AS/NZS 3112 are the harmonised Australian and New Zealand standards for AC Plugs and Socket Outlets.
The plug matching the socket outlet pictured on the left, used in Australia, New Zealand, Fiji, Papua New Guinea and many Pacific Island countries, has two flat pins forming an inverted V-shape plus an earthing pin. These flat blades measure 6.35 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 socket outlet in Australia provides a nominal voltage of 230 volts RMS at a maximum of 10 amps and always includes an earth connection. The Active (Line) terminal on each socket outlet is usually individually switched for extra safety.
"Shuttered" socket outlets are available, but this is not a requirement.
Argentina uses a similar plug, with pins 1 mm longer, but with the polarity reversed.
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 7.5 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 socket 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.)
If required, such dual socket outlets now can be obtained (at additional cost) utilizing insulation displacement as a means of connecting to the supply conductors, as can be seen in the illustration - below right. The benefits claimed for their use in these applications include up to 50 percent faster installation, due to the reduction in the stripping, twisting and screwing down processes.
There are several AS/NZS 3112 plug variants, including one with a wider ground pin used for devices drawing up to 15 amperes; socket outlets 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 socket outlets accept plugs of equal or of a lower current capacity, but not of higher capacity. For example, a 10 A plug will fit all socket outlets 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 socket 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 socket outlets 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 socket 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, 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.
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 on an American plug and socket outlet intended for use at 120 V which was patented in 1916 under US patent 1,179,728. Australian plugs will fit these obsolete American outlets perfectly. (While this socket outlet never became a NEMA standard design, the 50 A NEMA 10-50R, has a similar pin configuration in a larger form.) Argentina, Uruguay and China based their plugs and sockets on 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 socket is normally mounted with 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 socket outlets by 2005, which somewhat negates any 'advantage' of having the earth pin uppermost. The standard AS/NZS 3112:2004 introduced more stringent testing procedures to test for bending of the pins and subtle changes to the radius of the pin tips. The current version is AS/NZS 3112:2011, Approval and test specification—Plugs and socket-outlets.
The nominal voltage in most areas of Australia was set at 240 V in the 1920s. However, a change began in 1980 with the International Electrotechnical Commission (IEC) deciding to rationalise the 220 V, 230 V and 240 V nominal voltage levels around the world to a consistent 230 V.
This rationalisation was ostensibly made to improve the economics of making appliances by allowing manufacturers to produce a range of items with a rated voltage of 230V. In 2000, Standards Australia issued a system Standard, AS60038, with 230V as the nominal voltage with a +10% to –6% variation at the point of supply. (253 V to 216.2 V)
A new power quality Standard, AS61000.3.100, has recently been released that details requirements additional to the existing systems Standard. The new Standard stipulates a nominal 230V, and the allowable voltage to the customer’s point of supply is, as mentioned, +10% to –6%. However, the preferred operating range is +6% to –2%. (243.8 V to 225.4 V) 
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 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 national standard NBR 14136, which is loosely based on the IEC 60906-1 standard. NBR 14136 defines two types of socket outlets and plugs: one for 10 A, with a 4 mm pin diameter, and another for 20 A, with a 4.8 mm pin diameter. 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.
- United States Patent and Trademark Office: US patent 1,179,728
-  Insulated pins on plug tops
|Wikimedia Commons has media related to AS 3112.|