Changing plug socket. Earth question

JohnW2 · 5 Aug 2017

EFLImpudence said:
No, BG - the OP's picture.

Right. The MK Data Sheet has, of course, always said "13A per socket outlet" but, despite my valiant attempts to find out from them in the past, I've never really understood exactly what they mean by that in relation to a double socket - i.e. whether a double socket has one or two "socket outlets". I was have thought the answer was 2, in which case the 'rating' would be 2 x 13A, but that would be inconsistent with MK's famous statement that serious thermal damage could result from sustained total currents greater than 22A!

Kind Regards, John

stillp · 5 Aug 2017

JohnW2 said:
I was have thought the answer was 2, in which case the 'rating' would be 2 x 13A, but that would be inconsistent with MK's famous statement that serious thermal damage could result from sustained total currents greater than 22A!

Not really inconsistent - the manufacturer is free to quote a short-term current rating that differs from that for "sustained currents".

deadshort · 5 Aug 2017

JohnW2 said:
"13A per socket outlet"

It's a double socket =26a

DS

JohnW2 · 5 Aug 2017

stillp said:
Not really inconsistent - the manufacturer is free to quote a short-term current rating that differs from that for "sustained currents".

They are - but, I would say that it is really only reasonable if they make it clear that such is what they are quoting, and that their product could not safely cope with the specified load if it were "sustained".

Kind Regards, John

JohnW2 · 5 Aug 2017

deadshort said:
It's a double socket =26a

I cannot deny that 13A x 2 = 26A. However, as I have often quoted before:

MK said:
....Research by ourselves and third party organisations has shown that all MK double sockets can safely withstand a continuous load of 19.5A for an indefinite period. Increasing the load slightly will begin to cause heat and mechanical stresses on the components in a relatively short period. Testing showed that a load of 22.3A was sufficient to cause heat stress that would cause a browning of the faceplates and sufficient heat to cause insulation damage to cable cores. A load of 24A for 43 hours was sufficient to cause significant heat damage to the material in which the socket-outlet was situated and within 75 hours sufficient to cause significant damage that would lead to the very real potential of fire....

Would you be happy with that performance if, as you seem to think, the product is 'rated' at 26A total?

Kind Regards, John

stillp · 5 Aug 2017

JohnW2 said:
They are - but, I would say that it is really only reasonable if they make it clear that such is what they are quoting, and that their product could not safely cope with the specified load if it were "sustained".

Of course, and they have done so in the text you have quoted.

stillp · 5 Aug 2017

"Testing showed that a load of 22.3A was sufficient to cause heat stress that would cause a browning of the faceplates and sufficient heat to cause insulation damage to cable cores."
A pity they don't state the time for which their product can withstand that current. I wonder why they used 22.3A?

"A load of 24A for 43 hours was sufficient to cause significant heat damage to the material in which the socket-outlet was situated and within 75 hours sufficient to cause significant damage that would lead to the very real potential of fire"
Again, a strange value of test current, but if the socket-outlet was mounted as for the BS1363 heat-rise test, i.e. embedded in a wooden block, with the plugs fitted with heaters, then that is a pretty good performance. In a plastered wall it would probably withstand more current (or suffer less damage).

On the occasions when a user is likely to connect 2 x 3kW loads to a twin socket-outlet, it seems less likely that those loads would remain connected for such long periods.

In case you're wondering what my position on this issue stems from, my previous employer sold a range of accessories that included twin socket-outlets that were tested to withstand 26A, and could do so for some time (I don't know the figure, but it was some hours) without damage. However, they also sell a lower cost range that is tested only to the 14A + 6A specified in BS1363, so they don't publicise the better performance of the more expensive range.

JohnW2 · 5 Aug 2017

stillp said:
Of course, and they have done so in the text you have quoted.

They have, but that document which I often quote bits of, is 'ancient', was being quoted in another forum, and no-one seems to know where it came from (it was originally cited, a good few years ago, as being from "an MK catalogue"). The MK Technical Support chap I spoke to (in/around 2011, if I recall correctly) said that he knew nothing of that particular statement, nor whether the results it mentioned still applied to their (then) current products.

What is for sure is that the current "Technical Data Sheet" does not say anything like that. As I said, it merely says "13A per socket outlet", which some people (like DS) take to mean that it is 'rated' at 2 x 13A, with nothing to suggest that their product cannot safely carry 26A total for 'long periods'.

Kind Regards, John

deadshort · 5 Aug 2017

Why quote old data ?

DS

stillp · 5 Aug 2017

Well, if it says 13A per socket-outlet, and there are two socket-outlets...
Do they say how long for?

JohnW2 · 5 Aug 2017

stillp said:
A pity they don't state the time for which their product can withstand that current. I wonder why they used 22.3A?

Yes, it's a pity - and I wondered that, too.

stillp said:
Again, a strange value of test current ....

Indeed.

stillp said:
On the occasions when a user is likely to connect 2 x 3kW loads to a twin socket-outlet, it seems less likely that those loads would remain connected for such long periods.

Very much so. I think I would personally struggle to find more than one 'plug-in' 3kW loads in my house. Other than the tumble dryer, most other things are generally 2 kW or less. There may be some 3 kW electric heaters out there, but I haven't got one (and fan heaters are generally 2kW).

stillp said:
In case you're wondering what my position on this issue stems from, my previous employer sold a range of accessories that included twin socket-outlets that were tested to withstand 26A, and could do so for some time (I don't know the figure, but it was some hours) without damage. However, they also sell a lower cost range that is tested only to the 14A + 6A specified in BS1363, so they don't publicise the better performance of the more expensive range.

Interesting. Are you saying that they knew that the cheaper range would not withstand 26A for an appreciable time without damage, or did they simply not test them at that current, and therefore could not make claims (and could not guarantee performance) at the higher current.

I suspect that the truth is that many manufacturers simply "don't know" in relation to their products, since they probably do not go any further than the test required to satisfy BS1363.

Kind Regards, John

JohnW2 · 5 Aug 2017

stillp said:
Well, if it says 13A per socket-outlet, and there are two socket-outlets...

As I said, the MK guy I spoke to was not certain whether, in terms of what they had written, a double socket has one or two "socket outlets".

stillp said:
Do they say how long for?

No.

... and nor do any of the other "13A-rated" BS1363 accessories say anything about how long they can carry 13A. I've always assumed that the implication is that they can carry 13A 'indefinitely' - but do you think that is necessarily the case?

Kind Regards, John

JohnW2 · 5 Aug 2017

deadshort said:
Why quote old data ?

Because it appears to be the "most recent" detailed information that is available (at least, that I have found). If you have something more recent, please share it with us.

Kind Regards, John

stillp · 5 Aug 2017

JohnW2 said:
Are you saying that they knew that the cheaper range would not withstand 26A for an appreciable time without damage, or did they simply not test them at that current, and therefore could not make claims (and could not guarantee performance) at the higher current.

The latter, I believe.

JohnW2 said:
the MK guy I spoke to was not certain whether, in terms of what they had written, a double socket has one or two "socket outlets".

It seems pretty clear from BS1363 that a twin has two s/o. The definition of socket-outlet includes "an accessory having a set of three socket-contacts" and the definition of 'multiple socket-outlet is "a combination of two or more socket-outlets".

JohnW2 said:
I've always assumed that the implication is that they can carry 13A 'indefinitely' - but do you think that is necessarily the case?

I would assume the same; although BS1363 doesn't actually require that, it does specify that the voltage drop test is performed at 13A, and the heat rise test uses 14A until thermal stability is reached (or 8 hours, whichever is first) which reinforces our assumption.

deadshort · 5 Aug 2017

JohnW2 said:
What is for sure is that the current "Technical Data Sheet" does not say anything like that.

DS

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Changing plug socket. Earth question

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