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Old 18th Oct 2012, 11:51 am   #41
ssaunders
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Default Re: 13 amp plug question

Thanks for all your replies to this thread, but as one of the correspondents observes, we still do not have definitive answer and without shelling out for a defunct BS, we are unlikely to answer this important question.

So, in pursuit of nothing less than a comprehensive explanation of our rectilinear friend, I have fired a mail to the God of plug tops: MK Electrical (Technical Support).

I will update you all in due course!
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Old 18th Oct 2012, 12:07 pm   #42
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Default Re: 13 amp plug question

We could also have a quick ask here.

http://www.fam-oud.nl/~plugsocket/UnknownSpecimen.html
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Old 18th Oct 2012, 12:44 pm   #43
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Default Re: 13 amp plug question

Update: The technical support guy at MK asked his colleagues and none of them know. Undaunted I have suggested that he goes and asks the guys who play cards in the canteen every lunchtime - every company has them and they know everything.
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Old 18th Oct 2012, 12:54 pm   #44
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Default Re: 13 amp plug question

I've mailed Oof at http://www.fam-oud.nl/~plugsocket/UnknownSpecimen.html to see if he can shed any light on the issue.
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Old 18th Oct 2012, 5:12 pm   #45
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Default Re: 13 amp plug question

Quote:
Originally Posted by ThePillenwerfer View Post
Is it like this one on my workshop hoover?

- Joe
I have a cream Bakelite MultiKontact plug the same as that knocking around somewhere. unused and wrapped in brown paper

Jan
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Old 18th Oct 2012, 5:53 pm   #46
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Default Re: 13 amp plug question

Maybe the little slot was use as a locating slot during manufacturing to assist some peice of automated proccesing
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Old 18th Oct 2012, 6:17 pm   #47
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Default Re: 13 amp plug question

Quote:
Thanks for all your replies to this thread, but as one of the correspondent's observes, we still do not have definitive answer
The answer is apparently in clause 15 of the original edition of the standard, BS1363:1947, which mandates a visible earth conductor according to
http://en.wikipedia.org/wiki/BS_1363

I have always understood this to be the function although don't specifically recall reading BS1363:1947. It is corroborated by the many catalogues advertising visible earth connections on many types of plug. I cannot think of any plug in which the notch does not reveal the conductor. There is a lot of circumstantial evidence that this is the only 'correct' purpose for the slot.

Lucien
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Old 18th Oct 2012, 6:53 pm   #48
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Smile Re: 13 amp plug question

Hi,
I've about half a dozen switched MK plugs; brown, cream, and a white one! I've also got an MK plug with spring loaded sleeves as mentioned recently in another thread. On most of the MK plugs I have, the locating piece that fits into the hole next to the earth pin has broken off.
I wonder if the hole was to reduce the chances of damp condensing inside the plug. Something that seems unnecessary these days as modern plugs don't have said hole.
Cheers, Pete
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Old 18th Oct 2012, 6:58 pm   #49
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Default Re: 13 amp plug question

Maybe. These days with central heating being so widespread condensation would be as big a problem.

These holes certainly pre-date BS1363, though that could well have incorporated the then current best practice.

- Joe
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Old 19th Oct 2012, 8:18 am   #50
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Default Re: 13 amp plug question

The answer is apparently in clause 15 of the original edition of the standard, BS1363:1947, which mandates a visible earth conductor

Which is I believe what I stated in post number two

Neil
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Old 19th Oct 2012, 10:00 am   #51
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Default Re: 13 amp plug question

Hi Neil,

I think posters have drawn a distinction between the descriptive terms "earth connection" (in post #2) and "earth conductor". The former presumably includes the join between the pin and wire, but the latter only the cable. It seems like a small difference, however, we are now up to post #51! Like most threads, posters use their own terminology which may not be interpreted as intended.

Peter
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Old 19th Oct 2012, 10:22 am   #52
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Default Re: 13 amp plug question

I accept that allowing an easy inspection of the earth connection is the stated purpose. However, I've looked at several of my plugs and can't see the wire through the hole never mind if it's securely connected.

It seems strange how as safety standards have raised that this feature was dropped.

- Joe
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Old 19th Oct 2012, 12:48 pm   #53
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Smile Re: 13 amp plug question

Hi,
Just to add a bit of fuel to the debate;
I've just had a look at the 1960s MK plug I mentioned above (no.48) which has the spring loaded sleeves and it does NOT have a hole at the top. Just a notch to locate the cover. Also, I had a look at some WG plugs from the 1970s, (available in various colours from Woolworth's) and they don't have a hole either!
So. . .
Cheers, Pete
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Old 19th Oct 2012, 1:03 pm   #54
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Default Re: 13 amp plug question

Quote:
it does NOT have a hole at the top. Just a notch to locate the cover.
Cheaper to modify just one mould tool rather than both.
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Old 19th Oct 2012, 3:44 pm   #55
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Default Re: 13 amp plug question

Quote:
Originally Posted by ThePillenwerfer View Post
I accept that allowing an easy inspection of the earth connection is the stated purpose. However, I've looked at several of my plugs and can't see the wire through the hole never mind if it's securely connected.

It seems strange how as safety standards have raised that this feature was dropped.

- Joe
Don't forget that earthing was the 'in thing' in 1947. It was to be the new 'vital' safety measure, and as such, had to be seen to be safe.

Now, a loose earth wire inside a plug is a bigger hazard than no earth at all; and a disconnected earth gives no warning. So naturally, there would have been an inclination to cater for this possible source of discredit.

Of course nowadays earthing is little more than an embarrassment, as far as portable appliances go; and so it is 'played down', with vast tonnage of unearthed brassware openly exposed in every B&Q lighting department. The day of earthing is over; insulation is the new policy.

Even the name of the earth pin has been changed; it's now the 'insulated (of course) shutter-opening device', or some such.
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Old 20th Oct 2012, 6:50 am   #56
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Default Re: 13 amp plug question

Quote:
Originally Posted by Brigham View Post
Even the name of the earth pin has been changed; it's now the 'insulated (of course) shutter-opening device', or some such.
I can assure you that the name of the earth pin has not been changed! What did change, in 1994, was the introduction of "Non-Rewirable 13A Plugs with Plastic Socket Shutter Opening Pins". This was done by means of a Product Approval Specification from BSI, numbered PAS 003:1994. In 1995 the plastic pin was incorporated into the revised standard, BS 1363-1:1995 and renamed as an "Insulated Shutter Opening Device (ISOD)" which is defined in clause 3.23 as: "protrusion from the engagement surface of the plug, in place of a brass earth pin, made of insulating material having dimensions similar to those of a brass earth pin". The use of an ISOD is permitted only for "non-rewirable plugs for class II applications". The description and restrictions remain in the latest version of the standard: BS 1363-1:1995 +A4:2012. An earth pin is still an earth pin.

Getting back to the original point about the hole, clause 15 of BS 1363:1947 is quite clear, it states "The connection of the flexible conductor to the earthing plug pin shall be visible when the cover of the plug is in position". I can confirm that I inspected a copy of BS 1363:1947 held in the National Library of Scotland earlier this year, and took notes on that very point.
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Old 20th Oct 2012, 1:28 pm   #57
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Default Re: 13 amp plug question

QED. At Last.
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Old 20th Oct 2012, 5:34 pm   #58
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Default Re: 13 amp plug question

Socketman,

Welcome to the forum and thank you for posting well researched, authoritative information.

A bit of speculation and musing has its place and can be pleasant, but there comes a point when it's time to get the proper answer.

PMM
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Old 20th Oct 2012, 8:35 pm   #59
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Default Re: 13 amp plug question

Thanks from me too, I have always understood this to be the case but never read the original BS. There is quite a lot of discussion of electrical fittings here from time to time, so you might find other threads of interest if you are a connector specialist!

Lucien
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Old 21st Oct 2012, 11:10 am   #60
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Smile Re: 13 amp plug question

Hi,
In that case then, why were some plugs made without the inspection hole such as the ones I mentioned in my previous post? was this requirement relaxed in the 60s or 70s?
Cheers, Pete
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