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Technical Information:
The lockable earth pin plug is the same dimensions as a standard BS1363 plug only that it incorporates a lockable earth pin and a rotating lockable screw on the plug top. The plug lock is wired the same as a standard BS1363 plug and is also fitted together with the single cross head threaded screw which is between the earth pin and the live and neutral pins just like a standard plug.

The only difference is that the earth pin has two spring loaded rubber pins that protrude once the plastic disc is rotated. If for any reason one of the two pins can’t protrude then only one pin will lock the earth pin into the socket. Once the plastic rotating disc is turned anti-clockwise then the protruding rubber pins will retract back into the main earth pin. This can prevent the plug from either being inserted or removed from a socket, extension lead or box adapter.

LockmyPlug Earth

Picture showing one side of the small 2 mm diameter rubber locking pin, can also be locked outside the socket to prevent un authorized use of the electrical appliance.

Lock my Plug
3D CAD drawings here
The centre of the 2mm locking pin is 11.5mm from the bottom of the plug base.
Also 11.5mm from the bottom of the earth pin.
The 2mm rubber pin is round (not square) and both pins are connected together using a 1mm spring.
The top of the earth pin that's inside the plug has a 3mm hole in the centre that is approximate 24mm deep inside the earth pin.

Below you can see the blue plunger is seated in between the two lockable rubber socket pins and covering the 1mm gray spring. This is the normal unlocked position so that you can insert the lockable BS1363 plug into a standard 3 pin socket be it single, double or triple socket.
This will also fit into any extension lead socket, in fact any socket that accepts a standard 3 pin BS1363 plug.

The earth wire is connected to the side of the pin and not on the top like some plugs.
Naturally we use the top of the earth pin for the plunger to open up locking pins when in the socket.

LockmyPlug Earth

You can see how the blue conned separator separates the two rubber locking pins with a downward plunger movement.

LockmyPlugHow it works

When the plunger is retracted back via the plug top cam movement the gray 1mm spring will return back to its original state which will retract the two rubber locking pins.

The plunger and the plug top cam is connected together by a nylon quick fit connector but you could use a spring to retract the plunger if required, see below drawing.


With some sockets you will have a earth bar (normally at the top on a MK socket) or plastic barrier / obstacle in the way of one of the rubber lockable earth pins.

This will not be a problem as the conned separator is connected to the plunger by a flexible connection which will still move one of the rubber lockable pins into the socket to lock the plug. When the plunger travels back, returns back to unlock position the gray spring will return back to its normal position and retract the rubber lockable pin / pins from the socket.

For more information on materials and the Product Investigation of a 3 pin plug


The plug top has a rotating disc which when turned moves the plunger down. The centre of the plunger is attached to the centre of the disc by a press fit nylon connector. This allows the plunger to return back to its home position once the plug top rotating disc is turned anti-clockwise 360 degrees. There is no need for a spring to return the plunger back to its home position but could be added if required, see FIG 4.

The rotating disc on the top of the plug has a slot to lock and unlock the plug from the socket.

The 2mm diameter hard plastic conned separator fits over the 1mm diameter spring (see FIG 3). As well as separating the earth rubber locking pins it also is used to centre the locking mechanism. The 1mm spring will travel vertically into the separator body when a downward motion is introduced (2mm downward travel) This conned separator is made out of plastic which is non conductive material.

FIG 6 - Top side view of the earth pin.
LockmyPlug Earth
LockmyPlug Earth

The lockable earth pin (patent approved) is simple in the way it locks the plug in or out of the socket via 2 protruding pins either side of the earth pin top and bottom.

Once the 3mm diameter plastic plunger (blue in colour) is rotated downward then the two rubber 2mm pins (green in colour) that's held together by a 1mm spring will move outward locking the plug into the socket.
In some plug sockets, only one of the rubber pins will lock due to the top of the earth bar or the socket plastic being an obstruction. This is why we had to use a 1 mm spring in between the plunger and the separator.
One rubber pin is enough to lock the plug into the socket. The earth pin still maintains conductivity and does not compromise the BS7671 17th edition wiring regulations and will still carry half the current capacity of the main cable in a earth fault condition.

The reason we use rubber pins is so that the socket does not get broken when you try and pull out a plug that's been locked into the socket. At all times the socket has to maintain its integrity.

LockmyPlug Earth