Why does 13A plug and socket system have flat pins when most others are round?

[marconi]

I have no reference but I seem to remember that the inspection hole was to make it easy to see that the CPC had indeed been connected to the top pin because the idea of earthing appliances supplied by flexible cords and plugs was new and some folk simply did no bother to connect the green wire ( and cut it back) because they failed to understand its importance to safety.

 

[marconi]

 

[Lucien Nunes]

Square pins = 'Modern wiring system in use here.'

Here is my reasoning:

In 1947 we had a bewildering selection of round pin sizes in the UK: 3-pin plugs to BS546 in three current ratings: 2A, 5A & 15A.
2-pin versions to BS372 in 2A, 5A and 15A that weren't interchangeable - the spacing was different, you couldn't put a 5A 2-pin plug in a 5A 3-pin socket.
A few 10A still survived, having been part of the Lundberg range that spawned BS73 / BS372.
Manufacturer-specific types included Wandsworth and original MK gauges in various current ratings (MK offered both their own gauge and BS gauge plugs at one time. Theirs were more compact for the same rating).
European plugs based on the 19mm pin spacing would turn up in the UK and loosely fit the 5A 2-pin.

About the only plug on sale that did not have round or modified round pins was the original Wylex type. All in all it was difficult for the householder to be sure of which was which.

With the coming of BS1363 there was a paradigm shift. The size of plug no longer defined the rating of appliance it was to be used with. A fuse was essential due to the 30A circuit rating. The presence of an earth was pretty much guaranteed. The visually distinctive square pins carried the message that this was a new plug or socket using the new system, not just another unknown size. It also permitted a new design of contact and I believe MK patented one form of the socket construction but I would need to look this up carefully to see how the dates indicate the cause and effect in the development path.

The designers of the other competing 13A plugs didn't go this route. The DS plug had modified round pins (the earth was grooved, the line pin was a screw-in cartridge fuse) and closely resembled BS546 5A (it was the most compact of the three). The Wylex 13A was an alteration of their existing system with an ingenious twist. You could plug a new 13A fused plug into an existing 15A Wylex socket (on a 15A radial), but not an unfused 15A plug into a 13A on a 30A ring. The idea presumably was to encourage existing Wylex users to stick with them. Wylex 13A plugs and sockets were engraved with 'Ring Main System' in a circle or similar to distinguish them, without which the 13A and 15A were confusingly similar.

Finally, it could be called a 'square pin plug' and everyone would know what you were talking about, even if they didn't know their amps from their volts. In contrast look at the situation with BS EN 60309, the plug formerly known as BS4343. Some people call it by a brand name (Ceeform, Marechal, Commando) and others by its colour (blue plugs, red plugs). No-one can agree what to call it because it doesn't have an 'official' name (discounting the long-winded title of the standard) nor one outstanding distinguishing feature.

 

[pirate]

PA Testing may be boring, but it does provide some amusing plugs and extension leads for the museum, especially those ones from the big river which have a fuse which is not connected to anything, and cables smaller than bell-wire...

 

[Midwest]

must be quite old then.

Possibly written in 1969

 

[Midwest]

Square pins = 'Modern wiring system in use here.'

Here is my reasoning:

In 1947 we had a bewildering selection of round pin sizes in the UK: 3-pin plugs to BS546 in three current ratings: 2A, 5A & 15A.
2-pin versions to BS372 in 2A, 5A and 15A that weren't interchangeable - the spacing was different, you couldn't put a 5A 2-pin plug in a 5A 3-pin socket.
A few 10A still survived, having been part of the Lundberg range that spawned BS73 / BS372.
Manufacturer-specific types included Wandsworth and original MK gauges in various current ratings (MK offered both their own gauge and BS gauge plugs at one time. Theirs were more compact for the same rating).
European plugs based on the 19mm pin spacing would turn up in the UK and loosely fit the 5A 2-pin.

About the only plug on sale that did not have round or modified round pins was the original Wylex type. All in all it was difficult for the householder to be sure of which was which.

With the coming of BS1363 there was a paradigm shift. The size of plug no longer defined the rating of appliance it was to be used with. A fuse was essential due to the 30A circuit rating. The presence of an earth was pretty much guaranteed. The visually distinctive square pins carried the message that this was a new plug or socket using the new system, not just another unknown size. It also permitted a new design of contact and I believe MK patented one form of the socket construction but I would need to look this up carefully to see how the dates indicate the cause and effect in the development path.

The designers of the other competing 13A plugs didn't go this route. The DS plug had modified round pins (the earth was grooved, the line pin was a screw-in cartridge fuse) and closely resembled BS546 5A (it was the most compact of the three). The Wylex 13A was an alteration of their existing system with an ingenious twist. You could plug a new 13A fused plug into an existing 15A Wylex socket (on a 15A radial), but not an unfused 15A plug into a 13A on a 30A ring. The idea presumably was to encourage existing Wylex users to stick with them. Wylex 13A plugs and sockets were engraved with 'Ring Main System' in a circle or similar to distinguish them, without which the 13A and 15A were confusingly similar.

Finally, it could be called a 'square pin plug' and everyone would know what you were talking about, even if they didn't know their amps from their volts. In contrast look at the situation with BS EN 60309, the plug formerly known as BS4343. Some people call it by a brand name (Ceeform, Marechal, Commando) and others by its colour (blue plugs, red plugs). No-one can agree what to call it because it doesn't have an 'official' name (discounting the long-winded title of the standard) nor one outstanding distinguishing feature.

I said all that in #3

 

[Octopus]

The I.E.E had 22 meetings (no surprise there then).

Before they could on which biscuits to have with their tea?

 

[static zap]

And why did the old plugs have an aperture above the earth pin?

As a kid I've seen it , attached to bell wire ... and stuffed in back of 2 core valve radio Earth ... (Ant ..more of same going to bed frame)

Who wants bell wire -passing live terminals ! Woolworth days ...arrr

(Vaguely remember up market brown 5A round pin, round bodied plug + pull knob)

 

[sparkdog]

I remember when I was an apprentice being told that the aperture was so you could see the earth wire was connected, I was suitably impressed.

 

[GeorgeCooke]

I wouldn't agree most other socket systems have round pins. The whole of North America and most of South America have flat pins. As do Australia, New Zealand, Japan, China, and several SE Asian countries.

 

[CACJL]

Did you ever come across the 13 Amp ones with the live piin being the fuse DS I think was the maker, as in Dorman and Smith, my Parents had these in their House when I was a Lad

I have, back in the sixties the council houses of Leamington Spa were fitted with sockets for this type of plug and only one shop in the town stocked the plugs and fuses.

 

[Pete999]

I have, back in the sixties the council houses of Leamington Spa were fitted with sockets for this type of plug and only one shop in the town stocked the plugs and fuses.

Where the houses what they called "Steele houses"

 

[w0z]

[QUOTE="
Does anyone know why the designers opted for square pins rather than continue with round pins, as other plug/socket systems eg. MK commando have done.

[/QUOTE]
Because someone invented these first but couldn't find a use for them...

 

[static zap]

Does anyone know why the designers opted for square pins...

They obviously were not painful enough to reduce damage to them when
knelt /or trodden on with bare feet ....
(until someone invented the plastic cover .. Spoiling the plug "awareness" lesson !)
... I have seen plenty of sleeved pin misshapen (From large feet incidents)
.. did same happen with round pins ? ...

 

[David1967]

Square pins = 'Modern wiring system in use here.'

Here is my reasoning:

In 1947 we had a bewildering selection of round pin sizes in the UK: 3-pin plugs to BS546 in three current ratings: 2A, 5A & 15A.
2-pin versions to BS372 in 2A, 5A and 15A that weren't interchangeable - the spacing was different, you couldn't put a 5A 2-pin plug in a 5A 3-pin socket.
A few 10A still survived, having been part of the Lundberg range that spawned BS73 / BS372.
Manufacturer-specific types included Wandsworth and original MK gauges in various current ratings (MK offered both their own gauge and BS gauge plugs at one time. Theirs were more compact for the same rating).
European plugs based on the 19mm pin spacing would turn up in the UK and loosely fit the 5A 2-pin.

About the only plug on sale that did not have round or modified round pins was the original Wylex type. All in all it was difficult for the householder to be sure of which was which.

With the coming of BS1363 there was a paradigm shift. The size of plug no longer defined the rating of appliance it was to be used with. A fuse was essential due to the 30A circuit rating. The presence of an earth was pretty much guaranteed. The visually distinctive square pins carried the message that this was a new plug or socket using the new system, not just another unknown size. It also permitted a new design of contact and I believe MK patented one form of the socket construction but I would need to look this up carefully to see how the dates indicate the cause and effect in the development path.

The designers of the other competing 13A plugs didn't go this route. The DS plug had modified round pins (the earth was grooved, the line pin was a screw-in cartridge fuse) and closely resembled BS546 5A (it was the most compact of the three). The Wylex 13A was an alteration of their existing system with an ingenious twist. You could plug a new 13A fused plug into an existing 15A Wylex socket (on a 15A radial), but not an unfused 15A plug into a 13A on a 30A ring. The idea presumably was to encourage existing Wylex users to stick with them. Wylex 13A plugs and sockets were engraved with 'Ring Main System' in a circle or similar to distinguish them, without which the 13A and 15A were confusingly similar.

Finally, it could be called a 'square pin plug' and everyone would know what you were talking about, even if they didn't know their amps from their volts. In contrast look at the situation with BS EN 60309, the plug formerly known as BS4343. Some people call it by a brand name (Ceeform, Marechal, Commando) and others by its colour (blue plugs, red plugs). No-one can agree what to call it because it doesn't have an 'official' name (discounting the long-winded title of the standard) nor one outstanding distinguishing feature.

Really informative and interesting read. I can remember in the early 70's my grandfather having a dazzling array of plugs and sockets including an adapter to connect a round pinned appliance into a light bulb socket

 

[David1967]

Really informative and interesting read. I can remember in the early 70's my grandfather having a dazzling array of plugs and sockets including an adapter to connect a round pinned appliance into a light bulb socket

 

[littlespark]

I was trying to figure out if that was an original publication…. But then figured, if it was, then “she” would be asking about kitchen appliances… and “he” would be telling her to get on with it, woman!

Jest!

 

[ColinACJL]

(A sad admission: as a lad I collected plugs by make and colour and displayed them on a shelf in my bedroom - I liked for example the style of the 'Rock' make. I had therapy and am now recovered but some interest remains. Who remembers makes such as Rock, WG, Nettle, Wylex, Empire, Walsall(?)?)

Does anyone know why the designers opted for square pins rather than continue with round pins, as other plug/socket systems eg. MK commando have done.

And why did the old plugs have an aperture above the earth pin?

Really informative and interesting read. I can remember in the early 70's my grandfather having a dazzling array of plugs and sockets including an adapter to connect a round pinned appliance into a light bulb socket

I remember back in the sixties all the council houses in Leamington Spa had 13 amp plugs were the live pin was a screw in fuse.
When the ring main was introduced after WW2 with a 30 Amp fuse at the consumer unit, the appliances where fitted a fused plug, usually a 3 or 13 amp, 1, 2, 5, 7 and 10 amp fuses were also available. Square pin instead of round pin to make it obvious it was not a 15 amp plug. Southampton College of Technology used Wylex sockets plugs.

 

[brianmoooore]

ncluding an adapter to connect a round pinned appliance into a light bulb socket

`Have one of these in my toolkit. Not so important these days, with battery powered tools, but was indispensable on rare occasions, back in the day.

 

[w0z]

Not quite on topic but there can't be many of these (or anyone with a round pin 3 pin plug still in use - bearing in mind that if you want to force a 2 pin it's shuttered so pencil at the ready).