EP0033411A2

EP0033411A2 - An alternating current socket-outlet for electric equipment

Info

Publication number: EP0033411A2
Application number: EP80303289A
Authority: EP
Inventors: Yutaka Ichikawa
Original assignee: HIRAKAWA ELECTRIC WIRE Manufacturing Co Ltd
Current assignee: HIRAKAWA ELECTRIC WIRE Manufacturing Co Ltd
Priority date: 1980-01-17
Filing date: 1980-09-18
Publication date: 1981-08-12
Also published as: EP0033411B1; DE3068044D1; EP0033411A3; JPS56106382U; JPS5924140Y2

Abstract

An alternating current socket-outlet for electric equipments having a body member (10) fixed to a stationary system, a pair of connector members (20), a pair of shutter members (40a, 40b) movable between a first position to cover the connector members and a second position to uncover the connector member, an elastic member (30) urging the shutter members to the first position, and a front cover (50) to guide a pair of the pins (60) of a plug (200) adapted to engage the connector members (20).

In order to prevent an electric shock or fire accident, etc., the electric outlets covered by the shutter members (40a and 40b) are uncovered only when the two symmetric, equivalent pushing forces are applied to the shutter members.

Description

The invention relates to an alternating current socket-outlet for electric equipments; a pair of shutter members adapted to cover the openings to receive a pair of electrically conductive connector members are moved to uncover the openings when the two equivalent pushing forces are applied to the shutter members.
In the prior art, e.g., British Patent No. 1,43,611 is disclosed a socket-outlet for electric equipments which has a shutter means in the form of two shutter members adapted to cover the holes for electrically conductive connector members. This socket-outlet has the shutter members which are urged into contact by springs. The hole for an earth pin of a plug is covered by two cam shaped members on the shutter members. When the pin is inserted into the hole, the earth pin engages the cam shaped members to force apart the shutter members.
In accordance with this socket-outlet for electric equipments, even if pushing the cam members by a member other than the earth pin of the plug, the shutter members may be moved to enable the member to contact with the conductive connector member, and hence an infant and so forth are in danger an electric shock by mistake.
The invention as claimed is intended to provide a remedy. The invention provides an alternating current socket-outlet in which a pair of shutter members adapted to cover the openings to receive a pair of electrically conductive connector members are moved to uncover the openings only when the two equivalent pushing forces are applied to the two shutter members.
The advantages offered by the invention are mainly that even if the pushing force is applied to one of the two shutter members, they do not move; therefore even if an infant and so forth play a trick with a member other than the plug, the shutter members do not move, thereby an electric shock accident and the like can be avoided.
One way of carring out the invention is described in detail below with reference to drawings which illustrate preferred embodiments, in which:

Figure 1 is an exploded view of a preferred embodiment in accordance with the invention,
Figure 2 is a perspective view illustrating the relation between a plug and a socket-outlet in accordance with the invention,
Figures 3(A)-3(C) show one of shutter members, with
Figure 3(A) being a perspective view, and Figures 3(B) and 3(C) showing sectional views taken on lines B-B and C-C of Figure 3(A) respectively,
Figures 4(A) and 4(B) are sectional views of one preferred embodiment of the invention, with Figure 4(A) and 4(B) showing the socket-outlet before and after connecting with plug pins respectively,
Figures 5(A)-5(C) show one preferred embodiment of the invention, with Fgure 5(A) being a view in elevation of a body member of a socket-outlet, and Figures 5(B) and 5(C) showing the states of the socket-outlet without the front cover before and after connecting with plug pins respectively,
Figures 6(A)-6(D) show one of preferred emodiments of fitting an AC socket-outlet of the invention into a chassis, with Figure 6(A) showing fitting members,
Figures 6(B) and 6(C) showing perspective views of them before and after fitting them respectively, and
Figure 6(D) showing a longitudinal sectional views of them after mounting,
Figure 7 is a perspective view illustrating the second preferred embodiment in accordance with the invention,
Figures 8(A)-8(C) show one of the shutter members of Figure 7, with Figure 8(A) being a perspective view, and Figures 8(B).and 8(C) showing sectional views taken on lines B-B and C-C of Figure 8(A) respectively,
Figure 9 is a perspective view illustrating the third preferred embodiment in accordance with the invention,
Figure 10(A) is a exploded view of a socket-outlet with the shutter members in accordance with the invention,
Figure 10(B) is a perspective view of a base member taken on line B-B of Figure 10(A),
Figure 11 is a perspective view of a table tap in accordance with the invention, and
Figure 12 is a-perspective view of a flush type AC socket-outlet embedded in a wall in accordance with the invention,

As shown in Figure 1, an AC socket-outlet in accordance with the invention comprises a body member 10, a pair of electrically conductive connector members 20 adapted to receive pins or blades of a plug, a spring 30, a shutter means in the form of two shutter members 40a and 40b, a front cover 50 having a guide 55 for guiding the plug to insert the pins into holes 52.
The body member 10 comprises a pair of openings or holes 11 adapted to receive the connector members 20 each in the form of slit sleeve, an opening or hole 12 to receive a spring 30, two pair of guide grooves 13a and 13b to regulate movements of the shutter members 40a and 40b respectively, recesses 14 formed'in the upper and lower faces of the body member 10 to allow the fitting member described hereinafter to fit therein, a fitting projection 15 formed in each recess 14, slits 16 formed on both sides of the recess 14 to fix the fitting member in place in cooperation with the fitting projection 15, a lip 17, and a cavity 18 to receive the shutter members 40a and 40b therein.
A- air of L- shaped shutter members 40a and 40b comprise guide projections 41a and 41b adapted to engage guide grooves 13a and 13b respectively, engaging portions 42 each of which engages one of the pins of the plug to be moved in both vertical and horizontal directions and has the first and second inclined faces 42a and 42b, and spring stopping portions 43a and 43b to engage both ends 30a and 30b of the spring 30. The front cover 50 has four pins 51 adapted to be inserted into the corresponding holes 19 formed in the body member 10, and guide holes 52 to allow the pins of the plug to pass therethrough and to guide toward the engaging portions 42 of the shutter members 40a and 40b. The plug guide 55 has the inner diameter corresponding to the outer diameter of the collar 71 of the plug described hereinbelow, and a predetermined height, and it is integrally formed with the front cover 50.
Figure 2 shows a situation in which an AC socket-outlet assembly 100 is not yet connected with a plug 200. The _AC socket-outlet assembly 100 has a front cover 50 having a guide 55 for plug 200 and holes 52 for guiding pins 6₀ of the plug, the body member having the recess 14, the fitting projection 15 and the slit portions 16, and the connector members 20. The plug 200 comprises a pair of pins 60 to be inserted into the guide holes 52 and a body member 70 having a collar 71. The pins 60 each has an electrically conductive end portion 60a and an insulated coating portion 60b.
Figures 3(A)-3(C) show one 40b of the shutter members shown in Figure 1 in further detail and in particular, the form of the engaging portion 42 can be accurately seen from the sectional views of Figures 3(B) and 3(C). That is, as shown in these drawings, the engaging portion 42 has two inclined planes 42a and 42b which are formed respectively on the two planes perpendicularly intersecting each other. When the pins 60 of the plug 70 are inserted through the guide holes 52 into the body member 10, the point of each pin 60 first engages the shutter member 40b at the position V₁ and then, while permitting it to move downward, engages it at the position V₂ with further insertion of the pin 60 ( as the pins 60 of the plug can not shift its vertical position, the shutter member 40b is shifted ). When the point of the pin 60 engages the shutter member 40b at the position V₂, it engages the latter at the position h_l in a cross section C-C and with further insertion of the pin 60, it leads to engage the latter at the position h₂, whereby moving the latter in a right diredtion M₂. As is obvious from the above, the shutter member 40b is continuously moved from the downward direction to the rightward direction by receiving the pushing force of the pin 60. _Likeweise, the shutter member 40a is also subject to a series of upward and leftward movements which are symmetric with the shutter member 40b.
Figures 4(A) and 4(B) show situations obtained before and after the AC socket-outlet 100 is electrically connected with the pins 60 of the plug 200 respectively. In Figure 4(A), the shutter members 40a and 40b cover the holes 11, and hence the connector members 20 through elastic forces of the spring 30. By applying the two symmetric and equivalent or similar forces to the engaging portions 42a and 42b of the shutter members 40a and 40b through a pair of the pins 60 of the plug 200, a series of movements of the shutter members described with respect to Figures 3(A)-3(C) are provided, thereby resulting in electrical connections of the pins 60 to the connector members 20 as shown in Figure 4(A). The collar 71 of the plug body 70 is well fitted into the inner wall of the guide 55 for the plug 200.
Figures 5(A)-5(C) show front views of the body member 10 of the socket-outlet. - Figure 5(A) shows the body member 10 including the holes 11 for the connector members 20 inserted, the above described guide grooves 13a and 13b for the shutter members, the opening portion 12 for the spring 30, the fitting projection 15 formed in the recess 14. Figure 5(B) shows a situation where the holes 11 and hence the connector members 20 are covered by the shutter members 40a and 40b through the spring 30 inserted into the opening portion 12. Figure 5(C) shows a situation where the shutter members 40a and 40b were moved from the covered position to an uncovered position to achieve an electrical connection of the connector members 20 with the pins 60 of the plug 200 through a series of movements of the shutter member described above. In this case, the guide projections 41a and 41b of the shutter members 40a and 40b slide in the guide gooves 13a and 13b of the body member 10, thereby facilitating the above mentioned movements of the shutter members 40a and 40b.
Figures 6(A)-6(D) show one of the preferred embodiments for fitting the AC socket-outlet 100 described above into a chassis 300 equipments. The socket-oultet 100 is fitted into the chassis by two fitting members 80. Each fitting members comprises a front end portion 81, an enlarged base portion 82 and a hole 83 engaged with the recess 14 of the body member 10. The AC socket-outlet can conveniently and stably fitted into the chassis; first each fitting member 80 is fixed into the recess 14 of the body member 10 by fitting the projection 15 into the hole 83 while sliding the enlarged base portion 82 in the slits 16 on the body member 10; and then the body member 10 is pushed into a hole on the chassis 100 until the elastic end portion 81 and the lip 17 of the body member 10 grasp the chassis therebetween.
In the above construction, when inserting the plug 200 into the plug guide 55 in such a way that the collar 71 of the plug body 70 fits to the guide, the pins 60 of the plug are inserted into the guide holes 52 and then is engaged with the connector members 20 through the operations described with respect to Figures 1-5.
As is apparent from the above embodiments, the present invention can provide a high safety electrical connector from the facts that the AC socket-outlet 100 has the shutter members 40a and 40b; one can not make contact with the connector members 60 from the exterior when the collar 71 of the plug body 70 is fitted into the plug guide 55; and the pins 60 each has the insulated portion 60b.

Figure 7 shows another emodiment of the invention in which the plug guide 55 indicated in the emodiment described above is excluded. Since the same parts as those of the latter embodiment are represented by the same reference numbers, overlapping description is omitted.
Figures 8(A)-8(C) show another construction of the shutter member 40b. The construction of this shutter member is the same as that shown in Figures 3(A)-3(C) except that a fitting portion 42 comprises a curved surface.
Figure 9 shows further another embodiment except that the pins 60 of a plug 200 are in the from of blade and guide holes 52 are in the form of slit.
Figure 10(A) is an exploded view of a duplex socket-outlet or receptacle having the two shutter means 40 described above. The duplex socket-outlet comprises a front cover 510, two shutter means 40 each in the form of two shutter members 40a and 40b, a base or body member 520, two fittings 530 and a rear cover 540.

The front cover 510 is of conventional type, and includes two recessed plug seats 511 each formed with a pair of holes 512 adapted to receive two pins of a plug, and an opening 516 formed in one of the side walls to accept a flexible cord-400. In the interior of the front cover 510 are formed an internal thread 513 provided in the middle of the cover for engaging a cap screw 561 upon assembly, two recessed portions 515 which engage the corresponding convexed portions 521 of the base member 520 respectively and which are formed just under the holes 512, and four threaded holes or internal threads formed in the four corners ( not shown ) adapted to engage the corresponding four cap screws 560 respectively.
As shown in Figures 10(A) and 10(B), the base member 520 includes a pair of the convexed portins or projections 521, four openings 522 each adapted to receive one end 531 of each fitting 530 which come into contact with the pins of a plug, two opening 523 each adapted to receive a spring 30, four pairs of guide grooves 524 each pair to regulate the motion of shutter member 40a or 40b, and two cavities 525 each to allow the shutter means 40 to be fitted into it, a hole 526 to allow the cap screw 561 to be put through it when the front cover 510 and the base member 520 are assembled with the screw 561, four threaded holes 527 each adapted to engage one of four cap screws 550 for fixing the plug pin receiving fittings 530 to the base member 520, and two recesses 528 each adapted to engage the middle convexed portion 533 of the fitting 30.
Each fitting 530 comprises two contacting segments 531 each adapted to contact with a pin of a plug and pressed into the form of a hollow semi-cylinder for providing a large area contact with the rod-shaped pin of the plug, two holes 532 each formed in the position corresponding to the threaded hole 527 of the base member 520 and a middle convexed portion-533 adapted to engage the recess 528 of the base member 520 and having an internal thread 534 to engage a cap screw 550 by which an eyelet 520 of a lead wire 410 of the cord 400 is connected to the fitting 30.
The rear cover 540 comprises four holes 541 for engaging the cap screws 560 formed in its four corners, a loose hole 542 for engaging the cap screw 561 formed in its central portion, four loose holes 544 for engaging the cap screws 550 adapted to fix the fittings 530 to the base member 520, and two rectangular projections 543 each formed around a pair of holes 544.
The fittings 530 to engage'the pins of the plug are fabricated from a tin-plated phosphor bronze plate. The other members are fabricated from the same material as that of the body member of the AC socket-outlet, that is, a 20% glass fiber-polybutylene terephthalate composite.
The procedure for assembling the duplex socket-outlet with shutter members is as follows:

.(1) Incorporation of the fittings into the base member: Insert the contacting segments 531 of each fitting 530 into the openings 522 of the base member 520, engage each hole 528 of the base member 520 with the convexed portion 533 having the internal thread 534 of each fitting 520, drive each cap screw 550 through the hole 532 of the fitting 530 into the corresponding threaded hole 527 for fixing each fitting 530 to the base member 520.
(2) Attachment of the front cover to the base member: Insert each spring member 30 into the respective opening 523 of the base member 520 and incorporate each shutter means 40 into the respective cavity 525 of the base member 52₀, then mount the front cover 510 on the base member 520, whereupon fit the convexed portion 521 of the base member 520 into the corresponding recessed portions 515 of the front cover 510, pass the screw 561 through the hole 542 of the rear cover 540 and the hole 526 of the base member 520, and then drive the screw 561 into the threaded hole 513 of the front cover 510 for integration of the base member 520 and the front cover 510 into one unit. By this integration the prescribed functions are provided for the shutter means 40 incorporated into the cavities 525.
(3). Connection of a two-wire cord to the socket-outlet: After the integration of the base member 520 with the front cover 510, strip off the insulator from the wires 410, and attach the respective stripped off wire terminal 420 in the form of eyelet to the convexed portions 533 of the fitting 530 by inserting the screw 550 into the eyelet and driving it into the threaded hole 527.
(4) Mounting the front cover on the rear cover: After the connection of the cord to the socket-outlet, align each of four corner's holes 541 of the rear.cover 540 with the corresponding respective internal thread (not shown) formed in the four corners of the front cover 510, and drive each of four cap screws 560 to fix them without putting the cord 400 between them.

Figure 11 shows a table tap 600 fitted with the two shutter means according to the invention. This table tap is movable at will along with an extensible cord 400 connected to the connector members accommodated in its body member.
Figure 12 shows a flush type of socket outlet 700 embedded into a wall 800 of a building, and having the shutter means in accordance with the invention In addition, this flush type of socket-outlet may be provided, for example, in a floor 900 or the ceiling of a building.
The products of the present invention meet the rules according to " CEE-7 " (International Comission on Rule for the Approval of Electric Equipment, 1963). The rules applied to an AC sodket-outlet are as follows:

1. Restriction from the rules

(1) Connector member
- material: Cu-alloy (>58%Cu) with high corrosion resistance
- elastic properties: 1.0-5.0 kg after inserting into and withdrawing a plug from the socket-outlet 5000 times
(2) Body member and front cover:
- withstand voltage: no damage for 2000^VAC, 1 min.
- insulation resistance: > 5M ohms between connectors, and connector and body member for 500^VDC, 1 min.
- moisture resistance: to meet said whthstand voltage and insulation resistance without deformation, tear, etc. after treatment with a 91-95%, relative humidity for 48hrs at 23°C
- heat resistance: to meet said withstand voltge and insulation resistance without deformation, tear, etc. after treatment with 100°C, 1 hr
- rise in temperature: 45°C after energizing with 4A, 1 hr
- burning resistance: no danger of gas-ignition after keeping for 2 min. at 300^o _C
- impact resistance: no damage after test with a 250 gr hammer, 0.5N/m impact force
- lifetime: the same as those of said withstand voltage and rise in temperature after a 5000 time inserting-withdrawing test at rated voltage and current
(3) The other members, that is, shutter member, fitting member and spring member are not particularly restricted.

2. Restriction for the inventive product from its use

The inventive product is used as the AC socket-outlet which is installed in various electrial equipments and provides a power source from the latter to other electrical equipments. For example, a stereo sound system comprises a player, amplifier, tuner, speaker, etc. The player requires its own power source and the amplifier and the tuner also require the respective power source. If using a flush type of socket-outlet required for each of these-components, at least three socket-outlets are necessary. This makes no use of other electrical equipment while operating the stereo. For this purpose the power supply to the stereo is made from a household receptacle to the amplifier, and the power supplies to the player and the tuner are made from the socket-outlets installed in the amplifier.
The rateu voltage of the AC socket-outlet described above is 250 V in Europe against 100 V in Japan, and hence an electric shock to the human body, a fire and so forth are raised as a great problem. Therefore, in order to prevent a direct contact with the connector members when the AC socket-outlet is not served, the shutter means to cover the energized connector members such as that disclosed in British Patent No. 1436611 has been provided.
As described above, the present invention also provides the AC socket-outlet fitted with shutter means which cover the connector members from the exterior upon its service and prevent the contact of the energized:connector members with the plug pins used for the source of other electrical equipments unless the two symmetrically equivalent pushing forces are applied to both shutter members upon its service.
The requirements of a user for the AC socket-outlet described above are as follows:

(a) the lifetime is equal to or longer than the subject electrical equipment;
(b) the fitting means to the electrical equipment is simple and the holding force after fitting is stable and there is no play;
(c) a small size;
(d) the materials used are chemically harmless to the respective componentsof the electrical equipment; and
(e) inexpensive.

3. Selection of the material used for each member of the AC socket-outlet

(1) Body member and front cover

From a consideration of the requirements to meet the above mentioned rules based on CEE, and of their workability and cost, polybutylene terephthalate was selected as a material for them. However, this material was insufficient to meet the impact resistance of the AC socket-outlet. After a variety of investigations, it has been found that a composite comprising 20% glass fiber-polybutylene terephthalate can satisfy all of the above requirements. The typical properties of the composite are as follows:

(a) high strength and stiffness in the wide range of tempertures,e.g., 1900 kg/cm² at -30°C, 500 kg/cm² at 150^o _C;
(b) the lowest water absorption rate in engineering plastics, i.e., 0.25% after the humidity treatment with 95% relative humidity for 96 hrs at 23°C;
(c) high heat. deformation temperature (deformation resistance,18.6 kg/cm² at 200-213°Cy with solder resistance, > 3 sec at 400°C;
(d) improved dielectric breakdown voltage, 28 kv/mm at 23°C; volume resistivity, 2.7 X 10¹⁵ ohms.cm with treatment 90% relative humidity, 48 hrs at 23°C;
(e) excellent fluidity as a thermoplastic material reinforced with glass fiber and short in moulding cycle due to a distinct melting temperature and a faster crystallization rate; and
(f) improved burning resistance and no danger of gas- .ignition at 300°C for .2 min.

(2) Shutter member

By considering smooth slide between the plug pins and shutter members, the latter and body member of the AC socket-outlet as well as the desired properties in wear resistance, heat resistance and stiffness, polyamide resin reinforced with mineral matter was selected as a material for the shutter member.

(3) Fitting member

The fitting member for installing the socket-outlet on electrical equipments has to hold the former fitted on the latter and is not allowed to increase its settling and fatigue after a plug insertion-withdrawal test of 5000 times. From these respects, polycarbonate superior in mechanical, in particular, elastic property was selected as a material for the fitting member.

(4) Connector member

The characteristies required for the connector member enabling the direct connection of a plug pin to the socket-outlet are as follows:

(a) to have a force of 1.0-5.0 kg for holding a single pin of a'plug after inserting into and withdrawing the plug-from the socket-outlet 5000 times;
(b) to include copper more than 58%;
(c) good soldering; and
(d) good corrosion resistance and workability.

From these characteristics, a tin-plated phosphor bronze plate was used as a material for the connector member.

(5) Spring

This spring is one of the most important members to achieve the invention, and shall be stable in mechanical properties, in particular, elastic property and excellent in corrosion resistance. In order to meet the elastic property required for enabling a shutter member to return to a predetermined position after inserting into and withdrawing a plug from the socket-outlet 5000 times, a stainless steel (SUS 304, WPB) in the form of a coiled spring (wire diameter, 0.5 mm, mean diameter of coil,4.6 mm, length over coil, 4.5-5.0 mm) was selected.

4. Assembling and engaging means of each member

(1) Fixation of connector members 20 to body member 10 Referring to Figure 1, the body member 10 is provided with the openings 11 each adapted to receive the connector member 20 and the slots (not shown) formed in the rear face each to allow the terminal 21 of the connector member 20 to pass through. Fixation of the connector member 20 to the body member 10 are carried out by means of the projections 22 formed in the connector member 20 after passing through the slot.
(2) Engagement of spring 30 with body member 10 The spring 30 is inserted into the opeing 12 formed in the body member 10 and holdedbyboth side walls of the opening 12.
(3) Fixation'of spring 30 to shutter-members 40a and .4 Ob
Oppose a pair of L-shaped shutter members 40a and 40b against each other in:a predetermined position, insert one end 30a of the spring 30 into the spring stopping portion 43a of the shutter member 40a and then insert another end 30b of the spring 30 into the spring stopping portion 43b of the opposite shutter member 40b.
(4) Engagement of shutter members 40a and 40b with body member 10
Engage the guide projections 41a and 41b of the shutter member 40a and 40b with the corresponding guide grooves 13a and 13b of the body member 10 respectively, insert the formers into the latters and put the shutter members between the body member 10 and the front cover 50, leaving a small gap therebetween to provide the desired movements of the shutter members.
(5) Fixation of front cover 50 to body member 10 Fixation of the front cover 50 to the body member 10 is carried out by inserting four projected pins 51 of the front cover 50 into the corresponding holes 19 provided in the front face of the body member 10.

Claims

1. A shutter apparatus for electric outlets, comprising a pair of the outlets (20), a shutter means in the form of two shutter members (40a, 40b) movable between a first position to cover the outlets and a second position to uncover the outlets, and an elastic member (30) urging the shutter members to the first position, characterised in that the shutter members (40a, 40b) each has a force receiving plane (42) which produces the force urging the shutter member from the first position to the second position against the elastic member (30) when the shutter member is subject to two symmetrically equivalent pushing forces.

2. A shutter appatatus as claimed in claim 1, in which the force receiving plane (42) of each shutter member (40a, 40b) has a first plane (42a) to produce the force for urging the shutter member in the vertical direction and a second plane (42b) to.produce the force for urging the shutter member in the horizontal direction.

3. A socket-outlet, comprising a body member (10) fixed to a stationary system, a pair of connector members (20) accommodated in the body member, a shutter means in the form of two shutter members (40a, 40b) movable between a first position to cover the connector members and a second position to uncover the connector members, an elastic member (30) accommodated in the body member and urging the shutter members to the first position, and a front cover (50) having a pair of guide holes (52) to guide a pair of the pins (60) of a plug (200) adapted to engage the connector members (20), characterised in that the shutter members (40a, 40b) each has a force receiving plane (42) which produces the force urging the each shutter member from the first position to the second position against the elastic member (30) when the shutter members are subjected to two symmetrically equivalent pushing forces by a pair of the plug pins (60) inserted from the guide holes (52).

4. A socket-outlet as claimed in claim 3, in which the force receiving plane (42) each has a first plane (42a) adapted to produce the force urging the shutter member toward the vertical direction and a second plane (42b) adapted to produce the force urging the shutter member toward the horizontal direction.

5. A socket-outlet as claimed in claims 3 and 4,..in which the front cover (50) has a guide (55) for guiding the pins (60) of the plug (200) into the guide holes (52).

6. A socket-outlet as claimed in claim 3, in which the body member (10) has a fitting member engaging portion comprising a recess (14) formed on the surface of the body member, a projection (15) formed in the recess, and slits (16) formed on the both sides of the recess.

7. A socket-outlet as claimed in claim 3, in which the stationary system is a fixed cabinet for electrical equipments.

8. A socket-outlet as claimed in claim 3, in which the stationary system is a wall (800), a floor (900) or the ceiling of a building.

9. A table tap, comprising a body member (600) which is movable at will along with an extensible cord (400) having a pair of conductors, at least one pair of connector member (530) accommodated in the body member and connected to the conductors of the extensible cord, at least one shutter means each in the form of two shutter members (40a, 40b) movable between a first position to cover the connector members and a second position to uncover the connector members at least one elastic member (30) each accommodated in the body member and urging the shutter members to the first position, and a front cover (510) having at least two pairs of guide holes (512) to guide a pair of the pins of plug adapted to engage the connector members (530), characterised in
that the shutter members (40a, 40b) each has a force receiving plane (42) which produces the force urging each shutter member from the first position to the second position against the elastic member (30) when the shutter members are subjected two symmetrically equivalent pushing forces by a pair of the plug pins inserted from the guide holes (512).

10. A table tap as claimed in claim 9, in which the force receiving planes (42) each has a first plane (42a) adapted to produce the force urging the shutter member toward the vertical direction and a second plane (42b) adapted to produce the force urging the shutter member toward the horizontal direction.