AS 3112 is an Australian standard for mains power plug. It is also known as a Type I plug.
The plug matching the socket pictured on the left, used in Australia, New Zealand, Fiji, Papua New Guinea and Tokelau, has two flat pins forming an inverted V-shape plus an earthing pin. These flat blades measure 6.5 by 1.6 mm with the Active and Neutral pins of 17.35 mm in length set 30° to the vertical on a nominal pitch of 13.7 mm and the Earth pin being 20 mm in length. A standard power outlet in Australia provides a nominal voltage of 230 volts at a maximum of 10 amps and always includes an earth connection. As in the UK, its outlets are individually switched for extra safety. Argentina uses a similar plug, with pins 1 mm longer.
There are unearthed versions of the plug used with this outlet having only the two flat inverted V-aligned pins, without the Earthing pin. Such plugs are only to be used for devices where other safety standards are in use (e.g. double insulation) and these plugs are rated at a maximum of only 2.5 amps. They are not available separately but only integrally with power cords specifically designed for the purpose.
A view of the Wiring Side of a typical dual power outlet is also shown on the right, together with an annotated view of the mechanism, without the front cover. (One "Rocker" switch has been disassembled to show its operation.)
There are several AS/NZS 3112 plug variants, including one with a wider ground pin used for devices drawing up to 15 amperes; sockets supporting this pin will also accept 10 A plugs. There is also a 20 A variant, with all three pins oversized, and 25 and 32 A variants, with the 20 A larger pins and the earthing pin forming an inverted "L" for the 25 A and a horizontal "U" for the 32 A. These sockets accept plugs of equal or of a lower current capacity, but not of higher capacity. For example, a 10 A plug will fit all sockets but a 20 A plug will fit only 20, 25 and 32 A outlets.
A variant of the Australian standard 10 amperes plug has a socket on the back to allow connection of a second appliance to the same outlet. This type of plug is known officially as a "socket adapter plug" but is referred to colloquially as a "piggy-back plug" or, in New Zealand, as a "tap-on" plug. In Australia the plug is now available only as part of a pre-assembled extension cord, or by special order. In New Zealand rewirable PDL 940 "tap-on" plugs are more widely available.
Other versions include a round earth plug with a rating of 10 A, and a 110 V 10 A version that has round active & neutral pins with a flat earth pin.
The active terminal of the Plug is the first pin from the Earth pin in a clockwise direction when viewed from the wiring side. Likewise, it is the first 'socket' from the Earth 'socket' in a clockwise direction when viewing a power outlet. Care should be taken if Argentinian standards or faulty wiring swaps the active and neutral pins. Care also should be taken with the 10 A version with the round pin as physically compatible, but electrically incompatible NEMA 7–15 connector used for 277 V 15 A connections is encountered in commercial or industrial settings in the Americas.
The Chinese CPCS-CCC (Chinese 10 A/250 V) plugs and sockets are almost identical, differing by only 1mm longer pins and installed "upside down". Note that whilst AS 3112 plugs will physically connect, they may not be electrically compatible to the Chinese 220 V standards.
Originally there was no convention as to the direction of the Earth pin. Often it was facing upwards, as power outlets in China now do but it could also be downwards or horizontal, in either direction. The pin orientation was codified in the 1950s with the Earth pin required to face downwards (Citation Needed), so that the longer Earth pin will be the last to lose contact if the inserted plug is tugged downwards. If products destined for the Chinese market are exported, the bottom entry plug becomes a top entry plug, and the customer will often take advantage of the situation by suspending the power cord upwards.
Australia's standard plug/socket system was originally codified as standard C112 (floated provisionally in 1937, and adopted as a formal standard in 1938), which was superseded by AS 3112 in 1990. An American version was manufactured and used for grounded equipment (like washers in laundry rooms) in the 1940s and early 1950s, and appears to have existed as far back as 1916, shown in US patent 1,179,728. Australian plugs will fit these American outlets perfectly. There's also another American outlet, the NEMA 10-50R, that looks quite similar, but is about 10% larger.
While in 1937 there was no "Standards Australia" in existence, it was then that the design was adopted as a result of a "Gentlemen's Agreement" between manufacturers Fred Cook of Ring-Grip, Geoffrey Gerard of Gerard Industries and Brian Harper Miller of the State Electricity Commission of Victoria (SECV). The design was based very closely on the existing American 240 Volt plug and power outlet design and it seems that the same American design is the reason that Argentina, Uruguay and China are now also using (essentially) the same design. New Zealand also adopted the Australian design, since Australian equipment and many electrical appliances were exported to that country. One of the reasons behind the adoption of that particular design was that it was cheap to make; the flat pins could be easily stamped out of sheet brass, in contrast to round pins or thicker rectangular ones used in other countries. This was also a consideration when the Chinese authorities officially adopted the design in relatively recent times, despite the considerable inroads the British plug had made, due to its use in Hong Kong. The Chinese made one change, however; the earth pin is at the top. This is considered to offer some protection should a conductive object fall between the plug and the socket.  
However, a major update AS/NZS 3112:2000 was released in 2000. This mandated active and neutral insulated pins on the plugs used with these power outlets by 2005, which somewhat negates any 'advantage' of having the earth pin uppermost. The current issue of the standard is AS/NZS 3112:2004 which introduced more stringent testing procedures to test for bending of the pins and subtle changes to the radius of the pin tips.
In Brazil, this kind of plug is commonly found in high-power appliances like air conditioners, dishwashers, and household ovens. The reasons why they have been (unofficially) adopted for this use may be the robustness and high-current bearing capabilities, the impossibility of inverting phase and neutral pins, or the fact that Argentina, a border country, uses this plug and used to be more developed than Brazil in the past (meaning that people had more access to some kinds of electrical appliances and/or to electricity itself) so there may have been a flux of high-powered appliances from Argentina to Brazil at some point of time.
Nowadays, Brazil has adopted the IEC 60906-1 standard, which prescribes a high-current version, with earth pin and slightly larger pins (4.8mm instead of 4mm) that can carry up to 20A. New apparatus has been sold with the new plug, so the tendency is the usage of the "Australian" plug to fade away.
- "Australian Mains Plug Variants – AS/NZS 3112". Access Communications Pty Ltd. 2007-04-19.
- http://patft.uspto.gov/netahtml/PTO/srchnum.htm and type in the patent number
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