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Origin of Australian plugs and sockets |
 general info |
AS/NZS 3112 |
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Origin of Australian plugs and sockets |
general info |
AS/NZS 3112 |
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| Australian
10A - 250V plugs, based on a now obsolete US design, dates back to
1937. New Zealand adopted the standard that is now known AS/NZS3112.
The standard is also used in Papua New Guinea. The same type of plug, but with reversed polarity, is used in Argentina (IRAM 2073 standard). In China (PCR) the plug is used for appliances that require earth connection (GB 2099 standard). |
| Australian 3-pin
plug and socket Information written by David Inkster (Meadows, SA).* Source: Silicon Chip Mailbag, issue 162, 10 March 2002. "..... The design was adopted, around 1930, as a result of a "Gentlemen's agreement" (there was no Standards Australia then) between Fred Cook of Ring-Grip, Geoffrey Gerard of Gerard Industries, and Brian Harper Miller of the SECV. They based the design very closely on an existing American plug, and although that American design has apparently now faded into obscurity, I believe that same American design is the reason that Argentina and Chile and probably also China, also use essentially the same design. New Zealand copied the Australian design as Australian electrical appliances and equipment were exported across the Tasman. One of the reasons behind the adoption of that particular design by the three Australian gentlemen 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. An interesting piece of trivia is that this is referred to in Hong Kong as the "emu foot" or "emu track" plug, as the socket when viewed with the earth slot uppermost does resemble the track of an emu. I thank Dennis Perry and Norm Zerner (presently and formerly of Gerard Industries) and Max Steen, a former colleague of mine in the Approvals Branch at ETSA, for their help with this information." ETSA: Electricity Trust of South Australia SECV: State Electricity Commission of Victoria |
Standard The Australian power connections were ratified as a formal standard C112 in 1937, redesigned as Australian Standard 3112 in 1981 and harmonized with the New Zealand Standard in 1993.  George
P. Knapp at Harvey Hubbell Inc., Bridgeport (CT) design for a flat
blade plug with ground connection. US patent 1179728 was granted on
18 April 1916 and expired in 1933.
Figs. 3 (socket) and 4 (plug) illustrated the patent application.  Example
of an early Australian C112 standard plug made by Ring-Grip.
The museum is grateful to Steven McDonald for permitting to show the
photos.
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| a, d |
The Hubbell design with angled power pins
has not made it to become a popular domestic earthed socket in the US,
probably
because standard not earthed plugs with parallel straight blades do
not fit. The design has been used for many decades for 15A-125V /
10A-250V split phase connections. See US
plug history for details. It never received the status of a NEMA
standard. Orientation of the earth connection was not defined in the Hubbell patent, but in 'both split phase and Australian / New Zealand sockets it is the lower, vertical connection. Fig. 4 of patent US1179725 (see above) shows that plug blades originally had notches for a more stable grip with socket contacts. Image 'd' shows a 1950s Hubbell plug that has the now commonly used circular holes, rather than notches. |
| b | 10A-250V standard socket made by the
Australian
company Energo, probably in the 1940 - '50s. See also note below. |
| c | Modern AS/NZS 3112 socket with mandatory
switch. Wall sockets with two, separately switched outlets are very
common. |
| e | Classic AS C112 plug, made by the
Australian company Marcolite. Each of the pins have notches, similar
to the plug model in Knapp's patent. Earth pin is 3 mm longer than
(angled) power pins, both in patent description and Australian / New
Zealand standard plugs. The additional length ensures that earth
connection is made first. |
| f | Modern 10A-250V AS/NZS 3112 plug. Compared
to plug 'e', essential differences are: (1) from 2005 power pins must
have
insulating sleeves to eliminate risk of an electric shock by a not
fully inserted plug¹, and (2) cord side entry, rather than top end;
side entry makes it impossible to retract a plug by pulling
the cord rather than plug casing. ¹ AS/NZS 3112 sockets do not have a recess. |
| note |
From the 1914 design by George P. Knapp (patented in 1916) up to now nothing has been changed regarding dimensions and orientation of socket contact slots, which means that each of the plugs shown on this page fits perfectly in each of the sockets. |
| * I like to thank Stephen Furley who has drawn
my attention to the
relation between the now obsolete American socket and the Australian C112 standard. Information can be found also on ECN Electrical Forum. |
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