Installing extra appliance, electric supply advice needed

[Smiffy7]

Sorry to drag up an old thread, but...

I've got a double socket and I had to get the 32mm pattress converter box in the end (the socket didn't fit inside the 16mm box), so this takes up quite a bit of extra space behind the washing machine, which is particularly large I might add.

Are there any technical or safety reasons why I really shouldn't use a flush fitting "converter socket" like this: http://www.screwfix.com/p/clipsal-converta-socket-1-gang-to-2-gang-polycarbonate/12849??

Thanks

 

[ban-all-sheds]

Why not just sink a 2-gang box into the wall?

 

[stem]

You could always do this.

Untitled

• stem
• 16 Dec 2014
• 1

The downside is that you could can only use one appliance at a time, but I can't see this would present a problem for most folks.

 

[JohnW2]

You could always do this. ... <diagram> ... The downside is that you could can only use one appliance at a time, but I can't see this would present a problem for most folks.

I think that's unnecessarily complicated. It would probably be difficult to find a suitable (small) changeover switch and to locate it somewhere that was accessible. If, as you suggest would not be a problem, one were only going to use one of the appliances at the time, there would be no problem running them both off a double socket, even in the minds of those people who have concerns about running two 'heavy' loads off the same double socket.

Kind Regards, John

 

[stillp]

A double socket only has to be able to cope with a total of 20A. Not necessarily enough to run both a tumble drier and a washing machine.

No, no, no!
A double 13A socket has to be able to "cope with" 26A, unless you believe that 2 X 13 = (something other than 26). Each of the outlets has to withstand a test at 14A. If you'd said something like "only has to be able to cope with a total of 20A for a long time" you would have been less wrong.
The standard requires all 13A outlets to be tested at 14A. The 20A is a test for overheating; one outlet is loaded at 13A, the other at 6A, with the socket-outlet mounted in a wooden block. after a period of time which I can't remember (I'm away from my standards this week) the socket-outlet must not be damaged by excessive heat.
So, for short periods, both outlets of a twin socket-outlet must be able to supply 13A. Some manufacturers' products can withstand a total load of 26A for long periods without being damged by heat, but they will become too hot to touch (as they would at 20A) and the plugs might also be damaged (as they might at 20A).

 

[JohnW2]

... So, for short periods, both outlets of a twin socket-outlet must be able to supply 13A. Some manufacturers' products can withstand a total load of 26A for long periods without being damged by heat, but they will become too hot to touch (as they would at 20A) and the plugs might also be damaged (as they might at 20A).

I'm not sure that we'll ever really get to the bottom of this 'double socket issue', but maybe it's time that I again wheeled out material I've posted here more than once before. Firstly, the following, posted in December 2009 in the IET forum, purports to being a direct quote from the then MK Catalogue:

All MK socket-outlets are manufactured to comply with BS1363 part 2: 1995 and are rated at 13A per unit. Double socket-outlets have been manufactured and tested to exceed this rating by margin that allows electrical safety and reduces the risk of heat and mechanical damage to components due to overloading. It should be noted that BS1363 part 2: 1995 does not allow double sockets to operate at twice the permissible maximum loading and it should be remembered that double socket-outlets are not manufactured to be able to withstand a 26A load for sustained periods of time.

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.

MK recommend that users of their sockets consult professional design Engineers when designing installations to avoid the possibility of heat and mechanical stress to components and installations caused by overloading of MK socket-outlets.

The following, initially posted by me in March 2011, is also 'interesting'...

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

 

[stillp]

The important part of the text you derived from MK is "it should be remembered that double socket-outlets are not manufactured to be able to withstand a 26A load for sustained periods of time"
That was the point of my earlier post, i.e. that the ability to withstand 26A is time-dependent.
Your conversation with someone at MK might well have been interesting to you, but I don't think either of you had a copy of the product standard in front of you during the discussion. I've discussed this, in person, with several members of the responsible BSI committee. Most go a bit quiet when asked to state the length of time that their products can withstand 26A, but I haven't had anyone tell me that their twin socket-outlets can only supply 20A. If they did of course they wouldn't meet the standard.
John, you use the word "rated", seemingly without understanding that a rating is only "a value quoted by the manufacturer". A current rating can be for example short-term, long-term, elevated temperature, enclosed, free air, etc., so unless you add a descriptor, the term "rating" is meaningless.

 

[JohnW2]

The important part of the text you derived from MK is "it should be remembered that double socket-outlets are not manufactured to be able to withstand a 26A load for sustained periods of time" ... That was the point of my earlier post, i.e. that the ability to withstand 26A is time-dependent.

Well, yes, that goes without saying. Indeed, I do not doubt that a double socket could carry a total of 40A or more for a short period of time without coming to any harm.

John, you use the word "rated", seemingly without understanding that a rating is only "a value quoted by the manufacturer". A current rating can be for example short-term, long-term, elevated temperature, enclosed, free air, etc., so unless you add a descriptor, the term "rating" is meaningless.

I obviously understand that, but one has to remember that the 'users' are just ordinary members of the general public, who are quite likely to assume that any 'rating' is (unless otherwise stated) a 'long-term', continuous use, one.

I get quite a lot of flak whenever this issue is being discussed, simply because I mention the view I've heard expressed by many electricians that running two 'heavy' loads (e.g. a WM and dryer) from a double socket not uncommonly results in plug and/or socket damage. As I've said a good few times, I've never experienced this myself, despite having lived with a WM+dryer run off a double socket for many years in the past. Do you (and others) think that the electricians who report these problems have dreamt them, or what? - my personal experience is obviously extremely limited, so I have to rely on what is said by those who are dealing with electrical installations every day.

Kind Regards, John

 

[ban-all-sheds]

No, no, no!
A double 13A socket has to be able to "cope with" 26A, unless you believe that 2 X 13 = (something other than 26).

Or unless you believe that it doesn't have to be able to cope with that much load in order to comply with BS 1363.

Each of the outlets has to withstand a test at 14A.

Simultaneously?

The standard requires all 13A outlets to be tested at 14A.

Simultaneously for doubles?

What sort of test? How does a double socket have to perform when asked to deliver 28A?

The 20A is a test for overheating; one outlet is loaded at 13A, the other at 6A, with the socket-outlet mounted in a wooden block. after a period of time which I can't remember (I'm away from my standards this week) the socket-outlet must not be damaged by excessive heat.

Indeed.

Is there another test, with a different time, which a socket has to pass at a load of 26A in order to comply with BS 1363?

So, for short periods, both outlets of a twin socket-outlet must be able to supply 13A.

Is that short period defined in BS 1363?

Is the temperature rise over that period defined in BS 1363?

Is the amount of acceptable damage at the end of that period defined in BS 1363?


Basically, if someone buys a DSO which complies with BS 1363, what assurances to they get from the fact that it complies about its ability to cope with a load of 26A?

Some manufacturers' products can withstand a total load of 26A for long periods without being damged by heat, but they will become too hot to touch (as they would at 20A) and the plugs might also be damaged (as they might at 20A).

I haven't checked, but I would hope that a plug would be required to survive, undamaged, the temperature excursion allowed for a socket and vice-versa.

 

[JohnW2]

Some manufacturers' products can withstand a total load of 26A for long periods without being damged by heat, but they will become too hot to touch (as they would at 20A) and the plugs might also be damaged (as they might at 20A).

I haven't checked, but I would hope that a plug would be required to survive, undamaged, the temperature excursion allowed for a socket and vice-versa.

We obvioulsy don't know what stillp meant by 'long periods' but, even at 24A (let alone 26A) the MK material I recently quoted said

...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.

... and, although I may be wrong, I wouldn't really have expected any other manufacturer's products to be appreciably 'better' than MK's in this respect.

Kind Regards, John

 

[ban-all-sheds]

And some are probably worse.

My point is that unless the standard requires it, and therefore requires a successful test to prove it, nobody can rely on a DSO being able to deliver more than 20A for any length of time without damage or failure, because the standard does not require it.

 

[JohnW2]

And some are probably worse. My point is that unless the standard requires it, and therefore requires a successful test to prove it, nobody can rely on a DSO being able to deliver more than 20A for any length of time without damage or failure, because the standard does not require it.

Quite so. It's not really rocket science. If the Standard requires no test at >20A, then compliance with the Standard obviously cannot be relied upon to indicate, or even necessarily imply, how the socket will perform at such currents, for any period of time.

As you know, my own feeling about the whole topic is very simplistic. Since the vast majority of 'users' (the general public) have no reason to think that a double socket cannot safely supply 2 x 13A loads for reasonable (maybe even substantial) periods of time, I am surprised (if not rather amazed) that the appropriate Standard does not require (with appropriate tests) such sockets to be able to safely cope with that situation. We all know that the vast majority of users will not try to draw 26A for long periods, but the corollary of that is that we can also strongly suspect that (in the absence of any guidance to the contrary) at least a few will try to do that.

Kind Regards, John

 

[stillp]

... and, although I may be wrong, I wouldn't really have expected any other manufacturer's products to be appreciably 'better' than MK's in this respect.

I would.

 

[stillp]

As I've said in other threads, I believe the history is that, at the time BS 1363 was drafted, the plastics available were not able to cope with the heat produced by a prolonged test at 26A total, let alone the 28A that extrapolation from the other test would imply. However, given that the manufacturers have no great incentive to give themselves more onerous tests to perform, the standard has not been updated in that respect. Also, we apply diversity to all sorts of things, so why shouldn't BS 1363?
The fact that two socket-outlets are adjacent does not alter the fact that each has a current rating of 13A. There is no need for the standard to state the obvious.

 

[ban-all-sheds]

Whether they are or not, does a DSO have to demonstrate any ability to support a load of 26A in order to comply with BS 1363?