Double Feed into Switch

[JohnW2]

EDIT: That exact quote also seems to be all over the internet, on many different forums - being the only statement available about double socket loading.... and without naming an actual source

Yes, it's all over the place, and is nearly always attributed to "an MK catalogue", although I haven't seen anyone able to say 'which one'.

However, it is so specific and detailed that I have to assume that it is real (and probably 'from MK') rather than 'fiction'.

Having said that, I find it a little hard to reconcile "... all MK double sockets can safely withstand a continuous load of 19.5A for an indefinite period." with "...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.". Furthermore, if it's really true that 22.3A can cause "... browning of the faceplates and sufficient heat to cause insulation damage to cable cores.", then I would start to wonder whether BS1363 is necessarily safe/adequate in only requiring a product to pass a temp-rise test at 20A (for one hour).

Kind Regards, John

 

[JohnW2]

I spoke to a bloke in MK's Tech Dept back then and he said that he believed that every socket was rated at 13A and the 19.5A test was just them being able to prove that the product could withstand supplying a 13A load continuously, with a percentage added on to show that the socket does not disintegrate at 13.5A.

OK, but you will also see what I've reported, several times, about what (more than one) bloke in MK's Tech Dept said to me 'back then' - none of them were certain, but all seemed to think that the rating of "13A per socket outlet" was probably intended to mean 2 x 13A for a double socket.

As I keep saying, if they really had intended what you suggest above (13A total maximum for a double socket), it's very hard to see why they would have written "13A per socket outlet (except 3 gang which is 13A in total)", if that also meant "13A in total" for double sockets. Furthermore, if they did believe that the total permissible for double socket was 13A, would they not have included a BS1362 fuse, as they do for triple sockets?

He said the 19.5A figure represented a load that exceeded 13A by 50%.

That's arithmetically true but, as above, I doubt that it is relevant. Also, as I have just written in another post, it seems odd that they suggest that 19.5A "indefinitely" is fine, but that 22.3A can cause cable core damage.

Kind Regards, John

 

[RandomGrinch]

Interesting!
The earliest reference I can find for the MK information, actually comes from this forum in 2004!
It doesn't seem as if the original post is available here, but there was a contemporary link

https://community.screwfix.com/threads/new-supply-for-building-site.25376/

So all we are looking for is the 2004 MK catalogue! It looks something like:

 

[JohnW2]

Interesting! ... The earliest reference I can find for the MK information, actually comes from this forum in 2004! It doesn't seem as if the original post is available here, but there was a contemporary link

I think you'll find that the DIYnot discussioin referred to was probably this one...

https://www.diynot.com/diy/threads/absolute-amateur-wants-to-know-if-im-overloading.8520/#post-41948

So all we are looking for is the 2004 MK catalogue! It looks something like:...

I'll leave you to address that "all". However, I'm not sure that the effort would be justified, since I think there is probably enough circumstantial evidence to satisfy ourselves that what we are seeing almost certainly did originate from an MK catalogue.

Having said that, the text you quote here (from the Screwfix forum) differs from what we have previously been looking at (that which talked about 19.5A, 22.3A etc). In what you now quote, this bit ...

... again seems to perpetuate the apparently common misunderstanding about Standards to which I keep referring. What BS1363-2:1995 "does not allow" is a double socket which cannot pass a temperature rise test involving 20A (14A+6A) for one hour (the 'minimum required standard'). Nothing in the Standard says that one cannot manufacture (and appropriately 'spec'/'rate') a socket that can "withstand 26A load for sustained periods of time" - and, as I keep saying, it's far from impossible that at least some of the double sockets around do come into that category.

Kind Regards, John

 

[RandomGrinch]

I think you'll find that the DIYnot discussioin referred to was probably this one...

https://www.diynot.com/diy/threads/absolute-amateur-wants-to-know-if-im-overloading.8520/#post-41948

Thank you!, Thats why the link didn't work. FWL_Engineer changed their name to Big_Spark...

 

[RandomGrinch]

... again seems to perpetuate the apparently common misunderstanding about Standards to which I keep referring. What BS1363-2:1995 "does not allow" is a double socket which cannot pass a temperature rise test involving 20A (14A+6A) for one hour (the 'minimum required standard'). Nothing in the Standard says that one cannot manufacture (and appropriately 'spec'/'rate') a socket that can "withstand 26A load for sustained periods of time" - and, as I keep saying, it's far from impossible that at least some of the double sockets around do come into that category.

Absolutely
Though, as the BS testing for a single socket-outlet with two socket contacts is only 20A as discussed, the simplest solution for a manufacturer to produce an accepted 26A double socket to BS, may be to suggest they are two socket-outlets and mark each one as 13A on the back?

 

[JohnW2]

Absolutely Though, as the BS testing for a single socket-outlet with two socket contacts is only 20A as discussed, the simplest solution for a manufacturer to produce an accepted 26A double socket to BS, may be to suggest they are two socket-outlets and mark each one as 13A on the back?

Indeed. In fact, if they did that, I suppose that they might even claim to have produced "an accepted 28A socket to BS", given that the temp rise test for a single socket is at 14A [and also, interestingly, that test requires a 20A total in the 'supply cable', so one has to find somewhere else (other than through the socket/plug) top send the other 6A!]

However, I don't think they ever do that. For a start, the meat of a double socket is almost invariably a single 'assembly', with just one marking - and I certainly haven't seen any double sockets with more than one mention of "13A" on the back.

I suppose that if one created a 'double socket' by using two 13A socket modules on a modular face place, one would again have a socket 'rated' at 2 x 13A (or 2 x 14A ), since I don't think the 'ratings' of such modules say anything about not applying if two such modules are used with the same faceplate/backbox!

In passing, a correction. Having just glanced at BS1363-2 (to confirm the above-mentioned figures) I am reminded that, although I have been talking about the temp-rise test being of 1 hour's duration, in truth it is 4-8 hours - apologies for that error of recall! In context, that presumably means that a double socket which passes the test (at 4 hours as the minimum) would probably pass the test with an appreciably higher current sustained just for the duration of maximum load (probably about 30 mins) likely to be seen with two kitchen appliances.

Kind Regards, John