GB2086136A

GB2086136A - Improvements in and relating to earth leakage circuit breakers

Info

Publication number: GB2086136A
Application number: GB8124660A
Authority: GB
Original assignee: B & R Relays Ltd
Current assignee: B & R Relays Ltd
Priority date: 1980-08-12
Filing date: 1981-08-12
Publication date: 1982-05-06
Also published as: GB2086136B

Abstract

An ELCB which may be embodied in a plug includes first and second contacts 11, 12 which are bridged by a metal plate 14 slidably mounted on a spindle 13. The ELCB is set by operating a pushbutton 16 to urge the plate 14 against the force of spring 15 such that the end 14b of the plate engages contact 12, where it is held by a cam latch 18 controlled by a solenoid 17. When the push button is released the spring 15 urges the end 14a of the plate against contact 11. When an earth leakage current is detected, the cam latch 18 is withdrawn and the plate 14 pivots to disengage from the contacts 11, 12. The ELCB is trip free in that upon depression of the pushbutton 16, it is not possible to bridge contacts 11, 12 with the member 14 whilst the cam 18 is withdrawn. The plug arrangement is further rendered trip free by arranging the pushbutton 16 in a recess 25 in a surface which mates with a socket, so that the pushbutton can only be operated when the plug is removed from the socket. <IMAGE>

Description

SPECIFICATION Improvements in and relating to earth leakage circuit breakers This invention relates to an earth leakage circuit breaker, hereinafter ELCB, and has particular but not exclusive application to a plug and socket connection.

As is well known, an ELCB includes a sensing circuit for sensing fault currents flowing to earth; contacts for making or breaking mains current supply to a circuit, and a solenoid for tripping or breaking the contacts in response to a sensed earth current; and a manual operating mechanism for re-setting the ELCB after the occurrence of an earth fault current. Existing requirements and standards stipuiate that for safety reasons, the operating mechanism must be "trip free" i.e. must not be able to close the ELCB contacts during the existence of an earth fault current Thus, for example, British Standard BS4293 states "It shall not be possible to hold the circuit breaker closed by the operating mechanism under conditions in which tripping should occur".

Prior trip free mechanisms have tended to be rather complicated and bulky mechanical arrangements which include mechanical linkages designed to prevent manual resetting of the contacts when the solenoid is energised, one such arrangement being described in our British Patent Specification No. 1,145,857.

The present invention is concerned with providing an ELCB having a simplified trip free mechanism, which may be compact enough for use in a plug and socket connection.

According to the present invention there is provided an ELCB comprising first and second spaced apart contacts for connection in an electrical current path, a movable member for bridging said contacts to provide electrical continuity to said path, spring means acting on the movable member, holding means for holding said movable member in engagement with said first contact and in such a manner that the spring means urges the movable member into engagement with said second contact so as to achieve said continuity of the current path, and such that when the movable member is released from said holding means, the spring means urges the movable member out of engagement with said first contact, earth leakage detection circuitry arranged to release said holding means in response to a detected earth leakage current, and manually operable means for moving said movable member against said spring bias and to a position to be engaged by said holding means, the ELCB being so arranged that the movable member will only contact both of said contacts when held by said holding means and said moving means is released to allow the spring means to urge the movable member into engagement with said second contact, whereby to prevent movement of said movable member by the moving means into concurrent engagement with both said contacts when said holding means is released in response to an earth leakage current.

In a particularly preferred form of ELCB according to the invention, the spring means comprises a compression coil spring fitted on a spindle, and the movable member comprises an elongate member formed with a central aperture fitted for sliding movement on the spindle, the first and second contacts being spaced apart longitudinally of the spindle for engagement with respective opposite ends of the movable member, said holding means comprising a solenoid operated latch for holding one end of the movable member in engagement with the first contact, and said manually operable means comprising a pushbutton arranged for sliding the movable member along the spindle against the force of the compression spring.With this preferred arrangement, when the push-button is operated, the movable member is moved into locking engagement with the solenoid operated latch, such that engagement is achieved between one end of the movable member and the first contact, and when the push-button is subsequently released, the spring urges the other end of the movable member into engagement with the second contact. When the solenoid operated latch is released, as will occur in the event of fault current, the spring urges the movable member clear of the first contact, so as to break the current path between the first and second contacts.If the push-button is operated whilst the solenoid is activated to release the movable member, the movable member can be moved against the bias of the spring into engagement with the first contact, but such movement displaces the movable member away from the second contact to as to prevent the push button operation from establishing a bridge across the first and second contacts, thereby rendering the ELCB trip-free.

The ELCB of the invention can be included with advantage in a plug or a socket, for use in a plug and socket connection. Preferably the manually operable moving means is so arranged that when the plug and socket are mated together they coact to shield the moving means in such a manner as to prevent the possibility of manual operation thereof, thereby further rendering the ELCB tripfree. Preferably the ELCB is included in the plug and the manually operable moving means includes a push button mounted in a recess in a surface of the plug which in use mates with a surface of the socket.

In order that the invention may be more fully understood, an embodiment thereof will now be described by way of illustrative example with reference to the accompanying drawings in which: Figure 1 is a schematic side view of an ELCB according to the invention, in a released condition; Figure 2 is a schematic end view of the ELCB shown in Figure 1; Figure 3 is a side view of the ELCB in a set condition; Figure 4 is a side view of an ELCB incorporating a modification relative to the configuration shown in Figure 1; and Figure 5 is a schematic illustration of the ELCB of Figure 4 embodied in a domestic 13 amp plug.

Referring to Figure 1, the ELCB includes a body member 10 which includes upper and lower fixed contacts 11, 12, arranged on opposite sides of and spaced along the length of a spindle 13. The spindle is mounted to be upstanding from the bottom 1 Oa of the body member 10. A moving contact member 14 in the form of a plate-like metal member with curved contact ends 1 4a, 1 4b, has a central aperture 1 4c through which the spindle 13 passes. The aperture 1 4c forms a loose fit on the spindle 13 such that the member 14 can turn relative to the spindle. In use, the contacts 11, 12 are connected in a current supply path, and the movable member 14 provides a bridge between the fixed contacts, to establish continuity of the current path.

A compression coil spring 15 is received on the spindle between the bottom 1 Oa of the housing and the movable member 14. A manually operable push-button 16 fits over the top end of the spindle and has a main body portion 1 6a which is cylindrical and which is slidably mounted in an aperture 17 in the upper part 1 Ob of the housing.

The push-button 16 also includes a flange 1 6b which limits upward movement of the pushbutton, and which also prevents the movable member 14 contacting the upperfixed contact 11 in the released state of the circuit breaker shown in Figure 1.

As can be seen from Figure 2, holding means in the form of a solenoid 17 which operates a camshaped latch 18, loaded by a spring 19, is disposed for holding the contact end 1 4b of the movable member 14 in contact with the lower fixed contact 12, The solenoid 1 7 operates to withdraw the latch 1 8 in response to an earth leakage fault current being detected by detection circuitry shown schematically at 20.

To set the ELCB, the push-button 16 is depressed so as to slide the movable member 14 down the spindle 13 against the force of the spring 15 until contact end 1 4b of the member 14 drives back the cam-shaped latch 1 8 and engages the lower fixed contact 12. The latch 18 then is driven back by the spring 19 to hold the contact end 1 4b in engagement with the contact 12.

When the push-button 16 is subsequently released, the spring 1 5 urges the contact end 1 4a upwardly into engagement with the upper fixed contact 1 such that the member 14 pivots about the latch 18 so that the member 14 bridges the contacts 11, 12 as shown in Figure 3. Upon detection of an earth leakage fault current, the circuit 20 operates the solenoid 1 7 to withdraw the latch 18, so as to release the contact end 1 4b from engagement with the lower fixed contact 12, and consequently the member turns to adopt the position shown in Figure 1, thereby breaking the continuity in the current path between the contacts 11, 12.

This arrangement has the advantage of being trip-free. In the event that the push-button is c-pressed to reset the ELCB when an earth leakage current exists, the solenoid 1 7 will be actuated and the cam 1 8 withdrawn, so that it will be possible to move the contact 14 into engagement with the lower fixed contact 12, but it will not be possible to cause the member 14 to pivot about the cam 18,to engage the upper fixed contact 11.

The described arrangement is also inherently safe in the event of contact welding. The most iikely contact weld is between the upper fixed contact 11 and the movable member 14 as these are the last contacts to make when the pushbutton 16 is released when setting the ELCB.

Now, the upper fixed contact can be made flexible in which case, if a contact weld occurs between contacts 11 and the movable member 14, the member 14 and contact 12 will open with a reduced gap, in the event of solenoid 17 operating in response to an earth leakage current.

A modification to the described ELCB is shown in Figure 4. An upstanding member 21 is integrally formed in the housing 10, and the spindle 13 is disposed asymmetrically between the contacts 11, 12, closer to the contact 11 than to contact 12, providing an amplification of the turning movement of the contact 14 relative to the movement of the push-button 16, for use in situations where the allowable movement of the push-button may be restricted.

The upstanding member 21 defines a pivot point so that when the push-button 21 is depressed, the end of member 14 which engages contact 11, abuts member 21 and the movable member 14 then pivots about member 21 until the other end of member 21 engages contact 12 and is held by the latch 18.

The ELCB is particularly suited to being embodied in a plug and socket connection, for example in a plug. In Figure 5 the ELCB is shown incorporated in a domestic 13 amp plug.

The plug has conventional earth, live and neutral pins for a 240v 50 Hz single phase domestic supply, the earth and live pins 22, 23 being shown. The housing 10 defines the plug body and is formed in two parts 1 Oa,b. The housing part 1 Ob carries a metal conductor 24 which connects the contact 11 to the live pin 22.

The housing part 1 Ob includes the upstanding member 21 and furthermore includes conventional means (not shown) for receiving an electrical cable, and appropriate connections are provided for the neutral and earth leads of the cable to the pins of the plug.

The live lead of the cable is connected by means, not shown, to the contact 12. Thus the ELCB will disconnect the live supply to the electrical cable in response to an earth leakage current.

The reset push-button 1 6a is positioned within a recess 25 formed in the surface 26 of the plug body 10 which mates with the socket, the pushbutton being mounted sufficiently deeply in the recess that the button is not depressed by virtue of fitting the plug into the socket. This reset pushbutton arrangement has the advantage that the plug body 10 and the socket cooperate when the plug is inserted in the socket, to shield the pushbutton 1 6 from manual operation, so that in order to reset the ELCB the plug must first be removed from the socket, consequently disconnecting the electrical supply from the ELCB and thereby further rendering it trip-free.

An indicator arm (not shown) can be attached to the movable member 14, the arm bearing a visual indicium such as a bar of colour, that cooperates with a window in the plug body to indicate the setting of the ELCB.

The plug may further be provided with a test push-button, which is not shielded in the manner of push-button 6, the test push-button being for actuating a circuit which simulates an earth leakage current to test if the ELCB is operative.

The test push-button will be operated with the plug inserted in the socket. The plug will then be removed and the push-button 6 depressed to reset the ELCB, and the plug will then be re-inserted in the socket for normal operation.

It will be appreciated that the described ELCB arrangement could be incorporated in the cooperating socket rather than the plug, and moreover could be incorporated in an adaptor socket or any other of the conventionally available 1 3 amp plug or socket outlet arrangements.

Moreover, the invention has application to plug and socket systems other than those of the flat pin 13 amp type.

Claims

1. An ELCB comprising first and second spaced apart contacts for connection in an electrical current path, a movable member for bridging said contacts to provide electrical continuity to said path, spring means acting on the movable member, holding means for holding said movable member in engagement with said first contact and in such a manner that the spring means urges the movable member into engagement with said second contact so as to achieve said continuity of the current path, and such that when the movable member is released from said holding means the spring means urges the movable member out of engagement with said first contact, earth leakage detection circuitry arranged to release said holding means in response to a detected earth leakage current, and manually operable means for moving said movable member against said spring bias and to a position to be engaged by said holding means, the ELCB being so arranged that the movable member will only contact both of said contacts when held by said holding means and said moving means is released to allow the spring means to urge the movable member into engagement with said second contact, whereby to prevent movement of said movable member by the moving means into concurrent engagement with both said contacts when said holding means is released in response to an earth leakage current.

2. An ELCB according to claim 1 wherein the spring means comprises a compression coil spring fitted on a spindle, and the movable member comprises an elongate member formed with a generally centrally disposed aperture fitted for sliding movement on the spindie, the first and second contacts being spaced apart longitudinally of the spindle and for engaging opposite ends of said elongate member, said holding means comprising a solenoid operated latch for holding one end of the movable member in engagement with the first contact, and said manually operable moving means comprising a push-button arranged for sliding the movable member along the spindle against the force of the compression spring.

3. An ELCB according to claim 2 wherein said aperture is so disposed that the movable member provides arms of different lengths extending from the spindle and for respectively engaging said contacts.

4. An ELCB according to any preceding claim including means limiting movement of said movable member by the spring means in such a manner that upon release of the movable member by the holding means the spring means moves the movable member to a position in which it neither engages the first or the second contact.

5. An ELCB according to any preceding claim including means defining a pivot so arranged that upon manual operation of said moving means the movable member is moved into engagement with the pivot and then pivots into engagement with said first contact.

6. An electrical plug or socket for use in a plug and socket connection and including an ELCB according to any preceding claim.

7. A plug or socket according to claim 6 wherein the manually operable moving means is so arranged that when the plug and socket are mated together they coact to shield the moving means to prevent manual operation thereof.

8. An electrical plug for use in a plug and socket connection and including an ELCB according to any one of claims 1 to 5, said manually operable moving means including a push-button mounted in a recess in a surface of the plug which in use mates with a surface of the socket.

9. An ELCB substantially as hereinbefore described with reference to Figures 1 to 3 or as modified in Figure 4 of the accompanying drawings.

10. An electrical plug substantially as herein described with reference to Figure 5 of the accompanying drawings.

New claims or amendments to claims filed on 7th December 1981.

11. An ELCB comprising a contact for connection in an electrical current path, a movable member for engaging said contact to provide electrical continuity to said path, spring means acting on the movable member, holding means for holding said movable member in such a manner that the spring means urges the movable member into engagement with said contact so as to achieve said continuity of the current path, and such that when the movable member is released from said holding means the spring means urges the movable member out of engagement with said contact, earth leakage detection circuitry arranged to release said holding means in response to a detected earth leakage current, and manually operable means for moving said movable member against said spring bias and to a position to be engaged by said holding means, the ELCB being so arranged that the movable member can only engage said contact when held by said holding means and said moving means is released to allow the spring means to urge the movable member into engagement with said contact.