“I normally refuse to join in campaigns but this seemed so important, and the ‘safety’ covers so absurd and dangerous, that I agreed”
Author, TV presenter & Patron of FatallyFlawed
Dr Adam Hart-Davis



“Sockets in the UK are designed to keep people safe. Our UK design has been better than the majority of other countries, for many years.  Socket covers are an absolute con and totally unnecessary.” 
Engineering, Maths and Science presenter on TV
FatallyFlawed Supporter

Johnny Ball

Size Matters!!

IMPORTANT: This information applies to BS 1363 sockets only   

This picture shows a socket which has been severely damaged by overheating.  One cause of overheating is poor contact between the plug pins and the socket contacts.  Inserting over-sized pins into the contacts, such as those found on many socket covers, may damage the contacts and lead to loose connections when a properly sized plug is inserted.  See the “Pro Feedback” page for real life examples.

Picture courtesy of RF Lighting.


Size does matter!  It matters a lot.
To understand why size is so important you need to know that sockets are designed to take standard plugs.  Plugs are not made to the size of the sockets, but must be made to very precise measurements which are defined in the BS 1363 standard.  All sockets made to the standard since 1947 will safely accept a standard plug, but if anything which is not standard is plugged into a socket then the results are unpredictable and damage or poor performance may result.  There are hundreds of different socket models in use, and it would be impossible for anyone to test a non-standard sized socket cover in all of them.  However, the makers of plug-in socket covers appear to have assumed that this does not matter - all plug-in socket covers we have tested fail to conform to the standard size and shape!  This causes a variety of problems.

Size problems include:

  • Pin length
  • Pin thickness
  • Pin position
  • Pin shape
  • Size of cover plate
Compare length

Pin length:  The picture above compares the pins of a standard plug with those of a couple of typical socket covers.  The centre (longer) pin is the earth pin, and you can see that neither of the dummy earth pins of the covers are quite the right length. (Both are outside specification, the LH being too short, and the RH too long.)  The main problem with the pin lengths is the other two pins, these are almost always too short, and you can see that both of these covers have pins which are much too short.  this is the main reason that socket covers are easy to put into a socket upside down, the other pins are too short to prevent it, as shown in the picture at right.  

Partial Ejection_length

“Pop Out”:   Socket covers which have pins which are just a few millimetres short, such as IKEA, Clippasafe etc, have a particular problem.  Depending on what socket you use them with the cover can be partially ejected as shown in the “cutaway” photo on the left.  The pin is not long enough to properly enter the electrical contact, only the shaped part on the end goes into the mouth of the contact, and that is a spring which compresses and forces the pin back out so that there is then a gap between cover and socket.  This gap is on the lower side of the socket cover which means it will not be noticeable to an adult viewing from above, but can easily be seen by a crawling child who can then use it to remove the cover.

Pin Thickness:  Over half the covers we have tested have pins which are too thick to safely put into a socket!  A pin which is too thick has to be forced into the socket, and this may result in permanent damage to the socket contacts.  If the contacts do not fit snugly when a plug is used in the socket then a poor connection can cause overheating, a socket fire may result (see photo at the top).   If the pins are too thin then they will not hold the cover in place, making it too easy to remove.  Some covers have earth pins which are too narrow and will not open the shutter all the way.  See photo at right - a narrow earth pin (from an emmay cover) is inserted, the cover has been cutaway so that you can see the shutters.  Pushing the complete cover into the socket will force open, and damage, the shutters.


Pin Position:  This is another thing which some manufacturers care little about.  This photo shows the warping caused when a Tesco “my baby’s” socket cover is plugged in.  The distance between dummy power pins is 2 millimetres less than allowed, resulting in the cover, which should lie perfectly flat, being buckled as shown.  It is impossible to predict what long term damage this causes to the socket.

earth profiles h earth profiles e

Pin Shape:  The photo on the left above shows the tip profiles of a real plug earth pin, and six dummy pins from socket covers.  On the right we see a side view of the same pins.  As you can see from the first plastic pin, it is perfectly possible to reproduce the correct shape of a brass pin.  The second plastic pin is roughly the right shape, but the chamfer is insufficient.  The next is a nasty blob shape, and the next is tapered (not allowed in BS 1363) and then cut square with no chamfer.  The fifth plastic pin is designed with a split (not allowed) and the shape is all wrong, the quality of the moulding has left an extraneous piece of plastic sticking up.  The final pin is again a poor moulding and the wrong shape.  The photos below are of the power pins which correspond to the above, they show similar issues.  Why does this matter?  Apart from illustrating the general low quality of most of the products, it matters a great deal when the cover is inserted in sockets which use the alternative method of shutter opening, in which case  the shape of the tips is very important .  The highest quality sockets (MK and some of those from Legrand and Hager) will only allow the shutters to open when all three pins, or sometimes just both power pins, are inserted simultaneously.  The shutters operate properly only when pins with the correct profile are applied to them.  (The small picture below is a detail of an MK “Logic Plus” shutter.)  If pins do not have the correct profile then they need to be forced past the shutter, and that can cause permanent damage to the shutter mechanism and the shutters!

power profiles e
power profiles h

Size of Cover Plate:  There are problems with the size of the cover plate in the vast majority of socket cover designs.

Suppliers of socket covers make claims such as
     “Prevents little children inserting their fingers or objects into sockets” (Mothercare)
     “Reduces the risk of children sticking a finger or an object into a wall socket” (IKEA) 
     “These safety socket inserts will prevent youngsters trying to poke things into plug sockets” (John Lewis)

When a socket has nothing plugged in, children are protected by a combination of the socket face plate and the internal shutters.  When a plug is inserted the shutters are opened, so the task of protecting the holes which accommodate the power pins is passed to the plug itself.  The safety of the plug is enshrined in BS 1363 which, amongst other things, demands that the periphery of the plug be at least 9.5 millimetres from any point on the power pins, this ensures that there is no way an object can be pushed into the same hole as the plug.  Now look at the photo above on the left, we have traced the outline of a standard plug onto the socket faceplate, in this case the actual distance from the power pin holes is 10.5 millimetres.  It would be reasonable to accept that a socket cover (which is not covered by any electrical standards or regulations) would provide similar protection to the plug, but in fact, as you can clearly see, this cover (from Mothercare) does not even cover the corners of the holes, let alone extend to the required 9.5 millimetres!  Ask yourself if this supplier can possibly be taken seriously.

The central photo shows a similar cover from IKEA.  Because the cover does not actually cover the holes, it is not difficult to insert a paper-clip right into the live contact, as shown here.  Clearly this cannot be said to “Reduce the risk of children sticking a finger or an object into a wall socket” as the use of the cover has made it possible to do just the opposite!  (Without the cover the internal shutters would have prevented this happening.)

The photo on the right shows a cover from John Lewis which has been cutaway to allow us to see the interior.  (Clippasafe and Boots sell covers of the same design.)  The cover has a hole through the dome shaped part which is intended to be used to help remove it from a socket, using the earth pin of a plug.  Inside the cover, not only is there a gap between the cover plate and the faceplate of the socket, but the domed feature provides direct access, through the removal hole, into the live contact of the socket (as indicated by the lamp attached to our needle probe).  Clearly the John Lewis (and similar) covers do not “prevent youngsters trying to poke things into plug sockets”!!!

A Fact Sheet which shows the pin dimensions of all the socket covers we have tested is available for download.

If you insert a socket cover which has pin dimensions which do not conform to BS 1363, it is a clear case of misuse of your socket.  Permanent damage can result.

If your home is rented, your landlord may demand that you pay for the replacement of all sockets which have been abused in this way.

Should you be unlikely enough to suffer an electrical fire in a socket, and there is evidence of the use of socket covers which do not conform to BS 1363 pin dimensions, then your insurance company may refuse to pay out on the basis of misuse of the socket.

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