The present invention relates to electrical plug adaptors used for adapting the pins of an electrical plug to a different configuration. An example is an adaptor having three pins in the conventional UK configuration adapted to receive a European style two pin plug. The invention is particularly concerned with such plug adaptors designed to receive a plug substantially permanently, in other words such that it cannot be easily retracted. A number of such plug adaptors are already available.

The present invention provides an electrical adaptor comprising a housing and a first set of pins extending perpendicularly from a first face of the housing in a first configuration, the housing having openings in a second face for receiving pins of a plug which extend therefrom in a second configuration, the housing further having contacts for interconnecting the respective sets of pins and securing means on the outside of the housing adapted to be extended over the plug after reception in said housing whereby to prevent removal of the plug from the adaptor.

The extendable securing means are preferably arranged to be extended in a direction normal to the plane of the second face of the adaptor. The securing means are preferably located on the side walls of the housing connecting the first and second faces, and maybe removable or secured thereto. In the preferred embodiment of the invention, the extendable securing means are in the form of a sleeve encircling the adaptor. The sleeve has a portion for encircling the plug which is advantageously stored, prior to use, in a rolled or concertinaed configuration around the adaptor. The material of the sleeve is preferably elastic and chosen to be in a stretched condition around the adaptor and still somewhat stretched when it encircles the plug after extension whereby to grip the plug and prevent its removal from the plug adaptor.

The invention also provides a plug assembly including an adaptor as described above complete with plug and extended securing means. The invention also provides a method of adapting a plug to a different configuration using an adaptor as described above.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a conventional European two pin plug; Figure 2 is a perspective view of a plug adaptor having the conventional

UK three pin plug configuration;

Figure 3 is a side elevation of a conventional European two pin plug;

Figure 4 is a side elevation of the plug adaptor of figure 2;

Figure 5 is a side elevation of an assembly of two pin plug and three pin plug adaptor according to the invention provided with a roll-back sleeve, the sleeve being shown in cross section;

Figure 6 is a view similar to figure 5 in which the sleeve has been partially rolled over the two-pin plug;

Figure 7 is a view corresponding to figures 5 and 6 in which the sleeve has been fully extended over the two pin plug;

Figure 8 is a side elevation of the completed assembly;

Figure 9 is a side elevation of a second embodiment of a completed assembly of adaptor and plug in which the respective sets of pins extend in perpendicular directions; and Figure 10 is a side elevation of a third embodiment of a completed assembly.

The preferred embodiment of the present invention provides a three pin plug adaptor 10 which can receive a two pin plug 30 by pushing the plug into the adaptor but which in the finished assembly resists retraction of the plug. The

three pin plug adaptor 10 comprises a housing having a front wall 11 from which the usual three pins 12, 13, 14 extend in parallel. A rear wall 15 of the plug adaptor housing is formed with an opening not shown for the insertion of the two pin plug 30 in the direction of arrow A (figure 3). The two parallel pins of the plug 30 are received in connections (not shown) in the plug adaptor 10. It should be noted that in this embodiment, the two pin plug 30 is inserted into the three pin plug adaptor 10 in a direction parallel with the longitudinal extent of the pins 12, 13 and 14.

As shown most clearly in figure 5, the plug adaptor 10 is provided with a sleeve 20 encircling its side walls. In the illustrated embodiment, the sleeve 20 has a first portion covering the side walls and a second "rolled back" portion, the function of which will be described below.

The sleeve 20 is fabricated from an elastic material and designed such that it is in a stretched condition when encircling the plug adaptor 10. The rolled back portion can be draw over the inserted two pin plug 30 using a small amount of finger pressure at which point the rolled back portion will tend to shrink so as to closely encircle the two pin plug 30. Figure 6 shows the sleeve 20 partly extending over the two pin plug 30 and figure 7 shows the rolled back portion fully extended over the two pin plug 30.

The elasticity of the material of the sleeve 20 may be chosen such that once it has been extended over the two pin plug 30 it cannot readily be rolled back using normal human strength to fully reveal and enable the retraction of the two pin plug 30. Thus, in the finished assembly, it is necessary to cut the sleeve 20 in order to separate the two pin plug from the three pin plug adaptor.

It will be evident from the drawings that it is advantageous that the two pin plug has a shoulder portion 31 adjacent its front face 32 which bears against the

sleeve 20 and assists in preventing removal of the two pin plug from the three pin plug adaptor.

Figure 9 illustrates an alternative embodiment of the invention in which a plug adaptor 40 is designed to receive a plug 45 such that the pins of the plug 45 (not shown) extend in a direction perpendicular to the pins of the plug adaptor 40.

A sleeve 46 similar to the sleeve 20 described above encloses a portion of the plug adaptor 40, the whole of the portion of the plug 45 extending from the adaptor 40 and a portion of the cable 47 extending from the plug 45. The adaptor 40 could have the UK standard three pin layout.

Figure 10 illustrates another embodiment of the invention in which the plug adaptor 50 has a two pin configuration and is designed to receive a plug 55 such that the pins of the plug and adaptor extend in parallel directions. The adaptor 50 could have the US standard two pin layout and the plug 55 could have the European (VDE) standard two pin layout. Again, a sleeve 56 similar to sleeve 20 encases a portion of adaptor 50, the whole of the exposed portion of the plug 55 and a portion of cable 57 extending from the plug.