GB2212328A

GB2212328A - Switching devices

Info

Publication number: GB2212328A
Application number: GB8726124A
Authority: GB
Inventors: Bernard Patry; Kenneth Wilson
Original assignee: Schlumberger Industries Ltd
Current assignee: Gemalto Terminals Ltd
Priority date: 1987-11-07
Filing date: 1987-11-07
Publication date: 1989-07-19
Anticipated expiration: 2007-11-07
Also published as: GB8726124D0; GB2212328B

Abstract

A switching device particularly for use with loads supplied under the "Economy 7" tariff in the UK, comprises two relays 34, 36 having respective movable contacts 32, 38, 40 with a contact 32 common to both relays. The two movable contacts 38, 40 are coupled together by a mechanical means 52 in such a manner that they cannot both make electrical contact with the common contact 32 simultaneously. Additionally, a device such as a cam 64, intended to be coupled to an on-off slider on the front of the switching device is provided for opening up the contact gaps to at least 3 mm, and preventing closure of the movable contacts 38, 40 onto the common contact 32, when the slider is in the off position. This arrangement meets safety requirements, while at the same time enabling the number of contacts in series with the load to be reduced, thus reducing heat generation, and so permitting a compact design to be achieved. <IMAGE>

Description

SWITCHING DEVICES This invention relates to switching devices, and is more particularly but not exclusively concerned with switching devices for use in a multi-tariff electricity supply system.

One well-known multi-tariff electricity supply system is that based on the so-called "Economy 7" tariff, under which cheap-rate electricity is provided during the night (typically from midnight till 7.00 am) and more expensive electricity is provided at other times. A typical load supplied by such a system is an immersion heater forming part of a domestic hot water system. The supply of electricity to the load is typically controlled by a switch, for example a time switch or a radio teleswitch, having a first switched output synchronised with the period of cheap-rate electricity supply and a second manually switched output, or "boost" output, for temporarily supplying the load, typidally for a "boost" period of up to one hour, outside the period of cheap rate supply.A typical example of a time switch which operates in this way is described in our United Kingdom Patent Application No. 2 130 449.

The two switched outputs of such a switch are typically provided via respective relays, whose contacts, when open, typically have a separation of about 0.5 mm. However, for reasons of safety, it is usually required that such a switch should include switching contacts in the live and neutral wires of the incoming mains supply which can open to a separation of at least 3 mm, so as to fully isolate the load from the incoming mains supply.

Additionally, the arrangement of the relays is normally required to be such that both switched outputs cannot be energised simultaneously. To meet these requirements, the switch is therefore usually provided with a separate manually-operable two pole switch whose contacts open to the required 3 mm, and at least one of the relays is normally a change-over relay whose switching contacts are arranged in series with those of the other relay.

This not only increases the cost of the switch, but also results in a situation where there can be up to four sets of switching contacts in series with the load, each set generating heat by virtue of its electrical resistance. The necessity of dissipating this heat makes it difficult to make the switch compact.

It is therefore an object of the present invention to provide a switching device in which these drawbacks are alleviated.

According to one aspect of the present invention, there is provided a switching device including first and second movable switching contacts, first and second coils associated with the first and second movable contacts respectively and each arranged to control the movement of its respective movable contact into and out of electrical contact with a common switching contact, and mechanical means arranged to transmit at least part of the movement of each of the first and second movable contacts to the other in such a manner that they cannot both contact the common contact simultaneously.

Conveniently, the first and second movable contacts are disposed on opposite sides of the common contact, and the mechanical means comprises means for maintaining a minimum separation of the first and second movable contacts greater than the dimension of the common contact in the direction of movement of the first and second movable contacts.

Thus the mechanical means may comprise an elongate bar having first and second longitudinally spaced slots for receiving the first and second movable contacts respectively, each contact being able to move longitudinally of its slot but the spacing between the adjacent ends of the slots being greater than said dimension of the common contact.

In a preferred embodiment of the first aspect of the invention, the switching device further comprises a manually operable switch, a first input terminal for connection to the live wire of a mains electricity supply, said first terminal being connected to said common switching contact via a first set of contacts of the manually operable switch, and first and second switched output terminals for connection to a load or loads, said first and second output terminals being connected to said first and second movable contacts respectively.

Desirably, the switching device also comprises a second input terminal for connection to the neutral wire of the mains electricity supply, and a neutral output terminal for connection to the load or loads, the second input terminal being connected to the neutral output terminal via a second set of contacts of the manually operable switch.

According to a second aspect of the invention, there is provided a switching device including a pair of relatively movable switching contacts, a coil for controlling the relative movement of the contacts from a first relative position in which the contacts are closely adjacent each other to a second relative position in which the contacts are in electrical contact with each other, and manually operable means for controlling the relative movement of the contacts from the first relative position to a third relative position in which the contacts are prevented from entering the second relative position and their separation is substantially greater than it is in the first relative position.

Advantageously, the switching device comprises first and second movable switching contacts each movable into and out of electrical contact with a common contact, the first movable contact and the common contact constituting said pair of relatively movable contacts, and a second coil for controlling the relative movement between the second movable contact and the common contact between first and second relative positions analogous to those of the first movable contact and the common contact, the manually operable means being further arranged to control the relative movement of the second movable contact and the common contact between said first relative position and a third relative position also analogous to that of the first movable contact and the common contact.

In a preferred embodiment of this second aspect of the invention, the switching device also includes mechanical means arranged to transmit at least part of the movement of each of the first and second movable contacts to the other in such a manner that they cannot both contact the common contact simultaneously.

Thus the mechanical means may comprise an elongate bar having first and second longitudinally spaced slots for receiving the first and second movable contacts respectively, each contact being able to move longitudinally of its slot as it is moved to its respective third relative position, but the spacing between the adjacent ends of the slots being greater than said dimension of the common contact.

In a preferred embodiment of the second aspect of the invention, the switching device further comprises a first input terminal for connection to the live wire of a mains electricity supply, said first input terminal being connected to said common contact, and first and second output terminals for connection to a load or loads, the first and second output terminals being connected to the first and second movable contacts respectively.

Desirably, the switching device also includes a second input terminal for connection to the neutral wire of a mains electricity supply, and a neutral output terminal for connection to the load or loads, the second input terminal being connected to the neutral output terminal via a pair of normally-closed contacts, and the manually operable means being arranged, when the first and second movable contacts are in their respective third relative positions, to open said normally-closed contacts to a separation similar to that between the common contact and each of the first and second movable contacts.

The switching device may be a time switch, in which case the coil or coils may be energised by control signals produced by an electronic timing and control circuit, or it may be a radio teleswitch, in which case the coil or coils may be controlled by a radio receiver which receives broadcast signals having digitally encoded control signals modulated thereon and an electronic circuit for demodulating and decoding the received signal to derive the control signals for application to the coil or coils.

The invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic representation of one embodiment of a switching module forming part of a switching device in accordance with the present invention; and Figures 2A and 2B are schematic representations of a second embodiment of a switching module forming part of a switching device in accordance with the invention, showing two different operative states of the module.

The switching module shown in Figure 1 is indicated generally at 10, and is intended to form part of a switching device of the same general kind as is described in our aforementioned United Kingdom Patent Application No. 2 130 449, ie a tariff time switch suitable for controlling a domestic hot water system in accordance with the aforementioned "Economy 7" tariff. As will become apparent hereinafter, the switching device includes two relays for controlling two switched outputs in accordance with the tariff, and electronic circuitry for controlling the energisation of the relays: however, for the sake of simplicity, details of the electronic circuitry have been omitted, since these details are not necessary to the understanding of the present invention.

The switching module 10 comprises first and second input terminals 12, 14 for connection to the live and neutral wires (not shown) of a mains electricity supply, first and second switched live output terminals 16, 18 for connection to the respective live input terminals (not shown) of respective loads such as the main and auxiliary (or "boost") heating elements of a domestic hot water system, a neutral output terminal 20 for connection to the respective neutral terminals of the loads, and an earth terminal 22 for connection to respective earth connections associated with the loads. As mentioned in our aforementioned UK patent application, in the case where the module 10 is connected to control a single load, the terminals 16, 18 can be connected together internally of the module by a shorting link (not shown).

The first (or live) input terminal 12 is connected via a capacitor 24 to a first power supply input 26 of the aforementioned electronic circuitry of the switching device: this electronic circuitry is indicated at 27 in Figure 1. The terminal 12 is also connected, via one set of switching contacts 28 of a two-pole manually-operable on-off switch 30, to a fixed contact 32, which is common to both of the aforementioned two relays, these relays being indicated generally at 34 and 36 respectively.

The relays 34 and 36 further comprise respective normally-open movable contacts 38 and 40 respectively, each separated from the common fixed contact 32 by a microgap of the order of 0.5 mm wide when in its open condition.

Movement of the contact 38 is controlled by a coil 42, while movement of the contact 40 is controlled by a coil 44, each coil being separately energisable via outputs 46 to 49 of the electronic circuitry 27. The use of relays with microgaps of the order of 0.5 mm wide considerably simplifies their design and reduces the current required for their operation, since the amount of movement required to close each of the movable contacts 38, 40 onto the fixed common contact 32 is relatively small.

The movable contacts 38 and 40 of the relays 34 and 36 are connected to the first and second switched live output terminals 16, 18 respectively.

The terminal 14 is connected to another power supply input 51 of the electronic circuitry 27 and, via the other set of contacts 50 of the switch 30, to the neutral output terminal 20. Both sets of contacts 28, 50 of the switch 30 open to a spacing of at least 3 mm when the switch is in its "off" condition. This 3 mm spacing is a safety requirement, necessary to enable an installer to work on the loads by merely switching the switch 30 of the switching device to its "off" condition, rather than disconnecting the loads from the switching device.

In use, and assuming the switch 30 is in its "on" condition, the electronic circuitry 27 energises the coil 42 of the relay 34 for the duration of the period of cheap rate (or off peak) electricity supply, while outside the period of cheap rate supply, the electronic circuitry 27 can be made to energise the coil 44 of the relay 36 by manual operation of a push button (not shown) for a period of up to one hour: this operation of a switching device in accordance with the "Economy 7" tariff is described in more detail in our aforementioned UK patent application. However, it will be noted from Figure 2 of that application that when "boost" is selected, there are four sets of contacts in series with the load (viz those indicated at 44, 46, 56 and 61 in Figure 2 of that application).In the switching device based on the switching module 10, on the other hand, there are never more than three sets of contacts in series with the load, viz 28, 38, 50 when the relay coil 42 is energised, or 28, 40, 50 when the relay coil 44 is energised. This considerably reduces heat generation, and so enables the switching device to be made in a relatively compact size.

As already mentioned, it is normally necessary to ensure that the two switched output terminals 16, 18 cannot both be connected to the live input terminal 12 simultaneously, since this could result in the input current to the switch exceeding the maximum current capacity of the live and neutral wires of the mains supply. This is achieved in the switching module 10 by ensuring that the two movable contacts 38 and 40 cannot both close onto the common fixed contact simultaneously.

To this end, the contacts 38 and 40 are loosely linked together by a mechanical device shown diagrammatically at 52, which has the effect of maintaining a minimum separation of the movable contacts greater than the thickness of the fixed common contact 32. The device 52 can take the form of an elongate plate or bar 54 having two longitudinally spaced slots 56, 58 extending longitudinally thereof, with the movable contacts 38, 40 engaging in respective ones of the slots and the distance between adjacent ends of the slots being greater than the thickness of the contact 32.Then if one of the movable contacts, say the contact 38, moves towards the contact 32 while the other movable contact 40 is already in contact with it, then before the contact 38 reaches the contact 32, its movement will be transmitted by the device 52 to the movable contact 40 so as to move the contact 40 away from the contact 32.

Alternatively, if a fault has caused the contact 40 to fuse to the contact 32, then the contact 38 will be prevented from closing onto the contact 32 by the device 52.

It will be appreciated that the switch 30 is provided for its 3mm contact spacing, ie it is necessary because the relays 34, 36 are of the microgap type. Figures 2A and 2B show another embodiment of the switching module, in which an alternative solution to the 3mm contact spacing requirement is provided.

Thus the switching module of Figures 2A and 2B is indicated generally at 60: it has many features in common with the switching device 10 of Figure 1, so these common features have been given the same reference numbers as were used in Figure 1, and only the points of difference will be described.

Firstly, the switch 30 of Figure 1 is omitted: its set of contacts 50 is replaced by a pair of normally-closed contacts 62, 63, of which the contact 62 is fixed and the contact 63 is movable, while its set of contacts 28 is not replaced, so that the input terminal 12 is connected directly to the fixed common terminal 32.

Secondly, the switching module 60 is provided with manually operable means 64 for increasing the spacing between the fixed common contact 32 and each of the movable contacts 38, 40 from the 0.5 mm microgap shown in Figure 2A to a spacing of at least 3mm, as shown in Figure 2B, and at the same time opening the normally-closed contacts 62 to a spacing of least 3mm.

The manually operable means 64 can take many different forms: for example, it can comprise a cam 66 disposed between respective extensions 68, 70 of the movable contacts 38, 40, this cam being rotatable in an anti-clockwise direction from the position shown in Figure 2A, where it does not interfere with the movement of the movable contacts 38, 40, to the position shown in Figure 2B, where it forces the extensions 68, 70, and therefore the contacts 38, 40, apart to the desired minimum spacing, and prevents the contacts 38, 40 from moving back towards the fixed common contact 32.

Attached eccentrically to the cam 66 is a rod 72, which is connected to the contact 63 so that the aforementioned anti-clockwise rotation of the cam 66 causes the rod to pull the contact 63 away from the contact 62 to the desired minimum spacing.

Rotation of the cam 66 is produced by moving a manually operable slider type control (not shown) on the front of the switching device from an "on" position to an "off" position.

It will be appreciated that in the switching module 60, there are never more than two sets of contacts in series with the load, viz 38 and 63, or 40 and 63. This further reduces heat generation, and thus further facilitates a compact design.

Many modifications can be made to the described embodiments of the invention. In particular, the manually operable means 64 can operate to move the common contact 32 rather than or as well as the movable contacts 38, 40 to achieve the desired minimum spacing: in the former case, the risk of distorting the movable contacts is avoided. Additionally, the relays 34, 36 can be replaced by relays which inherently have a 3mm contact gap, in which case the manually operable means 64 is not required to change the spacing of the contacts 38 and 40 with respect to the common contact 32: however, the manually operable means is still arranged to prevent the contacts 38 and 40 closing onto the contact 32 when the aforementioned slide is in its "off" position, in case the electronic circuitry 27 were to cause one of the relay coils 42,44 to become energised (for example because of a fault), and is still arranged to operate on the contacts 62,63.

Claims

1. A switching device including a pair of relatively movable switching contacts, a coil for controlling the relative movement of the contacts from a first relative position in which the contacts are closely adjacent each other to a second relative position in which the contacts are in electrical contact with each other, and manually operable means for controlling the relative movement of the contacts from the first relative position to a third relative position in which the contacts are prevented from entering the second relative position and their separation is substantially greater than it is in the first relative position.

2. A switching device as claimed in claim 1, comprising first and second movable switching contacts each movable into and out of electrical contact with a common contact, the first movable contact and the common contact constituting said pair of relatively movable contacts, and a second coil for controlling the arelative movement between the second movable contact and the common contact between first and second relative positions analogous to those of the first movable contact and the common contact, the manually operable means being further arranged to control the relative movement of the second movable contact and the common contact between said first relative position and a third relative position also analogous to that of the first movable contact and the common contact.

3. A switching device as claimed in claim 2, further including mechanical means arranged to transmit at least part of the movement of each of the first and second movable contacts to the other in such a manner that they cannot both contact the common contact simultaneously.

4. A switching device as claimed in claim 3, wherein the first and second movable contacts are disposed on opposite sides of the common contact, and the mechanical means comprises means for maintaining a minimum separation of the first and second movable contacts greater than the dimension of the common contact in the direction of movement of the first and second movable contacts.

5. A switching device as claimed in claim 4, wherein the mechanical means comprises an elongate bar having first and second longitudinally spaced slots for receiving the first and second movable contacts respectively, each contact being able to move longitudinally of its slot as it is moved to its respective third relative position, but the spacing between the adjacent ends of the slots being greater than said dimension of the common contact.

6. A switching device as claimed in any one of claims 2 to 5, further comprising a first input terminal for connection to the live wire of a mains electricity supply, said first input terminal being connected to said common contact, and first and second output terminals for connection to a load or loads, the first and second output terminals being connected to the first and second movable contacts respectively.

7. A switching device as claimed in claim 6, further comprising a second input terminal for connection to the neutral wire of a mains electricity supply, and a neutral output terminal for connection to the load or loads, the second input terminal being connected to the neutral output terminal via a pair of normally-closed contacts, and the manually operable means being arranged, when the first and second movable contacts are in their respective third relative positions, to open said normally-closed contacts to a separation similar to that between the common contact and each of the first and second movable contacts.

8. A switching device including first and second movable switching contacts, first and second coils associated with the first and second movable contacts respectively and each arranged to control the movement of its respective movable contact into and out of electrical contact with a common switching contact, and mechanical means arranged to transmit at least part of the movement of each of the first and second movable contacts to the other in such a manner that they cannot both contact the common contact simultaneously.

9. A switching device as claimed in claim 8, wherein the first and second movable contacts are disposed on opposite sides of the common contact, and the mechanical means comprises means for maintaining a minimum separation of the first and second movable contacts greater than the dimension of the common contact in the direction of movement of the first and second movable contacts.

10. A switching device as claimed in claim 9, wherein the mechanical means comprises an elongate bar having first and second longitudinally spaced slots for receiving the first and second movable contacts respectively, each contact being able to move longitudinally of its slot but the spacing between the adjacent ends of the slots being greater than said dimension of the common contact.

11. A switching device as claimed in any one of claims 8 to 10, further comprising a manually operable switch, a first input terminal for connection to the live wire of a mains electricity supply, said first terminal being connected to said common switching contact via a first set of contacts of the manually operable switch, and first and second switched output terminals for connection to a load or loads, said first and second output terminals being connected to said first and second movable contacts respectively.

12. A switching device as claimed in claim 11, further comprising a second input terminal for connection to the neutral wire of the mains electricity supply, and a neutral output terminal for connection to the load or loads, the second input terminal being connected to the neutral output terminal via a second set of contacts of the manually operable switch.

13. A switching device substantially as herein described with reference to Figure 1 of the accompanying drawings.

14. A switching device substantially as herein described with reference to Figures 2A and 2B of the accompanying drawings.