Safety Plug With Switch Means

The present invention relates to electric plugs, and relates more particularly to such an electric plug which has a switch controlled to close/open the circuit.

A regular electric plug is generally comprised of a housing, a base mounted in the housing, two metal contact plates mounted inside the base and respectively connected to the two conductors of an electric wire, and two metal plates respectively connected to the metal contact plates and extending out of the base and the housing for connection to an electric power outlet. This structure of electric plug is not safe in use because it can not protect against an overload. In order to protect against an overload, fuse means may be installed. There is also known an electric plug having two plug holes at the rear end for the connection of an external electric plug. However, because the plug holes at the rear end of the electric plug are exposed to the outside, a child may insert a metal object into the plug holes to close the circuit, causing an electric shock.

According to one aspect of the present invention, the safety plug comprises a first metal contact plate and a second metal contact plate respectively connected to the two conductors of an electric wire, a first metal blade and a second metal blade for connection to an electric power outlet, a cartridge fuse connected between the second metal contact plate and the second metal blade, a switch controlled to force the first metal contact plate into contact with the first metal blade to close the circuit, and a base mounted within a housing to hold the aforesaid members on the inside. According to another aspect of the present invention, the base has a rear panel, and two plug holes on the rear panel for the insertion of an external electric plug to connect the first metal blade and the second metal blade. According to still another aspect of the present invention, a slide is mounted in the housing and moved to close/open the plug holes of the rear panel of the base.

FIG. 1 is an elevational view of a safety plug according to a first embodiment of the present invention.

FIG. 2 shows the housing of the safety plug of FIG. 1 removed from the base thereof.

FIG. 3 is an exploded view of the safety plug of FIG. 1.

FIG. 4 shows an alternate form of the first metal contact plate according to the first embodiment of the present invention.

FIG. 5 is a side view in section of the safety plug shown in FIG. 1.

FIG. 6 is another sectional view of the safety plug shown in FIG. 1, showing the first metal contact plate forced into contact with the first metal blade.

FIG. 7 is a partial view in section of FIG. 1, showing the positioning of the switch in the switch sliding slot.

FIG. 8 shows a safety plug according to a second embodiment of the present invention.

FIG. 9 shows an alternate form of the first metal contact plage according to the second embodiment of the present invention.

FIG. 10 is an elevational view of the safety plug of the second embodiment according to the present invention.

FIG. 11 is an exploded view of the safety plug of the second embodiment according to the present invention.

FIG. 12 is a top view in section of the safety plug shown in FIG. 10.

FIG. 13 is a partial view in section of the safety plug shown in FIG. 8, showing the first metal contact plate forced into contact with the first metal blade.

FIG. 14 shows a safety plug according to a third embodiment of the present invention.

FIG. 15 is an exploded view of the safety plug of the third embodiment according to the present invention.

FIG. 16 is a sectional assembly view of the safety plug shown in FIG. 14.

FIG. 17 is similar to FIG. 16 but showing the first metal contact plate forced into contact with the first metal blade.

FIG. 18 shows an alternate form of the first embodiment of the present invention.

FIG. 19 is an exploded view of the alternate form of FIG. 18.

FIG. 20 is an elevational view of the alternate form of FIG. 18.

FIG. 21 is a sectional assembly view of the alternate form of FIG. 18.

FIG. 22 is similar to FIG. 21 but showing the first metal contact plate forced into contact with the first metal blade.

FIG. 23 is a partial view in section of FIG. 22, showing the positioning of the switch.

FIG. 24 shows an alternate form of the third embodiment of the present invention.

FIG. 25 is an elevational view of the alternate form of the third embodiment according to the present invention.

FIG. 25 is an exploded view of the alternate form of the third embodiment according to the present invention.

FIG. 27 is a top view in section of FIG. 25.

FIG. 28 is a sectional view taken along line 28--28 of FIG. 27.

FIG. 29 is similar to FIG. 28 but showing the first metal contact plate disconnected from the first metal blade.

FIG. 30 shows a slide mounted in the housing of the safety plug shown in FIG. 25.

FIG. 31 is similar to FIG. 30 but showing the plug holes of the rear panel of the base closed.

FIG. 32 is an exploded view of FIG. 30.

Referring to FIGS. 1 to 7, the safety plug 1, is generally comprised of a base 10, a housing 11, a first metal blade 12, a second metal blade 13, a first metal contact plate 14, a second metal contact plate 15, a cartridge fuse 16, and a switch 17. The base 10 comprises a first longitudinal trough 102, which receives the first metal blade 12 and the first metal contact plate 14, a second longitudinal trough 101, which receives the second metal blade 13 and the second metal contact plate 15, a first front slot 106 for the insertion of the first metal blade 12 into the first longitudinal trough 102, a second front slot 107 for the insertion of the second metal blade 13 into the second longitudinal trough 101, a rear wire hole 108 for the installation of the electric wire 9, a front stop edge 103 adjacent to the first front slot 106, an inward projecting strip 104 transversely projecting into the first longitudinal trough 102 in the middle at the top, and a post 105 in the first longitudinal trough 102. The second metal blade 13 is inserted through the second front slot 107 into the second longitudinal trough 101, having a rear end terminating in a forked coupling portion 131, which receives one end of the cartridge fuse 16. The opposite end of the cartridge fuse 15 is connected to the second metal contact plate 15. The second metal contact plate 15 has a pointed projection 151 forced into contact with one conductor of the electric wire 9. The housing 11 is covered on the base 10, having a longitudinal sliding door 111 and a longitudinal switch sliding slot 112. By opening the sliding door 111, the cartridge fuse 16 can be removed from the base 10 for a replacement. The switch sliding slot 112 is made on the housing 11 in the longitudinal direction. The first metal blade 12 is inserted through the first front slot 106 into the first longitudinal trough 102, having a curved rear contact strip 121 stopped between the front stop edge 103 and the post 105. The first metal contact plate 14 has a front contact tip 141 suspended above the curved rear contact strip 121, a curved middle section 142 supported on the post 105 below the inward projecting strip 104, and a rear connecting tail 143 connected to one conductor of the electric wire 9. The switch 17 is slidably coupled to the switch sliding slot 112 through a dovetail joint, having a downward press rod 171 stopped above the first metal contact plate 14. When the switch 17 is moved forwards, the curved middle section 142 is driven to force the front contact tip into contact with the rear contact strip 121 of the first metal blade 12. When the switch 17 is moved backwards, the curved middle section 142 of the first metal contact plate 14 immediately returns to its former shape to move the front contact tip upwardly away from the rear contact strip 121 of the first metal blade 12. FIG. 4 shows an alternate form of the first metal contact plate. As illustrated, this alternate form 14' has a pointed projection 140 at the rear end, which pierces the insulator of the electric wire 9 to make contact with one conductor therein.

Figures from 8 to 13 show a safety plug according to a second embodiment of the present invention. As illustrated, the base 20 of the safety plug 2 has a side opening 201, and a gap 202 in communication with the side opening 201; the first metal contact plate 24 is installed in the base 20 in vertical position, having one end connected to the electric wire 9, a bend 241 in the middle, and a front end inserted through the gap 202 and projecting into the side opening 201; the first metal blade 22 is installed in the base 20 in a vertical position, having a curved rear contact strip 221 spaced from the first metal contact plate 24; the switch 27 is slidably mounted in a longitudinal sliding slot 212 at one lateral side of the housing 21, having a press rod 271 pressed on the first metal contact plate 24 and moved with the switch 27 to force the first metal contact plate 24 into contact with the rear contact strip 221 of the first metal blade 22. The alternate form of the first metal contact plate 24' shown in FIG. 9 has a pointed projection 240 for piercing the insulator of the electric wire 9 to make contact with one conductor therein.

Figures from 14 to 17 show a safety plug 3 according to a third embodiment of the present invention. As illustrated, the base 30 has an inward pivot 305 and an inward projecting strip 304; the first metal blade 32 is mounted in the base 30, having a rear contact strip 321; the first metal contact plate 34 is mounted in the base 30 below the inward projecting strip 304 and connected to the electric wire 9, with its front end suspended above the rear contact strip 321 of the first metal blade 32; the switch 37 is a toggle switch turned about the pivot 305 of the base 30 and projecting out of the top side of the housing 31, having a sector-like bottom projection 371. When the switch 37 is turned backwards and stopped at the inward projecting strip 304, the first metal contact plate 34 is released from the first metal blade 32, and therefore the circuit is off; when the switch 37 is turned forwards, the first metal contact plate 34 is forced by the sector-like bottom projection 371 of the switch 37 into contact with the rear contact strip 321 of the first metal blade 32.

Figures from 18 to 23 show an alternate form of the first embodiment of the present invention, in which the base 10 has a rear panel 4 and two plug holes 41, 42 disposed on the rear panel 4 and aligned with the first metal blade 12 and the second metal blade 13 for the connection of an external electric plug; the rear contact strip 121 of the first metal blade 12 curves forwards, having a vertical mounting portion 1211 fastened to a mounting groove 106 inside the base 10.

Figures from 24 to 32 show an alternate form of the third embodiment of the present invention, in which the rear contact strip 321 of the first metal blade 32 is fastened to a mounting groove 308 in the base 30; the base 30 has a rear panel 5 and two plug holes 51, 52 on the rear panel 5 and aligned with the first metal blade 32 and the second metal blade 33 for the connection of an external electric plug; a slide 6 is mounted in the housing 31 and moved on the rear panel 5, having a slot 61, and a back rail 62 moved in a transverse groove 53 on the rear panel 5. When the slide 6 is moved to the left side to align the slot 61 with one plug hole 52, the plug holes 51, 52 are opened for the installation of an external electric plug. When the slide 6 is moved out of the operative position, external metal objects are prohibited from being inserted into the plug holes 51, 52 to close the circuit.