence, not only is the cost of the typical installation reduced by avoiding the provision of redundant switch operating means, but also the presence of a switch operating means inserted in a socket provides a visuai indication that the electrical connection at that socket has been interrupted.

It is also known for switches to incorporate indicator lamps to show when they are switched on. Such indicator lamps are normally made as an integral part of a special variant of a standard switch. Hence it is expensive to provide such indicator lamps on a switch. It is also necessary for the installer to anticipate the requirement for such indication and install such a switch before the user can use it.

It is an object of an embodiment of this invention to provide illuminated indication of when the switch is operated in such a manner that the user can avail himself of the facility when required without having to install a special switch in advance. This avoids the user having to specify in advance where such indicating means will be required, and as a result simplifies the specification of and reduces the cost of the initial installation.

According to a further embodiment of the present invention the switching system is provided with at least one said contact mounted fixedly to the casing. The casing surroundIng the conductor n this embodiment may be used as a body member to contain the switch components. The benefit cf tunis is that the number of discrete components required is reduced to a minimum.

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a section of conductor encased in a length of rigid ducting with a switch means according to the invention; and Figure 2 shows the switch means of Figure 1 with the switch in an operated state; and Figure 3 shows an alternative form of construction for the switch means which incorporates insulating means to prevent accidental contact with live parts; and Figure 4 shows the same switch means of Figure 3 with the switch in an operated state.

Figure 1 shows a section of rigid ducting 1, comprising a substantially continuous casing wall 2 encasing a supply line conductor 3 and a switched load conductor 4 which are electrically connected by switch means 5. The switch means 5 comprises a moving contact plate 10, with contacts 11 fitted at each end, the contact plate biased by compression spring 12 against fixed contacts 13 and 14. Fixed contacts 13 and 14 are fitted directly onto the conductor ends 23 and 24 of the conductors 3 and 4 respectively. The conductor ends 23 and 24 are formed from the conductors 3 and 4 by twisting, forging, cutting or other process such that a satisfactory fixing may be obtained for contacts 13 and 14. Contacts 13 and 14 are made such that the surfaces which face contacts 11 are coated with a suitable material to give the required electrical performance and life, suitable materials would include silver and silver alloy and sintered silver materials and silver containing other elements in a solid solution. The contacts 13 and 14 may be fixed by any process that provides suitable electrical and thermal conductivity and mechanical strength, and includes welding, brazing, riveting, crimping. It is also possible for the contacts to be formed by selectively plating or otherwise coating the ends 23 and 24 with a suitable contact material such as silver or a silver alloy. Like contacts 13 and 14, contacts 11 are made such that the surfaces which face contacts 13 and 14 are coated with a suitable material to give the required electrical performance and life, suitable materials would include silver and silver alloy and sintered silver materials and silver containing other elements in a solid solution. The contacts 11 may be fixed to moving plate 10 by any process that provides suitable electrical and thermal conductivity and mechanical strength, and includes welding, brazing, riveting, crimping. It is also possible for the contacts to be formed by selectively plating or otherwise coating the ends 21 with a suitable contact material such as silver or a silver alloy. An socket aperture 6 is provided in the casing wail 2 to enable the switch to be operated. =n the embodiment shown, conductors 3 and 4 are electrIcally connected by the switch 5 until the switch is operated, however the Invention would apply equally in the case where the conductors are normally electrically disconnected until the switch is operated when they are connected.

Figure 2 shows the same section of rigid ducting 1 as shown in Figure 1, with a switch operating means 50 fitted to socket aperture 6. Switch operating means 50 comprises a body 51 made cf a translucent insulating plastic, which has grooves 52 for retaining two flexible latches 53. The two flexible latches 53 have surfaces 54 to enable a user to flex the latches inwards to engage and disengage the prongs 55 from the socket aperture 6, hence enabling the insertion and removal of the switch operating means 50. The body 51 has a protrusion 56 designed to apply pressure against moving contact plate 10 so that when the switch operation means 50 is inserted into the socket aperture 6 the switch is broken to give the gap between the fixed contacts 13 and 14 and the contacts 11. Hence when the switch operating means is inserted the conductor 3 is electrically disconnected from conductor 4. The switch operating means also incorporates an indicator lamp 60 with lead wires 61 and 62, a current limiting resistor 63 being fitted in one lead wire. The lead wires 61 and 62 are connected to small resilient contacts 65 and 67. Figure 2 shows these resilient contacts 65 and 67 making electrical connection to the ends of the conductors 3 and 4. Hence if there is a sufficient potential difference between conductors 3 and 4 the lamp 60 will light. If there are other conductors in the vicinity of the conductors 3 and 4 that are shown, then it would be equally possible for the resilient contacts 65 and 67 to make contact with these other conductors instead, for instance the lamp could be connected across a permanent line and neutral conductors. If it is not required to have the indicator lamp function, then items 60 to 67 inclusive may be omitted without compromising the function of the switch operating means.

Figure 3 shows an alternative form of construction for a switch means which is shown in a section of rigid ducting 101, comprising a substantially continuous casing wall 102 made from an insulating material encasing a supply line conductor 103 and a switched load conductor 104 which are electrically connected or disconnected by switch means 105. The switch means 105 comprises a fixed contact 113 which is fitted directly onto the conductor end 123 of the conductor 103 and a moving contact 114 fitted directly onto resilient contact arm 124 of the conductor 104. The contact 114 on resilient contact arm 124 is biased by compression spring 112 against contact 113, hence electrical connection is made between conductors 103 and 104. The conductor end 123 and the resilient contact arm 124 are formed from the conductors 103 and 104 by twisting, forging, cutting or other process such that a satisfactory fixing may be obtained for contacts 113 and 114. Contacts 113 and 114 are made such that the surfaces which make electrical contact with each other are coated with a suitable material to give the required electrical performance and life, suitable materials would include silver and silver alloy and sintered silver materials and silver containing other elements in a solid solution. The contacts 113 and 114 may be fixed by any process that provides suitable electrical and thermal conductivity and mechanical strength, and includes welding, brazing, riveting, crimping. It is also possible for the contacts to be formed by selectively plating or otherwise coating the ends 123 and 124 wit a suitable contact material such as silver or a silver alloy. For certain applications it would be acceptable to use the bare ends of the conductors 103 and 104 for the contacts without any additional special contact materials covering the contact areas. Conductors 103 and 104 are located by upstands 170 and 171 which engage in detents 172 and 173 in the conductors. This prevents any relative movement of the contacts 113 and 114 due to thermal effects or external mechanical strain on the conductors. To ensure that there can be no accidental contact with live parts an insulating shroud 180 is fitted inside socket aperture 106 and attached to the inside of casing wall 102. The insulating shroud 180 has a hole 181 in which pin 182 is free to slide. The pin i82 is made frm insulating material and has a domed head 183 which is a larger diameter than hole 181 to prevent the end surface 184 of the pin rising above the substantially annular planar surface 185 of the shroud.

The dimensions of the pin 182 and its head 183 are such that there is clearance 187 between the domed head 183 and the top surface 125 of resilient contact arm 124.

This ensures that all the force from spring 112 is used to maintain the pressure between contacts 113 and 114.

Although Figure 3 shows upstands 170 and 171 from the casing wall 102 which locate the conductors, the same effect would be achieved by providing upstands or sprags on the conductors which press against the casing wall 102 or shroud 180. Although clearance 189 is shown between the shroud and the conductor end 123, shroud 180 could be used to support the conductor end 123 to help resist the force of spring 112. This could be advantageous as it would ensure that contact pressure is maintained.

Figure 4 shows the same switch means 105 of Figure 3 in the same section of rigid ducting 101, but with the switch in an operated state. The switch is operated by the switch operating means 250 fitted to socket aperture 106. Switch operating means 250 comprises a body 251, which has grooves 252 for retaining two flexible latches 253. The two flexible latches 253 have surfaces 254 to enable a user to flex the latches inwards to engage and disengage the prongs 255 from the edge 191 of the socket aperture 106, hence enabling the insertion and removal of the switch operating means 250. The groove 190 is formed in shroud 180 to provide clearance for the prongs 255. The body 251 has a protrusion 256 designed to apply pressure against pin surface 184 so that when the switch operation means 250 is inserted into the socket aperture 106 the switch is broken to give the gap 257 between the fixed contact 113 and the moving contact 114. Hence when the switch operating means is inserted the conductor 103 is electrically disconnected from conductor 104.

Although only conductors 3 and 4 are shown in Figure 1, and likewise in Figure 3 only conductors 103 and 104 are shown, there may be additional conductors also encased within the same length of rigid ducting. These additional conductors may be uninterrupted at the socket, and means may be provided to make electrical connection to the additional conductors for the purpose of connecting an electrical load or appliance.

In the embodiment shown in Figures 3 and 4, conductors 103 and 104 are electrically connected by the switch 105 until the switch is operated, however the invention applies equally in the case where the conductors are normally electrically disconnected until the switch is operated when they are connected.

A further embodiment of the switch that is not illustrated Incorporates an interlock mechanism to prevent operatIon cf the switch by any means other than the correspon-ing switch operatIng means. An advantage of this is that it is not possible for the switch to be broken, except by the InsertIon cf the corresponding switch operating means, which by its presence visually flags the operation of the switch. In this embodiment insertIon of a non-corresponding switch operating means would not operate the switch.

Claims

1. A switching system comprising a plurality of linear conductors enclosed in a casing, the casing having one or more sockets along its length, at least one conductor interrupted in the socket, the interrupted conductor having a pair of contacts at the point of interruption, and a switch means to electrically connect the contacts.

2. A switching system as claimed in claim 1, wherein at least one said contact is mounted fixedly to the casing.

3. A switching system as claimed in claim 1 or 2, wherein one said contact is movably mounted to the casing.

4. A switching system as claimed in any one of the preceding claims wherein the switch means includes a contact member movable to make an electrical connection between the fixed contacts.

5. A switching system as claimed in any one of the preceding claims wherein the movable contact member is biased to make the electrical connection.

6. A switching system as claimed in any one of the preceding claims wherein the switching system further comprises a switch operating means which is insertable into the socket to operate the movable contact member to break the electrical connection.

7. A switching system as claimed in claim 6 wherein the switch operating means is retained in the socket by one or more latches.

8. A switching system as claimed in claim 7 wherein the latch or latches are provided on the switch operating means.

9. A switching system as claimed in any one of claims 6 to 8 wherein a lamp is incorporated in the switch operating means so as to be electrically connectable between the contacts.

10. A switching system as claimed in any one of claims 6 to 9 wherein the switch operating means is arranged to act on a separate member acting on the movable contact member.

11. A switching system substantially as described with reference to the accompanying Figs. 1 and 2.

12. A switching system substantially as described with reference to the accompanying Figs. 3 and 4.