GB2292013A

GB2292013A - Electrical connection unit

Info

Publication number: GB2292013A
Application number: GB9512871A
Authority: GB
Inventors: Gopi Krishn Modgill; Colin Smith
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1994-07-30
Filing date: 1995-06-23
Publication date: 1996-02-07
Also published as: GB9415456D0; GB9512871D0

Abstract

An electrical connection unit has a manually-operable switch 17, 18 and a fuse 31 that can be removed through an opening in the front of the housing of the unit. The unit also has a time switch 40 mounted below the fuse 31 and the switch 17, 18 where it will be less affected by heat from the fuse and switch. <IMAGE>

Description

ELECTRICAL CONNECTION UNITES AND INSTALLATIONS This invention relates to electrical connection units and installations.

The invention is more particularly concerned with electrical connection units of the kind including a switch and a fuse and with installations including such a connection unit.

A conventional connection unit of this kind includes a manually-operable, double-pole switch and a fuse. The unit is connected between a mains electrical supply and an electrical appliance so that power supply to the appliance can easily be switched off and so that any fault in the appliance causing an excess power to be drawn burns out the fuse. The connection units can be either flush mounted, meeting BS4662:1970, or surface mounted, meeting BS5733:1979. Connection units are used with permanently wired-in appliances such as immersion heaters, or with appliances having plugs connected to sockets at inaccessible locations, such as behind the appliance or beneath worktops.

These appliances are often also controlled by a time-switch connected between the connection unit and the appliance. The time-switch automatically turns the appliance on and off at pre-set times so that, for example, water is heated when necessary or the appliance is operated when cheap tariff electricity is available.

The need to have both a connection unit and a time-switch means that the electrician has to connect two separate units, thereby involving increased cost. Also, additional wall space is required for the two units. If the units are to be mounted flush with the wall then it may be necessary to channel through the plaster and underlying brickwork. This can be a particular problem if the time-switch is installed after the connection unit has been installed, because of the disruption to decoration. Having two separate units also means that there is an increased risk of wiring faults and incorrect connection.

It is an object of the present invention to provide an improved electrical connection unit and an installation including such a unit.

According to one aspect ofthe present invention there is provided electrical connection unit including an outer housing, live and neutral input terminals, live and neutral output terminals, a live line extending between the live input terminal and the live output terminal, a neutral line extending between the neutral input terminal and the neutral output terminal, an electrical fuse connected in the live line, the fuse being removable through an opening in the housing, and a manually-operable switch on the housing connected in the live line, the unit including a time controller circuit connected to the live line between the input terminal and the switch, an electrically-operated switch controlled by the time controller circuit, the electricallyoperated switch being connected in the live line, a display connected to the time controller circuit, the display being visible on the housing, and manual control means for controlling the time controller circuit, and the manual control means being accessible on the housing.

The display is preferably mounted on a front face of the housing, the display not being mounted above the fuse or the electrically-operated switch. The opening through which the fuse is removable is preferably on the front face of the housing. The fuse may be contacted by spring electrical contacts and the unit preferably includes a second fuse.

According to another aspect of the present invention there is provided an installation including an electrical supply circuit, an electrical appliance and an electrical connection unit according to the above one aspect of the invention connected between the supply circuit and the appliance.

A fused electrical connection unit and an installation including such a unit, in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a circuit diagram ofthe unit and installation: and Figure 2 is a front elevation view of the unit.

The connection unit 1 is flush mounted in a recess 2 of a wall 3 and is connected between a power supply spur 4 from a ring main circuit 5 and an electrical appliance, such as an immersion heater 6, via a cable 7. Alternatively, the unit could be surface mounted and it could be connected in the ring main itself.

The connection unit 1 has a plastics housing 10 of square shape being about 80mm square and about 30mm deep. The unit 1 has two input terminals 11 and 12 connected respectively to the live and neutral lines of the spur 4. Within the housing 10, the live input terminal 11 is connected to a live line 14 extending to a live output terminal 21. Similarly, the neutral input terminal 12 is connected via a neutral line 15 to a neutral output terminal 22.

Earth continuity is maintained by a separate connector block 8, which locates on the back cover ofthe connection unit. A manually-operable switch 17 is connected in the live line 14 and this is ganged to a similar switch 18 in the neutral line 15. Both switches 17 and 18 are operated by a two-way finger lever 19 accessible on the front face 30 ofthe housing 10.

The connection unit 1 contains a fuse 31 connected in the live line 14 between the switch 17 and the live input terminal 11. The fuse 31 is a conventional wire filament within a ceramic tube, the wire burning out when current through it exceeds a nominal, set value, eg 13 amps. The fuse 31 is supported on a removable fuse holder 33 and is contacted by spring electrical contacts in the live line 14. The fuse can be removed and replaced through an opening 32 in the front face 30 ofthe housing 10, to the left of the switch lever 19, which is normally closed by the front of the fuse holder 33. The unit 1 also includes a second, thermal fuse 34 connected in the live line 14 on the opposite side of the switch 17. This fuse 34 is selected to burn out under the combined effect of high current and elevated local temperature.

The housing 10 of the connection unit 1 also includes a time control unit 40. The time control unit 40 comprises a time controller circuit 41 connected to an electrically-operated switch, such as a relay 42, a display 43 and control means 44. The relay 42 has two contacts 45 one of which is connected by a line 9 to a terminal 23 and the other of which is connected by a line 16 to a terminal 24. In the arrangement illustrated, a wire bridges the terminals 21 and 23 so that, when the relay 42 is closed, terminal 24 is connected to the live input terminal 11 via lines 16, 9 and 14. The heater 6 is connected to terminals 22 and 24 so that power supply to the heater is controlled by the relay 42. In an alternative arrangement, the wire bridging terminals 21 and 23 could be omitted so that a low voltage circuit could be connected between the terminals 23 and 24.This low voltage circuit would be isolated from the main supply but would be controlled by the relay 42 The display 43 is a liquid crystal display, which is mounted on the front face 30 of the housing 10 below the fuses 31 and 34, the switch 19 and the relay 42. The control means 44 takes the form of two push buttons, by which the user sets the times at which the appliance 6 is to be on and off. The time controller circuit 41 may be of any conventional construction, power for the circuit and the remainder of the control unit 40 being derived by a connection 46 to the live line 14 between the fuse 31 and the switch 17 and by a connection 47 to the neutral line 15 between the neutral input terminal 12 and the switch 18. In this way, power is supplied to the control unit 40 even when the switch lever 19 is in the off position. The circuit 41 preferably includes a rechargeable battery to provide back-up for the time-of-day and stored program if the mains supply should be disconnected or the fuse 31 burn out.

In normal manual operation, the switch lever 19 is in the on position so that both switches 17 and 18 are closed and the relay 42 maintains the contacts 45 closed. Current can flow through the connection unit 1 to the appliance 6. With high current loads, considerable heat is generated by the fuse 31, the relay 42 and the live and neutral current paths but, by ensuring that the display 43 is not mounted above the fuse or the relay, it has been found that the heat does not adversely affect the display. If there should be a fault in the appliance 6, or in the wiring between the connection unit 1 and the appliance, the fuse 31 will burn out and prevent further supply of current to the appliance. In some cases the fault current may be insufficient to blow the fuse 31; this is a particular problem with certain loads such as immersion heaters. The combination of this high current and the local heating produced instead causes the thermal fuse 34 to blow and thereby prevents damage to the unit.

When the appliance 6 is to be switched on and off automatically, the switch lever 19 is left in the on position and the time control unit 40 is appropriately set. Power supply to the appliance 6 will then be controlled by opening and closing of the contacts 45. Again, should any fault develop, either the fuse 31 or the thermal fuse 34 would burn out and prevent supply to the appliance 6.

The connection unit 1 of the present invention can be used as a direct replacement for an existing connection unit, in its existing wall recess, so that a time control function is provided without the need for any new wiring. Furthermore, no additional space is required and there is no need to disrupt existing decoration.

Claims

1. An electrical connection unit including an outer housing, live and neutral input terminals, live and neutral output terminals, a live line extending between the live input terminal and the live output terminal, a neutral line extending between the neutral input terminal and the neutral output terminal, an electrical fuse connected in the live line, the fuse being removable through an opening in the housing, and a manually-operable switch on the housing connected in the live line, wherein the unit includes a time controller circuit connected to the live line between the input terminal and the switch, an electrically-operated switch controlled by the time controller circuit, the electrically operated switch being connected in the live line, a display connected to the time controller circuit, the display being visible on the housing, and manual control means for controlling the time controller circuit, and wherein the manual control means is accessible on the housing.

2. An electrical connection unit according to Claim 1, wherein the display is mounted on a front face of the housing, and wherein the display is not mounted above the fuse.

3. An electrical connection unit according to Claim 1 or 2, wherein the display is not mounted above the electrically-operated switch.

4. An electrical connection unit according to any one of the preceding claims, wherein the opening through which the fuse is removable is on the front face of the housing.

5. An electrical connection unit according to any one of the preceding claims, wherein the fuse is contacted by spring electrical contacts.

6. An electrical connection unit according to any one of the preceding claims, wherein the unit includes a second fuse.

7. An electrical connection unit substantially as hereinbefore described with reference to the accompanying drawings.

8. An installation including an electrical supply circuit, an electrical appliance and an electrical connection unit according to any one of the preceding claims connected between the supply circuit and the appliance.

9. An installation substantially as hereinbefore described with reference to the accompanying drawings.

10. Any novel feature or combination of features as hereinbefore described.