Fullscreen HTML5Med Res (??MB)HTML4

The Aussie electrical plug and socket: Where did it come from? By John Hunter Most people never give it any thought, but have you considered where the design of the three-pin plug and socket used in Australia, NZ, and the South Pacific came from? Did you know it was actually an American design? B eing part of the British Empire, it was natural that Australasia would choose British wiring methods. So, it was hardly surprising that 200-250V AC mains supplies were adopted, with what was initially called the “Swan” base for light bulbs. This was named after the British inventor of the incandescent lamp, Joseph Swan. This soon became known as the bayonet base, which is still used today. But what about plugs and sockets for other appliances? Electricity to homes was initially for lighting only, so the ubiquitous socket on the wall, known as a power point (or “GPO” – General Purpose Outlet, in electrical parlance) did not exist yet. At the beginning of the 20th century, there were few domestic appliances as we know them today; just carbon filament lightbulbs. Refrigeration was not yet in a form suitable for domestic use; there was 32 Silicon Chip no radio or TV, and heating or cooking appliances were run from combustible fuel. However, this being a time of creative invention, other uses were Fig.1: typical of early appliances, this toaster is connected to the mains with a bayonet plug. Australia’s electronics magazine found for this electric supply. Soon came an explosion of all kinds of appliances running from “clean” and “labour saving” electricity. 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. Thus, appliances came fitted with bayonet plugs (or Edison screw plugs in the USA) – see Fig.1. To use such an appliance and not be in the dark at the same time, bayonet double-adaptors were available, with one socket for the light bulb and the other for the appliance (Fig.2). While this worked, it was a pain having to climb up to the light socket every time to connect or disconnect the appliance. Also, the light sockets could only supply up to about 5A; no good for a 2.4kW radiator! siliconchip.com.au The origins of this fea Fig.2: before wall-mounted sockets, appliances were connected to light sockets with bayonet adaptors. Also, no Earth connection was available. Nevertheless, this method of connecting low-power appliances was still common into the 1950s. It is not uncommon to see advertisements for appliances from that time still with a bayonet plug. For most appliances, wall-mounted sockets are clearly far more practical. In the USA, a plug and socket were developed by Harvey Hubbell with two flat parallel blades, to take the place of the wall-mounted Edison screw socket. Hubbell remains one of the largest manufacturers of electrical accessories in the USA to this day. Flat blades were chosen to mimic a knife switch, with its inherently reliable contacts. Britain and Europe used various cylindrical pin configurations. Although Continental Europe has persisted with a multitude of incompatible plug designs, the two-pin “Europlug” goes a long way to solve this problem, for double-insulated appliances at least (Fig.3). The UK replaced their multitude of round pin plugs and sockets with the square-pin BS1363 plug in 1949. Fig.3: the two-pin “Europlug” fits most Continental sockets, where different methods of Earth connection prevent full compatibility of three-pin plugs. siliconchip.com.au Way back in the Jan uary 2002 issue, we published a letter from some bloke with the un likely name of “Dick Smith” which read (in part): “By the way, how ab out doing some interesting invest igation. 3-pin mains plugs like those we have in Australia seem to be the same as used in parts of China , New Zealand and Argentina. Where did our 3-pin plug and socket design come fro m and why are they the same as used in those other countries?” Since his name was cle arly made ture . . . up, we had no choice but to ignore him. But then we got an other e-mail earlier this year from, you guessed it, a Mr D. Smith sugge sting the very same thing. That lead to a little discussion over some aspects of the Aussie GPO, so we did a bit of Googling. Then we discovered that John Hunter (who’s written for us in the past) is apparently a bit of an expert on the subject. Well, Mr Smith (if that is your real name!) – we hope tha t this article lives up to your expe ctations. Australia By the 1920s, Australia was using the British cylindrical pin plug and socket, but the two-flat-pin American plug was also in use. Sometimes one still sees ancient examples of these two-pin fittings in second-hand building material centres, still on their timber mounting blocks. Clipsal still makes the parallel twopin plug (Cat 492) and socket, which is approved for 250V where an Earth connection is not required, although these days it’s usually used with imported 120V equipment. However, the polarised version of this plug which appeared in the USA later, with a wider Neutral pin, was never used here (Fig.4). This can be a problem with some step-down transformers, fitted with the locally-made socket, if modern US appliances are to be plugged into them. While electrical safety wasn’t given the attention that it gets these days, it was realised that Earthing appliances was necessary, thus requiring three pins. Both the British and Americans had a three-pin plug which was being used here (Fig.5). The British plug was, of course, a cylindrical pin design, while the American one used flat pins. It 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. It was imported by General Electric, and was what most would recognise today as the “Australian” plug (see Figs.6-12). Americans know it as the “crowfoot”. This early three-pin plug design was not popular in the USA because of incompatibility with their existing two-pin plug. Nevertheless, there are plenty of surviving examples. It was considered obsolete before the NEMA (National Electrical Manufacturers Association) standards came into being, and was never allocated a type number. 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. It was chosen over the Fig.4: these plugs and the NEMA 5-15 sockets were introduced to North America after Australia had adopted their old two- and three-flat-pin configurations, and were not used here. The wider Neutral pin ensures consistent connection polarity. Fig.5: a selection of old American and English two- and three-pin plugs and sockets. These were commonly used in Australia prior to the American 3-pin type (at right) being standardised in Australia and New Zealand. Australia’s electronics magazine September 2020  33 Fig.6: three flat-pin fittings from a Canadian GE catalog, from 1915 (left) and 1920 (right). This three-pin American plug was patented in 1916 by G.P. Knapp of the Hubbell Company. British design because it was easier for local manufacturers to make flat pins. An article published at that time (see Fig.14) states “Efforts now being made by the Electrical Association of N.S.W. to standardise the types of power plugs in use will receive enthusiastic endorsement from many consumers.” “The necessity for improvement along this line is indicated by the results of the association’s investigations. In reviewing the existing position, a collection was made of every plug on the market. The amazing result was an array of 71 distinct versions.” “... After examining and testing every variety, the association decided that the ‘three-pin flat pin’ type of 10 ampere capacity was most suitable. Its advantages are positive contact, giving consistent efficiency and a high degree of safety (the third pin being an earth connection).” “Accordingly, this plug has been recommended to the Standards Association of Australia by the New South Wales trade body. The electrical traders of Victoria and South Australia are also in agreement, and have endorsed the recommendations.” The US design (Fig.15) was officially adopted in 1938 by the Australian Standards, with the only modification being to shorten the pins by about 2mm. Fig.16 shows the difference in pin length before and after the standard was officially adopted. In “Radio & Hobbies in Australia”, the “Serviceman Who Tells” article for December 1951 stated that mains sockets for the service bench should include a bayonet socket, a two-flat- Fig.7: the original Hubbell patent. It shows the common use of an Edison screw lamp socket to provide power to appliances. Fig.8: examples of US-made sockets in the author’s collection. These fit the modern Australian plug perfectly, and are rated at 125V/15A or 250V/10A. 34 Silicon Chip Australia’s electronics magazine pin socket and various cylindricalpin sockets. This indicates that a significant number of these fittings were still in use then. Safety features Some power points in Australia have had shutters, but they are not compulsory. A particularly problematic type of shutter arrangement was used in some sockets from the 1950s. It is actuated by the Earth pin of the plug being inserted, which then uncovers the Active and Neutral connections. This became a problem when twopin plugs started to appear in the 1960s. One would have to insert something into the Earth pin receptacle before inserting the plug, or plug in via a three-pin double adaptor, or simply dismantle the power point and remove the shutters. Soon after, power points with shutters relied only on the Neutral pin being inserted, solving this problem. Fig.9: examples such as these sometimes appear on the USA eBay website. siliconchip.com.au Fig.10: this Hubbell adaptor converts NEMA 5-15 to ‘crowfoot’. While one could still insert something into the Neutral socket, the polarity had been standardised, so there was minimal shock hazard. Power points for portable applications, such as caravans, are required to have double-pole switching since they may be used with extension cords with unknown wiring polarity. A further attempt at improving safety came in the late 1990s, when proposals were made to recess sockets, as is common in Europe. This was unpopular because of the multitude of existing plugs and plugpack transformers, which would not fit into recessed sockets. However, extension cord sockets fitted with a shroud did appear. In 2005, an alternative safety measure was introduced where plug pins were required to be insulated at the plug body end. Use elsewhere Fig.11: unless one knew that Hubbell is a US manufacturer, the assumption would be that this socket was made in Australia. Like Australia, NZ also imported electrical equipment and accessories from the USA, so it is perhaps not coincidental that both countries were using the same fittings. However, it is interesting to note that one wiring manual from the 1970s stated that British sockets were still permitted. Despite this, it does not appear that they were used then to any extent. For some years, NZ and Australian wiring rules have been the same (AS/ NZS 3000), allowing for a few local exceptions. Because of the Australian and NZ influence in the region, the three-flat- New Zealand also adopted the American design with apparently greater initial enthusiasm than Australia. There, another US design, the two-pin polarised “T” plug had also been used for 230V, along with the three-pin and two-parallel pin designs (see Fig.17). Fig.12: they are not particularly rare in the USA either. Here’s one in a collection of plugs seen on eBay. siliconchip.com.au Fig.13: this surviving example of a US-made (General Electric) 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. Australia’s electronics magazine Fig.14: one of several newspaper articles from 1929-30 explaining the problem of having around 70 different types of mains plug and socket in use, and the need to standardise. September 2020  35 Fig.15: from Popular Science, April 1942, this shows the three-flat-pin plug still in use in the USA. Note that Active and Neutral are swapped compared to the Australian standard. pin plug design is standard throughout Commonwealth areas of the South Pacific. Argentina also adopted the threeflat-pin American plug, but the Active and Neutral connections are reversed to that used elsewhere, following the original US configuration (Fig.18). The plug design is classified under the IRAM 2073 standard. Because of the polarity difference, Fig.16: the plug at left is a very early HPM, while the modern plug on the right has shorter pins, as specified by the 1938 standard. The slight difference does not cause any compatibility problems. power leads and accessories for the Argentine market cannot be sold in Australasia and vice versa. But in reality, someone travelling between South Pacific countries and Argentina wouldn’t have any problems. Properly designed appliances accommodate the possibility of transposed Active and Neutral connections. China is a late adopter of this plug design (see Fig.19). It is difficult to find Fig.17: this advertisement from 1939 mentions the three types of American plug in common use in New Zealand. 36 Silicon Chip Australia’s electronics magazine any information on when and why it was adopted. However, Chinese power points also allow the insertion of two-pin American and two-pin European plugs, usually via a separate socket on the same plate but sometimes with extra holes in the same socket (a bit like a multisystem travel adaptor). Unlike Australia and NZ, they are not switched, and the socket appears upside-down to the usual convention. This is apparently a safety measure, so that if something conductive falls across a partially inserted plug, it’s less likely to form a short-circuit between Active and Neutral (in the modern Australian plug, the pin base insulation provides a similar benefit). The Active/Neutral polarity in China is the same as Australasia. Papua New Guinea was a territory of Australia until 1975 and naturally adopted Australian wiring practices. Other Pacific islands such as Pitcairn Island, Fiji, Vanuatu, Tonga etc use Australian/NZ wiring practices, since accessories are imported from these countries. Polarity was not originally standardised There was no official Active/Neutral polarity convention initially. After all, AC has no polarity, so an appliance will work connected either way round. In fact, until the 1960s most plugs were not even labelled as to which pin was Active (sometimes known as “live”, “line”, “hot”, or “phase”); only the Earth pin was designated. There was even a common doubleadaptor design which reversed the polarity of one socket, since it was easier to make that way (see Fig.20). Appliances from the 1950s wired in the factory with the red (Active) and black (Neutral) wires transposed in the plug are not uncommon. With a history of using bayonet light sockets and two-pin plugs, it was assumed that appliances could be connected either way round (see Fig.23). This approach continued even into the 1970s. For this reason, where a switch was provided for a portable appliance, it was usually a double-pole type. Switched light sockets, as used with desk or standard lamps, are a common example of this. This was not as unsafe as it seems. The first generation of power points used separate switches and sockets. siliconchip.com.au Fig.18: an Argentine power point. Although this one is switched, that is not mandatory, unlike in Australia. They were not a complete assembly, with switch integral to the socket (known as “combinations”) – see Fig.21. It was mandatory that Active was switched, but how the socket was connected after the switch was not critical. So, if the switch was off, the appliance was dead with either connection. However, there was a “recommended” standard which eventually became official, apparently during the late 1960s. This stated that, looking at the socket, the pin at upper left was Active. An easy way to remember this is that a modern single GPO has the switch on the left and is thus closest to the Active pin. Australia & NZ probably adopted this convention for that very reason. With most people being right-handed, it is natural to insert the plug with the right hand, leaving the left to operate the switch. In the USA, where sockets are not usually switched, this was irrelevant. As to why Australian sockets are always switched, early documentation from the 1920s explains this. At the time, it was noted that flexible cords were a somewhat common cause of fires and other faults. Therefore, it was safer to switch off the appliance before the flexible cord, rather than leaving it live when not in use. Not always Earthed Many years ago, I took the cover off an ancient porcelain socket in a house that must have been wired in the late 1920s, and was rather surprised to see no Earth wire connection. siliconchip.com.au Fig.19: Chinese socket also allows the insertion of non-polarised two-pin US and European plugs. It was a typical power point of the era, with the switch and socket mounted on a 6in x 3in timber block. It was probably the first generation of the three-flat-pin socket used in Australia. As I later learned, this lack of Earth connection was permitted in the wiring rules. The condition was that the socket had to be Earthed if there were other Earthed objects 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, it’s unlikely to get a shock from it. Timber floors and walls make good insulators. To get a shock from a ‘floating’ appliance requires you to be part of a complete circuit to Earth. It appears this was allowed at least into the 1950s, and possibly later, but eventually it became compulsory to Earth all sockets. It was also in the 1970s that an Earth connection became required for all light fittings, even if out-of-reach of an Earthed object. Fig.20: a common older doubleadaptor design shows that the Active and Neutral polarity was not initially standardised as the adaptor swapped Active and Neutral top to bottom. points and switches were mounted on timber blocks. This, along with split seam steel conduit, was a legacy of British methods. While surfacemounted fittings and timber mounting blocks were still being installed later than this, flush-mount switches and power points were preferred for their modern appearance. These, like their US counterparts, sometimes had the switch and socket with separate cover plates, although single-unit “combinations” had appeared. Where the switch and socket Wall box dimensions It may also surprise some that it wasn’t just the three-pin socket we adopted from the USA, but also their wall box dimensions. Not only are the switch plate dimensions the same, but the screws used to secure the switch or socket have the same 6-32 thread. Australian fittings fit into a US wall box perfectly well, and vice versa. Until the late 1940s, most power Australia’s electronics magazine Fig.21: with separate switches and sockets, the socket polarity could be either way. The only requirement was that Active was switched. September 2020  37 Fig.23: the 1960s HPM plug on the left shows Live and Neutral polarity identification, but the older Ring Grip only shows the Earth connection. GPO plate orientation Fig.22: this assortment of power points shows the different pin orientations which have been used. Present standards require the Earth pin at the bottom. were still separate behind a standard cover plate, the polarity of the socket was still not guaranteed. By the 1960s, power points were being made with the mechanisms being part of one unit, with an integral switch plate. MEN system The MEN (Multiple Earth Neutral) system of earthing is another Americanism we adopted. In it, the Neutral is connected to Earth at the switchboard. The reasoning is that if the Earth connection to the water pipe (no longer recommended) or Earth stake has a high resistance, the fuse will still blow under fault conditions. The downside 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 be at mains potential. What we did not adopt was the American colour code, instead sticking to the British scheme of red for Active and black for Neutral. This later changed to the current scheme of brown for Active, blue for Neutral and Green/Yellow for Earth in appliances and leads, although the old scheme is still allowed for fixed wiring. 38 Silicon Chip Even though Australia adopted the US-style wall plate, one area of departure was that unlike in the USA, power points were mounted horizontally. Horizontal mounting of power points was not common in New Zealand. Instead, they kept to US practice and most power points there were mounted vertically. Whether the Earth pin was up or down was another variable. It’s normally down, but some manufacturers such as Clipsal for a while had it at the top. HPM during the 50s and 60s even had the socket rotated by 90° from the usual orientation (see Fig.22). For some time now, the official orientation has the Earth pin at the bottom. The reasoning behind this is that if a plug should be partially withdrawn from a socket, hanging down, the Earth pin will still make contact, with Active and Neutral disengaging first. There is an opposing point of view as implemented in some other countries, notably the UK. This is that the Earth should be uppermost because if the plug is partially withdrawn and a conductive object falls into the gap (Venetian blinds are one recorded example), it will not become live. As mentioned above, this also possibly explains the Chinese orientation. Mains voltage There are many different mains voltages in use around the world, for reasons of development and politics. The first reticulated power system, implemented by Edison from the Pearl Street (New York) power station in 1882, 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, Australia’s electronics magazine Fig.24: one common plug and socket (shown without wall plate), used for 240V in North America. had difficulty 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. But line losses quadruple due to the I2R rule. An improvement can be made by implementing a three-wire system where two 110V supplies are in series, giving 220V, with the common connection being Neutral. Provided the current drawn on both 110V supplies is close to equal, little current flows through the Neutral wire, and transmission losses are reduced. This scheme has been in used in the USA for a very long time now, except that the supply voltage has since been standardised at 240/120V, 60Hz. It does not seem to be widely known outside the USA, but most residences there do have a 240V supply. This is from a 240V centre-tapped winding on the pole transformer, the centre tap being the Earthed Neutral. However, the current per 120V branch of the circuit is still limited. This leads to the situation where domestic appliances that draw more than 1800W (15A <at> 120V) require a special 240V socket (Fig.24). There is a growing trend for American travellers to bring back kitchen appliances from Europe. After experiencing the faster heating time of 220-240V kettles and coffee machines, compared to the 120V version, they are keen to have a 240V socket installed at home. Europe In Europe, there was a mixture of 110V, 127V and 220V at 50Hz AC, or in a few instances, DC. If 127V seems siliconchip.com.au a little odd, it’s the phase-to-Neutral voltage of a 220V three-phase supply. However, 220V single-phase/380V three-phase was adopted as the standard, and the lower voltage systems replaced by the early 1980s. Siemens in Germany actively promoted 220/380V, 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 50Hz! It depended on who built the generating equipment as to what the voltage and frequency would be. This all changed with the commencement of the National Grid in 1926. Its completion resulted in a nationwide frequency of 50Hz 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. That didn’t quite happen, with each country going their own way. In 1946, the UK standard was changed to 240V AC. Australian mains voltage Australia followed British practice and chose 200-250V for the single-phase residential supply, thereby avoiding the disadvantages of the 110120V system. Two- or three-phase supply (400/415V between phases) to homes is common in Australia. Apart from providing increased efficiency for all appliances, it is also used domestically for high-power loads, such as instantaneous water heaters, large air conditioners and some workshop equipment. Australian-made electric ranges allow for a two-phase supply where this is available. But the mains voltage in Australia wasn’t always standardised – see Fig.25. At one point, New South Wales, Tasmania and Queensland standardised on 240V 50Hz, with Victoria on 230V 50Hz. Heading west, 210V 50Hz was used in South Australia, and 250V at both 40Hz and 50Hz in Western Australia. There were once two large towns using 110V: Launceston (50Hz), and Broken Hill (100Hz). Away from the capital cities, there was more variation, with 220-250V DC being used in some towns. siliconchip.com.au Fig.25: from the Radio Trade Annual, 1937, this shows the variation in Australian mains supplies at the time. The reason W.A. was the odd-oneout with regards to frequency is that the 40Hz generating plant had been imported from South Africa. DC mains were also used in a small part of the CBD of some capital cities. In Sydney, the DC supply existed in the northern part of the CBD until the end of 1985, but by that time remaining only for lift motors. DC mains was reticulated using the three-wire system, which meant that depending on what side of the mains the consumer was connected to, the supply could be either positive or negative with respect to Earth. By the 1950s, plans were afoot to standardise Australia on 230V 50Hz in line with the Empire, and many localities, especially those using DC, went through the conversion process. Australia’s electronics magazine 240V areas were to be left as-is, being within 10% of 230V. Presumably because the 240V areas outnumbered the others, this became the standard instead (although it has since changed back to 230V). Victoria changed to 240V in the early 1960s. Adelaide started to move away from its 210V supply in the 1950s, and Western Australia dropped to 240V in 1985. If it seems like a huge exercise to convert to a new supply system, it must be remembered that at the time, houses had few appliances. In the 1950s, apart from incandescent lamps in each room, there would be a toaster, jug, cooking range, and a radio. The more affluent would also have a refrigerator, washing machine and maybe a vacuum cleaner. September 2020  39 Fig.26: the T-socket used for Extra Low Voltage supplies (up to 32V) at up to 15A. It is recommended that where the supply is referenced to Earth, the bottom pin should be used for this. All the heating appliances and lamps previously operating on DC worked the same on AC. Similarly, universal type brushed motors work on either type of supply. Should the new voltage be markedly different, eg, converting from 110V to 240V, it was a simple matter to replace the lamps and elements, which were all standard types. In the case of 110V appliances not easily converted, a step-down transformer could be used. Where the voltage change was minor, appliances like radios could be switched to a different tap on the power transformer. If it was part of a radiogram, the pulley on the turntable motor would have to be replaced when changing from 40Hz to 50Hz. The few AC/DC radios usually needed no modification, since most included a barretter to stabilise the valve heater current, and could accommodate a wide range of voltage. New Zealand voltages New Zealand had standardised nationwide on 230V 50Hz right from the start, although in Wellington there was Where do you get those HARD-TO-GET PARTS? Where possible, the SILICON CHIP On-Line Shop stocks hard-to-get project parts, along with PCBs, programmed micros, panels and all the other bits and pieces to enable you to complete your SILICON CHIP project. SILICON CHIP On-Line SHOP www.siliconchip.com.au/shop 40 Silicon Chip Above, a special plug and receptacle will maintain the polarity of a cord-connected appliance. Such a plug can be inserted in only one way. Fig.27: we can see here the American origin of the Australian ELV socket. However, in the USA it was intended for 120V use. NZ used it for 230V. an unusual 105V 80Hz supply from a steam-driven power station. With the disadvantages of the low voltage supply becoming apparent, it was decided in the mid-1920s to change to the 230V standard. This was completed in the early 1930s, by which time the power source was hydroelectric. Australia and the new 230V standard Since 2000, the “official” standard for Australian mains voltage is 230V. In a sense, this is déjà vu for those living in Victoria. However, this was really a case of being politically correct, because the actual voltage was not changed from the nominal 240V. The same situation occurred in the UK, although a few years earlier. In the 1980s, the IEC proposed to standardise on two world voltages: 120V and 230V. This was to assist manufacturers in making electrical products for a global market. The idea was that 240V and 220V countries would “harmonise” their mains voltage. Thus, the UK and Australia, for example, would drop their mains supply by 10V, and Continental Europe would increase theirs by the same amount. In Australia, a “230V Committee” was established in 1994 to oversee this transition locally. The perfect bureaucratic situation could be imagined here, with much paper shuffling but nothing else. In effect, nothing actually changed as far as the consumer was concerned; all that was done was to reduce the lower mains voltage limit to -6% instead of the previous -10%. The nominal 240V still falls well within that. One will note that incandescent lamps (including halogen types) sold in Australia are still rated at 240V, to reflect Australia’s electronics magazine Fig.28: cylindrical Earth pin connectors originally intended for lighting circuits. the truth of the situation. As summed up in one letter to the UK magazine “Practical Electronics” some years ago the change was “...only on paper”. Extra Low Voltage and the “T” plug & socket 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. Another American socket had been adopted for these extra-low voltages known as a “T” socket (Figs.26 & 27), but unfortunately, many simply used the three-pin 240V type instead. Disastrous results awaited appliances so fitted with a three-pin plug, when taken to another location and plugged 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. In the modern day, 32V DC systems only exist in the hands of vintage technology enthusiasts, since appliances have not been made for this voltage since the 1960s. Rural off-grid electrical systems today tend to be solarpowered 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’s also commonly used for portable lead lights powered from 32V AC isolating transformers. As mentioned previously, the “T” siliconchip.com.au DEAD OR DYING BATTERIES IN YOUR EBIKE? Fig.29: the American parallel flat pin non-polarised plug has the same pin dimensions and spacing as the Australian plug. So it is possible (but not recommended!) to simply twist the pins to enable insertion into an Australian socket. plug and socket was used in NZ for 230V. At that time, Australia and NZ had their own independent wiring regulations. The present-day status of this connector in NZ is not entirely clear. It is conceivable there might be very old installations where sockets of this kind are still connected to 230V. That would obviously be unacceptable if it was also used for ELV. Cylindrical Earth pins This was initially introduced for use on lighting circuits. A typical situation would be in a commercial building with a false ceiling. Here, the luminaires are usually connected by flexible cable to fixed sockets (see Fig.28). However, it never became popular for that purpose, with the conventional three-flat-pin sockets usually preferred. Instead, the cylindrical Earth pin configuration became used for all kinds of “special” applications. For example, it has been used to differentiate between circuits supplied by uninterruptable power supplies or isolating transformers, and the ordinary public supply. Other uses include connecting remote switches (eg, a switch for a room light mounted in a bedside table). Sometimes it is used for low voltages, despite the existence of the “T” plug and socket. Essentially, it is used where compatibility with the standard mains 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 siliconchip.com.au damage a normal mains appliance. Once upon a time Until the 1980s, it wasn’t uncommon to see two-pin US plugs being used in Australian power points, as shown in Fig.29. This came about mainly from Japanese electronic equipment being sold in Australia from the 1960s onwards. Overseas travellers would also bring back appliances from foreign dutyfree stores. Because the pin dimensions and spacing are the same, a simple twist with a pair of pliers will enable the plug to fit into an Australian socket. There is, however, a shock hazard where the twisted pins prevent the plug from being fully inserted, and the plug has too narrow a body. There is also evidence that this weakens the pins and/or the connection to the cables. 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 not be done where an Earth connection is required. As regulations were tightened, all appliances sold in Australia must now be compliant with Australian Standards. References • Practical Electrical Engineering, Vol. 2, Newnes. • Radio Trade Annual, 1937. • Electronics Australia, January 1986. • Amateur Radio Action, Vol.9, Issue 12. • Evening News, Sydney, January 21st, 1930, p15. SC • Popular Science, April 1942. Australia’s electronics magazine SEGWAY? MOBILity BUGGY? GOLF CART? ESCOOTER? Premier Batteries can recell and/or custom manufacture Lithium Ion batteries for Segways, Ebikes, Electric Golf Carts, Scooters and Mobility Buggies – often with increased capacity and range etc. Quality cells are used and batteries are Fully Guaranteed PREMIER BATTERIES High quality batteries for all professional applications SUPPLIERS OF QUALITY BATTERIES FOR OVER 30 YEARS Unit 9, 15 Childs Road Chipping Norton NSW 2170 Tel: 02 9755 1845 email: info.premierbatteries.com.au Web: www.premierbatteries.com.au September 2020  41