Double Sockets - MK's position

[JohnW2]

Following the recent endless discussion about the 'current rating' of double sockets, I have now had the opportunity to discuss this with a technical support engineer at MK/Honeywell. I am therefore now fairly clear as to their position, even if it seems a rather unsatisfactory situation:

• 1. The statement in their technical literature for Logic Plus sockets which reads "Current rating: 13A per socket (except 3 gang, which is 13A total)" is not only confusing and ambiguous, but simply wrong - and his 'explanation' was that this literature was created by the marketing department, over whom the engineers have limited control! MK (MK's engineers) do not intend to imply EITHER that the double socket can only supply 13A total, OR that it can supply 26A total.
  
  2. Similarly, he did not really know why all double sockets have "13A" embossed on the back, again because this is not the intended 'rating' of either half or all of the double socket.
  
  3. MK do not claim, recommend or suggest that their BS1363 sockets have any greater current carrying capacity than anyone else's. In common with all manufacturers, they merely seek to comply with BS1363, in particular the 20A temperature rise test. MK's (engineers') only view on the 'rating' of their (and everyone else's) double sockets is therefore based on the BS1363 temp-rise-test figure of 20A - although he did add that he thought most designers would try to avoid a situation in which one double socket was likley to be loaded with as much as 20A (although it's not all that clear as to how that would be achieved - unless on installed only single sockets!).

So, that really answers the question I posed at the very start of that other infamous thread. The chap I talked to said that he would pass on my 'compliant' about the potentially misleading literature to their marketing department, but I don't think I'll be holding my breath whilst waiting for any changes! There doesn't seem anything more to discuss.

Kind Regards, John

 

[Paul_C]

All of which really goes to show that if you are going to fit double sockets, the safest approach is to use 20A radials, since however the system is designed you can't guarantee that somebody isn't going to connect two 3kW loads to the same socket.

 

[JohnW2]

All of which really goes to show that if you are going to fit double sockets, the safest approach is to use 20A radials, since however the system is designed you can't guarantee that somebody isn't going to connect two 3kW loads to the same socket.

One might think that, but the reality is that it would not afford all that much protection to a socket against a load of >20A for a substantial period of time.

A 20A Type B MCB can carry 22.6A 'indefinitely'. Fig 3.4 in Appendix 3 of the regs indicates that it will allow something like 28A for 10,000 seconds (just under 3 hours) and, although the graph stops at 10,000 hours, it looks as if it may well allow 26A for several more hours beyond that. Even a 16A Type B MCB would allow a bit over 20A for >3 hours (again, probably many hours).

If you really wanted to guarantee never exceeding the 'rating' of a socket, you'd probably have to stick with single sockets (perhaps in pairs, in double {not 2-gang} back boxes!) - but that's probably OTT.

Kind Regards, John

 

[joinerjohn]

Good job the 1st amendment to the 17th ed is due out later this year. I think you should raise this as a matter of some urgency with the IET, who will undoubtedly contact you straight away with their recommendations that 13 amp double sockets should now be technically re-named 26amp ish sockets.
No doubt the amendment will include the use of 4mm cable for all ring mains instead of 2.5mm. (just in case someone is foolish (and rich enough) to plug in 2 x 3kw heaters into one double socket)

 

[spongsdad]

I was praying that nobody would bother responding to your latest mind blowingly boring post, and then along comes Paul_C.

And your arrogance is incredible, do you really think that anyone would accept you're version of a conversation with a manufacturer.

Kind Regards, John

Boring? Well maybe. Arrogant? I don't think so. And whatever his faults, John W2 has far better manners than many contributors to this site.

 

[JohnW2]

Boring? Well maybe. Arrogant? I don't think so. And whatever his faults, John W2 has far better manners than many contributors to this site.

I'm sure that my posts will be boring to some (maybe many) - but people are free to ignore or block them. What fascinates me is those who clearly dislike my posts, or find them boring, but continue to spend their time reading and commenting (non constructively) about them. Mind you, I've been participating in electronic discussions since long before the World Wide Web (and probably even some of the members of this forum!) was born - so it is a form of behaviour with which I'm well familiar, and well practised at handling!

I certainly have many faults, but I'm pleased to see that you recognise that arrogance and bad manners are not amongst them!

Kind Regards, John

 

[kevindgas]

i found it interesting

on a similar note why don't they make a socket / double / triple where it plugs into a back box that has the wiring in it rather than the current system of having to wire the back of the socket and then ram the whole caboodle into the back box. i'm sure there is a reason but it would make wiring so much easier/neater.

 

[joinerjohn]

i found it interesting

on a similar note why don't they make a socket / double / triple where it plugs into a back box that has the wiring in it rather than the current system of having to wire the back of the socket and then ram the whole caboodle into the back box. i'm sure there is a reason but it would make wiring so much easier/neater.

Someone would still have to wire up the back box the front was plugging into though. Nice try.. Must admit though, I do like the light fittings that are like this , where the lamp holder plugs into the rose. Much easier.

 

[stillp]

John, I can't see anything in that MK literature that is wrong. The current rating of a 13A socket is ... wait for it ... 13A. That is not affected by whether or not there are two of them in the same device. They are therefore marked 13A. A 3 gang or more is protected by a 13A fuse and is therefore rated at 13A total.
It is a characteristic of dual BS1353 socket-outlets that they get hot when loaded to their full current rating. They are tested for temperature rise at 20A, since the requirement is that the temperature of certain parts does not exceed certain limits in normal use, and it would not be 'normal' for both socket-outlets of a dual to be fully loaded for a long period.
I suspect the technical support engineer you spoke to has not read the standard...

 

[JohnW2]

i found it interesting
on a similar note why don't they make a socket / double / triple where it plugs into a back box that has the wiring in it rather than the current system of having to wire the back of the socket and then ram the whole caboodle into the back box. i'm sure there is a reason but it would make wiring so much easier/neater.

I'm not sure it's really all that related, but I certainly agree that anything which did away with the "ramming the whole caboodle into the back box" would not only be welcome, but would undoubtedly also be safer (goodness knows what is sometimes going on 'out of sight' during that ramming process!). ... and that doesn't only relate to socket outlets.

However, apart from probable complexity (hence cost), I suspect the greatest problem would be that what you postulate would be reliant on 'plug/socket' connections to carry not only the full load of the socket (potentially 20A or whatever) but also the CPC - and that could well raise some design/regulation/Standard issues. Mind you, that same reliance on plug/socket connections also exists in many of the 'socket converters' which are around.

Kind Regards, John.

 

[JohnW2]

John, I can't see anything in that MK literature that is wrong. The current rating of a 13A socket is ... wait for it ... 13A. That is not affected by whether or not there are two of them in the same device. They are therefore marked 13A.

I agree that, other considerations aside, each 'socket' ('sets of 3 receptacles') has a current-carrying capacity of 13A. However, it's still, IMHO, confusing. The works of a 2-gang socket consists of a single moulding, which bears a single marking of 13A (not 2 x 13A). That's like the cylinder block of a 4-cylinder 1000 cc engine being 'marked' 250cc, rather than "1000 cc" or "4 x 250cc". However, if they did mark it 2 x 13A, that would obviously be a problem in relation to other considerations (temp rise of the whole 'device').

However, this is all old ground, and doesn't really need re-debating. My original question essentially arose from the fact that some people seemed to believe that MK 2-gang sockets were designed/able/rated to take a highrer total current than other makes, and I think I'm now pretty happy that such is not the case. The same is true of all 2-gang sockets - each of the 'sets of 3 receptacles', and associated switch (if there is one), has, per se, a current rating of 13A but, because of the temperature rise issue, none of them are intended to 'normally' carry total loads >20A. That's it

Kind Regards, John
edit: typos corrected

 

[stillp]

That's like the cylinder block of a 4-cylinder 1000 cc engine being 'marked' 250cc, rather than "1000 cc" or "4 x 250cc"

No it isn't John, because you can't choose to use just one cylinder of your car engine.

 

[JohnW2]

That's like the cylinder block of a 4-cylinder 1000 cc engine being 'marked' 250cc, rather than "1000 cc" or "4 x 250cc"

No it isn't John, because you can't choose to use just one cylinder of your car engine.

That is obviously true, but I still think that most people probably expect a 'specification' or 'rating' marked on an object to relate to all of that object, either as a total or in a "N x X" format. I'm sure that, if I thought for a while, there are many much better analogies. However, I don't think there is much point or mileage to be had in discussing this, since we are seemingly stuck with 'how it is'.

Kind Regards, John