The 13 amp plug and socket.

During the second world war the 13 amp socket was developed and in spite of it's age is one of the safest systems in use today. There are other systems where the plug is rotated to switch on etc. But they cost far more. There have been two changes the first which required a sleeve on line and neutral pins to ensure it is disconnected before you can touch the pins. And one make requires both live pins to be inserted together to move shutters but most still use the earth pin. Because it is all to a British Standard rather then a manufactures standard there are very careful dimensions which will not allow abuse. But there are a few ways the safety features can be defeated.

In order that adaptors can do their job and allow as many types of plug to be used as possible most defeat or allow to defeat some of the 13 amp plug and sockets safety features and where children are free range then the adaptors used should be kept to a minimum.

Other than the 13A plug and socket there are a few other British Plugs. The Shaver plug although similar to the European 16A two pin plugs are not the same. Forcing the 16A plugs into shaver sockets can damage the sockets and result in bad connections when correct shaver plugs are used after. The 2, 5, 15 amp round pin sockets are still sometimes found especially the smaller 2 and 5 amp which are often used for lighting so standard lamps and like can be switched with wall light switches. Also there are the special fused light switches. There use for anything other than what they are designed for can cause problems and one should not use adaptors on these specials they may not even be correct voltage. There was when the British home was first provided with power different tariffs for light and power and there were adaptors made to supply power from BA22d and Edison screw light fittings these were not to any British standard and are in the main dangerous with no earth connections.   

Adaptors

With the Harmonisation of European electrical items and use of computers etc. it is often necessary either to change the type of socket available or increase the number of sockets available.

Adaptor-oldYears ago we had multi adaptors that allowed multi items to be plugged into the wall but the4G-extention-lead ext-lead weight resulted in plugs not being soundly home and bad connections plus some had no fuse and some only fused some outlets and fires resulted. As a result most have been removed from the market. In the main these have been replaced by the extension lead with multi sockets which are both fused on all outputs and if long enough do not put a strain on the wall socket and even if a whole series is plugged into each other the maximum draw from the wall socket is still limited to 13A. These are further enhanced with neon indicators, switches, surge protectors etc. with some models.

Before the second world war the UK had a whole host of plugs and sockets 5amp-plugsomeshaver-outlet and during the war a number of groups got together and designed the UK 13 amp plug ready for the house building it was realised would be required once hostilities ended. However there have been some of the old type that have hung on to present day. The 5 amp plug has been used for clocks and the 1 amp shaver outlet and plug are very common. Older houses still use the old 15 amp round pin for emersion heaters but in the main the 15 amp has gone. The shaver socket is designed to take many types of plug and here I must point out although the Euro Plug may fit a shaver outlet it is likely to damage the socket as the euro pin spacing is a little larger than shaver plugs and they are only fused to 1 amp where Euro plugs may be used on items drawing up to 16 amps.

Now to other countries plugs and sockets wikipedia has done a very good description and I see no point in repeating it. Note:- The 13A outlet adaptor shown below has extended live sockets to allow shaver plugs as well as 13A plugs to be used with it. This is dangerous as it will also allow the earth pin to be plugged into the live with non shuttered models.
So I will start with the voltage. In Europe we have harmonised to 230 volt + 10% - 6% but in other countries 110 volt is used. voltage-range UK-US US-UK UK-US-transformer With the advent of the switched mode power supply some items like computers can run on a huge range of voltages without any transformers or switches to the left it shows a computer power supply able to run on 100-240 volt and 50-60Hz as a result both US to UK and UK to US adaptors have become available there are also items with switches to convert between the two supply voltages but most UK and US items can not be used with adaptors and need transformers. The one shown to the right has a maximum output of 100VA that is nearly same as 100W most of these do not convert the frequency only the voltage so an alarm clock would go slow also record player etc. Although most items would work OK. There are more expensive devices (The one shown costs about £18) which can also change the frequency these are called inverters rather than transformers. Also in the states they have 110 volt to earth but in the UK on building sites etc. we have 110 volt between phases and only 55 or 63 volts to earth. As a result all UK 110 volt equipment has duel pole switching and fusing where this may not be the case with equipment from the states so be very careful buying cheap US electrical equipment to use here in UK.

Schuko-plug-socket In to Europe we have less problems with only the types of plug being different. German Schuko sockets are not allowed in the Schuko-UK-adaptor-plug Schuko-UK2 UK because the plug can be put in either way around and so to use German equipment one needs an adaptor. We could if we wished fit the French sockets as they are not reversible but even so in the main we have three options. Cut the plug off and fit British,  Use an adaptor plug like shown to far left or use a plug in adaptor like shown left. Note the adaptor plug shown to the left has side connectors to transfer live and earth there are many on the market which do not connect the earth and can only be used with Class II devices i.e. those not requiring an earth. The adaptor plugs come in both Class I and Class II versions and are often fitted to commercially imported equipment to comply with British rule that items offered for sale in UK must be fitted with a UK plug.
Adaptors Foreign-Plugs2 Most hand portable equipment can have the Lives swapped so getting Line and Neutral right way around would not matter but this is not true to all equipment and there is still quite a lot where only the Line (On single phase equipment we call the Phase wire Line as both Line and Neutral are considered live.) supply is fused so there is a problem exporting some of our equipment to Germany where the Line and Neutral may be swapped.
shaver-adaptor-old Above are three similar adaptors to left is a shaver adaptor with no earth connection normally fitted with 1 amp fuse to BS 646 much smaller than the BS 1362 normally13 amp found in the centre version designed to allow a variety of foreign plugs to fit the UK socket. On the right of picture above and far right however are very dangerous versions without any fuse sometimes supplied with Chinese imports or very old with no fuse. This would allow a 32 amp draw from most 13 amp sockets well over there safe working load. Although the German Schuko plug will normally fit these adaptors they have no side contacts to connect the earth. And as with the version further up the page they all will allow the use of the American flat pin plug, some imports from China have American flat plugs but are 220V 50Hz and come with adaptor shown on the right which should always be changed for type centre or left in picture. The Electrical Safety Council have also identified some problems.

Extension Leads

In the UK you are not allowed to use a two core extension lead with a 3 pin socket. Since lawn movers etc. often only need two core cables they tend to have RCD-Plug Plug-wiring special two pin sockets often non reversible as overloads are often only in the Line supply. The shorter extension leads with an earth do not necessary need an earth leakage trip but anything over 15 meters will need an RCD somewhere this is because as the lead gets longer so does it's resistance get higher and with a short circuit to earth not enough current would run to blow the fuse in time. For a long time now it has been recommended that all sockets likely to be used outside should be protected by an RCD so as standard even long extension leads do not have RCD's fitted. But where all the sockets on a premises are not RCD protected then an RCD plug like shown to the left should be fitted. The standard plug is shown to the right with brown going to the fuse L for Line and blue to neutral N and green/yellow to earth E earth  note how the Line cable has been cut short this ensures should the cable ever be dragged out of the plug the Line is disconnected first. On the socket end of an extension lead the method of connection varies widely and to show one example could cause confusion it is better to use the instructions that come with the unit. Many pre-assembled units have the cable welded to terminals and can not be re-wired.

RCD's in domestic premises are in the main of two types. The 100ma RCD fitted in or near the fuse board/consumer unit is to protect against fire and short circuit but not personnel. The protect people and pets the trip needs to be a 30ma or lower there are some 10ma RCDs but not common. When the 30ma RCD is fitted in or near the fuse board/consumer unit it will be of the passive type that is should the power fail and then come back on again it will not trip. But to work the RCD needs voltage so as we move away from the main board we use an active type and with these if we lose power they need resetting.

A.C. is used in our homes because of how it can be transformed to lower or higher voltages but this also means it can react in unwanted ways also and one is with coiled extension leads and any extension lead reels should be unwound fully before using any power some are duel marked with how much load you are allowed when wound up and how much when extended. If it is being unwound just to get current capacity then the more untidy the better laying in neat loops may help cooling but not transformer effect.

2.5A-Socket 10A-SocketAs well as extension leads designed to allow distance between appliance and plug there are also what are referred to as lead sets the 10A CEE22 to right also comes in two types the heat resistance type has small grove in it is used in all sorts from computers to kettles and often has cable well below the 10 amp rating and care must be taken not to use too big of a fuse. The 2.5A cable to far left is often used in tape recorders. To save space with computers there are some special multi socket extension leads with surge protection etc. These can be extremely expensive and are not really within the scope of this article.

In non domestic premises extension and lead sets will be PAT tested and part of this test ensures the earth is in good condition where 25A is used but in the home access to these testing devices is unlikely so the user must dispose of any lead sets showing signs of ware or burning. Finally an example of what not to do.

Foreign-Plugs 13-16-HomemadeSome transformers come with foreign plugs two shown to the left which either need cutting of and changing to UK plug or an adaptor is required. Hanging heavy transformers from an adaptor in a 13 amp socket is asking for problems and the 16 amp socket to the right are not readily available in the UK and Tran-adaptI always bring a few back from each holiday. You can see how the tapered sides match each other and give a snug fit. Some transformers are designed to be adapted for each country the Ktec example to the left designed for a home router can run on 100 to 240 volt at 50 or 60Hz out put 12V at 0.8 Amp quite high for such a small unit and without opening we know it must be switch mode. Where the larger one far left for a Yaesu radio is only 0.2 Amp this points out how careful one has to be and why swapping adaptors can cause problems.

Accident-WaitingI would hope I don't need to point out what is wrong here and you can see how water and electricity don't mix.  

Although this is an extreme case extension leads across a wet lawn can be just as dangerous.

Eric        

Return to main page