GB2457217A

GB2457217A - Cascadable electrical connector

Info

Publication number: GB2457217A
Application number: GB0706985A
Authority: GB
Inventors: Emil Aminollah Baruch
Original assignee: BARUCH ENTPR Ltd
Current assignee: BARUCH ENTPR Ltd
Priority date: 2007-04-11
Filing date: 2007-04-11
Publication date: 2009-08-12
Also published as: WO2008125813A1; GB0706985D0

Abstract

An electrical connector 10, adapted to be connected in cascade with one or more like connectors, comprises a housing 22 provided with a plug power port 12, a socket power port 14 and a cable power poll 16. The connector may detect whether it is the first in a cascade, so that a fuse (26, Fig 3) of the first connector protects all the connectors and cables whereas the fuses of the later connectors only protect that connector's cable. The detection may be done by a spring-loaded probe (42, Fig 4) which is pressed into the housing by a normal wall socket surface plate 11 but allowed to spring out into a recess (54, Fig 4) in the previous connector. The connectors may be thinner than the length of the plug pins, with the pins and their respective sockets offset, and with insulation on the portions (60, 62, Fig 16) of the pins which are thereby exposed. The connectors may latch together.

Description

*1. 2457217 :ri ECTRICAL CONNECTORS FOR POWER SUPPLY

FIELD OF THE INVENTION

This invention relates to electncal connectors for power supoly.

BACKGROUND

Many electrical and household appliances are pred directly by the mans electricity, e.g. lVs, radios, computers, printers, and them are many others Normally, in the UK, this power is detained by a connection made via a 1A plug which is inserted into a wall-mounted socket tMth the increasing number of such appliances, particularly in and around the home, office or kitchen, the need for extra mains sockets has increased tremendously. The costs associated wth such wall sockets are very high and most people prefer instead to use one or more multi-outlet (multi-socket) tension cable connectors and to plug their appliances into sockets thereof, so that each appliance is connected through such a socket via the common cable of the extension cable connector to a common mains plug which is then plugged into the wall socket Such a connector can be awkward, be hazardous andior use qi too much space. * S.. * . .

I

THE INVENTION * I

: ** 20 According to one aspect of the invention, there is provided an electrical connector for power supply, comprlsing a plug powerport, asocketpowerportandacaep,p external, e.g. for connection thereto of a power.consuming apohance. The connector might have more than one cable * * power port The cable port may conprise an actual cable connected to, or for connection to, e.g. a power-consuming appliance, or may compnse means for (non-plug-in) electrical connection thereto of a cable, e.g. terminals, e.g. of a : 25 screw kind, orof a clampng kind e.g that effect electhcal connection when a cover portion of a housing (e.g a dam-like housing) of the connector is dosed.

According to another aspect of the invention, there is provided an electrical connector for power supply, comprising a housing provided with a plug power port; a socket pcwer port and a cable power port In embodiments of the invention, the connector is adepted to be connected in cascade with one or more like connectors, as e)ç)laned below.

Preferably, the connector conpnses drcuit-protecting means, which themselves preferably comprise drcuit-breaking means, more preferably fuse means. The circuit-protecting means are preferably arranged to protect in a first mode if the connector is connected as the first one of a plurality of like connectors connected in cascade and in a second mode if the connectorisconnectedas heseco doralateronejnsud,acasc anditmaybethatwtetirerornottheya operable to select a said mode when this connector is plugged in they are not so operable when a succeeding connector is plugged into this connector. In a preferred involvement, the drcuit-protecbng means are normally in said second mode when this connector is not plugged in, arid are operable to select said first mode when this connector is plugged in as a said first connector. For this purpose, the connector is preferably able to detect when it is the first one in a said cascade by detecting whether or not that into which itis plugged is a like connector, e.g. it detects that it is not plugged into a like connector itis plugged into a flat wall-socket plate.

The connector preferably conprises ensuring means ananged to ensure that, if the connector is connected as the first cHuit-biaaking by said drcuit.protecting means, then this shall intenupt pr stply to the remainder of the cascade.

Such a first connect to thus acts as a master.

Further the connector preferably comprises ensuring means arranged to ensure that, if the connector is connected as the second or a later one of a plurality of like said connectors connected in cascade and condeons at said cable port are such as to cause circuit-breaking by said cucuit-protecting means, then this shall not intem.pt per si4Dply to the next connector dctn the cascade, Such a second or later connector thus acts as a slave.

Preferably, the circuit-piotecting means are ananged to be switchablo between a first posdion protecting both the :. socket port and the cable port and a second position protecting the cable port but not the socket port

S * S..

In particular embodiments, the circuit-protecting means may comprise circuit-brealting means interposed in the line : ** 20 connection betwaen the plug and cable pow ports, and switching means to connect either side of the circuit-breaking *5S* means to the line connection of the socket port. The switching means may be arranged to connect the socket port line connection to the cable port side of the circuit-breaking moans in said first mode and to the plug port side of the circuit-breaking means in said second mode . 25 The connector preferably has proximity means to enable sensing of whether the connector is plugged into a preceding like connector. The proximity means may comprise a sensing device to sense whether this connector is plugged into a preceding like connector and the connector also comprises an indicating device to indicate to a succeeding like connector that it is plugged into this connector, The said circuit-protecting means may be connected to be responsive to the proximity means, and possibly so as to be in sad first position in said first mode and in said second position in said second mode.

It may be that the proximity moans are mechanical and the circuit-protecting means are mechanically operable theraby to be responsive as aforesaid Alternatively, the sensing means may utilise electrical proximity means, which may be light-operable, or take other forms as mentioned below.

Said sensing device preferably comprises a probe; more preferably, the plug port comprises electrical connecting pns and the probe is in the region of (e.g. arranged on a common face of the connector as) the pins. Preferably, the indicating device comprises a recess to accommodate thout interference the probe of said succeeding like connector to indicate to that connector that it is plugged into this connector.

The connector may comprise indcator means to ucicate when the connector is plugged into a like connector andor when the connector is not plugged into a like connector andfor when the connector is plugged into a connector not being a like connector. The connector may comprise indcator means to incate which ports are protected by drcufl-protecting means, e.g. the indcator means comprising means to light up adjacent each port (currendy) protected Preferably, the said plug and socket ports are on opposite sides of the aforesaid housing. It may then be that the plug port comprises electrical connecting pins and the socket port comprises sockets for like pns, and corresponcing said pins and sockets are in line.

4Ajternatively, the plug port comprises electrical connecting pins and the socket port comprises sockets for like pins, and correspondng said pins and sockets are offset It may then be that the connector is thin enough to be penetrated completely through by at least one said pin of a like connector next down a cascade of like connectors arid has recess means to accommodete such pin or pins prcecting through such next connector from the next but one like connector down the cascade. Preferably, in that case, at least the powar supply (e.g. line and neutral) pins have external root and end portions that are externally insulated. *.S. * S *

Preferably, the connector, adapted to be connected in cascade with one or more like connectors, comprises releasable * latch means whereby one such connector can be fastened to an aacent said connector in said cascade. For * *. 20 exarrple, said releasable latch means comprise a catch and a latch, and the connector comprises said latch on one side of the connector to catch the catch of the next preceng connector in said cascade and comprises said latch on its opposite side to be caught in the catch of the next succeeding connector in said cascade.

S

A connecor embodying the invention will usually be in which theplug portcomp anearth pin andtwo *: * ". 25 electrical power (e.g. line and neutral) pins shorter than the earth pin, the socket port comprises an earth socket and two power (e.g. line and neutral) sockets, and there is a protective cover for the power sockets adapted to be moved away by initial insertion of the Qonger) earth pin of a like connector into the earth socket Preferably, the plug and socket ports are in accordance with an official standard specification, more preferably in accordance with British Standard 1363 relating to the 13-amp system.

The connector may have a said cable power port adapted for (non-pIugn) removable connection thereto of a cete, and/or may have, connected to a said cable power port, a cable aid/or power-consuming appliance.

Accordng to another aspect of the invention, there is provided a cascade of connectors, each embodying the invention.

Preferably the first of the connectors in the cascade is plugged into a power sourte, e.g. a wall socket More preferably, the first connector has circuit-protecting means arranged to protect itself and the remainder of the cascade, and/or each of said connectors alter the first one in the cascade has circult-protecting means arranged to protect itself but none of the other said connectors in the cascade. In preferred embodiments, there is provided a said cascade in which the said cirtuit-protecting means are identical in all of the said connectors (though switched to different modes) Accordng to another aspect of the invention, there is provided a wander plug and socket hrid unit for mains supply.

Preferred entodiments of the invention aim to solve the proem of the dsadvantages mentioned above by prr.Mdn9 an alternative means to power muItle appliances via a mains wall socket, in a safe and secured way, other than using a common multi-outJet extension lead. The plug which is connected to the electilcal appliance in this case will also act as a socket for another aiance to be plugged into it As such, and by taking apprcpriate precautions, a chain or cascade of such plug and socket connectors can be connected to each other to give multiple use of a single wall socket in the same manner as an extension cale. By using these embodiments instead of an extension lead, the user gains an extra socket from the connector as it dot.bles up to power yet another appliance. A chairL!cascade of such connectors can be fomied to provide a multiple source of power for a range of appliances via one mains socket By using these entodments, the cost of purchasing and installing a mains wall socket for each appliance is eliminated, as each such connector embodiment acts as a socket as l as a plug.

Mother advantage over using a common extension lead is that in the case of the connector entodment, the appliance can be re-wired from its regular 13A plug to a connector entodying the invention; therefore, it becomes a 2-in-i unit i.e. a socket and plug. * a *I..

* *. 20 As indicated above, the first connector in a cascade thus acts as a master and each subsequent connector as a slave.

* The unplugged connector defaults to being a slave. * *

* *** PARTICULAR DESCRIPTION RELATING TO THE DRAWiNGS :: 25 Reference will now be made by way of exanle to the accompanying drawings, wtch: Figure lisa perspective view of a piior art common multi-way extension lead and a wall socket therefore; Figure 2 is a perspective view of a typlcal sequence of connectors embodying the invention showing how they will connect together to form a cascade that plugs into a well socket, and oompnses a master connector and stave connectors entodying the invention; Figure 3 is a circuit diagram showing master and slave connection dmuitry Figure 4 is schematic side view of a conventional wall socket, and a connector entodying the invention thout to be plugged into the wall socket and act as a master, Figure 5 is a view like Figure 4, showing an intermecate stage of the master being plugged into the wall socket, and a probe just ebout to be operated by the wall socket; Figure 6 is a view like Figure 5, showing the master plugged into the wall socket, and showing the probe pushed back into a recess in the connector being then fully operated by the wall socket; Figure 7 is a view like Figure 6 shcwng the master fully plugged into the wall socket and a stave parfly plugged into the master, and showing a probe of the stave just entering a recess ui the master thereby thUnguishing (to the probe) the master from a conventional wall socket; Figure 8 is a view like Figure 7 showing the masterfully plugged into the wall socket and the slave fully plugged into the master; Figure 9 is a partial vertical section through the wall socket and master at the intermediate stage shown in Figure 5, showing how the probe is about to actuate switching means of the master; Figures 10-15 are various views (detailed below) shcming the constiuction and operation of a latch mechanism for releasaty fastening aacent said connectors together; and * * * .. 20 Figure 16 is a schematic side view of another entodment of the invention, showing how housings of the connectors * * * S...

can be thinner than the lengths of their pins Referring to the drawings, Figure 1 shows a prior art multi-way mains extension lead 110 having several sockets 114 5'. arrdaplugll2thatplugsintoawallsocketlll.

5S***S * S The other Figures show embociments of the invention. In the Figure 2 embodment, an electrical connector 10 for making power supply connections corrpnses a plug power port 12 comprising pns 12, a socket power port 14 comprising socket holes 14, and a cte power port 16. Port 16 comprises an actual cable 18 connected to a power-consuming ptiance 20. A housing 22 is provided with the plug power port 12, the socket power port 14 and the cable power port 16. The connector lOis adapted, e.g., by its plug port 12 and its socket port 14 being on opposite sides of its housing 22, to be connected in cascade with one or more like connectors 10 as seen in Figures 2 and 16, as explained below.

Referring to Figure 3, the connector 10 comprises drtuit-protecting means 24, comprising circuit-breaking means 26, more particularly fuse means 26, and switching means 28. The arcuit-protecting means 24 are ananged to protect in a rst mode (switching means 28 in position 30) if the connector 10 is connected as the first one of a plurality of like connectors 10 connected in cascade and in a second mode (switching means 28 in position 32) if the connector 10 is connected as the second or a later one in such a cascade 34.

The driit-protecting means 24 of connector 10, whether or riot operable to select a sad mode when this connector 10 is plugged in, are not so ope,(e when a succeeding connector 10 is plugged into this connector 10, as will be explained in relation to Figures 4 to 9 below. The drcuit-protecting means 24 are normally in said second mode when Us connector 10 is not plugged in, and are cperable to select said first mode when this connector 10 is plugged in as a said first connector (master) 36. For this purpose, the connector 10 is able to detect when it is the first one in a said cascade 34 by detecting whether or not that into which it is plugged is a llke connector 10, e.g. not' if it is plugged into a flat wafl-socket plate 11.

The connector 10 comprises ensuring means (composing circuit-protecting means 24 and proximity means 42, 44 descrbed below) arranged to ensure that, if the connector 10 is connected as the second (slave), e.g. 38, ora later one of a plurality of like saidconnectors 10 connected in cascade and cordtns at said cable pod 16 are such as to cause circuit-breaking by said circuit-protecting means 24, then this shall not interrpt power supply to the next connector, e.g. 40, down the cascade 34. The ensuring means 24,42,44 are also arranged to ensure that, if the connector 10 is connected as the first one 36 of a plurality of like said connectors 10 connected in cascade and conditions at sad cable port 16 are such as to cause circuit-breaking by sad circuit-protecting means 24, 42, 44, then this shall interrupt power supply to the remainder of the cascade 34. * * *

The circuit-protecting means 24 are arranged to be switchable between a first poshon 30 protecting both the socket port 14 and the cable port 16 aid a second position 32 protecting the c�e port 16 but not the socket port 14. The * .. 20 circuit-protecting means 24 conipnse circuit-breaking means 26 interposed in the line L (not neutral N or earth E) * . * connection 46 between the plug (12) and cable (16) power ports, and switching means 28 to connect elther side of the circuit-breaking means 26 to the line connection 48 of the socket port 14. The switching means 28 comprise a single pole double throw switch 28 arranged to connect the socket port line conriectico 48 to the cable port side 50 of the circuit-breaking means 26 in sad first mode (30) and to the plug port side 52 of the circuit-breaking means 26 in said 25 secondmode(32).

The connectoi-e.g. 38, has proximity means 42,44 to enable sensing of whether the connector 38 is plugged into a preceding like connector 36. The proximity means 42, 44 comprise a sensing device 42 to sense whether this connector 38 is plugged into a preceding like connector 36 and the connector 38 also compnses an indicating device 54 to indicate to a succeeding like connector 40 that it is plugged into this connector 38. Means 42, 44 of connector 38 co-operate with neigouring device 54 of the preceding connector 36. When the connector 10 is the first in the cascade 34, e.g master 36, its sensing device 42 is actuated by e g. the walt-plate 11, in the manner illustrated in the senes of Figures 4 to 6, pushing sensing device into its housing 22 against spdng means 44, and in turn operates switching means 26 as seen in Figure 9. (When connector 36 is withdrawn from wall-plate 11, spnng means 44 pushes sensing device 42 back out to its original position seen in Figure 4.) When the connector 10 is a second or later one in the cascade 34, i.e. a slave, e.g. slave 38, sensing device 42 is uriactuated by irdcating device 54 when connector 381s plugged into connector 36, as illustrated in Figures 7 and 8, thus leaving switching means 28 in position.

Thus, the thcuit-protecting means 24 are connected to be responsive to the proximity means 42, 44, and are connected toberesponsivetottieproximitymeans42, 44 soastobein saidflrstposition3o in saidflrstmodeandin saidsecond position 32 in said second mode, and the proxinty means 42,44 are mechanical and the rcuit-protecthg means 24 are mechanically cperate theiy, as seen in Figure 9, to be responsive as aforesaid Said sensing diice 42 compnsesaprcbe42intheregionofthepins 12, infactarrangedatthecentreofthecomrnonfaceof(thehousing22 of) connector 10 as the pins 12, and said indicating device 54 of e.g. connector 36 corrnses a recess 54 to accommodate without interference the prct,e 42 of said succeeding like connector 38 to indicate to that connector 38 that it is plugged into Uiis connector 36. Probes 42 and indicating devices 54 a-e present in each connector 10 in the Figure 2 embodiment but are not shown for the sake of clanty.

Connector 10 also comprises indicator means 56, e.g. comprising neon bulbs, larrps or LEDs 56, connected as shown in Figure 3 to indicate when fuse 26 has broken drcui or connected by any suitae means (not shown but apparent to one skilled in the art) to indicate at least the position of switching means 28 and hence indicate when the connector is plugged into a like connector (position 32 and the line connection 50 live) andor when the connector is not plugged into a like connector (e.g. being off when not plugged in and off when plugged in aid the switching means 28 are in position 30) andfor when the connector is plugged into a connector not being a like connector (position 30) Similar indicator means 56 can indicate which ports 14, 16 are protected by arcuit-protecting means 26, e.g. compnsing means 56 arranged to light up acacent each port 14, 16 (currentiy) protected * S I...

e *e 20 Sincethesaidptugandsccketport12, 14areonoppositesidesofthehousing22andtheplugport12ccirnses S:*. electrical connecting pins 12 and the socket port 14 con'prises sockets 14 for like pns (12 of the next connector 10 down the cascade 34), corresponding said pins 12 and sockets 14 are inline, as seen dearly in Figures 2 and 4.

: . In an alternative embodmen illustrated in Figure 16, the plug port electrical connecting pins 12 and their * : . 25 corresponding (line for line, neutral for neutral, earth for earth) socket port sockets 14 are offset This allows the connectors 10 to be thin enough for one connector, e.g. 40, to be penetrated corrletety through by the said pins 12 of the like connector 41 next down the cascade 34 of like connectors 36, 38,40,42 and each connector, e.g. 38, has recess means 58to accommodate such pins 12 prr4ecting through such next connector 40 from the next but one like connector 42 cbwi the cascade 34. To satisfy safety considerations dee to the fact that pins 12 of the first slave connector 38 cannot conleteIy penetrate master connector 36 (when this is plugged into wall-plate 11) and are partially exposed at root portion 60 and the pins 12 of the second slave connector 40 will then have their end portions 62 exposed bevnd connector 38, the power siçply (line and neutral) pins 12 have such external root and end portions 60, 62 externally insulated In either position of a pin 12, i.e. as seen within connectcw 36 or within connector 38, electrical contact of the remaining, uninsulated portion 64 of the pin 12 within its accepting socket 14 is made possible because each pin 12 has a deitily cranked, springy, electrical contact blade 66 extending into that socket 14 in the t relevant positions In either ombodimen, but shown only in the Figure 2 embodiment for danty, the connector 10, adapted to be connected in cascade with one or more like connectors 10, compnses releasable latch means 70 whereL' one such connector 10 can be fastened to an adjacent said connector 10 in said cascade 34, Said releasable latch means 70 compnse a catch 72 and a latch 74; and the connector e.g. 38, oompnses said latch 74 on one side (the upstream side)ofth000nnector38tocatchthecatch72Othenextprdngconj, ector36insaidcascade34andccmpnsos said catch 72 on its opposite (downstream) side to be caught in the latch 74 of the next succeedng connector 40 in said cascade 34. The constn.jction and action of catch 72 and latch 74 are shown in more detail in Figures 10-15, as follows.

Figure lOis a schematic top view (schematically coimspondng to a horizontal section through the line 10-10) and a corresponckng side view and sectional end view of a catch 72 shown schematically in Figure 2; Figure 11 is a schematic front view (schematically rxirrespondng to a vertical section through the line 11-11) and a correspordng bottom view of a latch 74 to engage the catch 72; Figure 12 is a view like Figure 10 showing the catch 72 (seen in horizontal cross-section) engaged by the latch 74; Figure 13 is a view like Figure 11 showing the latch 74 at the Figure 7 stage, before the catch 72 has approached it * * * *. I *,., Figure 14 is a view like Figure 13 showing the catch 72 just before the Figure 8 stage, a chamfer 76 thereof having * I borne like acam 76 against the internal shoulders 78 of the latch 74 to dapress it against a spring 86; * *. 20 Figure 15 is a view like Figure 14 shcM'ing the catch 72 at the Figure 8 stage, fully engaged by the latch 74, as shown in schematic top view in Figure 12. I.

: . Button80isdopressedtodepresslatch74toreleasecatch72.

*II... * S

in each connector 10, the plug port 12 comprises an earth pin 12 and two electrical power (i.e. line and neutral) pins 12 shorter than the earth pn 12, and in each connector 10 and in the wall-plate 11, the socket port 14 comprises an earth socket 14 and two power (i.e. line and neutral) sockets 14, and there is a protective cer 68 for the power sockets 14 adapted to be moved away by initial insertion of the (longer) earth pin 12 of a connector 10 into each earth socket 12.

In each connector 10, the plug and socket ports 12, 14 are in accordance with an official standard specification, in particular Bntish Standard 1363 relating to the 13-amp system.

In the cascade 34 of connectors 10 each as described abie, the first of the connectors 10 in the cascade 34 is plugged into a power source 11, e.g. a wall socket 11, the first connector 36 has circuit-protecting means 24 arranged to protect itself and the remainder of the cascade 34, each of said connectors 38 etc after the first one in the cascade 34 has orcuit-protecling means 24 arranged to protect itself but none of the other said connectors 38 etc in the cascade 34, and the said clrcuit.protecting means 24 are identical in all of the said connectors 10, though stched to diferent modes in connector 36 and in connectors 38 etc. -9.

The connector 10 may also ha an electronic box 82 for monitoring, signalling onto the line L or out of the connector (e.g. by rac*o or ultrasonics) or (connected as shn) to act as a current surge protector 82, e.g. a filter 82 for current or ltage spikes, The madmiaii current is determined as fdlows: Ic = Chain (cascade) current (lc)max Maximum allowed chain current (which Is 13A In the UK) from a wall socket If Ic> (Ic) max then the master fuse 26 in the master connector 36 blows.

For the chain to operate: Im + lsx c (Ic)max for x I f Where.

Im:Mastercurrent * * * lsx = Slave current in the xth slave 38 etc *.S. * S

n =Total numberotslaves38etc * * 20 a. * For safe operation, the maximum current In such a chain must be limited to 13A in the UK which equates to about 3000 watts of por in the chain arrangement 34. In other countries it could be other values.

In the case of the current limit being exceeded through the chain 34, the fuse 26 is blown to *;... 25 protect the chain 34. In this manner, the current in the chain is limited to the value of the fuse in the master connector 36. This feature safeguards all the fuses 26 in all the slave connectors 38 etc, as the fuse 26 in a slave 38 etc. in the chain 34 only protects the overcurrent in the appliance it is connected to.

Each connector 10 comes th a latch means 70, that hocks onto the next connector 10 connected to it; this will secure the chain 34 against inadvertent or aEdentai breaking or coming apart There is a release button 80 to unlatch the relevant connectors 10 from one other. There is also a neon lamp power inctcator 56. In a master connector 36, the neon lamp 56 indcates power in both the apoliance 20 connected to the master 36 and the chain 34. In the slave connector 38 etc, the neon lamp 56 will indicate power only in the chain 34. The neon light 56 is on when there is 36 power in the appliance 20 and the fuse 26 is intact Switches 84 are for dsoonnecting the relevant indvidual appliances 20. The neon lans 56 and these switches 84 are pponal.

As descnbed above, when a slave connector 10 is inserted into a wall mains socket 11 or any other connector not having the proximity feature, the prcbe is pushed mechanically as shown in Figure 6, activating the double-throw switch 28. Activation of this switch 28 can alternatively be cbne ale rucalty by means of an LED and an opto-electronic sensor receiver which then activates a relay to initiate the changecwer However, the mechanical means comprising probe 42 is more favourable as it can be cheaper and safer. The activation can, in a further alternative, be done magnetically using proximity switdie hver, in this case the connector 10 would need to be defaulted to be a master36,anduseofarelaywouldalsobenecessary.

These errboments rely on a switching mechanism 28 to activate the master droult mode 36 and there can be numerous means ti which this activation is done, e.g: a In the caseof the preferred enibodment by a mechanical means and a switch.

* Optically by means of a transmitter and a receiver.

* Magnetically using proximity switches.

a Electrically by means of a contact, where the presence or absence of a contact can activate the relay.

Note that it is the absence of a recess in the wall mount socket 11 that indoates to the connector 36 that it is being plugged into a non-family membera The probe 42 is pushed in as it cannot find a said recess 54 in the ll socket 11 *.,. This action will consequentiy activate switch 28. When a second connector 38 is then plugged into the master * I S connector 36, the master 36 has a recess 54 into which the probe 42 of slave 38 enters dunng the pluggingn action of the connector 38 into connector 36. Therefore, connector 38 being identical to the first connector 36, the probe 42 * * 20 slides into the recess 54, inhibiting any inhibiting any action on the part of pithe 42 to cause switching of switch 28 to * S * take place, thus leaving the switch 28 in its default position 30 and its connector 38 remaining in its default slave mode.

For safety reasons, switch 28 is arranged to be in its neutral (default) position 30 or already in its final position 32 before . a the mains current can flow through the chain 34. In this way, sparking can be avoided and the switching of the mains *; . 25 supply through the chain 34 is not interrtted as the connector 10 is positioned as master connector 36 into the wall socket 11, or as the next connector 38 etc is plugged into this one. The length of probe 42 in this case is critical to the extent that it is long enough to operate the switch 28 to change over from default slave, as 38, to master 36 before the livepn l2of theplugport 12 touchesthe livesocket 141 of thewall socket 11.

The changeover from slave to master could be manual, but is far better if automatic, as provided in the above-described entodirnents, e.g. using pm*e 42.

It will be apparent to one skilled in the art, that features of the diferent embodments dsdosed herein may be omitted, selected, combined or exchanged and the invention is considered to extend to any new and inventive combination thus formed Where a preference or particulansation is statect there is implied the possibility of its negative, i.e. a case in which that preference orparliculansation is absent Many variations of the invention and entodments hereirbefore described will be apparent to people skilled in the art and all such variations are to be considered as failing within the scope of the invention.