Electric plug

[57] ABSTRACT

A simple inexpensive electric plug will lock into a wall socket. It accommodates a latch which fits, edgewise into a pin so as to give a great depth of locking surface. A cam-like incline automatically depresses the latch as it enters the socket or receptacle and a spring causes the latch to engage with the rear face of the receptacle front moulding. The latch may be depressed (so that the plug may be removed) by means of a pushbutton.

Claims, 7 Drawing Figures

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Patented July 11, 1972

3,676,831

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3,676,831

2

ELECTRIC PLUG

This invention relates to electric plugs and particularly to a plug which may be locked in relation to a standard wall socket so that movement caused by the power cord (as of a portable tool) will not loosen the plug. 5

Previous attempts to provide lockable plugs have sometimes demanded extra fittings for the face plate or even the socket itself. Very often the locking device itself comprises a thin latch of metal which can easily become bruised and hence unreliable or inoperative. In some cases one of the contact mem- 1C bers themselves was the latch and moved and the arcing tended to destroy or at least to deteriorate the locking feature. Many such devices were complex and required the use of accurate machining or some equivalent such as the use of coining dies. 13

Whatever the cause, previous proposals for such plugs which will lock easily in wall sockets have been found to have disadvantages; and the need still exists for an inexpensive but reliable electric plug that can be locked in position.

I have found that the problem may be solved by providing ²θ an electric plug having a pin with a U-shaped slot in it which extends longitudinally along the pin; a retractable latch accommodated in this slot allows the depth of the latch to be much greater than the thickness of the material of which the latch is made. This has the advantage that the metal does not ²³bruise easily and even if the leading edge of the latch is deformed, the locking operation is not inhibited. Furthermore, the latch may be pivoted at the free end on the pin; and a spring for automatically causing the latch to engage with the face plate may be provided within the body ofthe plug so that ³⁰a strong automatic locking force with an easy manual override may be provided.

In the drawings which illustrate one embodiment of my invention,

FIG. 1 is an end elevation of the complete plug;

FIG. 2 is a side elevation in section;

FIG. 3 is a plan view in section;

FIGS. 4 and 5 show the pin and latch assembly in side elevation and plan respectively; and ₄θ

FIGS. 6 and 7 show the pin member and latch member in perspective, respectively.

In FIG. 1 a three pin plug generally indicated by 10 has been illustrated having current carrying pins 12 and 14 and an earth pin 16, it being understood, of course, that the invention is not ₄₅limited to three pin plugs nor plugs having the particular rectangular section of pin that I have shown.

The latch of this invention is incorporated in current carrying pin 12 although, of course, it could also be accommodated in current carrying pin 14 or even the neutral pin 16. 50

Referring now to FIG. 2, it will be seen that current carrying pin 12 is attached to molded plastic member 18 by means of screw 20. A cable, not shown for the sake of clarity, enters the plug through hole 22 and its three leads are attached to the three pins 12, 14 and 16 by means of contact screws 24, 26, 55 and 28. Pin 12 accommodates a latch member 30 whose profile may be seen more easily in FIG. 7. This latch member is pivoted at the free end of pin 12 by a pivot member 32 which is, of course, flush with the two sides 34 and 36 ofthe pin 12 so as not to obstruct entry of the pin in the socket. 60

It will be seen from FIG. 6 that I prefer to make item 12 which includes side 34, side 36, bolting face 37 by a simple stamping and folding operation by methods well known in metal folding so as to eliminate any machining; of course, the holes are punched at the same time that the form is blanked 65 out of flat sheet.

I bias this latch member 30 to the latch extended position by means of a spring 40; and I prefer to retract the latch member automatically by spring 40 acting on the end of member 30 which is in the plug body. It will be easily understood that as 70 the plug is pushed in the socket, the inclined edge 38 bears against the slot in the face plate and compresses spring 40 until latch member 30 is completely within the pin 12, except of course for cranked extension 35. When the inclined edge 38 has passed the socket face plate the latch is moved up- 75 wardly by the spring 40 and latch face 42 formed as a notch in latch member 30 engages the back of the socket face plate; this prevents the plug from being loosened by the to-and-fro movement from the power coil inevitable in the use of power tools, hand lamps and the like. I prefer to provide pushbutton 44 of insulating material as it is convenient to stamp latch member 30 out of sheet metal. This pushbutton enables latch retraction by overcoming the spring 40 when it is desired to remove the plug from the socket.

It will be understood that the bend in member 30 after it leaves the pin 12 is not, broadly speaking, essential for operation of the latch. However, it is advantageous in the layout I have shown since not only does it allow the hole for pushbutton 44 to clear the hole 22 accommodating the power cord, but it also allows easy insertion of the pin 52 through hole 50 for retaining the pushbutton 44 as may be seen by reference to FIG. 2.

The remainder of the plug may be quite conventional and I have chosen to show a two part member comprising plastic parts 18 and 46 bolted together by nut and bolt assembly 48. It will, however, be evident that various other plugs now available on the market could well incorporate my invention as set out in the appended claims.