Most people never give it any thought every time they plug in an appliance, but have you considered where the design of the three pin plug and socket configuration used in Australasia came from? Did you know it is actually an American plug (albeit obsolete) we are using? Read on if this interests you...
Being part of the British Empire, it was natural that Australasia would choose British wiring methods. So it was hardly surprising that 200-250V mains supplies were adopted and what was then called the "Swan" base (soon to be known simply as the bayonet base) light socket, after the British inventor of the incandescent light bulb. But what of the sockets for portable appliances?
Need for connection of portable appliances.
Electricity supply to homes was initially provided for lighting only, so the ubiquitous socket on the wall, otherwise known as a power point (or GPO -General Purpose Outlet, in electrical parlance) did not exist at the time. At the beginning of the 20th century there were no domestic appliances as we know them today; just carbon filament light bulbs.
Refrigeration was not yet in a form suitable for domestic use; there was no radio or TV, and heating/cooking appliances were happily being run from combustible fuel. However, this being a time of creative invention meant that other uses were seen for this electric supply, and soon enough came an explosion of all kinds of appliances with "clean" and "labour saving" attributes to their claim. Being prior to the electronic age, such appliances were invariably based around motors and/or heating elements. Table fans, toasters, irons, etc. started to appear. Having acquired such an appliance the next thing to consider was where to plug it in. The only place of course was into a light socket. So, appliances came fitted with bayonet plugs. In order to use the appliance and not be in the dark at the same time, bayonet double adaptors were available with one socket used for the light bulb and the other for the appliance. Some even had a switch on one of the sockets. While this method works, the disadvantages are that one has to climb up to the light socket every time to connect or disconnect the appliance. Also, the light socket can only handle a maximum of 3 to 5A - no good for a 2.4KW radiator! And thirdly, no earthing connection is available. Nevertheless, this method of connecting low power appliances was still common into the 1950's, and it is not uncommon to see advertisements for appliances at the time fitted with a bayonet plug.
This bayonet double adaptor allows an appliance to be plugged into a light socket while retaining the light bulb. South Africa, where this one was made, was part of the British Empire and hence adopted the B22 bayonet light socket, as well as the British round pin mains sockets.
With desk and standard lamps appearing,
wall mounted sockets were seen as far more practical. And yes, the bayonet
socket was sometimes used for this purpose. In the U.S, a plug and socket
was developed by Harvey Hubbell with two flat parallel blades, to take
the place of the Edison screw socket for portable appliance connection.
Flat blades were chosen to mimic a knife switch with its inherently reliable
contacts. In Britain and Europe various incompatible round pin configurations
were used. While the UK introduced yet another plug, in 1949, which was
to be the new standard which remains to this day, continental Europe has
persisted with a multitude of incompatible plug designs.
Typical of early appliances is this radiator from the 1920's.
By the 1920's Australia was using the British round pin plug and socket, but the two flat pin American plug had also found its way here and was also in use. Sometimes one still sees ancient examples of these two pin fittings in second hand building material places, still on their wooden mounting blocks. Clipsal still make the parallel two pin plug and socket which is approved for 250V, although these days it's usually used with imported 120V equipment. However, the polarised version of this plug which later appeared in the U.S, having one pin wider than the other was never used here. Rather inconvenient when you want to plug in some U.S appliances to the locally made two pin socket fitted to a stepdown transformer. While electrical safety wasn't given the attention that gets these days, it was realised that earthing of appliances was a necessity, and thus three pins were required. Both the British and Americans had a three pin plug which were being used here. The British plug was of course was a round pin design, while the American one used flat pins. The American plug was not however their three pin plug of today (known as NEMA 5-15) but had two angled pins for the supply and another flat pin beneath for the earth.
Left image is from a Canadian GE catalog in 1915. On the right is from a 1920 catalog.
Original Hubbell patent.
Examples of U.S. made sockets. These are in use and connected for 240V (courtesy of WA2ISE).
Examples such as these sometimes appear on the U.S. Ebay.
This early 3 pin plug design was evidently not popular in the U.S because of incompatibility with their existing two pin plug, and surviving examples in that country are few and far between.
Closer to home, this GE socket was attached to an ancient homemade switchboard from the late 1920's -early 30's. The British socket on the right was found buried in my backyard. It was probably part of the original wiring in my house. Unfortunately, the cover, made of wood, was long gone. Fittings such as these are usually mounted on wooden blocks.
This surviving example of a U.S. made (General Electric U.S.A) power point is located in an old house in the Central West of NSW. Although still connected, it is doubtful anything has been plugged in for many years. This socket allows for the insertion of tandem blade plugs (horizontal pins) as well as the more common parallel pin plugs. The parallel pin socket is modern enough for it to be polarised - note that one pin is narrower than the other. Unlike the U.S., however, power points in Australia are required to be fitted with an adjacent switch.
Around 1930 an attempt was made by Clipsal
and Ring Grip (the predominant electrical accessory manufacturers at the
time), along with the State Electricity Commission of Victoria to
adopt the American design as the Australian standard.
The reason why it was chosen over the British design is because it was easier for local manufacturers to make plugs with flat pins rather than round ones.
This was one of several newspaper articles from 1929-30 explaining the problem of having around 70 types of plug and socket in use and the need to standardise.
Taken from Popular Science in 1942, this shows the 3 flat pin plug still in use in the U.S.
The U.S. design was officially adopted
in 1938 by the Australian Standards. The only change made was to make the
pins slightly shorter than the American design to improve the safety aspects
when a plug was partially withdrawn from a socket. A further attempt at
improving safety came in the late 1990's where proposals were made to recess
sockets (as common in Europe). This was unpopular because of the multitude
of existing plugs and plugpack transformers which would not fit into recessed
sockets. Come 2005, an alternative safety measure was introduced
where plug pins were required to be insulated close at the plug body end.
This shows the difference in pin length before and after the standard was officially adopted. The plug at the left is a very early Clipsal with the same dimensions as the American plug, while the modern plug on the right has shorter pin lengths as specified in the 1938 standard. The old plug still goes all the way into a modern socket.
It is mentioned in a Radio & Hobbies
"The Serviceman Who Tells" article from the 1950's, that one thing required
for the service bench should be a bayonet socket, a two flat pin socket
and a round pin socket. It was stated that although these fittings were
frowned upon, there were still some radios fitted with such plugs.
New Zealand also adopted the American design, possibly because of Australian fittings being sold there. However, they hung onto the British sockets for somewhat longer, and in fact I recall a NZ wiring book printed in 1979 stating the approval of the present day UK socket. Despite this, it appears they weren't actually used to any extent. For some years now, NZ has adopted the Australian Wiring Rules so wiring practices are much the same in both countries.
Because of the Australian and NZ influence in the region, the plug design is standard throughout most Commonwealth areas of the South Pacific.
Argentina also adopted the American plug, (presumably because of the proximity to the U.S) but the live and neutral connections are reversed to that used elsewhere. Possibly this is because they have simply used the U.S configuration where neutral is on the left when the earth pin faces down (see Fig. 7 in the above photo). The plug design is classified under the IRAM 2073 standard. Because of the polarity difference, power leads and accessories for the Argentine market thus cannot be sold in Australasia and vice versa. In reality, someone travelling between Australia and Argentina wouldn't have any problems. Properly designed appliances should accommodate the possibility of transposed neutral and live connections. I am aware of one IEC lead that tested reverse polarity at my place of work; probably one for the Argentine market that found its way in to Australia.
Argentine power point. Although this one is switched, this does not seem to be mandatory.
China is a late adopter of this plug design. It would be virtually impossible to find any information on when and why it was adopted. However, Chinese power points also allow the plugging in of two pin American and two pin European plugs. Unlike Australia and NZ, they are unswitched and the socket appears upside down to the normal convention. Presumably, the reasoning of having the earth pin at the top is that any objects falling in between a partially withdrawn plug will touch the earth and not the live pin.
Polarity not standardised.
It may surprise the younger generation that there was in fact no official polarity designation to start with. After all, AC has no polarity, so an appliance will work connected either way round. In fact, until the 1960's most plugs were not even labelled as to which way round the live and neutral connections should be; only the earth pin was designated. Not only that, there was a common design of double adaptor which reversed the polarity of one socket (easy to make it this way). Appliances from the 1950's wired in the factory with the red and black wires transposed in the plug are not uncommon. With a history of using bayonet light sockets, and two pin English and American plugs it was assumed that appliances could be connected either way round. It is for this reason that double pole switches were often fitted to appliances. Certainly, switched light sockets as used with desk or standard lamps always had a double pole switch. Even in the 1970's, I remember being told numerous times, "it doesn't matter which way you connect the top two pins".
At this point one may query how a power point could be wired with "wrong" polarity, when looking at a modern power point the terminals are labelled and even colour coded. No one in their right mind would connect it with live and neutral reversed. For one thing, the neutral would be switched instead of the live which is an obvious safety hazard.
Actually, it wasn't that bad. The first generation of power points had separate switches and sockets; they were not a complete assembly with switch integral to the socket.
That the live was switched was mandatory, but how the socket was connected after the switch was not standardised. So, if the switch was off the appliance was dead with either connection.
However, there was a "recommended" standard which eventually became official (late 60's -70's?). This stated that looking at the socket the top pin on the left was live. An easy way to remember this is that a modern single GPO has the switch on the left and is thus closest to the live pin.
The 1950's Ring Grip plug on the left has no live and neutral polarity markings, unlike the 1970's HPM on the right.
Not always earthed.
Back in 1979, I took the cover off an ancient porcelain socket in a house that must have been wired in the late 1920's - early 30's, and was rather surprised to see no earth wire had been connected to the socket. It was a typical power point of the era, switch and socket mounted on a 6" x 3" wooden block. In fact, it was probably the first generation of the three flat pin socket used in Australia. I find it quite amusing when people discover such things today and almost go into convulsive shock wondering how someone could wire the power points in a house in such a seemingly dangerous manner. Not only were power points wired like that by electricians, but it was permitted in the wiring rules. However, there was a condition to this, and that was a power point only had to be earthed if there were other earthed objects in the room within a certain distance of the power point. Hence, a power point in a bedroom might not be earthed, but one in a kitchen would be. This is not as dangerous as it may seem. Providing there are no other earthed objects within reach and the appliance becomes live then a shock will not be received. Think about it; a bedroom with wooden floors and walls is a good insulator. Unless you can complete the circuit to earth you're not going to get a shock.
It appears this was allowed into the 1950's and possibly early 60's by which time it was compulsory to earth all sockets.
It was only in the 1970's that an earth had to be run to all light sockets in a house.
A collection of accessories to horrify the Nanny State control freaks; at the top is a typical home made extension lead with figure eight cable and thus no earth. At bottom left is a bayonet to three pin socket adaptor useful for powering appliances where only a light socket is available. It also has no provision for earthing. The double adaptor is of a type that reverses live and neutral polarity on one of its outlets. Used in the right situation these items are actually perfectly safe.
American wall box dimensions adopted
It may also surprise some that it wasn't just the three pin socket we adopted from the U.S, but also their wall box dimensions. Not only are the switch plate dimensions the same, but even the screws to secure the switch or socket into the wall box have the same thread. It is possible to install an Australian fitting into a U.S wall box and vice versa. Until the late 1940's, power points and switches were usually mounted on wooden blocks. This, along with split seam steel conduit, was a legacy of British methods. While surface mounted fittings and wooden mounting blocks were still being installed later than this, in many post war homes flush mount switches and power points were being installed. These, like their U.S counterparts, consisted of the actual switch and or socket with a separate cover plate. As the switch and socket were still separate units, albeit behind a common cover plate, polarity of the socket was still not guaranteed. As an example, I work in a building from 1956 and there is a GPO above an adjacent desk with what would now be considered wrong polarity. By the 1960's power points and light switches were being made with the mechanisms and switchplates being one unit.
On the subject of wallboxes, in Australasia these are enclosed only for brick or concrete walls. For hollow walls plaster or stud mount brackets are used which are not enclosed. Mounting blocks are also open at the back. Elsewhere in the world, it seems the backs of fittings are always enclosed regardless of the mounting surface.
The M.E.N (Multiple Earth Neutral) system of earthing is another Americanism we adopted. Here the neutral is connected to earth at the switchboard. The reasoning is that if the earth connection to the water pipe or earth rod has high resistance, the fuse will still blow if there is a live to earth short. However, the downside to this is that if the neutral connection fails, and the earth connection is high resistance or non existent, then the earth wire and all that is connected to it could rise up to 240V. What we did not adopt was the American colour code, instead always sticking to the British with red for live and black for neutral. Australians ignorant of U.S wiring practices invariably connect the black to neutral and white to live when presented with an American power lead, whereas it should be the other way round.
Even though we adopted the U.S style wall box size, one area of departure was that unlike in the U.S, power points were mounted horizontally. As to whether the earth pin was up or down was another thing. Usually it has always been down, but some manufacturers such as Clipsal for a while had it at the top. HPM during the 50's and 60's had it in between; with the socket turned at 90 degrees from the normal position. Horizontal mounting of power points was not common in NZ; instead they kept to US practice and most power points there are mounted vertically.
These HPM power points show that the earth pin wasn't always on the bottom. The American style switch and socket is from 1956. As the switch and socket are separate items the socket can be wired with either polarity. In the middle is a late 1940's GPO mounted on a 6 to 240V shaver inverter. This orientation is used today with the Chinese socket. To the bottom left of this can be seen part of a bayonet socket which indicates this form of power connection was still being used. To the right is a GPO from 1967 when HPM was experimenting with a design that suited both horizontal and vertical mounting. Note these all have switches; Australia was the probably the first country to mandate switches on GPO's.
It is often asked why there have been so many different mains voltages. The answer to this is essentially one of development and politics. The first reticulated power system, implemented by Edison, was 110V DC. Given the prevalence of arc lamps at the time, this voltage suited two in series. Also, lamp making technology being as primitive as it was at the time, had a hard time making reliable lamps for higher voltages. However, as is well documented, a simple 110V reticulation system was very limited. For any given power, the current is doubled if the voltage is halved. The problem then, is that the line losses are actually squared. An improvement can be made by implementing a three wire system where two 110V supplies are in series, giving 220V, and the common connection is neutral. Provided the current drawn on both supplies is close to equal, little current flows through the neutral, and transmission losses are reduced. This is the scheme which has been in used by the U.S for a very long time now, except of course the supply voltage has since been standardised at 240/120V 60 cycles. However, the current per 120V branch of the circuit is still limited. This leads to the situation where domestic appliances that draw more than 15A (1800W) require a special 240V socket.
In Europe, there was a mixture of 110V, 127V and 220V operating at 50 cycles or in a few instances, DC. If 127V seems a little odd, it's the phase to neutral voltage of a 220V three phase supply. However, 220V single phase/380V three phase was soon adopted as the standard, and the lower voltage systems phased out. It appears that Siemens in Germany had done much to promote the 220/380V system with its advantages over the lower voltage systems.
In Britain with a very localised power generation and distribution system, there was little standard. Anything from 100V DC to 250V AC could be found. And the AC wasn't always 50c/s! Again, it would depend on who built the generating equipment as to what the voltage and frequency would be - each no doubt being "the best" in the eyes of its beholder.
That all changed with the commencement of the National Grid in the 1920's; the completion of which would implement a nationwide frequency of 50 cycles, and a standard residential voltage of 230V. It was intended that not only would the UK use 230V, but so would the rest of the British Empire. This didn't quite happen with each country going their separate ways as time went on. The UK eventually did standardise by the end of the 1960's, but at 240V.
It was hardly surprising that Australia followed British practice and chose 210-250V for the single phase residential supply, thereby avoiding the voltage drop, the requirement for heavy gauge wiring, and limited current availability inherent with the 110-120V system. Two or three phase supply (415V between phases) to homes is quite common in Australia. Apart from increasing efficiency in all electric homes, it is used on a domestic level for some instantaneous water heaters, and some workshop equipment. Australian made electric ranges allow for a two phase supply where this, or a three phase supply is available.
What has been standardised at 240V 50 cycles per second for many years in Australia was not always so. Generally, New South Wales, Tasmania and Queensland standardised on 240V 50c/s and Victoria on 230V 50c/s. Heading west, 210V 50c/s had been used in South Australia, and 250V at both 40 and 50c/s in Western Australia was used. There were two large towns using 110V; Launceston and Broken Hill. Away from the capital cities there was more variation, with DC being used in some towns (220-250V). The reason W.A. was the odd one out with regards to frequency, is that the 40c/s generating plant was imported from South Africa. DC mains was used in Sydney around the northern part of the CBD until the mid 1980's, but by that time remaining only for lift motors. The rest of the supply had been converted to AC by the 1950's. By the 1950's plans were afoot to standardise Australia on 230V 50 cycles in line with the Empire and many localities went through the conversion process. 240V areas were to be left as is, being within 10% of 230V. Probably because the 240V areas outnumbered the others, this actually became the standard instead.
Victoria changed to 240V in the early 1960's. 230V electricity meters are still visible on old houses there today. Adelaide started to move away from its 210V supply in the 1950's and Western Australia dropped to 240V in 1985.
If it seems like a huge excercise to convert appliances to suit a new supply, it must be remembered that at the time, houses had few appliances. In the 1950's, apart from incandescent lamps in each room, there would be a toaster, jug, and cooking range, and a radio. The more affluent would also have a refrigerator, washing machine, and maybe a vacuum cleaner.
The lamps are not frequency dependent, so they can be left in situ unless it's the voltage that's going to be changed. Likwise, all the heating appliances. Should the new voltage be markedly different, it was a simple matter to replace the elements, which were all standard types. The radio might require a reset of the voltage tapping on the power transformer but that would be all, unless it was part of a radiogram. There, the pulley on the turntable motor would have to be replaced when changing from 40 to 50 cycles. The few AC/DC radios usually needed no modification as they included a baretter to stabilise heater current for the valves, and could accomodate a wide range of voltage.
Extra Low Voltage DC
Rural homes not connected to any public supply usually used 32V DC, but sometimes 12V, 48V, or 110V DC, from a set of generator charged batteries. These would be charged from a stationary engine or a wind generator. A standard socket was available for these extra low voltages known as a "T socket", but unfortunately many simply used the three pin 240V type instead. Disastrous results awaited appliances so fitted, when someone unaware plugged them into a 240V power point. The two pin parallel blade plug and socket has also been used for non polarised ELV applications, particularly for 32V lead lamps. Although not ideal, it does prevent accidental connection to 240V.
Socket used for extra low voltage supplies (up to 32V). Current rating is 15A. It is recommended that where the supply is referenced to earth that the bottom pin be used for this.
We can see here the American origin of the Australian ELV socket. However, in the U.S. it was intended for 120V use.
In the modern day, 32V DC systems only exist in the hands of vintage technology enthusiasts, as appliances have not been made for this voltage since the 1960's. Rural type off grid electrical systems these days tend to be solar powered and use 12V DC for small systems. Large systems are usually 240V AC, inverter powered from a 24V or 48V battery bank.
The "T socket" (Clipsal 402/32) is nowadays mainly used for 12V applications, such as in a solar powered house, or for caravan, boat, and 4WD use. It also finds common use for portable lead lights powered from 32V AC isolating transformers.
The Round Earth Pin plug and socket.
This was initially introduced for use on lighting circuits. A typical situation would be in a commercial building with a false ceiling. Here the lights are usually connected by flexible cable to fixed sockets.
However, it never became popular for that purpose and the conventional three flat pin socket is usually used. Instead, the round earth configuration became used for all kinds of "special" applications. For example, it has been used to differentiate between circuits supplied by uninterruptable power supplies, and the ordinary public supply. Other uses include connecting remote switches (eg. switch for room light mounted in a bedside table). Sometimes it is used for other voltages. Despite the existance of a standard extra low voltage plug and socket, the round pin configuration has also been used for this purpose. Essentially, it is used where compatibility with the standard 240V connector is undesirable. With the increase in appliances fitted with two pin plugs, the design is no longer as incompatible as it once was. Therefore, the socket should not be fed with a voltage or frequency that could damage a normal 240V AC appliance.
Once Upon a TIme...
Because the American parallel flat pin non polarised plug has the same pin dimensions and spacing as the Australian plug, it is possible to simply twist the pins to enable insertion into an Australian socket. This used to be commonly seen with imported or duty free bought items but foreign manufacturers are now more aware of our requirements.
Until the 1980's it wasn't uncommon to
see two pin U.S. plugs being used in Australian power points as the above
photos show. This came about largely from Japanese electronic equipment
being sold in Australia from the 1960's onwards.
Overseas travellers would also bring back appliances from foreign duty free stores. Because the pin dimensions and spacing are the same, a simple twist with a pair of pliers will enable the two pin plug to fit.
It is also handy to know that European plugs will fit into a standard appliance cord as used with old electric jugs and toasters. However, this should only be done where no earth connection is required.
As regulations were tightened, all appliances sold in Australia must now be compliant with Australian Standards.
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