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Joined: Jul 2005
Posts: 223
I mentioned in another thread I had the details of where our plug & socket configuration came from. I've since OCR'ed the article which was printed in "Australian Amateur Radio Action" vol 9, issue 12 (March 1987). Here it is:

"Unless they've been overseas, or stayed in an international-standard hotel, the majority of Australians probably take the ordinary 3-pin electricity mains plug and socket for granted. But anyone who has encountered the various non-interchangeable types of 2-pin and 3-pin plugs and sockets in use in Europe, the UK and the USA will be aware of Australia's good fortune in having a standard design throughout the country.
Shortly after World War 2, in about 1949, the UK adopted a 13A parallel flat pin design which incorporates a fuse in the plug, but Australia had adopted its standard long before this. Tracing its history, however, was more difficult than I had expected and involved me in some correspondence.
My first letter, to the Energy Authority of New South Wales, produced the information that "existing Authority records do not include the history of the origin of the standard three-pin, flat pin plug and plug socket. Plug and plug sockets used in this country comply with the requirements of Australian Standard AS-3 112-1981 'Approval and Test Specification for Plugs and Plug Sockets'as published by the Standards Association of Australia. This standard was first published in 1937 as AS-Cl 12 and the Standards Association of Australia may have a copy of the original issue plus each subsequent revised edition in its library at Standards House, 80 Arthur Street, North Sydney 2060.
'A measure of control over the sale of certain 'prescribed' and 'proclaimed' electrical articles and fittings, including plugs and plug sockets, has been exercised in New South Wales since 1938. The initial scheme in 1938 operated under the provisions of the Local Government Act 1919 and the present scheme operates under the provisions of the Electricity Development Act 1945.
"Plugs and plug sockets are 'prescribed articles' pursuant to the Electricity Development Act 1945 and, as
such, may not be sold, hired or exposed or advertised for sale or hire unless they have been approved by the Authority or the approving authority in another State and are marked with the allotted approvals marking. Similar legislation applies on each Australian State or Territory
"The approval marking takes the form of a letter identifying the State of origin approval, eg 'N' for NSW, 'V' for Victoria, 'Q' for Queensland, etc, followed by a number allotted by the approving authority) identifying the person or company to who the approval was granted."
The Standards Association of Australia told me that the background information on the origin of the three pin, flat pin plug and plug socket was rather sketchy due to the time elapsed since its initial adoption. However, they supplied the following'.
"(a) The majority of the work would appear to have been carried out in Victoria by SECV with the help of Australian manufacturers.
"(b) The design is virtually identical to a pre-existing American configuration except that the pins are 2 mm to 3 mm longer.
"(c) The configuration was first published as an Australian standard in 1937 as AS-C 112. The current edition of this standard is AS-3 112-1981.
"(d) The current configuration also covers 15 amp and 20 amp 3-pin flat pin configurations. Again, Australia is in the fortunate position as the system was designed so that any plug will fit a plug socket with the same or a higher current rating but not the reverse.
"(e) This system is also used in New Zealand, Fiji and New Guinea, and to some extent in Argentina."
The State Electricity Commission of Victoria was rather tardy in replying to my letter, but a follow-up phone call produced the following:
"Archival records and minutes of meetings dating back to 1927 have been reviewed as staff have had the opportunity to do so and, although some references were noted of comments on the three-pin flat pin plug system, there are no specific comments on the origin of same.
"Inquiries have been made of former Electrical Approvals Board members and other long-serving personnel, but to date no specific information has been unearthed. At the present time we are following two lines of inquiry with retired personnel, but as one has been on extended holidays we have not been able to get in contact with him."
The SECV also made the suggestion that "one possible line of inquiry which may be fruitful may be Mr K Gerard of Gerard Industries (Clipsal) in South Australia as that firm has manufactured three-pin plugs and sockets for many years, possibly over 50 years."
And it was here that I struck gold. Mr Gerard was prompt in his reply and I cannot do better than quote directly from his letter to me:
Prior to World War 1 and during 1914-18, various plugs and sockets were imported from England and used in Australia.
During the early 1920s, it was difficult to import English plugs because of the shortage in production and at the same time it was noticed that a various assortment of plugs was being used in Australia and these plugs had round pins.
"Some American plugs, sockets and cord extension sockets were imported and these were of the flat pin type, ie 2-pin flat pin plug with the pins parallel and the 3-pin flat pin plug which had the configuration of the present 3-pin plug. Late in the 1920s, Ring Grip Ltd of Victoria and Gerard lndustries Pty Ltd (Clipsal) made 3-pin accessories to interchange with the US design.
"As Australia was committed to the 'earthing' system of supply, it was realised that a 3-pin plug was required.
"About 1934 a meeting was called by the SEC V, who was the leading supply authority in those days, at which a representative of the SECV, Standards Association, Mr Tivey from General Electric, Mr Fred Cook from Ring Grip, and Mr Geoff Gerard (my brother) from Clipsal were present. General Electric were importing their own 3-pin plug, etc, from the USA at that time. "The meeting, after reviewing all the plugs (English and American) being imported into Australia, decided to adopt the American 3-pin flat pin plug as an Australian Standard. The manufacturers' representatives considered flat pins were easier to make and their installation machines at the time were capable of making flat pins better then round pins.
"In adopting the USA configuration, the pins of the Australian design were shortened by 3 mm in length because of better safety standards against 'wrongful' insertion into sockets that were then produced and also to lessen the probability of personal contact with the pins when inserting plug into socket.
"A standard plug gauge was suggested, being similar to the one used by Clipsal in their plant, and this was submitted to the Standards Association of Australia and was finally published in a Standard Specification AS-Cl 12 for plugs and sockets in 1937.
This was adopted by all State supply
authorities and hence this 3-pin plug manufactured in Australia by Ring Grip and Clipsal became an Australian Standard.
"The design of 3-pin plugs has had a number of changes over the years since then, but the configuration of the pins has remained the same. People who travel to the USA, UK and Europe realise how fortunate we are to have a standard plug and socket throughout Australia."
I am indebted to those who went to considerable trouble researching on my behalf for supplying me with the information used in the preparation of this article."

Joined: Sep 2002
Posts: 1,498
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Very interesting reading! Yes, I know, I'm an extreme geek!

I wonder if the original American plug was intended mainly for Line (120V) + Line (120V) + Neutral, thus making it a 240V plug?

It seems most plug designs were fixed by ca 1960.

The Schuko existed, so did the American and the South African (old British) plugs.

I think the standard for the Swiss plug is from 1959, making it somewhat newer. Of course, this could simply be an update of an older standard. The Israeli plug is also rather new.

Don't know how old the French, Italian and Danish plugs are, but hardly any younger.

Joined: Jul 2005
Posts: 223
"I wonder if the original American plug was intended mainly for Line (120V) + Line (120V) + Neutral, thus making it a 240V plug?"

I've been wondering the same thing...if an Australian appliance was plugged into the equivalent 3 pin socket in the US, would the casing be connected to earth or neutral? Is it used for a straight single phase 240V supply with earth, or is it a 120V two phase supply with neutral on the 3rd pin? The appliance would obviously work either way, but I'd feel safer if the case was connected to earth and not neutral. The US method of wiring appears to use something like our M.E.N system so the neutral and earth would be at virtually the same potential.

Joined: Aug 2001
Posts: 7,520
Very interesting reading! Yes, I know, I'm an extreme geek!

Aren't we all at ECN? [Linked Image]

This does indeed make for interesting reading.

The "Crowfoot" receptacle has cropped up every so often in threads before, so I did a little searching. Here's what our own Bjarney had to say about it in this thread :

similar to what in the US used be called - in slang - a 'crowfoot' device - for its shape. Both were rated 125/250V 3-wire, non-grounding, but the grounded-neutral pin was improperly used as an equipment-ground connection.

Just to complicate things further though, take a look at the receptacle from this thread :

[Linked Image]

It's clearly designed to take either a "crowfoot" plug or an NEMA 1-15 type (but not a 5-15), yet the flat blade is clearly labeled as as ground, not a neutral.

Paging Bjarney....... [Linked Image]

The US method of wiring appears to use something like our M.E.N system so the neutral and earth would be at virtually the same potential.

Yes, the American system is equivalent to your MEN or the British PME arrangement. In fact at the main panel there can be a single neutral/ground busbar, bonded to the case and to which both the incoming supply neutral and the grounding electrode are connected. At sub distribution panels though, neutral and ground are kept distinct and separate.

There are still many American installations in which the dryer and range use a 3-wire connection (using the 10-30 and 10-50 receptacles), and the appliance frame is grounded to the neutral. This was allowed only where the circuit was fed directly from the main panel. If the circuit came from a sub-panel, then the 4-wire hookup was needed so that the ground was completely separate.

New installations now have to use the 4-wire system exclusively.

Joined: Nov 2002
Posts: 456
Around our farm, we used to have the crows foot recepticles, instead of the normal 5-15 type, and were wired similar to how a 5-15 would, one of the anlged slots to line, the other to the grounded conductor, the middle verical slot to earth.

Joined: Dec 2004
Posts: 329
I seem to remember reading somewhere here that these crowfoot 120V receptacles were some of the, if not the first grounding devices here in the states. It predates the NEMA 5-15, actually it predates NEMA. When a device needed to be grounded it used this crowfoot instead of the 1-15, simply because the 5-15 didn't exist yet. Later, after introduction of the 5-15(ok well after!)the crowfoot configuration was designated 10-20

[This message has been edited by IanR (edited 08-03-2005).]

Joined: Feb 2003
Posts: 288
The 1947 NEC Handbook mentions a requirement for at least one receptacle in the laundry area to be a three-wire type, with the third wire reserved for equipment grounding. There is no elaboration on the type of receptacle required.

The 1951 Handbook has the same requirement, but has an illustration of a duplex receptacle and plug of the configuration that we now know as NEMA 5-15. I believe it can be safely assumed that this configuration (now standard throughout North America) dates to 1950 or 1951.

I recently did some work on a 1950 house which had a porcelain Hubbell twist-lock receptacle in the laundry room. I am sure this was installed to meet the 1947 Code requirement. I am 99.9% sure it has never been used!

American sparkies who are familiar with the NEMA straight-blade chart frequently mistake the NEMA 10-20 for the Aussie/NZ configuration, but this is incorrect. The pix Paul posted on this thread are of a different USA standard, one dropped before the NEMA chart was created. Like most T-slots, it is rated 125V 15A/ 250V 10A (probably the origin of the Aussie 10A standard), whereas the 10-20 has wider-spaced pins and is rated 250V 20A.

I still see 10-20 receptacles on occasion. Here in Texas, they were used for window air conditioners in the '50s. If the house was upgraded to central A/C, the window unit receptacle was no longer needed, and therefore was never upgraded to later standards.

BTW, Woodhead still makes a line of devices in the 10/15A non-NEMA configuration that more or less matches the Aussie/NZ standard.

[This message has been edited by yaktx (edited 01-04-2006).]

[This message has been edited by yaktx (edited 01-04-2006).]

Joined: Aug 2001
Posts: 7,520
On the subject of the T-slot receptacles (meaning the old style with both sides a T-slot, not just one as with 5-20 and 6-20 NEMA types), I've wondered how and why these came into being.

If both 120 and 240V appliances could be wired with either parallel or tandem plugs at one time, it seems like it could have been a disaster waiting to happen for someone.

Joined: Dec 2001
Posts: 2,498
I think the standard for the Swiss plug is from 1959, making it somewhat newer. Of course, this could simply be an update of an older standard.
Well, it has clearly evolved from the old ungrounded system that has once been used all over Europe, 4mm round pins on 19mm centers.
Germany seems to be the only country that ever had ungrounded plugs with 4.8mm pins rated 10A. Austria simply never had any ungrounded plugs rated for more than 6A.

Joined: Feb 2003
Posts: 288
If both 120 and 240V appliances could be wired with either parallel or tandem plugs at one time, it seems like it could have been a disaster waiting to happen for someone.

This continues to cause confusion to the present generation of electricians.

The parallel vs. tandem issue should be considered separate from the 125 vs. 250 issue. In the early days, the medium Edison base was the only universal wiring device standard in the USA (and only after 1900, as the Thomson-Houston and Sawyer-Mann bases were also common before that). Several companies in the first two decades of the century produced two-piece "cap and base" plugs in different competing configurations. The most common of these were the parallel and the tandem. By 1936 (actually probably by the late '20s) the parallel device was most common, yet there were still enough tandems around to make T-slots a good idea.

The voltage issue is quite another matter. Several Electrical Nostalgia posts question the reason for a 10A 250V rating. Prior to about 1920 (I'm not exactly sure when, or which antique book I read this in, although they are all on my shelf), lighting circuits were to be fused at 10A. Originally, I think they were limited to 6A, as the medium Edison base was very early on limited to 660W. After about 1920, lighting circuits were allowed to be fused at 15A, as that is the actual ampacity of 14 AWG (2.08mm2) rubber wire. I guess the 250V rating was frozen at 10A since these devices were probably never used much at 250V.

I should mention that in those days there was no really strict rule limiting a particular receptacle configuration to a particular voltage. I gather that 32VDC farm installations used the exact same wiring devices as 120VAC installations at the time (I know for certain they used medium Edison-base devices). I've also heard that 120VDC installations in major cities used the same receptacles as AC installations elsewhere.

I have a variety of old devices here in a box:

Hubbell tandem Edison plug base, rated 300V 3A.

"C-H" (Cutler-Hammer?) "loop-prong" cap and base rated 660W 250V.

GE T-slot receptacles, one a single and the other a duplex, rated 10A 250V.

Porcelain Paulding T-slot duplex receptacle, rated 15A 125V and 10A 250V.

Arrow-Hart duplex T-slot (which I removed from the 1890s house where I lived in college), 15A 125V and 10A 250V.

I think that the tandem configuration was thought of as just another 120V configuration.

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