GB2177544A - Electrical devices provided with circuit-breakers - Google Patents

Abstract

An electric switch or socket assembly has a "circuit-breaker" and reset device, and a blocking member which in one position allows supply of current but prevents reset of the circuit-breaker, and in another position prevents supply of current but allows resetting of the circuit-breaker. The blocking member may comprise a resiliently biassed slidable shutter plate 60 arranged to block the reset device 38 when the apertures of a socket assembly are held open by plug pins in sockets 10, 12 so that the plug has to be removed to allow operation of the reset button 38 which cannot be depressed whilst the shutter plate 60 is moved to the open position. Alternatively the blocking member may interlock with a switch rocker preventing its movement to the "on" position if the reset button is pressed and also preventing operation of the reset button if the rocker is in the "on" position (Figure 7, not shown). <IMAGE>

Description

SPECIFICATION Electrical devices provided with circuit-breakers This invention relates to electrical plug sockets and switches provided with circuit-breakers intended to switch offthe current supplied in the event of an electrical fault in the circu it to which current is applied.

One type of circuit breaker in domestic use is the earth leakage circuit-breaker or residual current circuit-breaker or residual current circuit-breakerwhich is sensitive to leakage of currentfrom the circuit which it protects. Leakage generally indicates a fault which may be dangerous for the user. When no leakage is present in the circuitthe vector sum ofthe currents supplied to the high-voltage or "live" end of the circuit and the return currentthrough the lowvoltage or "neutral" end ofthe circuit is zero. If leakage occurs, this sum is non-zero. The residual current circuit-breaker is intended to detect this non-zero sum and open, that is to disconnect the current supply to the circuit, when the sum exceeds a predetermined magnitude.One type of circuit-breaker comprises a normally closed relay through which the currentfed to the circuit pases and detection of a non-zero sum above the predetermined magnitude results in opening of the relay to disconnectthe circuit. The circuitbreaker is normally provided with a reset device, such as a reset button, operation of which closes the circuit-breakerto allow the circuit to be re-connected when thefault has been rectified.

However there is often a risk of the user operating the reset device to reconnect the supplywithout troubling to rectifythefault,thus rendering the cir- cuit-breaker ineffective. The present invention is intended to provide an electric socket or switch comprising a circuit-breakerwhich cannot be reset while the socketorswitch is still capable of supplying current to the circuit, and in which the socket or switch cannot be caused to supply currentto the circuit while the reset device is in operation to hold the circuitbreaker closed.

According to one aspect of the present invention there is provided a socket or switch for supplying electric current, the socket or switch comprising a normally closed circuit-breaker which is openable to disconnectfeed of electric currentto the socket or switch, a reset device operable to close the circuitbreaker, and a blocking member movable between a first position in which the reset device may be operatedto close the circuit-breaker but the blocking member prevents supply of current by the socket or switch while the reset device is in operation, and a second position in which current may be supplied by the socket or switch when the circuit-breaker is closed but the blocking member prevents operation of the reset device to close the circuit-breaker.

The socket or switch may be of the kind which is permanently installed, for example on the wall of a room, or it may comprise an adaptor intended to be fitted to a wail socket. It may be a switch socket, that is a socket which is provided with its own switch.

The circuit-breaker maycomprisea relay through which the current supplied to the socket or switch passes, the relay opening in response to a signal provided by a detector of earth leakage current. The reset device may be manually operated and comprise a spring-loaded push button which, when pressed against its spring, pushes the armature of the relay into its closed position. The reset button may be mounted on a wall of a box containing the socket or switch and the pin-receiving apertures ofthe socket orthe rocker of the switch (or both, in the case of switch sockets) may be provided on the wall. The blocking member may comprise a shutter plate slid ing in its own plane mounted on the rearsurfaceof the front wall.

In the case of a socket the blocking member, when in its first position, may prevent supply ofcurrent from the socket by blocking at least one of the socket aperturesthrough which the pins of a plug must pass to connect an electrical appliance to the socket. The aperture may be blocked by a portion of the blocking member having an inclined surface so that, on inser tion ofa plug in the socket, the plug pin abuts the inclined surface ofthe blocking memberanddis- places the blocking member to its second position.

The blocking member may be urged towards its first position by resilient means such as a spring. The reset button may extend through an aperture in the blocking member and the button may be provided with an outstanding part such as a flange which, when the blocking member is in its second position, abuts a part of the blocking member adjacent the aperture to preventthe button being fully depressed and thus to prevent the button closing the circuit-breaker. The aperture may be such that when the blocking member is in its first position the button may be fully depressed, the outstanding part ofthe button passing through the aperture, so that the circuit-breaker may be closed.However the aperture should be such that, when the button is fully depressed, the blocking member is prevented from moving to its second position by abutment of the button against an edge of the aperture.

In the case of a switch the reset button may again pass through an aperture in the blocking member and, as in the case of a socket, the button when fully depressed may prevent the blocking member moving to its second position and the blocking member, when in its second position, may prevent full depression of the button to close the circuit-breaker. However in this case the blocking member in its first position may prevent feed of currentthrough the switch by interacting with the switch rocker.

The blocking member may have a partadjacentthe rocker which has an inclined surface to engage the rocker so that when the rocker is switched from its "on" to its "of" position, the blocking member moves from its second to its first position underthe action of resilient means such as a spring. The reset button can then reset the circuit-breaker but current cannot be fed from the switch because it is in its "off" position.

On moving the rocker to its "on" position the blocking member can return to its second position, in which the reset button cannot be fully depressed to reset the circuit-breaker.

The blocking member may also comprise a part which is movable independently of the remainder of the blocking member and which has an inclined surface engaging part ofthe button such that, when the button is depressed with the blocking member in its first position,the part moves into a position in which it prevents the switch rocker moving into its "on" position: thus current cannot be fed by the switch when the reset button is depressed.

According to another aspect ofthe invention there is provided a socket or switch for supplying electric current, the socket or switch comprising a normally closed circuit-breakerwhich is openableto disconnectfeed of electric current to the socketorswitch, the circuit-breaker comprising a resiliently biassed latch movable on opening of the circuit-breakerto prevent closure thereof until the latch is moved against its resilient bias, a reset devicefor closing the circuit-breaker and a blocking member movable between a first position in which it holds the catch against its resilient bias to allow the reset device to close the circuit-breaker but in which supply of current by the socket or switch is prevented while the reset device is in operation, and a second position in which current, may be supplied by the socket or switch when the circuit-breaker is closed but the latch prevents closing ofthe circuit-breakerwhen the circuit breaker is open.

Devices according to embodiments ofthe invention will now be described bywayofexamplewith reference to the accompanying drawings in which: Figure 1 shows a socket adaptor from the outside, Figure2 is a schematic cross-section of the adaptor of Figure 1, in which some parts are shown diagrammatically and some parts are omitted for clarity, Figure 3 is a schematic side view of a relay used in the adaptorof Figure 1, Figure 4 is a schematic view of the relay of Figure 3 perpendicular thereto, Figure5showsa plate used inthe adaptorof Figure 1, Figure 6is a schematic cross-section perpendicular to Figure 2 of part ofthe adaptorof Figure 1, Figure 7is a schematic plan view of parts of a switch according to another embodiment of the invention, Figures 8 and9 are schematic sections perpendicularto Figure 7 of parts of the switch, Figure 10 is a side view of a relay for use in the adaptororswitch of Figures 1 to9.

Figure 11 is a schematic plan view of parts of a switch according to yet another embodiment of the invention, Figure 12 is a schematic cross-section along XII-XII of Figure 11 with the switch in the "off" position, Figure 13 is a schematic cross-section along XIII XIII with the switch in the "on" position.

Referring to Figures 1 and 2, a circuit-breaker adaptor comprising a generally rectangular casing of plastics material comprising a box 2 to which is attached a lid 4 held on the box by screws at the corners (not shown in the drawing). The rear ofthe adaptor is provided with three metal pins to fit into the terminal apertures of a standard 13-amp electric supply sock- et; in the drawing the earth pin 6 and one ofthe current-carrying pins 8 are visible. The front of the adaptor is provided with terminal apertures of a stan dard 13-amp supply socket comprising earth aperture 10 and current-carrying apertures 1 2to receive the pins of a 13-amp plug.Circuitrywithin the adaptor connects pins 6 and 8 toterminals in apertures 10 and 12 respectively so that when pins 6 and 8 are inserted in a 13-amp wall socket and a 13-amp plug is plugged into apertures 10 and 12 in the usual manner the plug may be supplied with electric current.

The circuitry within the casing comprises a residual current circuit-breaker which is intended to disconnect pins 8 from apertures 12 in the event of earth leakage of current caused by a fault in any appliance plugged into apertures 10 and 12. The circuit-breaker is designed to disconnect pins 8 from apertures 12 when any leakage current exceeds a given value. This value may for example be 10 mA, 30 mA or 300 mA according to the degree of protection which the circuit-breaker is intended to provide.

The circuit-breakerwithin the casing comprises a detector device, indicated schematically at 14 in Fi gure 2, for detecting earth leakage current which is of conventional type and will not be described in detail; this device may be ofthetype used in earth leakage circuit breakers supplied under catalogue number 5725 by MK Electric Limited. Briefly, the earth leakage current detector comprises a coil through which the live and neutral current conductors to apertures 12 pass. If there is no leakage the vector sum ofthe currents through the live and neutral conductors to the apertures is zero. If leakage occurs this sum is non-zero and the coil emits an EMFwhich is afunction of the magnitude of the leakage current.

The EMF from the detector coil is fed by leads 16 to the coil 18 of a double-pole relay 19 shown in Figure 3 having fixed contacts 20 mounted on the chassis of the relay and movable contacts 22 mounted on the armature 24 ofthe relay. The fixed and movable contacts are electrically connected respectively to the pins 8 and apertures 12 atthe adaptor. The armature is pivoted on the relay chasis at 26to move between the open position shown in Figure 3, in which the fixed and movable contacts are separated, and the closed position in which contacts 22 and 20 are together. The armature is urged to its open position by a tension spring 27 connected to the chassis and to an end ofthe armature.

The relay comprises a permanent magnet 17 which attracts the armature to hold the armature in its closed position againstthe action of spring 27. The coil 18 and detector device 14 are arranged so that any earth leakage current detected by device 14 pro duces a magnet field from coil 18 which opposes the field ofthe permanent magnet. When the earth leakage current exceeds a predetermined magnitude (such as 30 mA), the field from the coil 18 is sufficient to allow the relay to open underthe action of spring 27.

The fixed contacts 20 are connected to the pins 8 by leads 28. The movable contacts are mounted on conducting strips 30 on the armature which are them- selves connected to leads 32 leading to the apertures 12. Pins 8 and apertures 12 are thus electrically connected when the relay is closed and isolated from each other when the relay is open.

As shown in Figure 2, the relay is fixed in the casing by screw 34 passing through the wall of box 2 and entering a threaded hole in the relay. The armature 24 ofthe relay is then adjacentthewall of lid 4and the lid wall is provided with a hole 36 in which is mounted a reset push-button 38 having out-turned flanges 40 to engagethe rearsurfaceofthewallto preventthe button escaping from the housing. The rearofthe button comprises a stem 42 having a surface 44to abut the armature 24. The stem is dimensioned so that, when the button is in its normal position shown in solid lines in Figure 2, the armature 24 may remain in its open position but when the button is depressed, it pushes the armature to its closed position, thus estabishing electrical contact between contacts 20 and 22.The button 38 is urged towards its normal position by a coil spring 46.

As shown in Figure4,the rearedge 46 ofthe arma- ture is located at a distance from the base 48 ofthe relay and is provided with a projection 50 extending beyond edge 46. A dog 52 is arranged to slide along base 48 in the direction parallel to the axis of pivoting ofthe armature. The dog is dimensioned and positioned so that, when the armature is in its open position, it can slide between a first position shown in solid lines in Figure 4 and a second position shown in broken lines. In the second position it is situated behind the extending projection 50 of the armature and prevents the armature closing, when the dog is in its first position the armature may open and close freely.

The dog is urged towards its second position by ten- sion spring 54. When the armature is closed the dog is held in its first position by abutment against the side surface of projection 50. When the armature opens spring 54 draws the dog to its second position behind the projection 50 so that the dog locks the armature in its open position until it is positively displaced against the action of spring 54.

As shown in Figures 3 and 4 dog 50 is rigidly attached to a finger 56 which projects beyond the edge of base 48 ofthe relay in the direction of movement ofthe armature. A force exerted on finger 56 againsttheaction of spring 54 can move the dog from its second to its first position, thus unlocking the armature and allowing itto close. As shown in Figure 2the lid 4 of the adaptor is provided on its rear surface with a movable shutter 58 of electically insulating plastics material which is slidable in a plane parallel to the lid surface in the direction indicated by arrows A. The shutter is confined to this plane by plastics moulding 59fixedto lid 4.The shutter extends behind the portion ofthe lid provided with apertures 10 and 12 and is shown in Figures 5,6 and 7. Theshutter comprises a plate 60 having apertures 62 to allowthe current-carrying pins of a plug to enterthe adaptor from apertures 12 and an extension 64 having an inclined forward surface 66. When the shutter is in the position shown in Figures 5 and 6 apertures 62 are not aligned with apertures 12, so that the current-carrying pins of a plug cannot be inserted in the adaptor, and aperture 10forth earth pin is blocked by extension 64.When a standard 13-amp plug is plugged into the adaptorthe earth pin first enters aperture 1fand bears against inclined surface 66 so thatthe shutter is urged to slide such that extension 64 moves to a position where it is clear of aperture 1 O. in this position ofthe shutter apertures 62 of the shutter coincide with aper tures 1 2 so that the current-carrying pins ofthe plug, which are shorter than the earth pin, can enter the adaptor and engagethe terminals in the adaptorfor supply of electric current to the plug. The shutter is urged to its position shown in Figure 5 by a spring (not shown in the drawings).

The end of the shutter remote from apertures 62 comprises a plate 67 ofthe shape shown in Figure 5.

As shown in Figure 6 reset button 38 has wing flanges 68 extending outwardlyfrom the button behind the wall of lid 4 and portions 70 of plate 67 ofthe shutter are of such a shape and thickness that, when the shutter is moved to its position at which the current- carrying pins of a plug may be inserted through apertures 12 and 62, portions 70 are located behind wings 68 and prevent button 38 being depressed. On the other hand, when the shutter is in its position shown in Figure Sthe button 38 may be depressed and if it is held down the wings 68 can abut the edges of portions 70 so that the shutter cannot be moved into its position allowing insertion of the plug.

As may be seen in Figure 2, finger 56 ofthe relay which projects in front of the relay assembly extends into the plane ofthe shutter and is lodged in a hole72 in the shutter which has an edge 74 intended to abut the side ofthe finger. When the shutter is in the position shown in Figure 5, that is when the shutter prevents a plug being inserted in the socket, edge 74 presses against finger 56 and holds dog 52 in the position shown in solid lines in Figure 4, against spring 54, so that the dog does not obstruct opening and closing ofthe relay: thus, when the shutter is in the position of Figure 5, when the relay is open it can be closed by depressing the reset button.When the shutter is in its position allowing a plug to be inserted in the socket, edge 74 is displaced from the finger and does not prevent finger 56 moving to its position shown in broken lines in Figure 4. When the shutter moves to this position, when the relay is closed, dog 50 abuts the side of projection 52 against the action of spring 54; however when the relay opens dog 50 is moved by spring 54 to its position shown in dotted lines and once opened, the relay cannot be closed until the shutter returns to its position shown in Figure 5, when edge 74 moves finger 56, andthusthe dog,toallowthe relay to close.

It will be appreciated that in normal operation, when there is no plug in the socket the relay is closed, with the shutter in the position of Figure 5. When the three pins of a plug are inserted in the socket the shutter moves and, if there is no earth leakage current, the relay remains closed and electric current can be fed to the pins of the plug . However if an earth leakage current exceeding the predetermined limit occurs the relay will open, disconnecting the current source from the plug, and the dog then moves to its position preventing closure of the relay. When the adaptor is in this state the current feed to the plug cannot be restored by pressure applied to the reset button. The relay can only be reset if the plug isfirst removed, allowing the shutter to return to its position of Figure 5 and allowing the reset button to depress the relay armature to its closed position.

When the reset button is depressed in this way, holding the relay in its closed position, the shutter cannot be moved to its position allowing insertion of a plug because the wings 68 ofthe button then bear on portions 70 of the shutter and obstruct the shutter movement. Thus it is not possible to insert a plug in the socket while the relay is held closed by the reset button. On the other hand, when the shutter is in its position allowing insertion of a plug the portion 70 of the shutter is behind the wings 68 of the button and prevents the button being depressed.

The arrangement described above is such that, when an earth leakage currentsufficientto open the relay has occurred, the relay cannot be reset while the plug remains in the socket. When the plug has been removed the relay can be reset, howeverthe plug cannot be inserted while the reset button remains depressed. There is therefore no risk of a user overriding the circuit-breaker to feed currentto the plug while earth leakage persists.

In the embodiment shown in Figures7to 9 an earth leakage circuit-breaker is arranged to prtoect a circuit controlled by a rocker switch, which may be part of a switched socket intended to receive a plug or may be part of a fixed circuit installation. In this embodiment the earth leakage circuit-breaker including the relay is ofthe same type as in the embodiment of Figures 1 to 6. In Figures7to 9the movable armature 24 of relay 19 and the finger 56 for displacing the spring-loaded dog are shown. The switch in this embodiment comprises a housing having a front wall 102 and a rocker 100 of known type which opens and closes the circuit which it controls in known manner.As in the embodiment of Figures 1 to 6the circuit is broken on opening of the relay 19 in response to detection of earth leakage current exceeding a predetermined magnitude, such as 30 mA. Thefrontwall 102 ofthe housing of the switch assembly is provided with an aperture containing a relay reset button 38 provided with a coil spring 46 and depression of the reset button resets the relay as in the preceding embodiment; however the dog of the relay prevents closure when finger 56 attached to the dog is in its position shown in broken lines.

The switch unit has an inhibitor plate 104which is slidablein a plane immediate behindfrontwall 102 and is constrained in this plane by moulding 1 fixed to the frontwall 102. The plate has an aperture 108 through whichfinger56 passes andthe aperture forms an abutmentsurface 110to engageanddis- place the finger. When the inhibitor is in the position shown in Figure 8 the finger and dog are free to move to their position shown in dotted lines so thatwhen the relay has opened the dog moves to lock it in its open position and the relay cannot be reset. The inhibitor is urged to its position of Figure 8 by a spring 113.When the inhibitor is moved in the direction of arrow Rthe surface 110 movesthefinger56 inthe same direction, unlocking the relay and allowing itto be reset.

The inhibitor has an aperture 114through which reset button 38 passes but adjacent aperture 11 4the inhibitor has a portion of reduced thickness 112.

When the inhibitor is in its position of Figure 9 the reset button may be depressed to close the relay but in its position of Figure 8 portion 112 is situated behind the flange 116 of the button so that the button cannot be depressed: also flange 116 prevents the plate moving from its position of Figure 9 to that of Figure 8 when the button is held in its depressed position. With this arrangement the relay can only be reset when the inhibitor is in its Figure 9 position and the inhibitor cannot move to its Figure 8 position while button 38 is depressed.

The end ofthe inhibitor has a portion 11 6which extends towards the switch rocker having an inclined surface 118 and the rocker comprises an outwardly extending tab 120 to engage surface 118.

When the switch is in its "on" position, shown in Figure 8, the inhibitor may occupy its position preventing resetting of the relay but when the rocker moves to its "off" position the tab 120 bears against surface 118 and, moving downwardly, moves the in inhibitor to its position at which the relay, when open, is unlocked and can be reset by button 38.

The reset button is integral with an outwardly projecting tab 121 which bears on a sloping surface 122 of a second inhibitor 124 which is constrained to move in the same plane as inhibitor 104 and is urged by a spring to its position shown in Figure 8. When the reset button is depressed tab 121,bearing on surface 122, displaces the second inhibitor 124 in the direction of arrow "Y" in Figure 7. Inhibitor 124 is provided with an end part 126 extending towards the rocker and the rocker has an outwardly extending tab 128 at its end remote from tab 121. When reset button 38 is depressed tab 121 urges the shutter 124 against its spring 125 in direction Yso that part 126 overlaps tab 128.Part 126 and tap 128 are arranged sothatwhen the switch is in its "off" position (Figure 9) depression of button 38 moves part 126 behind tab 128 and abutment of part 126 and tab 12then prevents the switch being moved to its "on" position (Figure 8): thus the switch cannot be turned "on" while the reset button is depressed.

In the above-described embodiment, once the relay has opened in response to earth leakage the relay cannot be reset until the switch has been turned off; also the switch cannot be turned on while the button is held depressed to hold the relay closed. In this embodimentalsothere is no risk a userover-riding the circuit breaker to feed current through the switch while earth leakage persists.

In both of the embodiments described above an indicator may be provided to give a visual indication of the state of the relay (open or closed). One type of indicator, associated with the relay, is shown in Figure 10. The base of the relay has pivoted thereto a rotatable member 200 forming a crank having arms 202 and 204. The rotatable member is placed on one side of the armature 24 of the relay and the armature has an outward projection 208 to abut the surface of arm 202. The outer end of crank 204 is provided with a curved plate 210 serving as a "flag" to give avisual indication of the state of the relay.

Member 200 is provided with a further arm 212 which is connected to the base ofthe relay by tension spring 214.

As shown in Figure 1, the frontwall 4 of the adaptor is provided with a hole 216 positioned so that the outside surface of plate 210 is visible through the hole, a different part of the surface being visible for different angular positions of member 200 about its axis of rotation 218.

When the relay is open member 200 is in the position shown in Figure 10. When the relay closes projec- tion 208 bearing on arm 202 rotates member 200 clockwise as shown in the drawings, thus moving plate 210 so that a different partofthe plate is visible through hole 216. When the relay is opened member 200, urged by spring 214, moves anticlockwise. The different parts ofthe plate displayed bear different colours sothatthe colourseen through hole 216 gives an immediate indication ofthe state of the relay.

The embodiment shown in Figures 1 1 -1 3 com pris- es a switch unit which is similarto that of Figures 7-9.

The earth leakage circuit-breaker including the relay is again ofthe same type as in the embodiment of Figures 1 to 6 but for ease of comprehension in Figures 11-13 only the finger 56for displacing the spring-loaded dog is shown.

The switch ofthis embodiment again comprises a rocker 100, front wall 102 of a housing accommodating the switch, a relay reset button 38 and coil spring 46, as in the embodiment of Figures 7 to 9, so that depression of the reset button resets the relay and the dog ofthe relay allows closure ofthe relaywhen finger56 attached to the dog is in its position shown in solid lines in Figure 11 but the dog prevents closure ofthe relay when the finger is in its position shown in dotted lines.

In this embodiment the switch unit has an inhibitor plate 304 slidable in a plane immediately behind front wall 102 between the positions shown in Figures 12 and 13 and is constrained in this plane bymouldings fixed to the rear surface offrontwall 102. The inhibitor is urged to its position shown in Figures 11 and 12 by coil springs 313 engaging flanges on the inhibitor and on mouldings on the rearsurface ofthefrontwall.

The inhibitor has an aperture 308 through which finger 56 passes and the aperture forms an abutment surfaceto engage and displace the finger. When the inhibitor is in its position in Figures 11 and 12 the finger 56 is held in its position shown in solid lines so that in this position the dog is prevented from obstructing closure ofthe relay and the relay may be reset by depressing button 38. Howeverwhenthe inhibitor is moved in the direction shown by arrow R to its position shown in Figure 13thefingercan move to its position shown in dotted lines, indicated as 56'.

When the finger is in position 56' the dog ofthe relay will be in its position at which it prevents closure of the relay. Thus, if the relay is open and the inhibitor plate moves to its position of Figure 13 then the dog will move to its position preventing closure of the relay, driven by the tension spring ofthe relay and the fingerwill moveto its position 56'. If the inhibitor moves in this way whilethe relay is closed the dog cannot move, as it is obstructed by the armature of the relay, and the finger remains in its position shown in solid lines.

The inhibitor has an aperture 31 4through which reset button 38 passes but adjacent aperture 31 4the inhibitor has a pair of shoulders 312. The button 38 has an outstanding flange 316.Whenthe inhibitoris in its position of Figures 11 and 12 the reset button may be depressed to close the relay but in its position of Figure 13 shoulders 312 are situated behind the flange 316 so that the button cannot be depressed: also flange 316 prevents the inhibitor moving from its position of Figures 11 and 12 to its position of Figure 13 when the button is in its depressed position, because of abutment ofthe sides offlange 316 and shoulders 312.

The end of the inhibitor adjacent switch rocker 100 has a portion 322 having an inclined surface and rocker 100 has a tab 320 at one end to engagethe inclined surface. When the end of rocker 100 bearing tab 320 is depressed the inhibitor is moved from its position of Figure 12 to that of Figure 13 and when the rocker is fully depressed tab 320 prevents return of the inhibitor by abutment oftab 320 with the end surface 324 of portion 322. When the rocker is switched to its other position, tab 320 clears portion 322 and the inhibitor may move to its Figure 12 position, urged by springs 313.

The switch rocker is arranged so that the switch is "on" in the position of Figure 13 and "off" inthe position of Figure 12. During normal operation ofthe switch with the relay closed the inhibitor can move without affecting the power supplied by the switch.

When a circuit leakage causes the relay to open with the switch "on" the dog locka the relay and the reset button cannot be depressed until the switch is moved to its "off" position, when the reset button may be operated and the relay is not locked by the dog.

Howeverthe switch cannot beturned "on" again while the reset button remains depressed; thus the circuit-breaker cannot be over-ridden by holding the reset button down and then turning the switch on.

The embodiment of Figures 11 to 13 may be provided with a visual indicator showing the state ofthe relay, as in the preceding embodiments.

Claims (11)

1. A socket or switch for supplying electric current, the socket or switch comprising a normally closed circuit-breaker which is openableto disconnectfeed of electric current to the socket or switch, a reset device operable to close the circuit-breaker, and a blocking member movable between a first position in which the reset device may be operated to close the circuit-breaker but the blocking member prevents supply of current by the socket or swtich while the reset device is in operation, and a second position in which current may be supplied by the socket or switch when the circuit-breaker is closed but the blocking member prevents operation ofthe reset device to close the ciruit-breaker.

2. A socket or switch according to claim 1, in which the circuit-breaker comprises a relay and the reset device comprises a spring-loaded push-button which closes the relay when pushed against its spring.

3. Asocketorswitchaccordingtoclaim 1 or2 comprising a wall containing pin-receiving socket aperturesandlora switch rocker, the blocking member comprising a shutter plate slidable in its own plane parallel to said wall.

4. A socket according to any preceding claim comprising apertures to receive the pins of an electric plug, in which the blocking member in its first position blocks at least one of the apertures to obstruct insertion ofthe pins in the apertures.

5. Asocketaccording to claim 4, inwhichthe blocking member is resiliently biassed towards its first position and is provided with an inclined surface such that an inserted plug abuts the inclined surface and displaces the blocking membertowards its second position.

6. Aswitch according to claim 1,2 or 3, compris- ing a switch rocker and in which the blocking member in its first position interacts with the switch rocker to obstruct moving of the rocker to its "on" position.

7. A switch according to claim 6, i n which the blocking member is resiliently biassed towards its first position and is provided with an inclined surface such that the switch rocker abuts the inclined surface and displaces the blocking membertowards its second position when the switch rocker is moved from its "off" to its "on" position.

8. A socket or switch according to any preceding claim, in which the circuit-breaker comprises a resiliently biassed latch movable on opening of the circuit-breakerto prevent closure thereof until the latch is moved against its resilient bias, and the blocking memberwhen in its first position holds the latch against its resilient bias to allow the reset device to operate.

9. A socket or switch for supplying electriccurrent, the socket or switch comprising a normally closed circuit-breaker which is openableto disconnect feed of electric current to the socket or switch, the circuit-breaker comprising a resiliently biassed latch movable on opening of the circuit-breakerto preventclosure thereof until the latch is moved against its resilient bias, a reset device for closing the circuit-breaker and a blocking member movable between a first position in which it holds the catch against its resilient bias to allow the reset device to close the circuit-breaker but in which supplyofcur- rent by the socket or switch is prevented while the reset device is in operation, and a second position in which current may be supplied by the socket or switch when the circuit-breaker is closed but the latch prevents closing of the circuit-breaker when the circuit-breaker is open.

10. A socket or switch according to any preceding claim, provided with an indicator giving a visual indication of the open or closed state ofthe circuitbreaker.

11. A socket or switch, substantially as hereinbefore described with referenceto Figures 1 to 6or Figures7to9 or Figures 11 to 13 and Figure 10 ofthe accompanying drawings.