Why isn’t there a universal mains plug?

Lamp fitting adaptors

To fully understand this, we must first go back to the infancy of electricity and work forward through the history of mains power.

In the late 1870s to 1880s electricity was originally used by the general public only to provide illumination, by means of incandescent bulbs. Compared to Victorian era gas lights these were more expensive to run, but did not emit soot and carbon dioxide, and were safe and easy to switch on and off. Later, gadgets were invented that needed electric power, and these could only be connected to the mains supply through the lamp base fittings, via an adaptor.

Thomas Edison’s electrical system was comprehensive and he patented almost all the components, but not a plug and socket, as the inventor focused his research and development exclusively on lighting. This meant the market was soon awash with competing patterns.

• The earliest known design is T.T. Smith’s from 1883, in England, with two round pins. This became the contemporaneous standard UK plug, which has now since been replaced by a different design.
• A similar design was later pioneered in Germany, from which the current European plug type is distantly related but still recognisable.

The best known design is Harvey Hubbell’s from 1904 (US patent 774250): one half was left screwed into a lamp fitting, and the other half had two flat metal pins which could be easily pushed in and pulled out. This became the basis of the North American plug and socket.

1904: an electric iron powered from a lamp socket

This led to a situation where there were many competing designs within a country: each electricity provider and each equipment manufacturer seemed to have their own design, which was of course deliberately incompatible with those of their competitors. Import and export with other countries further complicated this. For example, the US National Electric Light Association (NELA) bemoaned the existence of 17 different and incompatible socket types in 1915, which they viewed as excessive, and also damaging for sales to the whole market.

This became so impracticable that the plug choice was rationalised down to a much narrower range, by a mixture of commercial forces from the market, regulation from the industry, and legislation from government. The period 1915-1917 approximately marks the transition of electrical appliances from novelty to utility, and coincides with a drive toward manufacturing efficiencies due to the First World War.

Before the Electricity (Supply) Act 1919 in the UK there were 642 providers supplying a mixture of AC and DC on 7 different frequencies and 44 different voltages.

Some years ago, the manufacturers were turning out over 175 types of lamp bases, which made it necessary to purchase a lamp that would fit the socket already installed. Through the simplification brought about the manufacturers are now turning out only six standard bases. There were also manufactured about three dozen different varieties of attachment plugs which were not interchangeable: through simplification the standard plug with the parallel blades resulted, the usefulness of which speaks for itself. Almost every kind of appliance on sale today is equipped with this standard plug. The result of these two simplifications is outstanding.

“The maximum consumption of current is within the limit of any ordinary lighting circuit making it possible to attach it to any ordinary lamp socket. […] In ordering please state voltage.” (December 1923)

Advertisements in printed media for electrical appliances along the theme of ‘Just screw into any lamp socket’ regularly appear as late as 1948 in the US. In fact, lamp socket adaptors are still widely commercially available in North America.

We have found even later examples in the UK, but these appear to be outliers and target specific needs: 1965 (doctors on call in rural areas), and 1972 (exporting equipment to Africa).

As these articles are generally used by those who have no knowledge of electricity, every precaution should be taken in the manufacture to guard against possible shocks even in the event of rough use. The insulation should be good and strong at every part, including the flexible wires and wall plugs or socket connectors. Neglect of these precautions has been known to lead to fatal accidents, and it is not uncommon to find domestic workers unwilling to use electric vacuum cleaners for fear of possible shocks. Cheap and trumpery forms of all electrical appliances should be avoided as dangerous; but the standard vacuum cleaners now on the market are well constructed and safe to use.

Electrical nationalism

Another issue was growing nationalism. Some countries wanted their own plug and socket; a classic example is Australia, which after importing a variety of types, including the English and American types, standardised on a third type in the 1920s. Tensions between neighbouring countries would lead them to deliberately use different systems, for example China and Taiwan. The Soviet Union used the same plug design as Central and Eastern Europe, but with narrower pins and apertures. In the event of invasion, communist (USSR) plugs would work in capitalist (Western) socket outlets, but not the reverse.

Countries in the Indian subcontinent, and also those in Sothern Africa, have plugs which are still dimensionally equivalent to the old UK BS546 and therefore physically compatible. However, the technical specifications have slowly been updated, and both have discrete approvals bodies. Whilst the plugs could be used interchangeably, in order to comply with local legislation, they must meet the new standards and carry the correct approvals. We dual stock SANS (South African) and BIS (Indian) power cords to ensure they may be legally imported and placed on the market.

There may also be an element of protectionism, to restrict the domestic market to only locally manufactured products.

If we could have complete standardization of sizes we would not have the dangerous practices which are so common in many homes, where heavy-load equipment is used on a two-pin socket with no earth and, not infrequently, the plug-wiring actually fixed incorrectly.

Somewhat to my surprise I found that the electric plug [of my small radio] did not fit the socket in my hotel room, whereupon I summoned the hotel’s engineer who replaced the electric plug with another one which would fit the socket. In the course of this he explained to me that there were (as I remember it) about twelve different types and sizes of electric plugs in current use in England.

New Thai socket, accepting both European style (round pins) and American style (flat pins)

Multi-sockets are possible to a limited degree. Where two different standards are reasonably close, this can be done without significant safety compromises. An example is modern Italian universale sockets which accept the smaller Italian 10A, larger 16A, and the European Schuko. Thailand actually reverse engineered their new plug to fit the EU/US dual-sockets in widespread use, creating both a great leap in safety and a very elegant solution.

If the standards are too dissimilar, or too many are attempted, the universal sockets become distinctly unsafe. They do not guarantee any polarity, switching, earthing, protection from live parts, or a particular current or voltage; furthermore apertures are unshuttered and so large as to pose a considerable electrocution risk from foreign objects, even with a plug inserted.

SPRING, the authority for consumer protection in Singapore, issued an official safety warning in 2009: ‘Risks of using Universal Portable Socket Outlet.’ It cited most of these reasons, and also noted that the particular units they tested had significant design issues, including undersized copper wire, and plastic casing that failed the heat test; both of which are fire risks. Universal sockets are therefore more likely to be of lower manufacturing quality than a fully approved part.

IEC 60906: an attempt at standardisation

The International Electrotechnical Commission published IEC 906 (now 60906-1) in 1986, recommending standardising on a completely new type for 250V. On paper a very good design, it has so far only been adopted by South Africa. Paraguay has recently added it as a national standard, so it may very slowly gain traction. Unfortunately designs are entrenched in national legislation and changing them will take considerable political will. The costs of changing mains wiring plus all plugs and sockets will be astronomical, so there would have to be a transitional period with both systems allowed of several decades. Conveniently, for 125V, IEC 60906-2 recommends a system identical to NEMA 5-15 used in North America.

“How standards proliferate,” courtesy of XKCD

This can also be achieved with detachable low voltage DC power cables between the power supply and gadget. The most common protocol by far is Universal Serial Bus, or USB. Originally developed in 1996 for data, with very low power capability, the latest UCB-C system offers up to 240W (48V 5A).

The next step is inductive charging, now common on smartphones and electric toothbrushes. A larger coil inside the base unit creates a magnetic field, which causes an induced current in a smaller coil inside the device. There is no need for any electrical (or even physical) contact between the two.

The search for a universal mains plug neatly brings us back to the very beginnings of electricity, with Faraday’s 1831 discovery of induction.