GB2169459A

GB2169459A - Switched lamp socket

Info

Publication number: GB2169459A
Application number: GB08531137A
Authority: GB
Inventors: Colin Terence Willis
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-12-18
Filing date: 1985-12-18
Publication date: 1986-07-09
Also published as: GB8531137D0; GB8431950D0

Abstract

A lamp socket has a pair of first contacts 20, 21 connected to the electrical supply and a corresponding pair of second electrical contacts 40, 41 for engagement by the terminals of a bayonet-type lamp bulb. Each contact is biased in a direction towards the lamp bulb. When no bulb is in the socket, the second contacts are isolated from the first contacts but when a lamp bulb is inserted into the sockets, the second contacts are caused to move into conducting engagement with the first contacts for normal use. When the lamp bulb is disengaged from the socket, the second contacts automatically move away from the first contacts and are therefore isolated thus avoiding an electric shock if touched. <IMAGE>

Description

SPECIFICATION Electrical socket This invention relates to electrical sockets and particularly, but not exclusively, to electric lamp sockets. Such electrical sockets are for supplying electric current to a corresponding plug fitting, which term is used in this specification to include both electrical plugs and electrical fittings in the nature of plugs such as lamp bulbs.

A disadvantage of conventional electrical sockets is that when switched on without a plug fitting being plugged in, live electrical terminals are exposed with the consequent risk of electric shock, for example if a child puts its fingers into the socket or an adult inadvertently does the same.

The invention accordingly provides an electrical socket for supplying electric current to a corresponding plug fitting, comprising: a housing, at least one first electrical contact mounted in the housing for connection in use to an electrical supply, and at least one second electrical contact for engagement by a or a respective terminal of the plug fitting when engaged with the socket, the or each second contact being mounted for movement between a first position isolated from the or a respective first contact and a second position in electrical connection therewith, the or each second contact being biassed towards its first position, the arrangement being such that engagement of the plug fitting with the socket causes movement of the or each second contact to its second position.

Thus when the plug fitting is disengaged from the socket, the biassing means moves the or each second contact to isolate it from the supply and hence no electrical shock is received if the or a second contact is touched.

Preferably, the or each second contact in its second position makes direct contact with the or the respective first contact.

The or each first contact may advantageously be mounted for movement towards and away from the or the respective first contact, the socket having means for biassing the or each first contact towards the or the respective second contact.

Typically, there would be two first contacts and two second contacts. These would provide for the usual live and neutral lines. However, in the case for example of a lamp socket for a screw type lamp fitting, there might be only one each of the first and second contacts for the live line, the conducting screw thread receiving the lamp being connected permanently to the neutral line.

In the case of two or more first contacts, these may be mounted to a first member removably attached to the housing.

In the case of two or more second contacts, these may be mounted to a second member also removably attached to the housing.

The socket may comprise means for locating the first and second members relative to one another.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded cross-sectional elevation of an electric lamp socket according to the invention; Figure 2 is a partially sectional exploded elevation of a second lamp socket according to the invention; Figure 3 is a plan view of part of the same socket taken in the direction of arrow Ill of Figure 2; and Figure 4 is a sectional view taken on line IV-IV of Figure 2.

Referring first to Figure 1, the socket comprises a housing formed in three parts, a base part 10, an intermediate part 11 and an outer part 12. These three parts are attachable together by means of internal threads 13, 14 formed on the base and outer parts 10, 12 respectively and which engage external threads 15, 16 respectively formed on the intermediate part 11. The base part 10 is formed with a central hole 17 to receive wires 18, 19 connected to an electrical supply.

The wires 18, 19 are connected respectively to two first contacts 20, 21 by means of conventional terminal screws 22, 23. The contacts 20, 21 are slidably mounted in corresponding bores 24, 25 formed in a first plate member 26. When assembled, the plate member 26 is clamped between the upper end (as seen in the drawing) of the intermediate part 11 and an internal shoulder 27 of the base part 10. Each of the first contacts is biased downwardly (as seen in the drawing) axially of the housing and towards second contacts which will be described hereinafter. The means providing this biassing is a respective coil spring 28, 29 located around the respective contact and acting between a head 30, 31 of that contact and the plate member 26.

Movement of the contacts 20, 21 in a direction away from the base part 10 is limited by laterally enlarged portions 32, 33 of the contacts, which portions are too big to pass through the bores 24, 25.

Two second electrical contacts 40, 41 are slidably mounted in corresponding bores 42, 43 in a second plate member 44 which is clamped, when assembled, between the lowermost edge (as seen in the drawing) of the intermediate part 11 and an inner shouider 45 formed on the outer housing part 12. Attached to the plate member 44 is the usual annular socket fitting 46 having two diametrically opposite slots 47 for receiving the lateral retaining pins provided on a conventional bayonet-type lamp bulb.

The slidable mounting of the second contacts 40, 41 allows movement thereof axially of the housing limited in a direction away from the base part 10 by lateral enlarged portions 48, 49 of the contacts which are too big to pass through the bores 42, 43. When the socket is assembled, the second contacts are movable between first, released positions (as indicated in the drawing) isolated from the first contacts and second positions in direct conductive contact with the first contacts. Coil springs 50, 61 located around the contacts 40, 41 provide means biassing the second contacts 40, 41 away from the first contacts 20, 21 and towards the first positions. The coil springs 50, 51 act between external shoulders 52, 53 of the second contacts and the plate member 44.

In order to locate the first and second plate members 26, 44, and therefore the first and second contacts, relative to each other, a rod 55 is secured to a central bush 56 fixed to the first plate member 26 and this rod is slidably received within a sleeve 57 secured to the second plate member 44. The rod 55 is co-axial, when the socket is assembled, with the central axis of the housing.

When the socket is assembled, insertion of a lamp bulb into the socket to engage its retaining pins with the slots 47 causes engagement of the lamp bulb terminals with the second contacts 40, 41 but the axial movement involved of the lamp bulb relative to the socket causes the second contacts to move towards and contact the first contacts 20, 21, the second contacts passing through holes 58, 59 formed in the intermediate part 11.

This causes electrical connection between the wires 18, 19 through the first contacts and second contacts to the lamp bulb terminals.

However, the socket has the great advantage that when the lamp bulb is withdrawn from the socket, the second contacts automatically move out of contact with the first contacts under the action of the springs 50, 51 and thus even if either or both of the second contacts are touched by a human hand, no electric shock will be received as the second contacts are isolated from the first contacts.

Figures 2-4 show a second embodiment of the invention which is similar in many respects to the embodiment of Figure 1, equivalent ele ments being indicated by the same reference numerals primed.

The second socket comprises a housing formed in three annular parts, a base part 10' and intermediate part 11' and an outer part 12'. These three parts are attachable together by means of internal threads 13', 14' formed on the base and outer parts 10', 12' respectively and which engage external threads 15', 16' respectively formed on the intermediate part 11'. The base part 10' is formed with a central hole 17' to receive wires (not shown) connected to an electrical supply. These wires are connected directly to two first contacts 20', 21' by means of terminal screws 22', 23'. The intermediate part 11' is formed with two slots 47' to receive the retaining pins of a conventional bayonet type bulb.

As in the first embodiment, the first contacts 20', 21' and the second contacts 40', 41' are elongate, rod-like members longitudinally aligned with each other. In this embodiment however, the first and second contexts are slidably mounted in respective aligned bores 60, 61 of a body member 62. This body member is formed in two identical or substantially similar halves 63, 64. These halves are formed with through holes 66 for accommodating screws or rivets for attaching the two halves together. The halves 63, 64 are also formed with apertures 67, 68 for receiving lateral extensions of locating members or washers 70, 71 through which the first and second contacts respectively can slide.

The body 62 is received snugly within the intermediate housing part 11' and is prevented from relative rotation with respect thereto by two lugs 73 which are formed integrally with the halves 63, 64 and which locate in respective notches 74 in the intermediate part 11'.

Each of the first contacts is biased axially of the housing towards its respective second contact by means of a respective coil spring 28'. Each spring is a coil spring located around the respective contact and acts between the respective locating washer 70 and a washer head 30' secured to the contact by peening. The ends of the first contact are "cupped" with depressions 69 to be contacted by the second contacts 40', 41', the purpose of these depressions being to prevent arcing. The upper ends of the second contacts 40', 41' are shaped in a roughly corresponding way. The depressions 69 are also formed by the peening process referred to above.

Each second contact is biased towards its respective first contact by means of a co-axial coil spring 50' acting between external shoulders 52' of the second contacts and the lower locating washers 71. Movement of the second contacts downwardly is limited by a respective washer 48' secured to the upper ends of the respective second contact.

The function of the socket of Figures 2-4 is similar to that of the socket of Figure 1.

When the socket is assembled, the second contacts are movable between first, release positions (as seen in Figures 2 and 4) isolated from the first contacts and second positions in direct conductive contact with the first contacts. Insertion of a lamp bulb into the socket to engage its retaining pins with the slots 47 causes engagement of the lamp bulb terminals with the second contacts but the axial move ment involved of the lamp bulb relative to the socket causes the second contact to move towards and contact the first contacts. The first and second contacts then move together against the action of both pairs of springs until the lamp retaining pins reach the upper ends of the slots 47'. In conventional fashion the lamp bulb is twisted so as to engage the retaining pins with the inner extremities of the slots 47', the biased slidable mounting of the first contacts compensating for the slight axial movement of the lamp bulb in a direction out of the socket as the retaining pins move to engage the extremities of the slots 47'.

It will be apparent that the described structure could be applied to a plug fitting as well as a socket, one or more of the terminals of the plug fitting being movably mounted in the same way as the second contact members.

Claims

1. An electrical socket for supplying electric current to a corresponding plug fitting, comprising: a housing, at least one first electrical contact mounted in the housing for connection in use to an electrical supply, and at least one second electrical contact for engagement by a or a respective terminal of the plug fitting when engaged with the socket, the or each second contact being mounted for movement between a first position isolated from the or a respective first contact and a second position in electrical connection therewith, the or each second contact being biassed towards its first position, the arrangement being such that engagement of the plug fitting with the socket causes movement of the or each second contact to its second position.

2. A socket as claimed in claim 1 wherein the or each second contact in its second position makes direct contact with the or the respective first contact.

3. A socket as claimed in claim 2 wherein the or each first contact is mounted for movement towards and away from the or the respective first contact, the socket having means for biassing the or each first contact towards the or the respective second contact.

4. A socket as claimed in any preceding claim wherein there are two first contacts and two second contacts.

5. A socket as claimed in any preceding claim wherein there are two or more first contacts mounted to a first member removably attached to the housing.

6. A socket as claimed in any preceding claim wherein there are two or more second contacts mounted to a second member removably attached to the housing.

7. A socket as claimed in claim 6 as dependent on claim 5 further comprising means for locating the first and second members relative to one another.

8. An electric lamp socket as claimed in any preceding claim.

9. An electric lamp socket substantially as hereinbefore described with reference to and as shown in the accompanying drawing.