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A service of PlugSafe |
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In a misguided attempt to solve the problem, far eastern entrepreneurs have developed various non-standard so-called universal sockets, but they have failed to understand why this is not safe. The example above is one of these which has been withdrawn from UK sale as having a serious risk of electric shock. It has two sets of socket apertures, the pair at the top are intended for two pin American and European plugs, the centre and lower apertures are intended to accept various three pin earthed plugs, including UK, American, Chinese, Australian and, apparently, the 5 amp BS 546 plug which is still used in many countries. There are many other types on the market, but all are a very bad idea! Here are some of the reasons why: Voltage: A fundamental reason for not using a single plug type is that there are two very different mains voltages used in the world, the European voltage is a nominal 230 V, the American voltage is a nominal 120 V, other countries use one or other of these. International standard IEC 60884-1 requires that a plug intended for one of these voltages may not fit into a socket intended for the other. Universal sockets do not comply with that standard. Plugging a 120 V appliance into a 230 V socket may result in a fire! Polarity: A normal mains supply consists of ‘earth’ (or ‘ground’), which is a safety connection for exposed metal parts (such as the casing of white goods); ‘neutral’, which is at approximately 0 V; and ’line’ which is at 120 V or 230 V. Both ‘neutral’ and ’line’ carry current, and are referred to as ‘live parts’. The UK and the US both use polarized plugs, but whereas the UK line connection in the socket illustrated is at bottom right, the US line is at bottom left! A switch fitted to an appliance is often in the line wire only, so it is important to make sure that the right connection is made. Universal Sockets have the terminals marked for UK polarization, meaning that it is incorrect for some other plugs, including US plugs. (The US also uses polarized two-pin plugs, with the neutral pin wider than the line pin, but universal sockets often accept these in either aperture, negating that safety feature as well! Sometimes both apertures are too small to accept the wider neutral pin.) |
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Earthing: UK and US plugs, as well as many others, use the third pin for earthing, however the German Schuko plug uses a side contact, and the French plug uses a pin projecting from the face of the socket, clearly neither of these contacts exist in a universal socket (the presence of either would prevent other plugs being used) so although the universal socket will accept both French and German plugs, neither will be earthed! (The picture above clearly shows the side contact making no connection.) In the event of a fault this is potentially lethal. |
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Fusing: The system of wiring used in the UK (called a ‘ring circuit’) includes 32 Amp protection for the fixed wiring and requires that there be an appropriately sized fuse in the plug which will prevent the flexible appliance cord overheating and catching fire in the case of a short circuit. Other countries use a radial system and rely on the protection (typically 16 Amp) for the fixed wiring to protect the flexible cord (which is fine for some appliance cords, but of doubtful value for lightweight cords such as those used with Europlugs). A universal socket will, by definition, accept non-BS 1363 unfused plugs so when connected to a UK ring circuit the flexible cord is not adequately protected. |
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Poor contact: Sockets are normally designed to make the maximum electrical contact with the pins of the plug. Because the contacts in a universal socket are designed to accept a variety of sizes and shapes they are seriously compromised, often doing little more than touching at a couple of points. A poor contact will result in arcing and/or overheating with the potential of fire. Insufficient mechanical stability: One of the functions of a socket is to securely hold the plug, but the overlarge apertures and poor contacts in a universal socket prevent this from happening. In addition, some plug types (such as the German Schuko) rely on the socket recess for additional stability, but universal sockets have no recess. Under-rated for most plugs: Universal sockets do not have a standard current rating, they often claim to be rated at 10 A, but most plugs are rated at higher currents, eg 13 A (UK), 15 A (US) and 16 A (French and German), a plug should only be used in a socket which has a compatible current rating. |
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Plugs can be mis-inserted (1): The overlarge apertures of a universal socket allows some plugs such as the Europlug and Schuko to be inserted into the wrong contacts, eg between line and earth. This is illustrated above. |
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Plugs can be mis-inserted (2): The overlarge apertures will also allow a BS 1363 earth pin to be inserted into the line aperture of a universal socket!. The left hand picture shows a power pin inserted into the neutral aperture, and an earth pin inserted into the line aperture. The apertures are so wide because they are designed to accomodate a BS 1363 plug (which defines the outer extremities) as well as a US NEMA plug (which defines the inner extremities). It can be clearly seen that the aperture width is more than enough to accomodate a BS 1363 earth pin. The centre picture is of a universal socket designed for an equipent panel, if this is mounted near to the edge of the panel then there is nothing to prevent the plug being inserted into the line aperture. The right hand picture shows a cheap, ubiquitous and illegal Chinese universal adaptor which facilitates the same dangerous situation. The Plugs and Sockets, etc. (Safety) Regulations 1994 control the selling of mains sockets in the UK. Universal sockets do not meet the requirements specified, and it is therefore not legal to supply them in the UK. Electrical Safety First (formerly the Electrical Safety Council) has commissioned a detailed report which describes the problems with universal sockets. PlugSafe continues to identify illegal offerings of universal sockets on UK websites, and works with Trading Standards to have such listings removed. An example of a withdrawn socket can be found on the EU RAPEX list here. |
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